WO2005105820A2 - Macrocyclic cadmium complexes - Google Patents

Abstract

The present invention provides (i) a complex of the formula M2L3, wherein M is Cd (II) and each ligand, L, is independently either a tetrabenzoporphyrin ligand or an azatetrabenzoporphyrin ligand and (ii) methods for synthesizing the complex. The present invention also provides methods for forming a thin film of this complex, for example use in a conducting device and use in detecting oxidising substances.

Description

Macrocyclic Cadmium Complexes

The present invention relates to novel cadmium complexes, in particular those comprising tetrabenzoporphyrins and structurally related ligands, which include phthalocyanines . The present invention also provides methods of synthesis of the complexes and various uses of the complexes. Phthalocyanines (Pcs) are a well-known class of macrocycles which, by virtue of their distinctive blue-green colours, have a major role as commercial dyes and pigments. Phthalocyanines are a subgroup of the tetrabenzoporphyrin class of macrocycles and are alternatively termed tetraaza- tetrabenzoporphyrins . The ease of tuning the properties of the ring system by introduction of substituents or incorporation of different metal ions or metalloid elements at the centre of the ring modifies and/or optimises a series of interesting photophysical and conducting properties. This has rendered specific examples suitable for a number of

'high-tech' applications. Thus phthalocyanine derivatives are used extensively as charge carriers in photocopiers, in laser/LED printing and as laser light absorbers for optical data storage systems including CD-ROMs . Other examples show promise for exploitation in devices such as solar cells and as gas sensors. The combination of photoexcited state properties, tunable by structure variation, has provided materials suitable for optical limiting and, in medicine, as singlet oxygen photosensitizers for photodynamic therapy (PDT) . Examples have also. been identified for a possible therapy for transmissible spongiform encephalopathies . The phthalocyanine ligand, Pc^2", which may be substituted or unsubstituted, has a heteroaromatic 18π- electron system and readily binds with two protons in the central cavity to form metal-free phthalocyanine, H₂Pc. The ligand also forms complexes with main group and transition metal ions. Thus, dilithium phthalocyanine (Li₂Pc) can be easily prepared by the action of lithium pentoxide on phthalonitrile. Similarly, reactions of a phthalonitrile with base and M(II) salts give rise to various divalent metal phthalocyanines, M(II)Pcs. Alternatively, metal phthalocyanines can be formed by reacting H₂Pc or Li₂Pc with a metal salt. Incorporation of trivalent metal ions, e.g. aluminium (III) or indium (III) , leads to metallated phthalocyanines bearing an axial ligand. In principle, valencies of trivalent metal ions are also satisfied within triple-decker sandwich .complexes, M₂Pc₃, (Figure 2). However, examples are relatively scarce and are known only for lanthanide (III) ions, indium (III) and bismuth (III) and are generally poorly characterised.

An interesting but small sub-group of phthalocyanines are those where normal valencies are not satisfied, resulting in free radicals. These are especially promising in the fields of molecular electronics and sensors. Structurally, the simplest example is monolithium phthalocyanine (LiPc) and is formed by chemical, electrochemical or photochemical oxidation of Li₂Pc (Figure 3) . It is an unexpectedly stable radical in air and one of the rare intrinsic organic semiconductors (single crystal σ = 2x10^"3 Ω^_1 cm^"1, thin films σ = 10^"4 - 10^"5 Ω^"1 cm^"1) . The ESR spectrum of the x-polymorph of LiPc in vacuo shows a narrow signal at g=2.002, indicating that the unpaired electron is delocalised over the whole phthalocyanine ring. In the presence of oxygen, the signal has been shown to broaden. This unusual magnetic property of LiPc makes it a useful ESR probe for oximetric applications under various physiological conditions.

The second type of radical phthalocyanines is the bis- phthalocyanines, MPc₂ (Figure 4) , formed from certain trivalent metal ions, notably the lanthanides and indium. Unlike the triple-decker sandwich complexes, M₂Pc₃, of these ions (which are not free radicals) , they have received considerable attention from the viewpoint of device development. The most common and best yielding synthetic preparation involves heating the phthalonitrile precursor with a metal triacetate at approximately 300 °C, without solvent, followed by chromatographic separation. The most studied examples are those containing rare earth elements. Substituted bisphthalocyanines, bearing alkyl, alkyl/aryl- oxy chains or crown ether moieties, have been obtained, some of which form liquid crystalline phases. Extension of the π- system can lead to bis-naphthalocyanines . Undoped single crystals of LuPc₂ show a room temperature conductivity of 6x10^"5 Ω^-1cm^"1 more than 6 orders of magnitude higher than that for standard divalent ion metallophthalocyanines (M(II)Pc; M= Cu, Ni) . The conductivity of LuPc₂ thin films is of the same order of magnitude (10^"s Ω^-1 cm^"1) . Another property exhibited by some of these materials is electrochromism, i.e. colour changes which result during electrochemical redox. In solution, four reversible and monoelectronic waves are observed, corresponding to one oxidation step and three reduction steps. UV spectra show the characteristic phthalocyanine bands, i.e. B-band (Soret) and Q-band. Furthermore, a transition from deep level toward the singly occupied molecular orbital (SOMO) is observed ca . 460 nm. Additionally, the unpaired electron gives rise to a band at ca . 900 nm corresponding to a transition to the lowest unoccupied molecular orbital (LUMO) . A transition in the near-infra red region also characterises the compounds but its assignment is uncertain. Neutral, reduced and oxidised forms of the compounds are easily distinguishable by UV.

This combination of optical and electrochemical properties leading to colour changes, redox activity, semiconductivity and thermal stability renders them suitable for applications in displays and optical memory devices, gas sensors for environmental and industrial monitoring and molecular electronics devices. It is desirable for the complexes to be as stable as possible, particularly when exposed to UV and visible light. There are very few reports on cadmium phthalocyanines in the literature. Cadmium phthalocyanines are discussed in the following published documents: (i) . A. B. P. Lever, P. C. Minor Inorg. Chem. 1981, 20 : 4015-4017; (ii) D. Villemin, M. Hammadi, M. Hachemi, N. Bar Molecules 2001, 6: 831-844; (iii) D. Lexa, M. Reix J. Chim. Phys . Phys . Chim . Biol . 1974, 71: 511-516; and (iv) B.D. Berezin Kinet . Catal . (Engl . Trans.) 1968, 9 : 437-438. Neither neutral radical species of cadmium phthalocyanines nor triple-decker cadmium phthalocyanines are disclosed in any one of these documents.

Cadmium phthalocyanine, wherein the Cd:Pc ratio is "1:1" and Pc is an unsubstituted phthalocyanine, is available from various commercial sources such as Sig a- Aldrich. This is not a neutral radical species nor a triple- decker species . Only one example of a biradical phthalocyanine- containing system has been described in the literature (N. Ishikawa, Y. Kaizu Coord. Chem. Rev. 2002, 226 : 93-101) . This system was self-assembled from two 15~crown-5- substituted LuPc₂ units. Complexation of two molecules by potassium cation resulted in a dimer with two unpaired electrons. There is no suggestion or disclosure in this document of any other bi-radical phthalocyanine and, in particular, no suggestion or disclosure that Cd may form a complex whereby one or more of its redox states is a free radical or diradical .

All documents mentioned above and from hereon are incorporated herein by reference. There is a desire to produce novel stable organic materials that are able to conduct electricity. It is also desirable to be able to produce materials that may show semi-conductive properties and/or variable optical properties under different conditions.

We have surprisingly found that it is possible to make novel cadmium complexes containing ligands having a tetrabenzoporphyrin structure and that these complexes display unexpected electronic properties.

The present invention provides a complex M₂L₃ wherein M is Cd(II) and each L is independently either a tetrabenzoporphyrin ligand or an aza-tetrabenzoporphyrin ligand. More specifically, each L may be a tetrabenzoporphyrin ligand or mono-, di-, tri, or tetraaza- tetrabenzoporphyrin. Preferably, one or more of the tetrabenzoporphyrins in the complex is a phthalocyanine ligand (a tetraaza-tetrabenzoporphyrin ligand) , and even more preferably, all tetrabenzoporphyrins are phthalocyanine ligands. The term "tetrabenzoporphyrin" hereinafter in this document includes in its scope both aza-tetrabenzoporphyrin and non-aza-tetrabenzoporphyrin.

The present invention will now be further described. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary or obviously incompatible. In particular any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous, unless obviously incompatible.

The present invention shall be exemplified with reference to the following drawings, in which: Figure 1 shows an unsubstituted phthalocyanine ligand, (left) and common metallated derivatives (right) ; Figure 2 shows the molecular structure of triple-decker phthalocyanines M₂Pc₃, wherein the phthalocyanine ligand Pc is unsubstituted, i.e. of the formula 1 as defined herein, wherein R¹ to R¹⁶ are all H and X¹ to X⁴ are all N; Figure 3 shows the preparation of a phthalocyanine radical LiPc from Li₂Pc, wherein the phthalocyanine Pc ligand Pc is unsubstituted; Figure 4 shows the molecular structure of bis- phthalocyanines MPc₂, wherein the phthalocyanine Pc ligand Pc is unsubstituted; Figure 5 shows the synthesis of ^λCd₂Pc'₃', an example of a complex of the present invention, (or, synonymously, Complex I), wherein Pc¹ is octakis (hexyl) phthalocyanine and shall be from hereon throughout the description of the figures and through the Examples, unless otherwise stated; Figure 6 shows MALDI-MS of A. CdPc ' (top spectrum) and B. Cd₂Pc'₃ (bottom spectrum); Figure 7 shows the UV-vis spectra of CdPc ' and CdPc'_3; Figure 8 shows the IR spectra of CdPc' (red) and Cd₂Pc'₃ (blue) (1800-600 cm-1 region); Figure 9 shows UV-vis spectra of Cd₂Pc ' ₃ exposed to I₂ vapours Figure 10 shows the X-ray structure of Cd₂Pc'₃; Figure 11 shows the torsion angle between Pc ' planes in Cd₂Pc ^■ ₃ ; Figure 12 shows Inner ligand (left) and outer ligand (right) of CdPc'₃; Figure 13 shows the molecular packing of Cd₂Pc ' ₃ in a unit cell; Figure 14 shows a cyclic voltammogram V of Cd₂Pc ' ₃ (0.5 mM) in THF (blue) and CH₂C1₂ (red) , at -40 °C, scan rate 100 mV/s, in presence of 50 mM BARF; Figure 15 shows an EPR signal of Cd₂Pc ' ₃ in the solid state at room temperature (approx. 20°C) ; Figure 16 shows an EPR signal of Cd₂Pc'₃ in the solid state at room temperature (top) , in solution in n-hexane (60mM) at room temperature (middle) and in solution in n-hexane (60mM) at low temperature (bottom) ; and Figure 17 shows a Conductivity profile of Cd₂Pc'₃ over a range of temperatures and voltages. Figure 18 shows a cross sectional view of a MOSFET transistor comprising a phthalocyanine of the present invention. It can be seen that silicon (n-type) forms a substrate, upon which is a layer of metal oxide and upon the metal oxide is a gate electrode which comprises two conducting metal conducting plates between which is the layer of phthalocyanine . Figure 19 shows a synthesis of a heteroleptic, or mixed ligand, complex of the present invention. The grey and black circles on the phthalocyanine ligands represent different substituents. These substitutents may be any suitable substituents, as mentioned herein, for Example those mentioned in connection with formula 1 above, and in the case of the synthesis in the Examples each grey circle represents a straight chain unsubstituted hexyl alkyl group and each black circle represents an unsubstituted oct-7-enyl group . Figure 20 shows a graph of the decomposition of

Complexes I, II, III, IV, VI and 6Cu (discussed in the Examples) under UV light.

