B. T. Ibragimov

A Simple Correlation between the Structures of Different Crystal Modifications of a Given Host–Guest Complex and their Crystallization Temperatures

The formation of different crystal modifications of a given host-guest complex depending on the crystallization temperature (pseudopolymorphism) is studied. It is shown that such pseudopolymorphism is a characteristic feature of versatile host compounds. A very important rule for host-guest chemistry is derived from the results of the X-ray structural investigations of pseudopolymorphs: the higher the crystallization temperature of the modification the more closed is the space occupied by guest molecules. On the basis of the formulated rule a recommendation for the topological control and solution of some central problems of supramolecular chemistry is proposed.

Inclusion complexes of the natural product gossypol. Recognition by gossypol of halogeno methanes. Structure of the dichloromethane complex of gossypol and single crystal conservation after decomposition

The structures of gossypol complexes are extremely sensitive to the halogenomethane present as the guest; e.g. changing the number of Cl atoms in chloromethane derivatives changes the structure of the gossypol complex. The crystals of C30H30O8·CH2Cl2 are monoclinic, space groupC2/c,a=21.320(4),b=19.199(6),c=15.765(2)Å, β=113.05(2)o,V=5916(2)Å3,Z=8,Dx=1.35 g/cm3,T=295 K. The structure has been solved by direct methods and refined to the finalR value of 0.084 for 1828 reflections. In the structure H-bonded gossypol molecules form columns, generating channels in the structure which are filled by guest molecules. After decomposition (desolvation) monocrystals of the complexes are conserved without destruction, in which there are rather wide and empty channels though slightly smaller than in the complex. An attempt is made to explain some peculiarities of the behavior of the gossypol polymorph formed on the basis of its structure with empty channels.

Inclusion complexes of the natural product gossypol

Abstract Gossypol, a biologically active compound with a wide spectrum of action (antiviral, immunosuppressive, antifertile, etc.), is a unique compound in the sense of inclusion complex formation. It gives clathrates with all 110 tested low-molecular organic substances. For 80 clathrates single cyrstals have been obtained and their crystallographic parameters have been determined. By the method of X-ray diffraction the structures of 30 inclusion complexes has been solved. The extreme divergence of gossypol clathrate structures is established: clathrates (H-clathrates) with cavities as isolated cells (cryptates), channels (tubulates), intersecting channels (intercalates), clathrates with mixed host-guest matrix and autoclathrates are observed. The existence of 20 groups of isostructural gossypol clathrates is found.

Polymorphism of Crystalline Inclusion Complexes and Unsolvated Hosts. Part 8

Crystallization of cyclotriveratrylene (CTV) from solutions in acetone at 40°C gave a new 4 : 1 host-guest complex instead of the conventional 2 : 1 clathrate (β-phase) whose X-ray crystal structure was determined. Data for 2(C27H30O6) · 0.5(CO(CH3)2): monoclinic, P21/c, a = 18.942(4), b = 24.697(5), c = 10.508(2) Å, β = 91.10(2)°, V = 4915(2) Å3, Z = 8, Dx = 1.257 g/cm3, T = 293 K, R = 0.077 (for 2694 reflections). One of the two crystallographically independent CTV molecules (molecule A) is stacked into columns characteristic of the CTV α- or β-phase complexes. Molecules B face each other enclathrating inside around the inversion center disordered acetone molecules giving rise to the molecular capsule. The acetone molecule is H-bonded simultaneously to both host molecules by C(H2)--H ··· O type bonds forming centrosymmetric dimers. Dimers are incorporated together with two A molecules into centrosymmetric units also by C(H2)--H ··· O type H-bonds. Packing of these units gives rise to the crystal structure of the clathrate.

Inclusion Complexes of the Natural Product Gossypol. Crystal Structure of the 2" 1 Complex of Gossypol with Amyl Acrylate

The crystal structure of a 2: 1 inclusion complex of gossypol withm-xylene has been determined by X-ray structure analysis. The crystals of C30H30O8·0.5C8 H10 are triclinic, space groupPl−,a = 8.478(1),b = 14.087(2),c = 14.411(2) Å, α = 115,39(1), β = 75.11(1), γ = 86.80(1)°,V = 1475.2(4) Å3,Z = 2,Dx = 1.29 g cm−3,T = 295 K, μ(CuKα) = 7.01 cm−1. The structure has been solved by direct methods and refined to the finalR value of 0.079 for 3910 observed reflections. The gossypol molecules are linked by intermolecular hydrogen bonds and form bimolecular layers parallel to the ‘ab’ plane. Disorderedm-xylene molecules occupy cavities between these layers. All polar groups of the gossypol molecule are packed in the interior of the bilayer while non-polar groups are directed outwards. An analysis of the crystal packing of other inclusion complexes of gossypol shows that such bilayers are formed in four complexes and three of those structures are generically related to each other.

