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

The heat capacity of (alpha, alpha'-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 degrees(T), H degrees(T)-H degrees(0), S degrees(T), and G degrees(T)-H degrees(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.