Heat Capacity and Magnetic and Structural Phase Transitions of the One-Dimensional Rhodium(I)-Semiquinonato Complex [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]

Heat capacities of the one-dimensional rhodium(I)-semiquinonato complex [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2] were measured by adiabatic and relaxation methods. A large heat capacity peak due to first-order phase transition was observed at 223.1 K. Transition enthalpy and entropy of the phase transition amounted to 4.344 kJ mol-1 and 19.42 J K-1 mol-1, respectively. When the complex was cooled rapidly, a supercooled metastable phase was obtained to undergo another small first-order phase transition at 62.2 K, which indicated transition enthalpy and entropy of 96.8 J mol-1 and 1.61 J K-1 mol-1, respectively. Magnetic phase transitions were found at 14.1 K for the metastable phase and at 14.7 K for the stable phase, which are antiferromagnetic from the magnetic field dependences of the magnetic transition temperatures.

(by N. Górska & Y. Miyazaki)

	Fig. 1. Molecular structure of [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2].
	Fig. 2. Magnetic susceptibilities of [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2].
	Fig. 3. Heat capacities of metastable and stable phases of [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2].