WO2005114683A1

WO2005114683A1 - Magnetisable composition and magnetic material comprising the same

Info

Publication number: WO2005114683A1
Application number: PCT/EP2005/005458
Authority: WO
Inventors: Dirk G. Kurth; Helmuth MÖHWALD; Ullrich Pietsch; Yves Bodenthin
Original assignee: MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V.
Priority date: 2004-05-19
Filing date: 2005-05-19
Publication date: 2005-12-01
Also published as: DE102004024872A1

Abstract

The invention relates to a magnetisable composition and a magnetic material comprising a coordination polymer with a number of polymeric components with a polytopic ligand and a metal ion, whereby the polymer components may be the same or different and further comprising an ampiphilic compound. The magnetisable composition displays reversible or irreversible transition from dielectric to paramagnetic behaviour and can advantageously be used for magnetic materials for data recording, for example, diskettes.

Description

MAGNETIZABLE COMPOSITION AND MAGNETIC MATERIAL CONTAINING THEM

The present invention relates to a magnetizable composition comprising a coordination polymer consisting of a multiplicity of polymer building blocks containing a polytopic ligand and a metal ion as well as a magnetic material comprising the magnetizable composition.

Magnetic properties of transition metal complexes or of supramolecular transition metal clusters or complexes have long been the focus of interest in a wide variety of application areas.

For example, WO 03/019695 A1 describes a molecular memory and a method for its production, the molecular memory consisting of a polymer which contains triazole derivatives and a metal with an electron configuration which allows a spin transition. Iron triazolates are mentioned as preferred molecules or complexes, which also contain ammonium triazolate as a further ligand, and chlorate or nitrate and tetrafluoroborate as counterions.

Similar compounds, in particular iron (II) complexes with triazolate ligands and tetrafluoroborate or chlorate, or a halogen as a counterion are known from EP 666561 AI. Furthermore, structurally analogous connections are described in EP 842988 AI.

These aforementioned compounds or classes of compounds can form ferroelectric hard magnetic properties due to the temperature-induced spin transition and are therefore particularly suitable as materials for use in the field of data processing, for example for magnetic recording media, magnetic read heads and the like. A summary of the current state of the art in the field of molecular magnetism is provided by the publication "Technology Early Detection - Technology Analysis Magnetism Volume 1 Molecular Magnets" published by the VDI Technologiezentrum Düsseldorf 1999.

Currently, the focus of interest is on metallosupramolecular mesophases. These mesophases consist of periodic arrays of transition metal ions that are coupled via ditopic bis-terpyridine ligands. For example, Schütte et al. in Angew. Chem. Int. Ed. 1998, 37, 2891 ff. Layers of a plurality of metallosupramolecular thin polyelectrolyte films which consist of the mesophases described above and which consist of polyelectrolyte layers, for example consisting of

Polyethyleneimine and polystyrene sulfonate are separated. However, these metallosupramolecular polyelectrolyte films have no magnetic properties, in particular neither para- or ferromagnetic properties, nor do spin-crossover phenomena occur.

The physical basis of many magnetizable materials is the occurrence of so-called spin crossover phenomena. In particular, the presence of semi-occupied d orbitals of transition metal ions is the cause of special properties of metallosupramolecular units, for example their strong absorption in the UV / VIS range, high quantum yields, a suitable long life of one of their excited states, luminescence phenomena and stable redox states. The splitting of the d orbitals in a ligand field of suitable symmetry and strength can cause, for example, either thermally induced or photoinduced spin transitions, ie spin crossover phenomena. The most frequently observed phenomena so far are the so-called light-induced trapping of the excited spin state (LIEST), reversal and low spin LIEST and also include the charge transfer from the metal (central atom) to the Ligands, for example in nitroprussite, the charge transfer from metal atom to metal atom in Prussian blue analogues, and also the ligand-dependent light-induced spin state change (LD-LISC) (for an overview of such phenomena, reference is made to the VDI manual mentioned above).