The present invention provides a complex M₂L₃ wherein M is Cd(II) and each L is a ligand of Formula 1:

Formula 1, wherein X¹ to X⁴ are each independently selected from CH or N and R¹ to R¹⁶ are each independently selected from H, C_x to C₂₀ alkyls, C₂ to C₂₀ alkenyls, C₇ to C₂₀ arylalkyls, C₇ to C₂o alkylaryls, halides (also referred to herein as halo) , a group of the formula SH, substituents of the formula YR¹⁷, substituents of the formula ZR¹⁸R¹⁹, wherein Y is selected from 0 or S, Z is selected from N or P, and R¹⁷, R¹⁸ and R¹⁹ are independently selected from H, Ci to C₂₀ alkyls, C₆ to Cι₈ aryls, C₂ to C₂₀ alkenyls, C₇ to C₂₀ arylalkyls and C₇ to C₂o alkylaryls. The complex may comprise ligands L that differ in their chemical formula, i.e. not all ligands L in the complex are necessarily the same.

The complex may be a heteroleptic complex. The present invention further provides a complex of the formula M₂LL'₂, wherein both L and L' are ligands as defined herein, and L and L' are different.

The present invention further provides a complex M₂L₂L' wherein M is Cd(II) and L and L' are both ligands of Formula 1:

Formula 1, wherein L and L' are different, X¹ to X⁴ are each independently selected from CH or N and R¹ to R¹⁶ are each independently selected from H, Ci to C₂o alkyls, C₂ to C₂₀ alkenyls, C₇ to C₂o arylalkyls, C₇ to C₂o alkylaryls, halides, a group of the formula SH, substituents of the formula YR¹⁷, substituents of the formula ZR¹⁸R¹⁹, wherein Y is selected from 0 or S, Z is selected from N or P, and R¹⁷, R¹⁸ and R¹⁹ are independently selected from H, Ci to C₂₀ alkyls, C_s to C₁₈ aryls, C₂ to C₂₀ alkenyls, C₇ to C₂₀ arylalkyls and C₇ to C₂₀ alkylaryls. Two adjacent groups from R_x to R₁₆ may together be of the formula -(CH)₄-, so as to, together with the two carbon atoms to which -(CH)₄- is attached, form a benzene ring. The resultant bicyclic system may then be naphthyl. Adjacent groups are, for example, R_x and R₂ or R₆ and R₇, but, for example R₄ and R₅ are not adjacent groups.

R¹ to R¹⁶ may be selected from H or Ci to C₂o alkyl, C₇ to C15 arylalkyls, C₇ to Cι₅ alkylaryls or C₂ to C₀ alkenyls. More preferably, R¹ to R¹⁶ are selected from H, Ci to C₁₀ alkyl or C₃ to Cn alkenyl . R¹ to R¹⁶ may be selected from H and Ci to C₈ alkyl, preferably from H and C to C₈ alkyl. "Alkyl" may be a substituted or non-substituted alkyl. The alkyl group may be a branched or straight-chain alkyl, preferably a straight-chain alkyl. R¹ to R¹⁶ may be selected from C to Ci_o alkyl groups . The alkyl may a branched or straight-chain alkyl. Branched chain alkyls include, but are not limited to, ¹Pr, ^LBu, ^fcBu and ^xPr. Preferably, the alkyl is a straight-chain alkyl, most preferably a C to C_Xo straight-chain alkyl.

"Alkenyl" may be a substituted or non-substituted alkenyl. R¹ to R¹⁶ is preferably selected from C₂ to C₁₆ alkenyl groups, preferably, C₃ to Cπ alkenyl groups. "Alkenyl" may be a terminal alkenyl group.

One or more of R², R³, R⁶, R⁷, R¹⁰, R¹¹, R¹⁴ and R¹⁵ may be H. All of R², R³, R⁶, R⁷, R¹⁰, R¹¹, R¹⁴ and R¹⁵ may be H. Preferably, one or more of R¹, R⁴, R⁵, R⁸, R⁹, R¹², R¹³, and R¹⁶ is H. More preferably, all of R¹, R⁴, R⁵, R⁸, R⁹, R¹²,

R¹³, and R¹⁶ are H. Preferably, one or more of R², R³, R⁶, R⁷, R¹⁰, R¹¹, R¹⁴ and R¹⁵ is independently an optionally substituted Ci to C_2o alkyl or C₂ to C₂o alkenyl . Still more preferably, each of R², R³, R⁶, R⁷, R¹⁰, R¹¹, R¹⁴ and R¹⁵ is independently an optionally substituted C₃ to Cι₀ alkyl or C₃ to Cu alkenyl, with each of the other substituents on the phthalocyanine ring optionally being H.

Preferably, R¹, R⁴, R⁵, R⁸, R⁹, R¹², R¹³ and R¹⁶ are each independently selected from a Ci to C₂o alkyl or C₂ to C₂₀ alkenyl, more preferably the alkyl is a Ci to C₂₀ alkyl, and even more preferably, a C₃ to C₆ alkyl. C₃ alkyl may be ⁿPr or ""Pr. C₄ alkyl may be ⁿBu, ^u or ^fcBu. C_s alkyl may be a straight-chain hexyl group.

R², R³, R⁶, R⁷, R¹⁰, R¹¹, R¹⁴ and R¹⁵ may be H, and R¹, R⁴, R⁵, R⁸, R⁹, R¹², R¹³ and R¹⁶ may each be a straight chain unsubstituted hexyl alkyl, that is, the ligand is an octakis (hexyl) phthalocyanine ligand. As used herein, "aryl" includes, but is not limited to, phenyl and naphthyl, preferably phenyl. Aryl also includes within its meaning in this document heterocyclic aromatic groups including, for example, pyridyl and thiophene groups. "Alkyl", "aryl", "alkenyl", "arylalkyl", and

"alkylaryl" may be substituted or unsubstituted groups. "Substituted" indicates having one or more non-H groups attached to one or more carbons of the group. Substituents include, but are not limited to, halides, Cι_₂₀ alkoxy groups, Cι_₂₀ alkylamino, Q.-20 amides, Cι.₂₀ esters, sulphides, di-sulphides, OH or C0₂H. The substituents may include groups which allow the complex to bind to the surface of a substrate, preferably a metal surface, which includes, but is not limited to a surface comprising gold. Such substituents include, but are not limited to -OH, -C0₂H -SH, or -S-S-R, wherein R is selected from a complex fragment having the formula 1 above or Cι-C₂o alkyl. If it is desired to produce a complex that will be suitable for binding to a metal surface, preferably one or more of Ri to Rι₆ is a Ci to C_2o alkyl sulphide or a Ci to C₂o alkyl thiol . Said alkyl may be a straight chain alkyl and preferably a Ci to C₂o straight chain alkyl, more preferably a C₄ to Cχ₈ straight chain alkyl, most preferably a C₆ to Cχ₅ straight chain alkyl . Preferably the sulphur atom in the alkyl thiol is attached to the most distal carbon of the alkyl group from the tetrabenzoporphyrin ring, to which the alkyl group is also attached. Preferably, the alkyl group to which the sulphur group is attached contains no other substituents. If the complex is of the formula M₂L₂L' as defined above, i.e., where the complex comprises two ligands L of the same formula and third ligand L' of a different formula, and it is desired to attach the complex to a metal surface, preferably L' is a ligand comprising one or more groups which allow the complex to bind to a metal surface as described above and the ligands L do not contain such groups .

"Halides" include F, Cl , Br and I. Preferably, the halides are selected from F and Cl . Preferably, X to X⁴ are each N. Although the present invention is generally described herein with reference to phthalocyanines, the invention is not to be construed as being so limited.

Preferably, the ligand is a substituted or unsubstituted phthalocyanine ligand. "Pc" shall designate a phthalocyanine, which may be either substituted or unsubstituted, unless otherwise stated below. Substituents may be those defined for R¹ to R¹⁵ above.

The complex of the present invention may be, and preferably is, a "triple-decker" complex, wherein the planes of each of the ligands are approximately parallel and a

Cd(II) ion is disposed between each pair of adjacent ligands in the complex.

The complex may be electronically neutral in one of its redox states, that is it has no overall charge. Such a complex with no overall charge has effectively two unpaired electrons and is a radical species. Without being bound by theory, it is believed that it is the unpaired nature of the electrons and the delocalization of the electrons over the π-system of one or more rings that give the present complex its electrically conductive nature. The complex may, however, be charged by the addition or removal of one or more electrons to/from the complex. For instance, exposure of the neutral complex to an oxidizing gas, such as halogens, particularly Cl₂, Br₂ and I₂, nitrogen oxides, particularly N0₂, can lead to oxidation of the complex. The present invention also provides a material or substance comprising a complex M₂L₃ of the present invention. The material or substance may be in solid, liquid or gaseous form. If in liquid form, the material or substance may be in solution. Preferably, the solution comprises a non-polar solvent. Preferred solvents include, but are not limited to, a hydrocarbon liquid comprising alkyl or phenyl compounds, chloroform, dichloromethane, a Ci to Cι₀ alcohol and tetrahydrofuran, and mixtures thereof. The alkyl liquid may be selected from, but is not limited to, pentane and hexane. The phenyl compounds may be selected from benzene, naphthalene and toluene. C_x to C₁₀ alcohol includes, but is not limited to, C_x to C₆ alcohol, preferably, methanol, ethanol and propanol .

The material may be in thermotropic liquid crystalline form.

Preferably, if in solid form, the material is preferably essentially pure. "Essentially pure" indicates a purity of at least 96%, by weight, of the complex in the material, even more preferably, at least 98%, most preferably 99.5%.

If in solid form, the material may be a crystalline material comprising the complex of the present invention. Preferably, the crystalline material is an essentially pure form of a complex of the present invention. The solid form of material may be in the form of a layer deposited on a substrate, preferably a thin layer. "Thin" layer indicates a layer that is preferably less than 1 mm thick, more preferably 100 μm, or less, thick, even more preferably 50 μm, or less, thick, most preferably 150 nm or less, thick. The thickness of the layer of the present invention may be as thin as the thickness of a single complex of the present invention. The thickness of a single complex will be dependent on the constituents on the ligands of the complex, but it may be of the order of 10-20 A (1 x 10^"10 m) . The thickness of the complex is in the present context the thickness as measured along the ^xaxis' of the complex that passes through the approximate N₄ centroid of each ligand when the complex forms a "triple- decker" complex.

The present invention provides a method for forming a thin film of a complex as herein defined on a surface of a substrate, the method comprising applying the complex of the present invention to the surface of the substrate so as to form the thin film.

