Thermal and spectral properties of Mg(II) and Cu(II) complexes with heterocyclic N-donor ligands

Abstract

The thermal decompositions of the complexes Mg(pc)·H 2O ( I), Mg(pc)·3H 2O ( II), Mg(pc)·4H 2O ( III), Mg(ac) 2·(na) 3.4H 2O ( IV) and Cu(pc)·5H 2O ( V), (where pc=2,6-pyridinedicarboxylate, ac=CH 3COO − and na=nicotinamide) have been investigated in an atmosphere of air in the temperature range 20–1000°C by means of TG and DTA. Though complexes I–III are similar (differ only in the number of water molecules), the kinetics of their thermal decomposition were different. The chemical composition of the complexes, the solid intermediates and the resultant products of thermolysis have been identified by means of elemental analysis and complexometric titration. Schemes of destruction of these complexes are suggested. Heating of these compounds first resulted in a release of water molecules. The thermal stability of these complexes can be ordered in the sequence: II=IV<III<I=V. The final products of the thermal decomposition were MgO (from complexes I–IV) and CuO (from complex V). Nicotinamide was coordinated to Mg(II) through the nitrogen atom of its heterocyclic ring. IR data suggested a unidentate coordination of carboxylates to Mg(II) and to Cu(II) in complexes I–V.