Polymeric isomorphism

No single crystal X-ray structure determinations have been reported for the monocarboxy-lates. The 2-carboxylate (picolinate) was claimed to be isomorphous with the copper(II) analogue however, which had square planar stereochemistry. On the basis of X-ray powder data, polymeric square planar structures were proposed for the 3-cart>oxylate (nicotinate) and 4-carboxylate (isonicotinate). 

The reaction of Cu(II) halides with Cu(R2Dtc)2 complexes was reported to give polymeric materials (270). At a later date the exact nature of these products was probed and, by means of the reaction of Cu(PipDtc)2 with CuBr2, complexes of the type Cu(PipDtc)2(CuBr) (n = 4, and 6) were isolated. The structures of these molecules have been determined and consist of polymeric sheets of individual Cu(PipDtc)2 molecules linked to polymeric CuBr chains by way of Cu-S bonds (Table IX). The Cu(PipDtc)2(CuG)4 homologue is x-ray isomorphous and probably isostructural with the corresponding bromo compound. 

The known Fe(OAlk)2 are green polymeric substances. The diffuse reflectance spectrum of Fe(OMe)2 indicates the octahedral coordination of iron atoms [6], According to the X-ray powder data its structure is isomorphous to those of other divalent metals, — i.e., resembles that of Fe(OH)2 (Mg(OH)2 type) [1656], The solubility is characteristic only of the derivatives of rather branched radicals — CH2Ph, CPh3 [114,941] — or of the phenoxides solvated by such bulky ligand as Dipy [941], The octahedral coordination is observed not only for the methoxide but quite unexpectedly for the derivatives 3,5-sus-... 

The electric conductivity was also measured for complexes of taper-shaped mesogens with oligo(ethylene oxide) central groups. The DC conductivity is in a range of 10 9 to 10 6 S cm-1 and shows a step-like increase at the crystal-columnar phase transition [86]. It was also shown that taper-shaped molecules adjacent to different endo-receptors such as crown ethers or oligo(ethylene oxide) chains were miscible with a poly(methacrylate) matrix and formed isomorphic phases [87]. Applications as columnar reaction media for polymerizations were foreseen. Comprehensive summaries of Percec s taper-shaped molecules can be found in the literature [88, 89]. 

Sc and Lu derivatives are isomorphous and polymeric containing [r/5-(C5H5)2Ln(p,-r] -CsHs)]. In the case of SmCp3, two crystallographically independent molecules bonded to each other by non-valence interactions has been observed [25]. 

Also possibly involving Mn—C bonds is the compound72 of the tricyanomethanide ion Mn C(CN)3 2 (Me2N)3PO 2. This colourless compound is not isomorphous with the octahedral Ni11 species, but also probably has an octahedral polymeric structure with bridging anions. 

Monopyridine compounds result from thermal degradation of the bis speties. They appear to have the polymeric structure (13) (MnCl2py is isomorphous with NiBr,py). Further thermal degradation sometimes leads to a well-characterized phase Mn3X6 2py . 

Most nonmetallic (or metalloid) elements form sulfides that if not molecular, have polymeric structures involving sulfide bridges. Thus silicon disulfide (12-VI) consists of infinite chains of SiS4 tetrahedra sharing edges, whereas the isomorphous Sb2S3 and Bi2S3 (12-VII) form infinite bands that are then held in parallel strips in the crystal by weak secondary bonds. 

The electrochemistry of the polymeric and isomorphous cobalt(II) and nickel(II) methylsquarates was also studied by Iwuoha et al. In aqueous solutions, they found evidence that both the nickel(II) methylsquarate and its cobalt analog were dissociated without any reversible redox processes occurring for the metal ions. However, the cyclic and Osteryoung square wave voltammograms, obtained using a Pt electrode for solutions of these complexes in dimethylformamide and dimethylsulfoxide, contained signals attributable to both ligand-based and metal-based redox processes 142). 

Similar results have been obtained by measuring the Raman spectra of partially polymerized crystals and by other spectroscopic techniques. Here, the vibrational frequency of the polymer chain can be used as a probe for the lattice strain in the vicinity of the dispersed macromolecules It should be noted that monomer and polymer are not strictly isomorphous. The mismatch between monomer stacking and polymer repeat of 0.2 A per addition step has to be accounted for by the monomer matrix. The raman frequencies shift accordingly to the lattice changes (cf. Fig. 11) in agreement with the random chain distribution. 

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