Typically, the reversal between a low spin (LS) and a high spin (HS) state is observed for transition metal ions with a 3d ⁿ (4 • n • 7) configuration, whereby the iron (II) ion has mostly been investigated so far. In the case of iron (II) ion, there is a ligand field with octahedral symmetry, with the d orbitals in the energetic ground state splitting into energetically lower lying t _2g and higher lying e subsets. Thermally induced

Spin transitions occur when the energetic separation between the t _2g and e _g orbitals is approximately k (ie the mean thermal energy of the environment). In the case of the iron (II) ion, the LS state results from a closed shell t _2d ⁶ configuration and the HS state from a t _2g ⁴ e _g ² configuration. The spin crossover from LS to HS state is generally accompanied by a change in the optical and in particular the magnetic properties.

The object of the present invention was to provide new metallosupramolecular mesophases which have magnetic, in particular para- or ferromagnetic, properties and can also be deposited as thin films on substrates.

This object is achieved by a magnetizable composition comprising a coordination polymer consisting of a multiplicity of polymer building blocks containing a polytopic ligand and a metal ion, wherein the polymer building blocks can be the same or different and further comprising an ampiphilic compound. The presence of an ampiphile phase at a certain temperature leads to a structural phase transition of the individual polymer chains into a lamellar superstructure of the magnetizable composition. The temperature depends on the type of composition according to the invention, ie the individual components, in particular on the type of ampiphilic phase. The polymer chains have a quasi one-dimensional rod-shaped structure made of polytopic ligands linked via metal ions.

When the magnetizable composition according to the invention is heated, the ampiphile phase goes into another phase (temperature-induced phase transition), which has the essentially octahedral coordination geometry of the

Transition metal centers disrupt. This leads to a changed splitting of the energy states of the d orbitals and thus to a spin crossover phenomenon which causes the development of ferroelectric properties of the composition according to the invention.

The ferroelectric properties of the composition according to the invention are either reversible or irreversible depending on the choice of temperature. The temperature setting advantageously controls the reversible or irreversible transition from the diamagnetic to the para- or ferroelectric state. This transition preferably takes place at room temperature or at a higher temperature.

The presence of a polytopic ligand is necessary to achieve a lamellar supra structure. The polytopic ligand or several of these polytopic ligands preferably coordinate in a square planar manner to the central atom, the resulting structure also being able to be slightly twisted.

The term “polytopic ligand” encompasses ligands with at least two identical or spatially separated different σ or π donor atoms, which are able to bind to a metal ion.

In a particularly advantageous embodiment, the polytopic ligand comprises the following structural element

(ι) _n (L ₂ ) _n

: L ₃ ) Π (L ₄

where R is a polyfunctional unit, L _x to L ₄ (also referred to as ligand set) are the same or different and further contain a donor atom which is able to bind to a metal ion - preferably coordinatively - and where n = 0 or 1 with with the proviso that at least two n = 1. This ligand structure element enables a coordination geometry that is particularly easy to control.

In the context of the present invention, the term donor atom encompasses all atoms which are capable of coordinatively binding to a metal ion in particular and comprises in particular σ or π donor atoms such as nitrogen, sulfur, oxygen, etc.

R, ie the so-called “turnstile” of the ligand is preferably selected from the group comprising a CC, a C heteroatom or a heteroatom-heteroatom bond, a C ₁ to C ₁₀ alkyl or alkenyl chain, an α, ω bisfunctional chain such as a α, ω bis alcohol, an α, ω bis thiol, an α, ω bis amine, an α, ω bicarboxylic acid, a bis, tris or tetrafunctionalized alicyclic, heterocyclic, aromatic or heteroaromatic ring system, a tris or tetracarboxylic acid , a tris or tetraamine, a tris or tetrathiol, a tris or tetra alcohol, a crown ether, porphyrins, porphyrinogens, complexes of pyridines, acetylenes, bipyridines linked by metal ions.

This makes it possible to achieve a large number of different “turnstiles” R (also called spacers), which can be used differently in terms of length, and which separate the 2, 3 or 4 ligand sets. The structural diversity enables the ligand to be specifically adjusted to the one to be coordinated Metal ion, to the desired lamellar mesophase etc.

