On the two closely related phases of [Ru(C5Me 5(η6-1,3-(Me2NCH2) 2C6H4)](BF4) and the reversible solid-solid order-disorder phase transition

Abstract

Crystals of the complex [Ru(C5Me5)(g6-1,3- (Me2NCH2)2C6H4)](BF4) have been examined over the temperature range 150–300 K via X-ray diffraction measurements. This study shows that the Ru complex is a twophase system in this T-range and the solid–solid transition is reversible. At 150 K, phase II (P21/c, Z0 = 4) is ordered and non-merohedrally twinned, a = 16.4396 (9) A ° , b = 17.3226 (4) A ° , c = 32.1874 (11) A ° , b = 91.375 (2) . At 295 K, phase I (Pbca, Z0 = 1) is disordered, a = 8.5071 (3) A ° , b = 17.1567 (3) A ° , c = 32.8250 (8) A ° . The relationship between the two phases is obvious because the packing remains similar in the two phases. The greatest structural changes between the two phases are found in the rows of adjacent cations [Ru(C5Me5)(g6-1,3- (Me2NCH2)2C6H4)]? packed along the a direction. These rows are ordered in phase II but are disordered in phase I. The phase transition is first order. Significant changes in thermal motion for the cations are considered as being the driving force for the occurrence of this phase transition.