Mechanism of phase transition in guanidinium 4-nitrobenzoate studied by calorimetric and spectroscopic methods.

Abstract

The noncentrosymmetric complex of guanidine with 4-nitro benzoic acid is known in the literature. The X-ray structure at room temperature was described. In our calorimetric (DSC) study the phase transition at ca. 183K was detected. This phenomenon has a typical continuous (second-order) character. The DSC studies were expanded, and the deuterated sample was measured, too. During the deuteration process, the temperature of the phase transition is changed. The detailed vibrational (infrared and Raman) studies were performed for normal and deuterated powder samples at room temperature. The mechanism of a phase transition was studied by vibrational spectroscopy, also. A temperature dependence infrared spectra were measured in the temperature range 11-300K. Additionally, the low-temperature spectra were measured for the deuterated sample. Based on these studies, the detailed assignments of observed bands were made.