GB2379930A

GB2379930A - Crystalline Calixarene Compounds

Info

Publication number: GB2379930A
Application number: GB0122846A
Authority: GB
Inventors: Christopher William Hall; Simon John Coles; Michael Barry Hursthouse
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 2001-09-22
Filing date: 2001-09-22
Publication date: 2003-03-26
Anticipated expiration: 2021-09-22
Also published as: GB0122846D0; GB2379930B

Abstract

A crystalline material comprising calixarene molecules wherein the molecules pack together to form a columnar structure thus defining a substantially tubular cavity in the crystal. The invention also provides a method of filtering a contaminated atmosphere comprising passing said atmosphere through the said crystalline material.

Description

Novel calixarene structures The present invention relates to novel crystalline structures formed by calixarene molecules, particularly, but not exclusively those that may be used to filter fluidic atmospheres.

Calixarenes are cyclic molecules that often have an ability to chelate with certain metallic species, the exact structure of the calixarenes determining the preferred metallic species to be chelated. Like many organic compounds, calixarenes may be recrystallised to form various crystalline structures. The nature of the structure formed will depend on numerous factors such as, inter alia, the solvent used, the speed of recrystallisation, the molecular structure of the calixarene, any metallic species present and the presence of impurities. The properties of the resulting crystal will depend to a large extent on the structure of the crystal. The present invention provides a crystalline material having a particular structure of interest. According to the present invention, a crystalline material comprising calixarene molecules wherein the molecules pack together to form a columnar structure thus defining a substantially tubular cavity in the crystal. This provides a material that may remove unwanted species from a fluidic environment.

The columnar structures may pack together to form a hexagonal or rectangular lattice.

This forms a dense array of such tubular structures. The mean plane of the macrocycles may be approximately parallel to the hexagonal or rectangular lattice.

This maximises the effective diameter of the tubular cavity for the particular macrocycle used.

The crystalline structure may comprise 6n molecules in each unit cell, wherein n=l to 10. It is preferred that n=l to 4 and more preferred that n=3.

It is preferred that the tubular cavity has a mean diameter of greater than approximately 4 . Such a cavity allows capture and possible retention of certain chemical species.

The long axis of the tubular cavity may be substantially parallel to one of the axes of the unit cell.

It is preferred that the crystalline material comprises a lattice that is trigonal on hexagonal, wherein a=1200, y=900 and c=lO-30 . Lattice parameter a may preferably be 10-50 .

It is preferred that the crystalline structure is formed in the absence of a metallic species.

It is also preferred that the crystalline structure comprises a calixarene of structure (1) :

In a second aspect of the invention, a method of filtering a contaminated atmosphere comprising passing said atmosphere through a crystalline material according to the present invention.

The present invention is described by way of example only with reference to the following figures of which: Figure 1 shows the chemical structure of a calixarene 1 that forms a crystalline structure in accordance with the present invention; Figure 2 shows the conformational structure of calixarene 1 in a crystalline structure in accordance with the present invention; and Figure 3 shows the supramolecular structure of 1 in a crystal in accordance with the present invention.

Synthesis of 1 Calixarene 1 (see figure 1) was synthesised by the reaction ofcalix [4] arene with bromomethylacetate according to Aoki et al. (J. Chem. Soc. Chem. Commun., 1992, 9, 730-732).

Recrystallisation of 1 Calixarene 1 was recrystallised into a crystalline material in accordance with the present invention from a methanol/chlorofonn mixture.

Determination of structure of calixarene 1 The crystal structure of calixarene 1 in accordance with the present invention was determined using conventional x-ray diffraction apparatus and techniques. A Nonius Kappa CCD area detector diffractometer was used, with Mo K-a radiation (k = o 0. 71073 A). The cell parameters were extracted from 13396 reflections using the following parameters : 6=1. 02-30. 51 h=-42-33 k=-30-42 1=-17-18 adsorption correction using multi-scan SORTAU, Blessing (1997, J Appl. Cryst., 30, 421-429) Refinement R (F) =0. 0436 mR (P2) =0. 1136 s=1. 04 (ö./cr) max=0. 002 O q Apmax = 0. 243eA O q Ap=-0. 197eAextinction correction by SHELXL extinction co-efficient 0. 00040 (7) scattering factors from International Tables for Crystallography (Vol. C)

