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

✍ Scribed by E. Mikuli; N. Górska; S. Wróbel; J. Ściesiński; E. Ściesińska

Publisher
Elsevier Science
Year
2004
Tongue
English
Weight
185 KB
Volume
692
Category
Article
ISSN
0022-2860

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✦ Synopsis

The phase transition in [Cr(NH 3 ) 6 ](BF 4 ) 3 at T h c ¼ 238:42 K (on heating) and at T c 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 T c 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 NH 3 and BF 4 2 groups. However, there were the distinct changes between the X-ray diffraction patterns before and after the T c : It suggests that the discovered phase transition is not connected with a change of the reorientational dynamics of the NH 3 ligands and BF 4 2 anions, but with the change of the crystal structure.

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Four phase transitions at: T h C1 ¼ 267:1 K, T h C2 ¼ 258:8 K, T h C3 ¼ 254:1 K and T h C4 ¼ 195:4 K (on heating) and at T c C1 ¼ 263:8 K, T c C2 ¼ 255:4 K, T c C3 ¼ 246:0 K (on cooling) were determined for [Ca(H 2 O) 4 ](ClO 4 ) 2 between 90 and 295 K by means of differential scanning calorimetry