The Thermodynamic Properties of (α,α′-Dipyridyl)bis(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt over the Temperature Range from T → 0 to 320 K

Abstract

The heat capacity of (g?,g?′-dipyridyl)bis(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt over the temperature range 7–320 K was studied by precision adiabatic vacuum calorimetry. A physical transformation observed at 134–222 K accompanied the reversible transition of the semiquinone-catecholate complex of low-spin cobalt into the bis-semiquinone adduct of high-spin cobalt. The enthalpy and entropy of this redox-isomeric transition were determined. The data obtained were used to calculate the standard thermodynamic functions of the complex, C p o (T), Ho(T)-Ho(0), So(T), and G o (T)-H o (0), over the temperature range from T → 0 to 320 K. The low-temperature heat capacity of the complex was analyzed using the Debye theory of the heat capacity of solids and its multifractal generalization. The conclusion was drawn that the complex had a predominantly chain structure.