Phase transition and molecular motions in [Cr(NH3)6](BF4)3 studied by differential scanning calorimetry, infrared spectroscopy and X-ray diffraction

The phase transition in [Cr(NH3)6](BF4)3 at Th c ¼ 238:42 K (on heating) and at Tc c ¼ 237:93 K (on cooling) was determined by differential scanning calorimetry (DSC). Fourier transform far infrared (FT-FIR) and middle infrared (FT-MIR) spectra were measured in the temperature range of 20–295 K. The spectra did not show significant changes at Tc temperature. Moreover, there were not characteristic changes in the temperature dependence of the full width at half maximum (FWHM) of the chosen modes connected with the internal vibrations of the NH3 and BF4 2 groups. However, there were the distinct changes between the X-ray diffraction patterns before and after the Tc: It suggests that the discovered phase transition is not connected with a change of the reorientational dynamics of the NH3 ligands and BF4 2 anions, but with the change of the crystal structure. q 2004 Elsevier B.V. All rights reserved