The thin layer of the material of the present invention may be formed using the Langmuir-Blodgett technique, spin coating, thermal evaporation or molecular self-assembly.

Such techniques are well known to those skilled in the art.

The Langmuir-Blodgett technique is a method in which a thin film of the complex of the present invention is formed on water before being transferred to a solid surface. If using the Langmuir-Blodgett technique and the complex of the present invention is not amphiphilic, it may be desirable to use a straight-chain alkyl carboxylic acid to stabilize the layer of the complex on water.

In the spin coating technique, the complex of the present invention is first dissolved in a solvent and then placed on the surface of a substrate it is desired to coat. The substrate is then spun rapidly to form the thin film on the surface. The invention further provides a method for forming a thin film of a complex as herein described on a surface of a substrate, said method comprising providing a solution of the complex of the present invention, wherein at least one of the ligands of the complex comprises one or more groups which allow the complex to bind to a surface of a substrate, providing a substrate surface contacting said solution of the complex with said substrate surface . The surface may be any surface to which the complex adheres and the complex may be chemically or non-chemically attached to the surface. Surfaces include, but are not limited to, metals or polymeric materials. Preferably, the surface comprises or consists of a metal; even more preferably the metal surface comprises or consists of one or more of silver, platinum or gold. The solution may be as defined above. The thin film may be a self- assembled monolayer of the complex on the substrate.

The present invention further provides a device for the conduction of electricity, the device comprising a material of the present invention. These devices include, but are not limited to, being in the form of a wire, a conducting portion of a printed circuit board, or a conducting portion of a processor chip or integrated circuit. The device may be in the form of a substrate upon at least part of the surface of which is deposited a thin layer of the material . The device may be a semi-conducting device.

The conducting device may be a device comprising a means for varying the bias voltage across the material of the present invention. Preferably, the bias voltage can be varied from -3 to +3 V, preferably from -2.5 to +2.5 V.

This can allow variation of the conductive properties of the material of the present invention, which can allow the material of the present invention to act as a switch with multi-level switching properties. Preferably, the device allows the bias voltage to be controlled to allow the device to display 2 or more conduction states, more preferably 6 or more conduction states, even more preferably 12 conduction states. Additionally, such a device may comprise a means for controlling the temperature, as the conductive properties are also dependent on temperature.

The present invention provides a use of the material of the present invention in an electronic memory device for use in integrated circuit boards (chips) . Preferably said memory device is selected from a random-access memory device and a read only memory device.

The present invention also provides a transistor device comprising a material of the present invention. Preferably, the transistor device comprises the material of the present invention in one or more semi-conducting portions of the transistor, i.e. in the n or p regions of the semi- conductor, preferably in the p region of the semi-conductor. The transistor device may be a field effect transistor, preferably a metal-oxide-semiconductor field-effect transistor (MOSFET) . Those skilled in the art would appreciate that a MOSFET transistor would usually comprise a gate electrode. If the transistor device is a MOSFET device of the present invention and it is wished to use the device as a detector of reducing or oxidising gases, preferably the gate electrode is replaced by a section comprising two conducting metal plates, between which is a material comprising or consisting the complex of the present invention. A layer of insulating metal oxide separates the gate electrode from a silicon substrate. An example of such a MOSFET device is shown in Figure 18. Thus, a capacitor is formed when a voltage is applied between the section comprising two metal plates and the silicon substrate. Use of such a device is exemplified in P.S. Barker et al, Thin Solid Films, 284-285 (1996) 94-97. The present invention provides a device for the detection of an oxidizing gas comprising a material of the present invention. The device may comprise a transistor as defined above, especially a MOSFET transistor defined above in which the gate electrode has been replaced by two metal plates, between which is a material of the present invention. In such a transistor of a given size that comprises a capacitor it will be appreciated that, at a fixed temperature, when a voltage is applied across the capacitor, the rate at which the capacitor is charged will vary depending on the concentration of oxidizing gas in contact with the capacitor. Therefore, for a given gas, a skilled person could determine, for a given temperature and a given size of capacitor the rate of increase of the drain current at a variety of known concentrations of reducing or oxidizing gas. From the data produced, it would be possible to then use the capacitor as a detector to determine an (unknown) concentration of reducing/oxidizing gas in contact with the capacitor.

The material of the present invention has been found to have an electrical conductivity that varies with the temperature of the material and voltage applied across the material. A particular example of a complex of the present invention for which the temperature and voltage-dependent nature of the conductivity is particularly pronounced is Cd₂Pc₃, wherein Pc represents a phthalocyanine ligand, which may be substituted or unsubstituted, and Cd is Cd(II) . The material of the present invention may therefore be used in thermostats or in heat-sensitive electronic-switching devices . The present invention further provides the use of a complex of the present invention in a material suitable for the conduction of electricity.

The present invention further provides the use of a material of the present invention to conduct electricity.

Preferably, the temperature of the material is below 38OK in order to allow conduction of electricity through the material . The present invention further provides the use of a material of the present invention as a semi-conductor or in a semi-conducting device. Preferably the temperature of the material is from 300 to 360K to allow for the material to act as a semiconductor. Preferably, the material is present as a thin layer on an insulating substrate when used in/on a semi-conductor device.

The present invention further provides the use of a material of the present invention as an insulator to electricity. Preferably, the temperature of the material is 38OK or above, most preferably, from 380 K to 40OK.

The present invention further provides a device for controlling the conduction of electricity wherein the device comprises a material of the present invention and a means for controlling the temperature of the material.

The present invention further provides a method of controlling the flow of electricity through a material, the material comprising a complex of the present invention, the method comprises adjusting the temperature of the material as required to either raise or lower the resistance of the material .

The present invention provides a method for use in the detection of an oxidizing substance, the method comprising: providing a material comprising a complex of the present invention, preferably in electrically neutral form, and exposing the material to an oxidizing substance. Preferably, the method further comprises observing the colour of the material before and after contacting the material with the oxidizing substance and then comparing the colour of the material before and after the contacting to detect a change in the material and the presence of the oxidizing substance.

The present invention further provides a method for the detection of an oxidizing substance, the method comprising: providing a material of the present invention comprising a complex of the present invention in electrically neutral form, exposing the material to a substance that may be or may comprise an oxidizing substance and observing a colour-change in the material if the material contacts an oxidizing substance. The colour change of the material is preferably from blue to green.

The present invention provides a method for use in the detection of a reducing substance, the method comprising: providing a material comprising a complex of the present invention, preferably in electrically neutral form, and exposing the material to a reducing substance. Preferably, the method further comprises observing the colour of the material before and after contacting the material with the reducing substance and then comparing the colour of the material before and after the contacting to detect a change in the material and the presence of the reducing substance.

The present invention further provides a method for the detection of a reducing substance, the method comprising: providing a material of the present invention comprising a complex of the present invention in electrically neutral form, exposing the material to a substance that may be or may comprise a reducing substance and observing a colour-change in the material if the material contacts a reducing substance.

The complex of the present invention has different light absorbencies, and therefore it has different colours, at various oxidation states. Therefore, for a given complex of the present invention, it is possible to create a list of a complex's light absorbency properties (and hence colour) under certain conditions, e.g. when in contact with different gases. When detecting whether a substance is oxidizing by exposure to the material, it is possible to tell from the general colour change whether the substance is oxidizing and, on comparison with the list, what oxidising gas may be present .

The present invention further provides a method of synthesizing a complex M₂L₃, the method comprising: contacting a source of Cd(II) with a compound LY₂ to effect formation of the complex, wherein M is Cd(II), Y is H or Li and L is a ligand as defined herein.

The present invention provides a method of synthesizing a complex of the present invention, the method comprising: providing a source of Cd(II), providing a compound of the Formula 2 below:

FORMULA 2 , wherein Y is selected from Li or H, and X¹ to X⁴ and R¹ to R^1S are as defined above, and contacting the source of Cd(II) and the compound of Formula 2 in a liquid to form a mixture.

The source of Cd(II) is preferably a salt of Cd(II). Examples of salts of Cd(II) include, but are not limited to, carboxylic acid salts. Preferably, the carboxylic acid salt is cadmium acetate (Cd (MeC0₂) 2) •

Preferably the liquid is a polar liquid, more preferably an alcohol, even more preferably a Ci to C₆ alcohol, most preferably a C₄-C₆ straight chain alkyl alcohol. The preferred alcohol is pentanol, most preferably 1-pentanol . Preferably the mixture is heated, i.e. at a temperature above room temperature (25°C) , to expedite the formation of the complex of the present invention. Preferably, the mixture is heated at the boiling point of the liquid. In the liquid, a mixture of "1:1" complex, that is ML, and the "2:3" complex, that is M₂L₃, may be formed. If a mixture is formed, preferably the 2:3 complex is purified. It has been found that CdL may be converted to Cd₂L₃ by taking a solution of CdL in CH₂Cl₂/MeOH and recrystallising the Cd₂L₃ from the solution.

The method of synthesizing the complex may further comprise effecting precipitation of the complex from the mixture. Precipitation may be effected by lowering the temperature of the liquid containing the complex below room temperature . The source of Cd(II) is preferably a salt of Cd(II).

Examples of salts of Cd(II) include, but are not limited to, carboxylic acid salts. Preferably, the carboxylic acid salt is cadmium acetate (Cd(MeC0₂)2) •

The present invention further provides a method of synthesizing a complex M₂L_3/ the method comprising: adding a polar protic solvent to a solution comprising a non-protic solvent and a complex of the formula CdL to effect precipitation of the of the complex M₂L₃, wherein M is Cd(II) and L is a ligand as defined herein.

The present invention provides a further method of synthesizing a complex of the present invention, the method comprising: providing solution comprising a non-protic solvent and a complex of the formula CdL, wherein L is a ligand of formula 1 as defined above, adding a protic polar solvent to the solution and allowing the complex of the present invention to precipitate. The polar protic solvent is preferably an alcohol, even more preferably a d to C₆ alcohol, most preferably methanol or ethanol . The non-protic solvent is preferably dichloromethane. The ratio of protic solvent to non-protic solvent, by volume, may be in the range of from 1:10 to 1:0.5, preferably of from 1:5 to 1:1, most preferably approximately 1:4.

The invention further provides a method of synthesizing a 'mixed ligand' complex, Cd₂LL'₂, wherein L and L' are different ligands. The method comprises: contacting a compound LY₂, with a complex CdL' in a non-protic solvent to form a mixture, adding a polar protic solvent to the mixture to effect precipitatation of the complex M₂LL'₂, wherein M is Cd(II), Y is H, L and L' are as defined in claim 14 and the molar ratio of LY₂:CdL' is from 2:3 to 2:5.

The method may comprise: providing n moles of a compound LH₂, wherein L is a moiety of Formula 2 defined above, wherein Y is H, providing m moles of a complex CdL', wherein L' is a ligand of Formula 2 as defined above, wherein n-.m is from 1:1.5 to 1:2.5, preferably from 1:1.8 to 1:2.2, more preferably about 1:2, contacting the n moles of the compound LH₂ with the m moles of a complex CdL in a non-aqueous solution, adding a polar solvent to the non-aqueous solution and allowing the complex Cd₂LL'₂ to precipitate. Preferably, the non-polar solution is a non-protic solution, most preferably, dichloromethane. Preferably, the polar solvent is an alcohol, more preferably a Ci to C₆ alkyl alcohol, preferably a Ci to C₄ alcohol, most preferably, methanol.

