Thermal and IR properties of Mg(II) complexes with heterocyclic ligands

Abstract

Thermogravimetry (TG), differential thermal analysis (DTA) and other analytical methods have been applied to the investigation of the thermal behavior and structure of the compounds Mg(pc)(na) 2·2H 2O ( I), Mg(pc)(Et 2na) 2·3H 2O ( II), Mg(pc)(mpc) 2·H 2O ( III) and Mg(pc)(ron)·2H 2O ( IV), where pc=2,6-pyridindicarboxylate, na=nicotinamide, Et 2na= N, N-diethylnicotinamide, mpc=methyl-3-pyridyl carbamate and ron=3-pyridylcarbinol (ronicol). Thermal decomposition of these compounds are multi-stage processes. The composition of the complexes and the solid state intermediate and resultant products of thermolysis had been identified by means of elemental analysis and complexometric titration. The possible scheme of destruction of the complexes is suggested. Heating the compounds first results in a release of water molecules. In complexes I, II and IV the loss of the molecular ligands (na, Et 2na and ron) occur (on the TG curves) in one step (−2na, −2Et 2na and −ron) and in complex III in two steps (−mpc, −mpc). The final product of the thermal decomposition was MgO. The thermal stability of the complexes can be ordered in the sequence: II< III< I< IV. Et 2na, na, and ron were coordinated to Mg(II) through the nitrogen atom of the respective heterocyclic ring. IR data suggest to a unidentate coordination of carboxylates to Mg(II) in complexes I– IV.