Polymorphism guest dependent

Most of the bile acid derivatives exhibit guest-dependent polymorphism. The typical host is CA, which forms at least 12 host frameworks, depending on guest sizes and shapes, as shown in Figure 8. Most organic guests form bilayer structures, which can be further classified into several subtypes on the... 

Figure 8 Guest-dependent polymorphism in CA inclusion crystals with (a) acetophenone, (b) y-valerolactone, (c) ethynylbenzene, (d) 2-fluoropropiophenone, (e) m-chloroaniline, (f) water (Form I), (g) water (Form II), (h) 3-methylcyclohexanone, (i) acetic acid, (j) m-fluoroaniline, (k) 1,2,3-trimethylbenzene, and (1) acrylonitrile. Hydrogen atoms are omitted for clarity. Carbon, nitrogen and oxygen atoms are represented by open, gray and tilled circles, respectively. 

It has been successfully demonstrated by the authors that macro cyclic heterocyclophanes 1-3 exhibit enzyme-like or rdceptor-like functions with remarkable substrate specificity in the solution phase Heterocyclophane 1 is of considerable interest, since 1 forms a molecular cavity inclusion crystal which is to be differentiated from the lattice (cavity) inclusion and an interesting guest-dependent polymorphism and plane chirality in the crystalline phase have been observed K... 

We report here the macrocyclic conformation of the complexed and the uncomplexed host molecules, hostrguest interactions, the molecular columns formed by stacking of the macrocycles and the guest dependent polymorphism (crystal structure). 

Pseudo-polymorphs [12b, 19], relevant for the following discussion, are characterized by the presence of solvent molecules that may differ in type and quantity and, of course, in the way of bonding within the crystal. Therefore, there is a difference in chemical composition between different solvates and between these and the unsolvated forms. Whether this would lead to a different behaviour in solution will depend on the nature of the encapsulated guest molecule in relation to that constituting the solvent. If the focus is on the chemically relevant species, the presence of solvent molecules will not be relevant however, for the purposes of crystal engineering, the solvent molecules present in pseudo-polymorphs will not be innocent partners. The guest molecules participate in determining crystal properties, even if the structure of the chemically relevant molecule or ion is not influenced. 

Fig. 16 Views and magnetic properties of the open-framework coordination polymers based on cobalt imidazolates. (a) Evacuated [Co(im)J-0 5Ch. (b) [Co(im)j4- (c) [Co(im)j]j. (d) [Co5(im)j 0.4Mb]j. (e) Plots of temperature dependence of ac susceptibility obtained at 0.1 Oe field for [Co(im)J 0.5Ch. A peak appears at 15 K, which is indicative of the ferromagnetic character of this compound, (f) Plot of the thermal evolution of the for [CoCiml lj at 10 kOe field. The inset shows the hysteresis loop at 1.8 K ( ) and 5.0 K (o). (Co, blue O, red C, brown N, violet H, white. Solvent guest molecules in (d) are represented as spheres) Reprinted from ref 168 [Tian YQ, Cai C-X, Ren X-M, Duan C-Y, Xu Y, Gao S, You X-Z, The SUica-Like Extended Polymorphism of Cobalt(ll) Imidazolate Three-Dimensional Erameworks X-ray Single-Crystal Structures and Magnetic Properties (2003) Chem Eur 1 9 5673]. Copyright WUey-VCH Verlag GmbH Co. KGaA. Reproduced with permission...

Kitazawa. T. Kikuyama. T. Takeda. M. Iwamoto, T. Silica-mimetic polymorphism of the Cd(CN)2 host lattice depending on the guest G in Cd(CN)2-xG clathrates. J. Chem. Soc., Dalton Trans. 1995. 3715-3720. 

This unique polymorphism of H-G packing is the result of small conformation changes of the host molecule, depending on the shape and/or the size of the guest molecule. For example, the host-guest stabilization of the I CH CU complex is optimized by a slight decrease in the cavity size (especially in the c-axis direction) and the slightly increased tilt of the benzene walls. Thus, the selection of crystal type. 

In the case of [14](4.2.2)DBA4b, too, polymorphs were formed depending on the conditions of crystal growth due to different intermolecular C-H/O interaction modes [67]. Depending on the crystal morphology, different fluorescence spectra, lifetimes, and photoconductivities were observed due to the different defects in crystals. Crystals of 4b containing various aromatic guest molecules were also reported [68]. 

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