The precipitation of Cd₂LL'₂ may be expedited by cooling the non-aqueous solution containing the LH₂ and CdL' below 25°C, preferably below 15°C, most preferably below 10°C, as long as the solution is not allowed to be below its freezing point .

The present invention further provides a method of forming a thin layer of the material of the present invention on or in a substrate, the method comprising placing a solution of the complex onto part of the surface of a substrate and moving the substrate relative to the solution of the substrate to allow the solution of the complex to spread out over the surface of the complex. Preferably, the substrate is spun. The thin layer may be a self-assembled monolayer of the complex on the substrate.

The present invention further provides a method of forming cadmium sulphide nanoparticles comprising providing a material of the present invention and contacting the material with H₂S gas to form cadmium sulphide.

The complexes of the present invention may be used in a photovoltaic device.

The present invention provides a photovoltaic device comprising the complexes of the present invent :!ιon. The present invention will now be exemplified with reference to the following non-limiting Examples.

Examples .

The Examples below demonstrate syntheses of a cadmium(II) triple-decker phthalocyanine sandwich complexes. It is believed that the class of molecule combining the triple-decker architecture and a diradical species is unprecedented and that the physical properties associated with such a structure are unique. The novel complexes of the Examples contain eight alkyl chains on each phthalocyanine moiety within the complex and these provide solubility in a variety of solvents.

In the following Examples Pc ' refers to a ligand of Formula I wherein X¹ to X⁴ are each N, R², R³, R⁶, R⁷, R¹⁰, R¹¹. R¹⁴ and R¹⁵ are each H, and R¹, R⁴, R⁵, R⁸, R⁹, R¹², R¹³ and R¹⁶ are each a C₆H₁₃ straight chain alkyl group .

Example 1: Synthesis of cadmium phthalocyanines wherein the Cd.Pc¹ ratio are 1:1 AND 2:3 (the "1:1" complex, CdPc', and Complex I, Cd₂Pc'₃, respectively).

1,4, 8, 11, 15, 18, 22, 25-Octakis (hexyl) hthalocyanine (500 mg, 0.42 mmol) in 1-pentanol (20ml) was brought to reflux. Cadmium acetate hydrate (99.99+%) (excess) was added and reflux continued for 60 minutes. The mixture was left to cool to rt . MeOH (50 ml) was added and the flask left in the fridge overnight. The green solid was filtered and washed with MeOH. The green solid was redissolved in THF and the solution filtered to remove the insoluble cadmium salt residue. The solvent was then removed under reduced pressure and the solid recrystallised rapidly from THF/MeOH to yield a green powder (350 mg, 64%) comprising the '1:1' complex.

[MALDI-MS: isotopic cluster at 1298. λ_max (n-hexane): 709, 643 nm. Found: C, 74.15; H, 8.72; N, 8.47%. C₈₀H₁₁₂N₈Cd requires: C, 74.01; H, 8.69; N, 8.63%. δ (400 MHz, C_SD₆) 7.65 (brs, 8H) , 4.4 (brs, 16H) , 2.2 (brs, 16H) , 1.7 (brs, 16H) , 1.25-1.45 (m, 32H) , 0.85 (t, 24H) ppm. δ (400 MHz, C6D6 containing pyridine-d5) 7.75 (s, 8H) , 4.63 (t, 16H) , 2.2 (m, 16H) , 1.6 (m, 16H) , 1.1-1.3 (m, 32H) , 0.75 (t, 24H) ppm.

Transitions observed optically K→Di 131.1 °C, D_1→D₂ 166 °C, D₂-→D₃ 192.8 °C, D₃-→I 244.4 °C]

In one experiment, a sample of CdPc' (1:1) was recrystallised from pyridine to yield dark crystals suitable for X-ray analysis. The structure resolved from X-Ray analysis (not shown) corresponds to a molecule with one Cd in the centre, slightly out of plane, bearing an acetate ligand coordinated through its oxygen atoms to the Cd atom. The cadmium is hexa-coordinated.

It appears that in the synthesis of "CdPC (1:1)" as described above in the Examples, the final product comprises the mono-acetate ligated derivative, i.e. CdPc 'Ac (1,4, 8, 11, 15, 18 , 22 , 25-Octakis (hexyl) phthalocyaninato cadmium(II) acetate).

[MALDI-MS: isotopic clusters at 2483.7 [CdPc₂] , 1555.0, 1582.1, 1298.8 [M-acetate] , 1186.9 [M-Cd-acetate] . λ_max (n- hexane) : 718 nm. δ (400 MHz, C₆D₆) 7.9 (s, 8H) , 4.82

(quintet, 8H) , 4.68 (quintet, 8H) , 2.31 (m, 16H) , 1.71 (quintet , 16H) , 1 . 39 (quintet , 16H) , 1 . 28 (quintet , 16H) , 0 . 81 (t , 24H) , - 0 . 29 ( s , 3H) ppm]

In further experiments, recrystallisation of CdPc' (1:1) from pyridine yielded dark blue crystals of [1,4, 8, 11, 15, 18, 22, 25-octakis (hexyl) phthalocyaninato] (pyridine) cadmium. The structure resolved from X-ray analysis (not shown) corresponds to a molecule with a central Cd atom, removed well out of the N4 mean plane, bearing a pyridine axial ligand. There is considerable distortion from a planar ring system.

[δ_H (CDC1₃, 400 MHz) 7.79 (s, 8H) , 7.01 (t, 1H) , 6.35 (m, 2H) , 5.35 (m, 2H) , 4.53 (m, 16H) , 2.11 (m, 16H) , 1.34 (m, 16H) , 1.22 (m, 32H) , 0.8 (t, 24H) ppm. _∞ (CH₂C1₂) 709 nm] .

1,4, 8, 11,15, 18, 22, 25-Octakis (hexyl) phthalocyaninato cadmium (350 mg, 0.27 mmol) was recrystallised thrice from CH₂Cl₂-MeOH to afford a dark blue crystalline material of the formula Cd₂Pc'₃ (Complex I) (150 mg, 44%).

[MALDI-MS: isotopic clusters at 2598.7 [M-Pc¹], 2484.8 [M-CdPC], 1299.1 [M-CdPC₂], 1187.1 [M-Cd₂PC₂]. λ_max (n- hexane) : 718 (ε= 1.3x105), 599 (ε = 0.6x105), 550, 484 nm. Found: C, 76.06; H, 8.95; N, 8.79%. C₂₄oH₃₃₆N₂4Cd2 requires: C, 76.17; H, 8.95; N, 8.88%. Mp . 220 °C (decomposes to metal- free) . ]

Complex I was originally obtained, surprisingly, during product purification of a reaction designed to prepare a simple cadmium phthalocyanine, viz, octahexyl-CdPc ' , by reaction of cadmium acetate and pre-formed octa-hexyl metal- free phthalocyanine (Figure 5) . The two cadmium atoms in Complex I are sandwiched between three phthalocyanine rings and are therefore octa-coordinated, as shown from the X-ray data obtained from the crystals. In the absence of any further cations present in the crystal, the species must correspond to a diradical .

Complex I has been fully characterised and the relevant data are given below. Its physical properties have been investigated by EPR spectroscopy and cyclic voltammetry. Its remarkable temperature dependent conducting properties have been evaluated and the material has been shown to form nanoparticles of the inorganic semiconductor, CdS, when treated with H₂S gas . CdPc' (shown in Figure 5) was produced by direct insertion of cadmium, using cadmium acetate in refluxing 1- pentanol, into the metal-free 1,4,8,11,15,18,22,25- octakis (hexyl) -phthalocyanine. The crude sample of CdPc¹, a green material, was first precipitated out using a large excess of methanol. The excess cadmium acetate was removed by filtration following dissolution of the green material in THF.

1, 4, 8, 11, 15, 18, 22, 25-Octakis (hexyl) phthalocyaninato cadmium(II) (the "1:1" complex) could be obtained pure by a quick crystallisation from THF/methanol . The product produced by the crystallisation sometimes contained Complex I. The 1:1 complex and Complex I could then be purified by column chromatography on neutral alumina, first eluting with a 10:1 mixture of petroleum ether:THF. A purple-blue fraction was collected first which corresponded to Complex I. The green band containing the 1:1 complex in the upper portion of the column could be eluted using a mixture of THF-methanol (2%) . Quick recrystallisation of the 1 : 1 product from the column in THF/methanol afforded the pure 1:1 product. Slow crystallisation induced the transformation of the 1:1 complex into the 2:3 complex. This latter compound could be obtained pure either from material recovered from column chromatography or by consecutive recrystallisations. A sample of the 1:1 complex was totally transformed after three recrystallisations from a solvent of dichloromethane-methanol (75% by volume of DCM, 25% by volume of MeOH) .

Both the 1:1 complex and Complex I gave satisfactory elemental analyses, 1H NMR spectra and MALDI mass spectra. The 1:1 complex exhibited an isotopic cluster at 1298 corresponding to the expected molecular mass (Figure 6) . The MALDI mass spectrum of Complex I did not show the expected molecular ion at 3782, however it showed isotopic clusters at: 2598.7, corresponding to M - Pc ' ; 2484.8 corresponding to M - CdPc'; 1299.1 corresponding to M - CdPC₂; and 1187.1 corresponding to M - Cd₂Pc ' ₂. These data are in good agreement with the proposed sandwich structure of Complex I .

The absence of the molecular ion peak for Complex I is probably indicative of the instability of the molecule under the conditions of the experiment. The 1H NMR spectrum in benzene-d₆ of the 1:1 complex showed the expected signals corresponding to the aromatic protons at 7.65 ppm and the benzylic protons at 4.4 ppm. However, these signals were very broad. The addition of a drop of pyridine-d₅ led to the sharpening of these signals to well-defined singlet and triplets, respectively. In benzene-d_s, the Complex I yielded very broad NMR peaks. Aromatic and benzylic protons are not observed distinctly, probably because of their proximity to the paramagnetic centre. Chloroform-d₃ was found to be a better solvent for this system. The 1H NMR spectrum exhibited a broad aromatic singlet. It appears that the benzylic protons signals are significantly shifted upfield relative to the 1:1 complex and are found at 2.65 ppm. The remainder of the spectrum is difficult to interpret although it is apparent that some of the signals in the alkyl chains are also shifted upfield with triplets visible at 0.82 and 0.93 ppm. These results confirm the paramagnetism of Complex I, which strongly perturbs the proton signals.

Addition of pyridine-d₅ to the NMR tube resulted in a near-instant colour change from blue to green, possibly due to the breaking up of the triple-decker sandwich complex. The most significant difference lies in the UV-visible spectra. The 1:1 complex yields a green solution in n-hexane and exhibits the expected UV-vis spectrum with a sharp non- split Q-band at 709 nm characteristic of metallated phthalocyanines . Complex I yields a dark blue solution in n- hexane and exhibits a complex spectrum with absorption bands at 867, 718, 646, 599, 556 and 483 nm (Figure 7) . Photodegradation in aerated solvents led to the metal-free compound.

