Thermodynamic properties of paramagnetic bis-o-semiquinonic cobalt complex with α, α′-dipyridyl between T→0 and T=350K

In adiabatic low-pressure and dynamic calorimeters the temperature dependence of the standard molar heat capacity C-p,m(0) of the paramagnetic o-semiquinonic cobalt complex with alpha, alpha'-dipyridyl (alpha,alpha'-bpy)Co(Cat) (SQ) has been determined at temperatures in the range T = (5 to 350) K mainly with an accuracy of about 0.2 per cent. In the interval from T = 270 K to T = 375 K, a physical transformation, i.e., a transition caused by a reversible transformation of the semiquitione-catecholate form of the complex to the bis-semiquinonic one, has been revealed. The enthalpy and entropy of the transformation (the phenomenon known as redox isomery) were estimated. The experimental data were used to calculate the thermodynamic functions C-p,m(0)/R, Delta(0)(T)H(m)(0)(R . K), Delta(0)(T)S(m)(0)/R, and Phi(m)(0) = Delta(0)(T)S(m)(0) - DeltaH(m)(0) (where R is the gas constant) in the range T --> 0 to T = 350 K. (C) 2002 Elsevier Science Ltd. All rights reserved.