Polymorphism of Inclusion Complexes and Unsolvated Hosts. I. Trimorphism of the Host-Guest Complex of Gossypol with Dichloromethane. The Structure of the β-Phase

The formation of host-guest complexes of gossypol at different temperatures has been investigated for the same pressure and concentration. Gossypol forms three different clathrates with dichloromethane within the temperature interval of 22-36 °C. Single crystals of these three modifications (phases) were obtained and their crystallographic parameters measured. The structure of the α-phase has been determined previously and the γ-phase is isostructural to the inclusion complex of gossypol with benzene, while the structure of the β-phase has been solved during the present research. Crystals of C30H30O8·CH2Cl2 are triclinic, space group P1, a = 8.604(1), b = 11.858(2), c = 14.405(2) (Å), α = 84.60(1), β = 89.14(1), γ = 89.73(1)°, V = 1463(1) Å3, Z = 2, R = 0.089 for 2419 observed reflections.Under ambient conditions gossypol forms unstable tubulates of the α-phase; the γ-phase is a stable cage-type clathrate (cryptate) and the host-guest complex of the β-phase is a clathrate of intermediate tubulato-cryptate type.

Further development of the general rule correlating guest space topology and guest content in polymorphs of the given inclusion compound with crystallization temperatures

The rule correlating topology of guest space and guest content of polymorphic modifications of the given clathrate with their crystallization temperatures has been formulated by the author in 1999. Considering new polymorphic modifications of 18 host–guest complexes obtained in the past years, excellent satisfaction of the rule has been found in practically all cases. Nevertheless, two polymorphic clathrates indicate to necessity of involving specific host–guest interactions. The rule has been developed taking into account this feature and reformulated for more clarity.

SORPTION OF AMMONIA, METHYLAMINE AND METHANOL BY THE P3 POLYMORPH OF GOSSYPOL. SYNTHESIS OF UNSYMMETRICAL MONOAMINE DERIVATIVES OF GOSSYPOL BY A SOLID -STATE REACTION

The P3 polymorph of gossypol has wide, empty channels andstrongly absorbs linear amines. One of the two gossypol aldehydegroups is located near the channel wall. This situation allowsreaction of the amines with half of a gossypol molecule,yielding unsymmetric monoaminoderivatives of gossypol in highyield and by a simple, solid-state method.

Inclusion complexes of the natural product gossypol. The formation of different gossypol polymorphs on decomposition of channel type inclusion complexes

The existence of seven gossypol polymorphs has been established. Two of them are obtained by direct crystallization from solution. The remaining five polymorphs are the products of desolvation of channel type complexes (tubulates). Each isostructural group of the complexes on decomposition gives one polymorph. Gossypol thus possesses specific peculiarities in terms of the decomposition of its tubulates, and also the absence of thermotropic polymorphic transitions.

Inclusion complexes of the natural product gossypol. Crystal structures of gossypol complexes with benzene and chloroform as guests

The crystal structures of the lattice inclusion complexes of gossypol with benzene and chloroform have been determined by X-ray structure analysis. The crystals of (C30H30O8)2 · C6H6 (GPBNZ) are triclinic, space groupPI,a = 11.241(3),b = 14.986(4),c = 17.380(4) Å, α = 98.89(2), β = 99.86(2), γ = 98.91(2)°,V = 2800(2) Å3,Z = 2,Dx = 1.32 g cm−3, μ(CuKα) = 7.35 cm−1. The structure has been refined to a finalR value of 0.050 for 6146 observed reflections. The crystals of C30H30O8·CHCl3 (GPCLF) are monoclinic, space groupC2/c,a = 28.464(4),b = 8.948(1),c = 26.480(4) Å, β = 108.93(2)°,V = 6380(2) Å3,Z = 8,Dx = 1.33 g cm−3, μ(CuKα) = 30.42 cm−1. The structure has been refined to a finalR value of 0.100 for 1980 observed reflections.GPCLF forms an intercalate-type structure and GPBNZ a clathrate-type structure. There are, however, some similarities in the packing mode of the host molecules in these two structures. On a basis of comparison of the crystal packing of GPCLF and GPBNZ one can postulate that in the desorption process of the intercalate-type GPCLF complex an intermediate clathrate structure of the GPBNZ-type should be formed.