Comparison of IR spectra (1800-600 cm^"1 region) showed two very different absorption patterns (Figure 8) . Spin- coated films of Complex I were prepared from n-hexane solutions (2 mg/0.1 ml) at 2000 rpm on glass slides. The films appeared uniform and dark blue in colour. The UV-vis spectrum was similar to the solution spectrum, indicating minimum aggregation.

In a preliminary experiment, a film of the Complex I was exposed to I₂ vapours and the colour of the film was observed to change instantly from blue to green. The UV-vis spectrum of the oxidised film was recorded. The process appears totally reversible and the film reverted to blue within a few minutes in air, with the original UV-vis spectrum band shape. The film was submitted to a few cycles of these without apparent degradation (Figure 9) .

X-RAY CRYSTAL STRUCTURE OF COMPLEX I Data collection, structure determination and refinement The crystals of Complex I are black, needle prisms. A single crystal, ca 0.7 x 0.12 x 0.12 mm, was mounted in oil on a glass fibre and fixed in the cold nitrogen stream on a Rigaku R-Axis lie image plate diffractometer equipped with a rotating anode X-ray source (Mo-Kα radiation) and graphite monochromator . Using 4° oscillations, 48 exposures of 52min. each were made. Total # of reflections recorded, to θ_max = 25.4°, was 24748 of which 15926 were unique (Rint = 0.076); 9586 were 'observed' with I>2σι. Data were processed using the DENZO/SCALEPACK programs.

Information on these programmes may be found in Z.

Otwinowski, W. Minor 'Processing of X-ray diffraction data collected in oscillation mode', Methods in Enzymology, Vol.

276, Macromolecular Crystallography, part A, Eds. C.W. Carter, Jr., R.M. Sweet, Academic Press 1997, 307-326. The structure was determined by the direct methods routines in the SHELXS program and refined by fullmatrix least-squares methods, on F2's, in SHELXL. Further details on SHELXS programme may be found in G.M. Sheldrick, SHELX- 97, Programs for crystal structure determination (SHELXS) and refinement (SHELXL) , University of Gδttingen, Germany 1997. The non-hydrogen atoms were refined with anisotropic thermal parameters . Hydrogen atoms were included in idealised positions and their Uiso values were set to ride on the Ueq values of the parent carbon atoms. At the conclusion of the refinement, wR₂ = 0.120 and Ri = 0.099 [see the reference in relation to SHELXS above] for all 15926 reflections weighted w = [σ² (F₀ ²) + (0.0436P) ²] ^_1 with P = (F₀ ²+2Fc²)/3; for the 'observed' data only, R_x = 0.052.

In the final difference map, the highest peaks (to ca 0.48 eA^"3) were close to the Cd atom. Scattering factors for neutral atoms were taken from the reference: 'International Tables for X-ray Crystallography', vol. C, Kluwer Academic Publishers, Dordrecht 1992 , 500, 219, 193.

Computer programs used in this analysis have been noted above or in Table 4 of the reference: S.N. Anderson, R.L. Richards, D.L. Hughes J^". Chem . Soc . , Dal ton Trans . 1986, 245. These were run on a Silicon Graphics Indy at the

University of East Anglia, or a DEC-AlphaStation 200 4/100 in the Biological Chemistry Department, John Innes Centre.

Complex I, comprises three phthalocyanine ligands linked by coordination through two cadmium ions (Figure 10) . Complex I lies on a centre of symmetry. We refer to the 'outer' ligands, of N(l)-N(40) and N(l ' ) -N(40' ) and their side-chains, and to the 'central' ligand, of N(51)-N(70) and the symmetry related N(51' ) -N(70' ) and their side-chains. The Cd atoms lie between the outer and central ligands, displaced 1.222(2) A from the N₄ mean-plane of the outer ligand, and 1.742(2) A from the N₄ plane of the central ligand. Correspondingly, the Cd- N distances to the outer ligand have a mean value of 2.340(3) A whilst the mean distance to the central ligand is 2.62(3) A.

Coordination of the Cd atoms is eightfold in a pattern closer to square-antiprism than square prism; the mean acute torsion angle of the type N (1) -Xl-X2-N(51) is 34.1(2)° (where XI is the centroid of the four coordinated N atoms of the outer ring, and X2 is the centre of symmetry) (Figure 11) . In a strict square-antiprism, the torsion angle would be 45°; in a square prism, the angles are 0°.

The central ligand is approximately planar; the two independent C₆ rings are tilted 3.76(11)° and 1.90(10)° from the central N4 plane, and opposite C6 rings are (by symmetry) parallel.

The outer ligands have an 'inverted umbrella' conformation; the four C6 rings tilt away from the N₄ mean- plane by angles of 12.57(12)°, 8.72(12)°, 13.17(12)° and 8.65(12)°, and opposite C6 rings diverge by 24.12(14)° and 17.18 (14) ° (Figure 12) . In this triclinic cell, all the Cd₂Pc'₃ molecules lie parallel. There is stacking along the a axis, with substantial overlap of the cores of the outer ligands with their symmetrically related neighbours (Figure 13) .

CYCLIC VOLTAMMETRY The different redox processes of Complex I were studied by cyclic voltammetry. The voltammograms in CH₂C1₂ and THF (Figure 14) showed several reversible monoelectronic and multielectronic transfer processes. This range of redox processes is remarkable and suggests that the properties of the material should be very sensitive to a variety of different oxidants and reductants and thus should have potential as a sensor. See above for the electronic spectra resulting from exposure of a film to iodine vapour which causes a colour change from blue to green.

EPR SPECTROSCOPY The EPR spectra of Complex I in the solid state at room temperature show a strong signal at g = 2.008 (Figure 15) . This value is consistent with the occurrence in whole or in part of a phthalocyanine radical species.

Similar g values are obtained in solution in n-hexane (60 μM) , both at room temperature and at low temperature. The EPR line appears slightly narrower at low temperature (Figure 16) .

CONDUCTIVITY The conductivity of a spin-coated thin film of Complex I deposited onto interdigitated electrodes was measured and found to possess a unique profile. Four regions are distinguishable over a range of temperature and voltages (see Figure 16) . Region A: between 100-200 K, the nature of the observed conductivity is independent of temperature. There is then a sudden jump in conductivity at 220 K. Region B: between 220- 280 K, there is a continuous increase in conductivity with temperature at a particular voltage. Region C: between 300- 360 K, the conductivity is independent of voltage again. There is then a sudden jump from insulating to semiconducting state at a particular voltage. Region D: between 380-400 K and above, the film behaves as an absolute insulator.

This unusual behaviour suggests that the material and analogues could find applications in heat sensitive electronic switching devices, e.g. as a molecular thermostat in nanoscale machines .

PHOTOSTABILITY STUDY The stability of the following compounds was assessed and compared using UV and visible light.

Complex I R=n-C₆H₁₃ Complex VI R=n-C₆Hι₃ Complex II R=n-C₈Hι₇ Complex III R-n-Cι₀H2i Complex IV R= (CH₂) ₆CH=CH₂

Spin-coated films of the compounds were obtained onto glass slides from suitable solutions in an organic solvent. One set of slides was exposed to visible light and a second set of slides was exposed to UV light. The photodecomposition was assessed by monitoring the decrease in the absorption of the Q-band in the UV spectra of the films. 6Cu was used as the reference as Cu derivatives are known to be generally more stable. A graph showing the decomposition of films of complexes 6 Cu, I, II, II, IV and VI is shown in Figure 20. The results are discussed below.

It is apparent that for most of the complexes there is an initial sharp decrease in absorption of the Q-band, followed by a levelling. This indicates that following an initial fast rate of decomposition, the decomposition slows significantly.

It is clear from the Figure 20 that the most stable of the cadmium derivatives tested are Complex VI and Complex IV. Complex IV exhibits a stability comparable to that of 6Cu with 27% decrease over the same period. Complex VI appears the most stable with only 9% decrease. As expected, decomposition under normal visible light occurs at a slower rate. 40% decomposition was observed over 75 days for Complex I.

Synthesis of further homoleptic dicadmium phthalocyanines

I Synthesis of starting materials

Synthesis of Metal-free 1,4,8,11,15,18,22,25- octakis (alkenyl) phthalocyanines

2-(0ct-7-enyl_i)furan: Furan (4.3 g, 0.063 mol) in tetrahydrofuran (30 ml) was cooled to -78 °C. n-BuLi (2.5 M in hexane) (35 ml, excess) was added and the solution allowed to warm to room temperature and stirred for 5 hrs.

The suspension was cooled to -78 °C and 8-bromooct-l-ene (12 g, 0.063 mol) was added. The solution was allowed to warm to room temperature and stirred overnight. The solution was poured onto water (100 ml) and the organics were extracted with diethylether (3x50 ml) , washed with brine (50 ml) , dried (MgS0₄) , filtered and the solvent evaporated to yield the desired product (12.9 g, 100%). [δ_H (CDC1₃, 60 MHz) 7.3 (m, 1H) , 6.3 (m, 1H) , 5.5-6.2 (m, 2H) , 4.8-5.2 (m, 2H) , 2.6 (t, 2H) , 1.2-2.3 (m, 10H) ppm].

2- ( Undec -10- enyl ) furan The product was prepared in the same way using 11- bromoundec-1-ene (13 g, 0.056 mol). This yielded 2- (undec- 10-enyl) furan (12.4 g, 100%) as a pale orange oil which was used without further purification. [δ (CDC1₃, 60 MHz) 7.3 (m, 1H) , 6.3 (m, 1H) , 5.5-6.2 (m, 2H) , 4.8-5.2 (m, 2H) , 2.6 (t, 2H) , 1.2-2.3 (m, 16H) ppm].

2, 5-Bis(oct - 7-enyl )furan : 2 - (Oct-7-enyl) furan (12.9 g, 0.063 mol) in tetrahydrofuran (30 ml) was cooled to -78 °C. n-BuLi (2.5 M in hexane) (30 ml, excess) was added and the solution allowed to warm to room temperature and stirred for 5 hrs. The suspension was cooled to -78 °C and 8-bromooct- 1-ene (13 g, 0.068 mol) was added. The solution was allowed to warm to room temperature and stirred overnight. The solution was poured onto water (100 ml) and the organics were extracted with diethylether (3x50 ml) , washed with brine (50 ml) , dried (MgS0₄) , filtered and the solvent evaporated to yield the desired product (19.2 g, 100%) . [δ_H (CDC1₃, 60 MHz) 5.5-6.2 (m, 2H) , 5.8 (s, 2H) , 4.8-5.2 (m, 4H), 2.6 (t, 4H) , 2.0 (m, 4H) , 1.7 (br s, 16H) ppm].