Crystal structure Hexagonal lattice, a=32. 840 (5) , c=13. 918 (3) , a=90 , y=1200 V=13000 (4) 3 Z=18 Dx=1. 307Mg m-3 The structure of the crystalline material formed by calixarene 1 in accordance with the present invention is now described with reference to figures 2 and 3. The calixarene molecules pack together to form tubular, columnar structures. The tubular structures pack together in a hexagonal lattice as shown in Figure 3. It may be said the crystal structure is of a honeycomb in nature. Each tubular structure is formed by the stacking of three calixarenes one upon another, alternately offset by 60 , giving overall C3 symmetry. The three stacked molecules give a dimension c of 13. 9 ISA. The tubular orifice defined by the columnar packed calixarene molecules has an internal diameter of 4. 83 (9) . The driving force for the formation of this structure is probably the pi-pi stacking/interlocking between the calixarene rings and dipole-dipole interactions between the lower rim methyl ester groups. This is demonstrated by the head-to-tail arrangement of the carbonyl groups on the lower rim. The angles about the meso C atoms (C (l), C (8), C (17) and C (24) ) are reasonably close to ideal tetrahedral geometry indicating a macrocycle that is substantially strain-free. The upper rim of

calixarene 1 forms a cavity with separations between meso carbon atoms of 5. 067 (6), 5. 075 (6), 5. 079 (8) and 5. 070 (7) A. Cross-ring distances between meso carbon atoms are 7. 312 (7) and 7. 031 (6) A. The asymmetry of the macrocycle is caused by the lower rim substituents which form a number of intramolecular hydrogen bonds with each other. The angles of the aromatic rings with respect to the mean plane of the macrocycle (defined by the meso carbon atoms) are 71.70 (4) and 68.46 (3) for the alkyl ester functionalised rings whilst those for the hydroxyl substituted rings are 42.35 (4) and 37.86 (5) . Thus the hydroxyl substituted rings are allowed to lie more in the plane of the macrocycle due to their relatively small functional groups on their lower rims that due to the intramolecular interactions in which they are involved.

The pendant ester groups are locked in position by strong hydrogen bonding between the hydroxyl substituent and the oxy-linkage between the calixarene and the ester.

There is a further interaction between the carbonyl group of the ester and the hydroxyl

substituent, making it a bifurcated donor. The relevant hydrogen bonding parameters are shown in Table 1 :

D-H...A D-H( ) H...A( ) D...A( ) Angle (DH... A) 01-HI... 06 0. 84 1. 92 2. 7262 (14) 159.9 05-H5A... 02 0. 84 1. 99 2. 7987 (15) 160.6 01-HIA... 07 0. 84 2. 88 3. 4142 (16) 123.7 05-H5A... 03 0. 84 2. 90 3. 4434 (16) 124. 3 Table 1-hydrogen bonding parameters for calixarene 1 in a crystal structure in accordance with the present invention It is anticipated that the crystalline structure of the present invention as illustrated by the structure formed by calixarene 1 will be useful in the removal of unwanted species from fluidic, particularly gaseous, atmospheres. It is anticipated that the tubular orifices formed by the calixarenes will be able to entrap the unwanted species and thus remove them from the fluid to be filtered.

It is anticipated that calixarenes having a molecular structure different from that of calixarene 1 will form similar structures having substantially tubular cavities therein.

Non-uptake of recrystallisation solvent is believed to be key in the formation of such structures.

Claims

Claims 1. A crystalline material comprising calixarene molecules wherein the molecules pack together to form a columnar structure thus defining a substantially tubular cavity in the crystal.
2. A crystalline material according to claim 1 wherein the columnar structures pack together to form a hexagonal or rectangular lattice.
3. A crystalline material according to claim 2 wherein the mean plane of the macrocycles are approximately parallel to the hexagonal or rectangular lattice.
4. A crystalline material according to any one preceding claim comprising 6n molecules in each unit cell, wherein n= 1 to 10.
5. A crystalline material according to claim 4 wherein n=l to 4.
6. A crystalline material according to claim 4 wherein n=3.
7. A crystalline material according to any one preceding claim wherein the tubular cavity has a mean diameter of greater than approximately 4 .
8. A crystalline material according to any one preceding claim wherein the long axis of the tubular cavity is substantially parallel to one of the axes of the unit cell.
9. A crystalline material according to any one preceding claim wherein the lattice is

trigonal on hexagonal, wherein a=120 , y=90 and c=10-30A.
10. A crystalline material according to claim 9 wherein a= 1 0-50 .
11. A crystalline material according to any one preceding claim wherein the crystalline structure is formed in the absence of a metallic species.

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12. A crystalline material according to any one preceding claim comprising a calixarene of structure (I) :
13. A crystalline material substantially as hereinbefore described with reference to figures 1,2 and 3.
14. A method of filtering a contaminated atmosphere comprising passing said atmosphere through a crystalline material according to any one preceding claim.