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

Thermogravimetry (TG), differential thermal analysis (DTA) and other analyt ical methods have been applied to the investigation of the thermal behavior and structure of the compounds Mg(pc)(na)(2). 2H(2)O (I), Mg(pc)(Et(2)na)( 2). 3H(2)O (II), Mg(pc)(mpc)(2). H2O (III) and Mg(pc)(ron). 2H(2)O (IV), wh ere pc=2,6-pyridindicarboxylate, na=nicotinamide, Et(2)na=N,N-diethylnicoti namide, mpc=methyl-3-pyridyl carbamate and ron=3-pyridylcarbinol (ronicol). Thermal decomposition of these compounds are multi-stage processes. The co mposition of the complexes and the solid state intermediate and resultant p roducts of thermolysis had been identified by means of elemental analysis a nd complexometric titration. The possible scheme of destruction of the comp lexes is suggested. Heating the compounds first results in a release of wat er molecules. In complexes I, II and IV the loss of the molecular ligands ( na, Et(2)na and ron) occur (on the TG curves) in one step (-2na, -2Et(2)na and -ron) and in complex III in two steps (-mpc, -mpc). The final product o f the thermal decomposition was MgO. The thermal stability of the complexes can be ordered in the sequence: II<III<I<IV. Et(2)na, na, and ron were coo rdinated to Mg(II) through the nitrogen atom of the respective heterocyclic ring. IR data suggest to a unidentate coordination of carboxylates to Mg(I I) in complexes I-IV. (C) 2000 Elsevier Science B.V. All rights reserved.