SPECTROSCOPIC AND CRYSTALLOGRAPHIC STUDY OF PHASE-TRANSITIONS IN ZN BIDIMENSIONAL COMPLEXES

The solid phases which appear when heating crystalline bis n-decyl and n-dodecyl ammonium tetrachlorozincates (C10Zn and C12Zn for short) we re studied using differential scanning calorimetry, X-ray diffraction and infrared and Raman spectroscopies. The unit-cell parameters of the different phases were determined. For C10Zn as well as for C12Zn, the room temperature stable phase is a well-ordered interdigitated layer structure with chains in all-trans conformation. A great mobility of t he chains is observed when raising temperature within the phase, but t he formation of specific sequences of bonds, mainly kinks gt(2n-1) g' and end gauche forms, abruptly occurs at the first transition temperat ure at the same time as the cell parameters change. The consecutive in crease in the chain diameter induces a partial disinterdigitation. A s econd phase change at higher temperature leads to a highly disordered form in which only the inorganic matrix keeps a bidimensional crystall ographic organization, before reaching the isotropic phase.