In a preferred embodiment, L _x to L ₄ each contain at least 2 donor atoms which are the same or different. This applies, for example, to complexes from the group of the N-donor, P-donor, S-donor and O-donor atoms, with structural units which are derived from basic structures such as, for example, pyrazoles, pyridines, benzothiazoles, phosphazoles, azobenzenes, phenantroline or else mixtures thereof homologous compounds, further dioxane,

Tetrahydrofuran, γ-butyrolactone, thiophene, pyrrole, furan, pyrimidine, γ-pyran, pyrroline, dithiane, dioxoles, oxathiolane, diazole, α-pyran, azepine, 1,2 oxathiolane, porphins, porphyrins, porphyrinogens and their mixed donor-substituted homologs Corrin, phthalocyanines, indole, indolizine, pyrazole, indazole, oxazole, isoxazole, thiazole, isotiazole, triazoles, tetrazoles, 1,2,4 thiadiazole, 1,3,4 thiadiazole, pyridazine, pyrimidine, pyrazine, triazine and their derivatives.

It is further preferred in another embodiment of the invention that L ₁ and / or L ₂ are negatively charged and comprise so-called “hard” donor atoms, preferably negatively charged oxygen atoms, such as, for example, alkyl, aryl carboxylates and alkyl and aryl alcoholates. The metals are preferably selected from metal ions selected from the group consisting of the ions of Fe, Ru, Mn, Os, Ni, W, V, Nb, Ti, in particular from metals which are able to form octahedral complexes. If “hard” ligands are used, oxophilic metal ions such as Ti, Nb, Zr, Hf and in particular metal ions from the lanthanide group such as La, Ce, Nd, Sm, etc. are preferred.

The ampiphilic compound is preferably selected from the group consisting of sulfates, sulfonates, carboxylates and phosphates, borates, which contain an organic radical. In the case of "hard" ligands, in particular negatively charged ligands, the ampiphilic compound is a positively charged compound, for example an ammonium compound. The organic radical is preferably selected from optionally substituted C _x to C ₂₀ alkyl or alkenyl chains, aryl or Heteroaryl or mixed aryl / heteroaryl chains with 1 to 15 aryl or heteroaryl units or an aralkyl chain with 1 to 15 aralkyl units.The exact number of ampiphiles is determined by the charge of the complex consisting of central atom (s) and ligands (charge compensation) and In addition, further electrostatic interactions, in particular, can occur, so that a non-stoichiometric number of ampiphiles can also be present in the composition according to the invention.

The reaction of the organic residue can in particular also control the temperature dependence of the magnetization. In general, the shorter the chain or length of the organic residue, the lower the temperature at which the spin crossover effect occurs. The longer the chain of the organic residue is, the higher the temperature that has to be applied in order to enable a spin crossover. The organic radical is preferably a C _λ bis

C ₂₀ prefers a C ₅ to C ₁₆ alkyl or alkenyl chain, since these compounds are particularly simple by conventional methods can be produced. There are preferably at least two organic radicals on the ampiphilic compound

The object of the present invention is further achieved by a magnetic material comprising a carrier and a magnetizable composition according to one of claims 1 to 10. According to the invention, a magnetic material is obtained which has either a reversible or irreversible ferroelectric character. As explained above, the magnetization is based on a

Phase conversion of the ampiphile phase, which is reversible in a certain temperature range and can therefore be used preferably for read and write applications (read and write). Above this material-dependent temperature window, the phase transition and thus the magnetization is irreversible (the initial phase is not formed again), so that this material is preferably used for write-only applications. The magnetic material is preferably used for a wide variety of applications, such as read heads, magnetic storage materials, molecular switches, etc.

The magnetizable composition is preferably arranged as a monolayer on the carrier and, in an even more preferred embodiment, is a Langmuir-Blodgett film that is easy to manufacture and configure. It goes without saying that not only Langmuir-Blodgett film, but all other films known per se to the person skilled in the art and their production processes, for example. Doctor coating (spin coating), spraying, vapor deposition, etc. can be used in the context of the present invention.

