Structural Analysis of the Intermediate Phases of (n-C₁₃H₂₇NH₃)₂ZnCl₄ by Single Crystal Diffraction

Abstract

The structure of (n-C₁₃H₂₇NH₃)₂ZnCl₄ consits of two-dimensional layers of alkylamonium chains stacked alternately with layers of isolated ZnCl₄ terrahedra. Consecutive layers are linked by H-bonds between the N and Cl atoms. In the temperature range from 20 to 50[ddot]C, five different phases could be identified, four of which were analyzed by single crystal diffraction. In each phase, all the chains are essentially parallel. In the room temperature phase, the direction of the chains is inclined with respect to the normal to the layer whereas it is nearly parallel to the normal in the other phases. The phase which is stable directly above room temperature is chracterterized by the total disappearance of the kinks observed in the room temperature phase. They reappear in the phases stable at higher temperatures but at varying positions and on varying chains depending on the phase. All the transitions but one have a first order character and are reversible. The room temperature phase of an untreated sample cannot be recovered after a heating cycle and must therefore be considered metastable.