2, 5- Bis ( undec -10- enyl ) furan The product was prepared in the same way using 2- (undec-10-enyl) furan (12.4 g, 0.056 mol) and 11-bromoundec- 1-ene (13 g, 0.056 mol). This yielded 2 , 5-bis (undec-10- enyl) furan (22.23 g, 100%) as a pale orange oil which was used without further purification. [δ_H (CDC1₃, 60 MHz) 5.5- 6.2 (m, 2H) , 5.8 (s, 2H) , 4.8-5.2 (m, 4H) , 2.6 (t, 4H) , 2.0 (m, 4H) , 1.7 (brs, 28H) ppm].

3 , 6-Bis (oct - 7-enyl )phthaloni trile : 2 , 5-Bis (oct-7- enyl) furan (19.2 g, 0.063 mol) and fu aronitrile (7 g, 0.09 mol) in dry tetrahydrofuran (10 ml) were placed in the fridge for 14 days. ^XH NMR spectrum indicated ca. 40% conversion to the desired adduct . This was added to dry tetrahydrofuran (100 ml) previously cooled to -78 °C. Lithium bis (trimethylsilyl) amide (1 M in THF) (100 ml) was added slowly and the solution was allowed to warm up to room temperature and was stirred overnight. The black solution was poured onto water (300 ml) and the organics extracted with diethylether (3x100 ml) , washed with brine (100 ml) , dried (MgS0) , filtered and the solvent evaporated. The product was purified by column chromatography over silica (eluent: petroleum ether (bp. 40-60 °C) /dichloromethane 5:1, increasing polarity to 1:1). The product was recrystallised from ethanol (3.58 g, 16%) [Mp.34.4 °C. m/z 348 [M] . Found: C, 82.42; H, 9.38; N, 7.84%; C₂₄H₃₂N₂ requires: C, 82.71; H 9.25: N, 8.04%. δ_H (CDCl₃, 60 MHz) 7.4 (s, 2H) , 5.4-6.0 (m, 2H) , 4.7-5.2 (m, 4H) , 2.8 (t, 4H) , 1.2-2.2 (m, 20H) ppm].

3, 6 -Bis ( undec- 10 -enyl ) phthalonitrile This product was prepared in the same way using 2,5- bis (undec-10-enyl) furan (20 g, 0.054 mol) and fumaronitrile (4.5 g. 0.058 mol). This yielded 3 , 6-bis (undec-10- enyl) phthalonitrile (3.56 g, 15%). [δ_H (CDCl₃, 60 MHz) 7.44 (s, 2H) , 5.5-6.2 (m, 2H) , 4.8-5.2 (m, 4H) , 2.9 (t, 4H) , 2.0 (m, 4H) , 1.4 (brs, 28H) ppm. Mp . 58°C. m/z 433 [M⁺] . Found:

C, 83.12; H, 10.03; N, 6.01%. C₃₀H₄₄N₂ requires: C, 83.28; H, 10.25; N, 6.47%] . Metal -free 1,4 , 8 ,11,15, 18,22 ,25 -octakis (oct-7'- enyl ) phthalocyanine : 3 , 6-Bis (oct-7-enyl) -phthalonitrile (1.38 g, 0.004 mol) was refluxed in pentan-1-ol (10 ml). Lithium metal (excess) was added slowly to the refluxing solution. Reflux was continued in the dark for 6 hrs. The solution was allowed to cool and acetic acid (10 ml) was added and the solution stirred for 30 mins . Methanol (50 ml) was added and the green precipitate was filtered and washed with methanol. The product was purified by column chromatography over silica (eluent: petroleum ether (bp. 40- 60 °C) /dichloromethane 4:1). The product was recrystallised from tetrahydrofuran-methanol (520mg, 38%) [m/z 1396.2 [M] . Found: C, 82.6; H, 9.36; N, 7.84%; C_9eH₁₃₀N₈ requires: C, 82.59; H, 9.39; N, 8.03%. λ_max (dichloromethane, εxlO⁵) 727 (0.63), 700 (0.52) nm. M.p. 80.7 °C (K→D₂) 130.5 °C (O₂→O_X)

151.7 °C (D_1→I) . δ_h (c₆d₆, 270 mhz) 7.78 (s, 8H) , 5.6-5.8 (m, 8H) , 4.9-5.1 (m, 16H) , 4.59 (t, 16H) , 2.22 (m, 16H) , 1.93 (m, 16H) , 1.69 (m, 16H) , 1.3-1.5 (m, 32H) , -0.39 (s, 2H) ppm] .

Metal -free 1,4 ,8,11,15,18 ,22 ,25 -octakis (undec-10 - enyl ) phthalocyanine

The product was prepared in the same way using 3,6- bis (undec-10-enyl) phthalonitrile (2.025 g, 0.047 mol). This yielded metal-free 1, 4, 8, 11, 15, 18, 22 , 25-octakis (undec-10- enyl) phthalocyanine (774 mg, 38%). [δ_H (C_SD₆, 270 MHz) 7.8 (s, 8H) , 5.6-5.8 (m, 8H) , 4.9-5.1 (m, 16H) , 4.6 (t, 16H) , 2.3 (m, 16H) , 1.8-2.0 (m, 16H) , 1.6-1.8 (m, 16H) , 1.4 (m, 16H) , 1.2-1.4 (m, 64H) , -0.4 (s, 2H) ppm. m/z 1732 [M⁺] . Found: C, 83.48; H, 10.18; N, 6.23%. C₁₂₀H₁₇₈N₈ requires: C, 83.18; H, 10.35; N, 6.47%. λ_max (dichloromethane, εxlO⁵) 728.5 (1.23), 700.5 (1.02) nm. Mp . K-D 52.5°C D-I 116.7°C] .

Synthesis of metal-free 2,3 ,9 ,10 ,16 ,17 ,23 ,24 octakis (hexyl) phthalocyanine 4 , 5-Bis( hexyl ) phthalonitrile

Triphenylphosphine (1.25 g, 5 mmol), NiCl₂(PPh₃)₂ (1.56 g, 2.5 mmol) and LiCl (3 g, 70 mmol) were stirred in dry THF (50 ml) under N₂ atmosphere to yield a blue solution. A solution of 2.5 M ια-BuLi in hexanes (2 ml, 5 mmol) was added via a syringe and the solution turned deep red. 4,5- Dichlorophthalonitrile (5 g, 25 mmol) was added at once and the solution changed colour to light brown. This was left to stir for a few minutes, and then the solution was cooled down to -78°C. A 0.5 M solution of hexylzincbromide in THF (100 ml, 50 mmol) was added dropwise. The mixture was left to warm to room temperature and was stirred overnight. The solution was poured into 5% aqueous HCl (100 ml) and the organics extracted with ethylacetate (2x50 ml) . These were further washed with 5% aq. HCl (30 ml) , 5% aq. NaOH (30 ml) and brine (30 ml) , dried (MgS0₄) , filtered and the solvents removed under reduced pressure. TLC analysis (eluent: petroleum ether (bp. 40-60°C) /dichloromethane 1:1) indicated 3 main products which were separated by column chromatography on silica. A first separation was performed (eluent: petroleum ether (bp. 40-60°C) /dichloromethane 1:1) and two fractions were obtained, the first containing triphenylphosphine, the second a mixture of products. A second separation was performed on this latter fraction (eluent: petroleum ether (bp. 40-60°C) /ethylacetate 5:1).

Three products were obtained and identified by ^αH NMR spectroscopy as 4-hexylphthalonitrile [δ_H (CDC1₃, 400 MHz) 7.7 (d, IH, J 10Hz) , 7.59 (s, IH) , 7.52 (d, IH, J 10Hz) , 2.7 (t, 2H) , 1.6 (quintet, 2H) , 1.29 (m, 6H) , 0.81 (t, 3H) ppm], 4-chloro-5-hexylphthalonitrile [δ_H (CDC1₃, 400 MHz) 7.78 (s, IH) , 7.68 (s, IH) , 2.79 (t, 2H) , 1.62 (quintet, 2H) , 1.22- 1.38 (m, 6H) , 0.88 (t, 3H) ppm] and the desired 4,5- bis (hexyl) phthalonitrile (1.12 g, 15%) . [δ_H (CDC1₃, 400 MHz) 7.57 (s, 2H) , 2.67 (t, 4H) , 1.55 (quintet, 4H) , 1.23-1.4 (m, 12H) , 0.85 (t, 6H) ppm] . Metal -free 2 ,3 ,9 ,10 , 16 , 17 ,23 ,2 -octakis (hexyl )ph thalocyanine

The product was prepared in the same way using 4,5- bis (hexyl) phthalonitrile (1.12 g, 3.75 mmol). This yielded metal-free 2 _; 3 , 9, 10, 16, 17, 23, 24-octakis (hexyl) hthalocyanine (500 mg, 45%) . [ ax (THF) 704.5, 666.5 nm] .

Synthesis of metal -free 2, 3 , 9, 10 , 16, 17 ,23 , 24 -octakis (hex-5- enyl ) phthalocyanine 2, 3 -Bis (hex-5-enyl )buta-l, 3 -diene To a solution of t-BuOK (11 g, 0.1 mol) in dry n-pentane (50 ml) under N₂ was added at rt a solution of 2.5M n-BuLi in hexanes (40 ml, 0.01 mol). The mixture was stirred for 10 min. Then a solution of buta-1, 3-diene (4.1 g, 0.05 mol) in n-pentane (10 ml) was added dropwise. The solution was stirred for 30 min and turns deep orange. The solution was cooled to -78°C. Dry THF (50 ml) was added, followed by 5- bromopentene (15 g, 0.1 mol) in THF (20 ml). The solution was left to warm to room temperature and stirred overnight . The pale yellow solution was poured into water (200 ml) and the organics extracted with ethylacetate (3x 50 ml) . These were dried (MgS0₄) , filtered and the solvents removed under reduced pressure to leave a pale yellow oil (12 g crude) which was used further without purification. [δ (CDC1₃, 400 MHz) 5.75-5.88 (m, 2H) , 4.92-5.07 (m, 8H) , 2.24 (t, 4H) , 1.3-2.0 (m, 12H) ppm].

Diethyl -4 , 5-di (hex-5-enyl )phthalate

The pale yellow crude oil obtained above (12 g) containing 2, 3-bis (hex-5-enyl) buta-1, 3-diene was refluxed in toluene (50 ml) in the presence of diethylacetylenedicarboxylate (7 g, 41 mmol) for 1 hr. DDQ (10 g, 44 mmol) was added slowly in portion to the refluxing solution. Reflux was continued for lhr. After cooling, the solid was filtered off. The solvent was removed under reduced pressure and the residue purified by column chromatography on silica (eluent: CH₂C1₂- petroleum ether (bp. 40-60°C) to yield diethyl-4,5-di (hex-5- enyl) phthalate as a pale orange oil (3.8 g, 0.01 mol). [δ_H

(CDC1₃, 400 MHz) 7.48 (s, 2H) , 5.72-5.82 (m, 2H) , 4.9-5.0

(m, 4H) , 4.25-4.35 (q, 4H) , 2.63 (t, 4H) , 2.08 (m, 4H) , 1.57

(quintet, 4H) , 1.48 (quintet, 4H) , 1.32 (t, 6H) ppm].

