Crystal architecture and mesophase structure of long-chain N-alkylpyridinium tetrachlorometallates

The N-hexadecylpyridinium derivatives [C16-PY](2)[MCl4] (M = Cd(1), Zn(2)) were prepared and structurally characterized by Xray diffraction methods. The crystal structure of I reveals a layered arrangement with alternation of monolayers of interdigitated cations with layers of isolated [CdCl4](2-) anions. C-H...Cl-Cd interactions reinforce the association between anions and cations in the polar region of the supramolecular structure. Both 1 and 2 display a thermotropic smectic A phase in addition to some high-temperature crystalline modifications. The thermal polymorphism of the salts was studied by X-ray powder diffraction, differential scanning calorimetry (DSC), and thermal optical microscopy. The structural and mesomorphic characteristics of I and 2 are compared with those of the analogous salts along the series [C16-Py](2)[MCl4] (M = Co, Ni, Cu, Zn, Pd, Cd). (C) 2002 Elsevier Science B.V. All rights reserved.