The magnetic material according to the invention can also be applied to the carrier as a magnetizable composition in the form of a plurality of layers arranged one above the other and, depending on the production method, results in highly ordered and anisotropic layers as well as unstructured films, especially Langmuir-Blodgett films. Langmuir-Blodgett films are particularly preferred when highly ordered or anisotropic layer systems are to be used. Anisotropic layer systems are very particularly preferred if the magnetic material according to the invention interacts with polarizing radiation (light, neutrons). In this case, the material according to the invention is preferably used for detectors, LC displays, etc. In addition, the film layers can also be present as so-called "volume phases" if the ligands used can be crosslinked with one another and thus cross-linked "films" are formed.

An additional cover layer is preferably arranged above the uppermost layer of the magnetic composition in order to protect it from mechanical or other influences and external influences, so that, for example, a magnetic data carrier is protected from external damage. The additional cover layer is preferably transparent and consists, for example, of commercially available polymers, flexible glasses, etc.

In a preferred method for producing a magnetic material according to the invention, the magnetizable composition is heated so that the crystalline packed ampiphile phase is melted and the lattice of the monomolecular layer arrangement is deformed for steric reasons (greater mobility of the organic residues of the ampiphile phase) and disturbing the octahedral coordination symmetry around the metal central ion. This leads to a distortion of the octahedral symmetry by splitting the orbitals into two subsets with t ₂ or e _g symmetry and thus to a spin phase transition. In other words, the heating ("melting") of the ampiphilic phase leads to a mechanical deformation of the laminar superstructure which is on the arrangement of the metal ion according to the invention with the polytopic ligand is based.

The magnetizable composition is preferably heated to a temperature of from -50.degree. C. to 100.degree. C., very particularly preferably from -10.degree. C. to over 60.degree. C., so that a large number of very different materials can be obtained which are very particularly preferably stable at room temperature and only later be converted into a reversible or irreversible spheroelectric material. As already explained above, the transition temperature is also determined by the chemical nature of the ampiphile phase, in particular by its type (sulfate, phosphate, etc.) and the type of bound organic residues.

Further advantages and refinements of the present invention can be seen from the attached figures. It goes without saying that the present invention is not limited only to the features disclosed in detail, but also to any combination of the features explained above and to be explained below.

Fig. 1 shows a schematic representation of the magnetizable composition according to the invention;

2 shows Langmuir-Blodgett monolayers or multilayers obtainable from the composition according to the invention;

3 shows the SQUID magnetization curves of two Fe (II) -PAC-Langmuir-Blodgett films consisting of 11 or 15 monolayers, 4 shows schematically the influence of the ampiphile phase on the orbital symmetry when the composition according to the invention is heated.

5 shows various examples of polytopic ligands according to the invention

embodiments

1. Production of a composition according to the invention

1.1 Synthesis of the metallosupramolecular polyelectrolyte:

1,4- bis (2, 2 ', 6', 2,2 '-terpyrid-4'-yl) benzene (I) (51.9 mg, 0.039 mmol) in toluene (100 ml) was treated with Fe (OAC ) ₂ (16.5 mg, 0.092 mmol) in methanol (30 under reflux under an inert atmosphere. After 30 minutes, the deep blue solution was concentrated under vacuum until the reaction product MEPE (= metallosupramolecular polyelectrolyte) (II) precipitated. The precipitate became washed with hot toluene and dried (yield 18%) The precipitate is soluble in methanol and ethanol, for elemental analysis the compound was isolated as bromide by precipitation from an aqueous solution.

H NMR (CD ₃ OD, room temperature): δ = 9.74 (H3 '), 8.95 (H3), 8.75 (HAr), 8.10 (KBr): 1602, 1462, 1433, 1403, 1160, 831, 786, 731 cm ^"1; Elemental analysis, calculated for: C ₃₆ H ₂₄ N ₆ FeBr ₂ ^• 6H ₂ 0: C 50.0, H 4.2, N 9.7, found: C 49.9, H 3.2, N 9.9.

1.2 Synthesis of the composition according to the invention

The reaction product MEPE (II) obtained in step 1.1 was reacted with dihexadekyl phosphate (DHP) and gave the

Polyelectrolyte-ampiphilic complex (PAC) as shown in Fig. 1. Found under the special synthesis conditions 6 DHP molecules per structural unit [Fe ₃ ] ²⁺ . DHP forms a charged hydrogen bridge network that binds to MEPE via electrostatic interactions. The surface-active nature of DHP allows the PAC complex to be formed at the air-solution interface. The resulting Langmuir-Blodgett monolayer was transferred to a solid support using known techniques. Langmuir-Blodgett multilayers were obtained by successive deposition of several monolayers in a row, as described, for. B is shown schematically in FIG.