4 , 5 -Bis (hex- 5 -enyl )phthalic acid

Diethyl-4, 5-di (hex-5-enyl) phthalate (3.8 g, 0.01 mol) was refluxed in ethanol (50 ml) . A 20% solution of NaOH in water (5 ml) was added and reflux continued for 2 hrs. After cooling, this was poured into 5% aq. HCl (100 ml) . The organics were extracted with ethylacetate (2x 50 ml) , washed with brine (50 ml) , dried (MgS0₄) , filtered and the solvent evaporated to yield 4 , 5-bis (hex-5-enyl) phthalic acid as a pale thick oil (3.1 g, 94%) . [ δ_H (CDC1₃, 400 MHz) 9.79 (brs, 2H) , 7.62 (s, 2H) , 5.72-5.82 (m, 2H) , 4.9-5.0 (m, 4H) , 2.65 (t, 4H) , 2.12 (m, 4H) , 1.6 (quintet, 4H) , 1.5 (quintet, 4H) ppm] .

4 , 5 -Bis (hex- 5 -enyl ) phthalic anhydride 4, 5-Bis (hex-5-enyl) phthalic acid (3.1 g, 9.4 mmol) was refluxed in acetic anhydride (50 ml) for 3 hrs. The solvent was removed under reduced pressure and the residue was filtered through silica, eluent: dichloromethane, to afford 4, 5-bis (hex-5-enyl) phthalic anhydride as a pale oil (2.5 g, 84%). [δ_H (CDC1₃, 400 MHz) 7.75 (s, 2H) , 5.72-5.82 (m, 2H) , 4.9-5.0 (m, 4H) , 2.74 (t, 4H) , 2.1 (m, 4H) , 1.62 (quintet, 4H) , 1.5 (quintet, 4H) ppm]. 4 , 5 -Bis (hex- 5 -enyl )phthalimide

4, 5-Bis (hex-5-enyl) hthalic anhydride (2.5 g, 7.9 mmol) and urea (500 mg, 8.3 mmol) were heated until urea was entirely melted. Heating was applied for another 10 min then the mixture was cooled and solidified. The residue was dissolved in hot ethanol (20 ml) . The insoluble material was removed by filtration. The solvent was removed to yield 4,5-bis(hex- 5-enyl)phthalimide ( 1.7 g, 68%). [δ_H (CDC1₃, 400 MHz) 7.6 (s, 2H) , 5.72-5.82 (m, 2H) , 5.3 (s, IH) , 4.9-5.0 (m, 4H) , 2.65 (t, 4H) , 2.1 ( , 4H) , 1.62 (quintet, 4H) , 1.5 (quintet,

4H) ppm. v_max (neat) 1705 cm^"1] .

4 , 5 -Bis (hex- 5 -enyl )phthalamide 4, 5-Bis (hex-5-enyl)phthalimide (1.7 g, 5.4 mmol) was dissolved in ethanol (10 ml) and added to a concentrated aq. NH₃ solution (50 ml) . This was stirred for 2 days at rt . The precipitate was filtered off, washed with water and dried in air to afford 4 , 5-bis (hex-5-enyl) phthalamide (1.7 g, 94%). [δ_H (CDC1₃, 400 MHz) 7.59 (s, 2H) , 5.72-5.82 (m, 2H) , 4.9-5.0 (m, 8H) , 2.72 (t, 4H) , 2.1 (m, 4H) , 1.62 (quintet, 4H) , 1.5 (quintet, 4H) ppm. v_max (neat) 1648 cm^"1] .

4 , 5-Bis (hex-5-enyl )phthalonitrile 4, 5-Bis (hex-5-enyl) phthalamide (1.7 g, 5.1 mmol) was dissolved under a N₂ atmosphere in dry pyridine (20 ml) and the solution cooled to 0°C in an ice bath. P0C1₃ (2.35 g, 15 mmol) was added slowly. The solution was allowed to warm to rt and poured into water (100 ml) . The organics were extracted with CH₂C1₂ (2x50 ml) , washed with brine (50 ml) , dried (MgS0₄) , filtered and the solvent removed under reduced pressure. The residue was filtered through silica gel, eluent: toluene, to afford 4, 5-bis (hex-5- enyl) phthalonitrile (1.3 g, 86%) . [δ_H (CDC1₃, 400 MHz) 7.54 (s, 2H) , 5.72-5.82 (m, 2H) , 4.9-5.0 (m, 4H) , 2.68 (t, 4H) , 2.1 (m, 4H) , 1.6 (quintet, 4H) , 1.49 (quintet, 4H) ppm].

Metal - free2 , 3 , 9 , 10 , 16 , 17 , 23 , 24 -octakis (hex-5 enyl ) phthalocyanine

The product was prepared in the same way using 4, 5-bis (he -

5 -enyl) phthalonitrile (1.3 g, 4.4 mmol). This yielded a metallated2,3,9,10, 16, 17 , 23 , 24-octakis (hex-5- enyl) phthalocyanine, probably lithium (500 mg) . [δ_H (THF-d₈, 400 MHz) 9.25 (s, 8H) , 5.91-6.1 (m, 8H) , 5.0-5.16 (m, 16H) , 3.27 (t, 16H) , 2.32 (m, 16H) , 2.08 (m, 16H) , 1.83 (m, 16H) ppm. λ_max (THF) 680, 614 nm] . This compound was heated in acetic acid to yield the less soluble metal-free derivative. [λ_maχ (THF) 703, 667 nm. MALDI-MS 1170.8].

II Preparation of the further homoleptic Cd₂L₃ complexes The following complexes were prepared in analogous syntheses to Cd₂Pc ' ₃ in Example 1 above. The starting quantities and reaction conditions are the same as in Example 1, unless otherwise stated. Example 2 : Synthesis of Dicadmium

Tris ( 1 , 4 , 8 , 11 , 15 , 18 , 22 , 25 -octakis ( octyl )phthalocyaninat ) , Complex II

Dicadmium Tris (1,4, 8, 11, 15, 18, 22,25- octakis (octyl) phthalocyaninate) was prepared from

1,4, 8, 11, 15, 18 ,22, 25-octakis (octyl) phthalocyanine. A pure dark blue powder was obtained after one recrystallisation of the crude product from CH₂Cl₂/Me0H (80% yield) [MALDI-MS: isotopic clusters at 3043.1 [M-Pc] , 2933.2 [M-CdPc] , 1523.1 [M-CdPc₂] , 1411.2 [M-Cd₂Pc₂] . λ_max (n-hexane): 872, 719, 644, 599, 547, 484 n . Found: C, 77.34; H, 9.75; N, 7.31%. C₂₈₈H₄₃₂N₂₄Cd₂ requires: C, 77.64; H, 9.77; N, 7.54%. Mp . 151 °C] .

Example 3 : Synthesis of Dicadmium Tris ( 1 , , 8 , 11 , 15 , 18 , 22 , 25 -octakis ( decyl )phthalocyaninate ) , Complex III

Dicadmium Tris (1, 4, 8, 11, 15, 18, 22, 25- octakis (decyl)phthalocyaninate) was prepared from 1,4, 8, 11, 15, 18, 22, 25-octakis (decyl) phthalocyanine. The crude product was dissolved in hot CH₂C1₂. Upon cooling,

1,4, 8, 11, 15, 18, 22, 25-octakis (decyl) phthalocyaninato cadmium crystallised and was removed by filtration. The blue mother liquor was concentrated and methanol was added. A dark blue powder crystallised (15% yield) [MALDI-MS: isotopic clusters at 3380.6 [M-CdPc] , 1747.3 [M-CdPc₂] , 1635.4 [M-Cd₂Pc₂] . λ_max (n-hexane): 718, 647, 599, 550, 483 nm. Found: C, 77.70; H, 10.32; N, 6.33%. C₃₃₆H₅₂₈N₂₄Cd₂ requires: C, 78.69; H, 10.38; N, 6.55%. Mp. 109 °C] . Example 4 : Synthesis of Dicadmium Tris-

( 1 , 4 , 8 , 11 , 15 , 18 , 22 , 25 -octakis ( oct -7 -enyl )phthalocyaninate ) , Complex IV

Dicadmium Tris (1,4, 8, 11, 15, 18 , 22 , 25-octakis (oct-7- enyl) phthalocyaninate) was prepared from

1,4, 8, 11, 15, 18,22, 25-octakis (oct-7-enyl) phthalocyanine . A pure dark blue powder was obtained after one recrystallisation of the crude product from CH₂Cl₂/MeOH (77% yield) [δ (400 MHz, CDC1₃) 7.65 (br) , 6.09 (m) , 5.66 (m) , 5.2 (m) , 4.8 (m) , 2.4 (q) , 1.0-2.2 (m) ppm. λ_max (n-hexane): 718, 647, 599, 550, 483 n . Mp. 174 °C] .

Example 5: Synthesis of dicadmium tris l, 4 , 8,11,15, 18,22, 25- octakis (undec -10 -enyl) phthalocyaninato ) , Complex V.

Synthesis of 1 , 4, 8 , 11, 15, 18,22 ,25-octakis(undec-10- enyl ) phthalocyaninato cadmium

Metal-free 1,4, 8,11,15, 18 , 22 , 25-octakis (undec-10- enyl) phthalocyanine (90 mg, 0.05 mmol) was refluxed in pentanol (10 ml). Cd(OAc)₂ hydrate (50 mg, excess) was added and reflux continued for 45 min. The hot solution was poured into excess methanol (50 ml) and placed in the fridge. The green precipitate was filtered. The residue was washed with THF. The organic solution was poured into excess methanol and placed in the fridge. The green solid was filtered and 1,4, 8, 11, 15, 18, 22, 25-octakis (undec-10-enyl) phthalocyaninato cadmium was obtained as a green powder (72 mg, 78 %) . [δ_H (C₆D₆, 400 MHz) 7.72 (s, 8H) , 5.72-5.79 (m, 8H) , 4.94-5.03 (m,16H), 4.41 (m, 16H) , 2.28 (m, 16H) , 1.95 (m, 16H) , 1.76 (m, 16H) , 1.49 (m, 16H) , 1.27-1.37 (m, 64H) ppm. λ_max (hexane) 709 nm] .

Synthesis of dicadmium tris(l, 4 , 8 , 11 , 15 ,18 ,22 , 25- octakis (undec -10 -enyl ) phthalocyaninato ) , Complex V. Dicadmium tris (1, 4 , 8 , 11, 15, 18 , 22 , 25-octakis (undec-10- enyl)phthalocyaninate) was prepared from 1,4, 8, 11, 15, 18, 22 , 25-octakis (undec-10-enyl) phthalocyaninato cadmium. A dark blue powder was obtained after one recrystallisation from CH₂Cl₂/methanol (54% yield) . [δ_H (C₆D₆, 400 MHz) 8.12 (br) , 5.96-6.04 (m) , 5.69-5.79 (m) , 5.14-5.26 (m) , 4.94-5.02 ( ) , 3.14 (m) , 1.22-2.44 (m) ppm. λ_max (hexane) 717, 643, 600, 483 nm] .

Example 6: Synthesis of dicadmium tris (2 , 3 , 9 , 10 , 16 , 17 , 23 , 24 - octakis( hexyl ) phthalocyaninato) , Complex VI.

