Reversible crystal-to-crystal phase transition of an octahedral zinc(II) complex with six dimethylsulfoxide

Abstract

Reversible crystal-to-crystal phase transition was observed for a zinc(II) complex [Zn(dmso)6][BPh4]2 [hexakis(dimethylsulfoxide-κO)zinc(II) bis(tetraphenylborate)] (dmso: dimethylsulfoxide) at 230 K. The reversibility was ascertained by a single-crystal X-ray method, and the phase transition temperature was determined by the differential scanning calorimetry (DSC). In the crystal at 293 K, the complex cation was centrosymmetric, and the six dmso moieties were disordered, while in the crystal at 90 K, reported previously, the symmetry around the zinc(II) ion was lower, and only one dmso moiety was disordered. It was concluded that the sulfur inversion motion of the dmso moieties was taking place in the high-temperature phase and that the motion stopped in the low-temperature phase. From the conformational analysis, the driving force of the phase-transition was attributed to the crystal packing effect of the bulky tetraphenylborate anions, which imposed the volumetric compression of the flexible complex cations.