Thermal characterization of nitrogen monoxide dissociation reactions of nitrosyl complexes in the solid phase. Mononitrosylcobalt(III) complexes with mixed ligand tetradentate Schiff bases

Abstract

Thermal NO dissociation reactions in the solid phase of mononitrosylcobalt(III) complexes with the formula, CoL 4NO (L 4 denotes tetradentate ligands such as bzacen, salen and its 5-NO 2, 5-Cl, and 5-Me derivatives 2 2 The following abbreviations are used in this paper; bzacen is N,N′-ethylenebis(2-benzoyl-1-methylethylideneaminato); salen, N,N′-ethylenebis(salicylidenaminato); 5-NO 2-, 5-Cl-, and 5-Me-salen are N,N′-ethylenebis(5-nitro-, 5-chloro-, and 5-methylsalicylideneaminato), respectively. ) have been investigated by means of TG, DSC, and pyrolysis gas chromatographic analyses. The complexes eliminated one mole of NO per mole in the 160–300°C range and reproduced CoL 4 complexes which possessed X-ray diffraction patterns similar to those of authentic CoL 4 complexes. The kinetic analyses indicated that the NO dissociation process followed a first-order equation; the activation enthalpy values were 120–124 kJ mol −1, being invariable irrespective of the nature of L 4. The values of heat of NO dissociation, determined by the DSC method were in the range 40–50 kJ mol −1. From these thermochemical data and the data of heat of solution of NO, the NO dissociation energies in solution were calculated to be 52–61 kJ mol −1. The thermal data were discussed in terms of the nature of the CoNO bond.