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 tetra-chlorozincates (C10Zn and C12Zn for short) were 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 the chains is observed when raising temperature within the phase, but the formation of specific sequences of bonds, mainly kinks gt2n-1 g′ and end gauche forms, abruptly occurs at the first transition temperature at the same time as the cell parameters change. The consecutive increase in the chain diameter induces a partial disinterdigitation. A second phase change at higher temperature leads to a highly disordered form in which only the inorganic matrix keeps a bidimensional crystallographic organization, before reaching the isotropic phase.