Quantum chemical study and low-temperature calorimetry of phase transition in V4S9Br4

The phase transition in a mixed-valence tetranuclear compound V4S9Br4 was studied by DFT calculations and low-temperature high-precision calorimetry. According to DFT data, the phase transition of the low-temperature modification may be accompanied by C4v→C2v symmetry lowering and electron spin pairing. A weak exchange-correlation interaction discovered between μ4-S2− and S2− ions in V4S9Br4 may play an important part in multicentered interactions. Experimental calorimetric data show that the phase transition is a displacive phase transformation.