Isostructural polymers

Almost similar connectivity and magnetic properties are observed in the porous solid [Fe(C 0 )(4,4 -bpy)(H30)j] 3HjO [177]. Chains of Fe(II) metal ions bridged by squarate ligands are connected through 4,4 -bipyridines to form a framework with 1-D channels fiUed with water molecules. Interestingly, the dehydration/rehy-dration process in this coordination polymer, as well as in other isostructural polymers with other metal ions, is fuUy reversible and accompanied with a continuous change of the colour [178]. 

The last of these is perhaps the best criterion for metallic characteristics. Most other types of inorganic substance are effectively insulators, or semiconductors whose conductivity increases with temperature. Semiconductors constitute a borderline area some lie between metals and three-dimensional polymers (e.g. GaAs, isoelectronic and isostructural with elemental germanium), while others have structures which could be described as ionic (e.g. PbS, which has the NaCl structure). 

In order to evaluate the influence of additional methyl groups at the para-position of the SAr groups, we also reacted Cul under analogous conditions with bis(p-tolylthio)methane in acetonitrile in a 2 1 molar ratio (Scheme 8). An X-ray diffraction study revealed that colorless polymer 10 of general formula [ Cu4((jl3-I)4 p-p-TolSCI 12ST0I) 2] is isostructural with 9, crystallizing in the monoclinic space group C2/c. 

Borazine is isoelectronic and isostructural with benzene. Poly(borazylene), a polymer of borazine and its derivatives, is reported extensively as a precursor of BN-coated ceramic libers.86 Polymeric borazine oxide derivative is claimed to be flame resistant (Figure 9.10).87... 

To suppress the formation of self-complementary monomers and their polymerization by making the external pockets of the cryptates too small to host the external cesium ions, H2L5 (13) with bulkier phenyl groups was used. To that end, stoichiometric amounts of H2L5, alkali acetates, and divalent hexacoordinate metal acetates were reacted (Scheme 6). Since the polymers meso-14 are isostructural, only the structure of meso- 14e is discussed in detail. In meso- 14e, two 2 -metallocryptate... 

The rapid development of carborane chemistry is mainly due to their practical applications. For instance, the potential utility of carborane polymers as gaskets, O-rings, and electrical connector inserts has been reported. Their functionality for solvent extraction of radionuchdes as well as the potential medicinal value of the isoelectronic and isostructural boron analogues of biologically important molecules has been the subject of many review articles. For example, a number of boron compounds have been found to possess anti-inflammatory and antiarthritic activity in animal model studies. Boron compounds have also been implicated in studies designed to probe the importance of the so-called anionic subsite of acetylcholine esterase and Ach receptors. But, by far the most interesting practical apphcations of carboranes are in areas of boron neutron capture therapy (BNCT) and supramolecular assembly. 

Owing to the special principles of topochemical reactions polydiacetylene copolymers can only be obtained if the comonomers form mixed crystals. Apart from this obvious preparative aspect mixed crystals are of interest because it can be expected that the monomer reactivity and the polymer properties can be effectively varied by the crystal composition. Similar effects have been successfully demonstrated in the isostructural doping of organic charge-transfer crystals In addition, it can be... 

Initially polymeric KC and RbC o were thought to be isostructural. Indeed, the lattice parameters of the three AC o polymers with A=K, Rb, Cs are similar [58]. However, the strong dilferences in the physical properties, in particular the magnetic susceptibilities, electrical conductivities [10] and MAS spectra [59] indicated some undetected structural differences. Brouet et al. [60] suggested from an analysis of MAS spectra that the main difference is in the relative orientation of neighboring C<,o chains. The MAS spectrum shifts are determined in principle both by inter and intra fullerene interactions and are sensitive to small structural differences. Some of the 16 inequivalent C lines of the polymer are well resolved and it was found that the C MAS spectra of polymeric RbCgo and CsCgo on the one hand, and polymeric KC o on the other, are very different (Fig. 13). 

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