Metal-free 2,3, 9, 10, 16, 17, 23, 24-octakis (hexyl) phthalocyanine (500 mg, 0.42 mmol) was refluxed in pentanol (20 ml). Cd(0Ac)₂ hydrate (200 mg, excess) was added and reflux continued for 45 min. The hot solution was poured into excess methanol (70 ml) and placed in the fridge. The blue precipitate was filtered. The residue was washed with THF. The solvent was removed and the residue recrystallised from CH₂C1₂-methanol as a fine blue powder (305 mg, 56%) . [λ_max (dichloromethane) 663, 490 nm. MALDI-MS 6375.1 (30%, Pc₅Cd₄) , 5081.3 (100%, Pc₄Cd₃) , 3782.6 (35%, Pc₃Cd₂) , 2595.7 (5%, Pc₂Cd₂) . MALDI-MS 1298.8 (55%, PcCd) , 2598.4 (15%, Pc₂Cd₂)] .

Example 7: Synthesis of dicadmium tris (2 , 3 , 9, 10, 16 , 17, 23 , 24 - octakis (hex-5-enyl ) phthalocyaninate ) , Complex VII. The product was prepared in the same way from metal- free 2 , 3 , 9, 10, 16, 17, 23 , 24-octakis (hex-5-enyl) phthalocyanine (100 mg, 0.08 mmol) to yield a fine blue powder (54 mg, 51%) . [λ_max (hexane) 659, 481 nm] .

Example 8: Synthesis of a heteroleptic dicadmium phthalocyanine of the formula Cd₂L₂L ' , wherein L is Pc' and L¹ is a ligand of Formula 1 above, wherein X¹ to X⁴ are each N, R², R³, R⁶, R⁷, R¹⁰, R¹¹. R¹⁴ and R¹⁵ are each H, and R¹, R⁴, R⁵, R⁸, R⁹, R¹², R¹³ and R¹⁶ are each an oct-7-enyl group, Complex VIII. Two equivalents of 1, 4, 8, 11, 15, 18 , 22, 25- octakis (hexyl) phthalocyaninato cadmium [PcA] ( 20.37 mg, 15.7 μmol) and one equivalent of 1,4,8,11,15,18,22,25- octakis (oct-7-enyl) phthalocyanine [PcB] (10.9 mg, 7.8 μmol) were dissolved in dichloromethane (3 ml) . Methanol (1 ml) was added and the flask placed in the fridge overnight . More methanol (2 ml) was added and the flask placed in the fridge overnight. The crystallised blue powder was filtered, washed with methanol and dried (24 mg, 76%) [λ_max (n-hexane) : 718, 646, 598, 551, 482 nm. δ (400 MHz, CDC1₃) 7.65 (brs), 6.1 (m) , 5.65 (m) , 5.2 (m) , 4.8 (m) , 2.66 (brs), 2.4 (q) , 1.95 (brs), 1.4-1.9 (m) , 1.0-1.3 (m) , 0.7 (t) ppm. Mp. 196 °C (dec). MALDI-MS: isotopic clusters at 2691.7 [30%, PcACdPcB] , 2483.6 [60%, PcACdPcA] , 1506.9 [45%, PcBCd] , 1298.8 [100%, PcACd] ] .

Claims

Claims :

1. A complex of the formula M₂L₃, wherein M is Cd(II) and each ligand, L, is independently either a tetrabenzoporphyrin ligand or an aza-tetrabenzoporphyrin ligand.

2. A complex as claimed in claim 1, wherein each L is a ligand of Formula 1:

Formula 1, wherein X¹ to X⁴ are each independently CH or N; and R¹ to R^1G are each independently H, halo, of the formula Y^¹⁷, of the formula ZR¹⁸R¹⁹ or one of the optionally substituted groups: d. to C₂₀ alkyl, C₂ to C₂o alkenyl, C₇ to C₂₀ arylalkyl and C₇ to C₂o alkylaryl; wherein Y¹ is O or S; Z is N or P; R¹ is H or one of the optionally substituted groups: c₂ to C₂₀ alkyl, C₆ to C₁₈ aryl C₂ to C₂₀ alkenyl, C₇ to C₂₀ arylalkyl and C₇ to C₂₀ alkylaryl; and R¹⁸ and R¹⁹ are each independently H or one of the optionally substituted groups: C_x to C₂₀ alkyl, C₆ to C₁₈ aryl, C₂ to C₂o alkenyl, C₇ to C₂₀ arylalkyl and C to C₂₀ alkylaryl .

3. A complex as claimed in claim 1 or claim 2, wherein at least one of R¹ to R¹⁶ is a substituted d to C₂o alkyl, substituted C₆ to Ciβ aryl, substituted C₂ to C₂₀ alkenyl, substituted C₇ to C₂₀ arylalkyl or a substituted C₇ to C₂₀ alkyl ryl .

4. A complex as claimed in claim 3, wherein at least one of R¹ to R¹⁵ is a C_x to C₂₀ alkyl, C₆ to C₁₈ aryl, C₂ to C₂₀ alkenyl, C₇ to C₂o arylalkyl or a C₇ to C₂o alkylaryl substituted with one or more substituents selected from halo, a Cι-₂o alkoxy group, a Cι_₂₀ alkylamino group, sulphides, di-sulphides, SH, OH or C0₂H.

5. A complex as claimed in any one preceding claim, wherein at least one of R¹ to R¹⁶ is a Ci to C₂o alkyl thiol .

6. A complex as claimed in any one preceding claim, wherein each of R¹ to R¹⁶ is independently H or an optionally substituted C_x to C₂o alkyl group.

7. A complex as claimed in any one of claims 1 to 5, wherein each of R², R³, R⁶, R⁷, R¹⁰, R¹¹, R¹⁴ and R¹⁵ is H.

8. A complex as claimed in claim 7, wherein each of R¹,

R⁴, R⁵, R⁸, R⁹, R¹², R¹³ and R¹⁶ is independently an optionally substituted C_x to C₂₀ alkyl or an optionally substituted C₂ to C₂o alkenyl .

9. A complex as claimed in claim 8, wherein each of R¹,

R⁴, R⁵, R⁸, R⁹, R¹², R¹³ and R^1S is independently an optionally substituted C₃ to Cι₀ alkyl or an optionally substituted C₃ to C_lx alkenyl .

10. A complex as claimed in any one of claims 1 to 5, wherein each of R_lf R , R₅, R_8/ R₉, Rι₂, Rχ₃, and R₁₆ is H.

11. A complex as claimed in claim 10, wherein each of R₂, R₃, R₆, R₇, Rio Rii, ι₄ and R_i5 is independently an optionally substituted C_x to C_2o alkyl or an optionally substituted C₂ to C₂₀ alkenyl.

12. A complex as claimed in claim 11, wherein each, of R₂, R₃, R₆, R , io R-ii, Ri4 and Rχ_S is independently an optionally substituted C₃ to C₁₀ alkyl or an optionally substituted C₃ to Cx alkenyl .

13. A complex as claimed in any one preceding claim, wherein each of X¹ to X⁴ is N.

14. A complex as claimed in any one preceding claim, wherein the complex is of the formula M₂LL'₂, wherein both L and L' are ligands as defined in any one of claim 1 to 13, and L and L' are different.

15. A substrate having on a surface thereof a thin layer of a material comprising a complex as defined in any one of claims 1 to 14.

16. A substrate as claimed in claim 15, wherein the layer has a thickness of 100 μm or less.

17. A substrate as claimed in claim 15 or claim 16, wherein the substrate comprises a metal or a polymeric material .

18. A substrate as claimed in claim 17, wherein the substrate comprises silver, platinum or gold.

19. A method for forming a thin film of a complex, wherein said complex is as defined in any one of claims 1 to 14, on a surface of a substrate, the method comprising applying the complex to the surface of the substrate so as to form the thin film.

20. A method as claimed in claim 19, wherein the method comprises employing the Langmuir-Blodgett technique, spin- coating, thermal evaporation or molecular self-assembly to form the thin layer.

21. A method as claimed in claim 19 or claim 20, wherein the surface comprises a metal or a polymeric material .

22. A method as claimed in claim 21, wherein the surface comprises one or more of silver, platinum or gold.

23. A conducting device comprising a complex as defined in any one of claims 1 to 14.

24. A conducting device as claimed in claim 23, wherein the device is in the form of wire, a conducting portion of a printed circuit board, a processor chip or an integrated circuit .

25. A conducting device as claimed in claim 23 or claim 24, wherein the bias voltage across the device can be varied from -3 V to +3 V.

26. A conducting device as claimed in any one of claims 23 to 25, wherein the device further comprises a means for controlling the temperature of the device.

27. Use of a complex as defined in any one of claims 1 to 14 in an electronic memory device.

28. A transistor device comprising a complex as defined in any of claims 1 to 14.

29. A method for use in the detection of an oxidizing substance, the method comprising: providing a material comprising a complex as defined in any one of claims 1 to 14, optionally in electrically neutral form, and exposing the material to an oxidizing substance.

30. A method as claimed in claim 29, the method further comprising observing the colour of the material before and after contacting the material with the oxidizing substance and then comparing the colour of the material before and after the contacting to detect a change in the material and the presence of the oxidizing substance.

31. A method of synthesizing a complex M₂L₃, the method comprising: contacting a source of Cd(II) with a compound LY₂ to effect formation of the complex, wherein M is Cd(II) , Y is H or Li and L is a ligand as defined in any one of claims 1 to 13.

32. A method as claimed in claim 31, wherein the source of Cd(II) is a carboxylic acid salt of Cd(II).

33. A method as claimed in claim 31 or claim 32, wherein the source of Cd(II) and the compound LY₂ are contacted in a liquid.

34. A method as claimed in claim 33, wherein the liquid is a C₄-C₆ straight-chain alcohol.

35. A method as claimed in claim 34, wherein the liquid is pentanol .

36. A method of synthesizing a complex M₂L₃, the method comprising: adding a polar protic solvent to a solution comprising a non-protic solvent and a complex of the formula CdL to effect precipitation of the complex M₂L₃, wherein M is Cd(II) and L is a ligand as defined in any one of claims 1 to 13.

37. A method of synthesizing a complex ₂LL'₂, the method comprising: contacting a compound LY₂, with a complex CdL' in a non-protic solvent to form a mixture, adding a polar protic solvent to the mixture to effect precipitatation of the complex M₂LL'₂, wherein M is Cd(II), Y is H, L and L' are as defined in claim 14 and the molar ratio of LY₂:CdL' is from 2:3 to 2:5.

38. A method as claimed in claim 36 or claim 37, wherein the polar protic solvent is an alcohol.

39. A method as claimed in claim 38, wherein the alcohol is a Ci to C₆ alcohol .

40. A method as claimed in any one of claims 36 to 39, wherein the non-protic solvent is or comprises dichloromethane .

41. A method as claimed in any one of claims 36 to 40, wherein the ratio of protic solvent to non-protic solvent, by volume, is in the range of from 1:10 to 2:1.

42. A method of forming cadmium sulphide nanoparticles comprising contacting a material comprising a complex as defined in any one of claims 1 to 14 with H₂S gas to form the cadmium sulphide nanoparticles .