The magnetic properties of the Langmuir-Blodgett multilayers were measured using temperature-dependent SQUID measurements, the results of which are shown in FIG. 3. The samples were diamagnetic up to room temperature but became paramagnetic when heated above room temperature. The phase transition from diamagnetic to paramagnetic behavior is reversible.

The occurrence of paramagnetism in the composition according to the invention or in the material according to the invention is associated with the deformation of the coordination geometry as a result of the structural phase transition of the amiphile mesophase at elevated temperatures, as is shown schematically in FIG. 4.

Claims

1. Magnetizable composition comprising a coordination polymer consisting of a plurality of polymer building blocks containing a polytopic ligand and a metal ion, wherein the polymer building blocks can be the same or different, further comprising an ampiphilic compound.

2. Magnetizable composition according to claim 1, characterized in that the polytopic ligand has the following structural element

wherein R is a polyfunctional unit, L _λ to L _{4 are the} same or different and contains a donor atom which is capable of coordinatively binding to a metal ion and n = 0 or 1 with the proviso that at least two n = 1 are.

3. Magnetizable composition according to claim 2, characterized in that R is selected from the group comprising a CC, a C hetero atom or a hetero atom hetero atom bond, a C _x to C ₁₀ alkyl or alkenyl chain, an α, ω bisfunctional chain such as an α, ω bis alcohol, an α, ω bis thiol, an α, ω bis amine, an, ω bicarboxylic acid, a bis, tris or tetrafunctionalized alicyclic, heterocyclic, aromatic or heteroaromatic ring system, a tris or tetracarboxylic acid, a tris or tetraamine, a tris or tetrathiol and a tris or tetraalcohol, a crown ether, porphyrins, porphyrinogens, complexes of pyridines, acetylenes, bipyridines linked by metal ions.

4. Magnetizable composition according to claim 3, characterized in that 'L _x to L ₄ each contain at least two donor atoms which are the same or different

5. Magnetizable composition according to claim 4, characterized in that L ₁ to L _{4 are} selected from the group consisting of N-donor, P-donor, S-donor and O-donor atoms.

6. Magnetizable composition according to one of the preceding claims, characterized in that the metal ion is selected from the group consisting of the ions of Fe, Ru, Mn, Os, Ni, W, V, Nd, Nb, Ta, Hf.

7. Magnetizable composition according to any one of the preceding claims, characterized in that the ampiphile compound is selected from the group consisting of sulfates, sulfonates, carboxylates, borates and phosphates which contain an organic radical.

8. Magnetizable composition according to claim 7, characterized in that the organic radical is an optionally substituted C ₁ to C ₂₀ alkyl or alkenyl chain, an aryl or heteroaryl or. is a mixed aryl / heteroaryl chain with 1 to 15 aryl or heteroaryl units or an aralkyl chain with 1 to 15 aralkyl units.

9. Magnetizable composition according to claim 8, characterized in that the organic radical is a C _x to C ₂₀ , preferably a C ₅ to C ₁₆ alkyl or alkenyl chain.

10. Magnetizable composition according to claim 8 or 9, characterized in that there are at least two organic radicals which are the same or different.

11. A magnetic material comprising a carrier and a magnetizable composition according to any one of claims 1 to 10.

12. Magnetic material according to claim 11, characterized in that the magnetizable composition is arranged as a monolayer on the carrier.

13. Magnetic material according to claim 11, characterized in that the magnetizable composition is arranged in several layers on the carrier.

14. The magnetic material of claim 12 or 13, further comprising a cover layer over the magnetic composition.

15. A method of making a magnetic material, wherein the composition of any one of claims 1 to 10 is heated.

16. The method according to claim 15, characterized in that is heated to a temperature of -50 ° C to 100 ° C.

17. The method according to claim 16, characterized in that is heated to a temperature of -10 ° C to over 60 ° C.