Thermoanalytical and IR-spectral investigation 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 behaviou r and structure of the complexes Mg(pc)(na)(3). 3H(2)O (I), Mg(pc)(py)(2). 2H(2)O (II), Mg(pc)(pic)(2). 2H(2)O (III) and Mg(pc)(caf)(2). 4H(2)O (IV), where pc=2,6-pyridinedicarboxylate, na=nicotinamide, py=pyridine, pic=gamma -picoline and caf=caffeine. The thermal decomposition of these compounds i s multi-stage processes. The chemical composition of the complexes, the sol id intermediates and the resultant products of thermolysis have been identi fied by means of elemental analysis and complexometric titration. Schemes o f destruction of these complexes are suggested. Heating of these compounds first resulted in a release of water molecules. In complexes I, II and IV t he loss of the molecular ligands (na, py and caf) occur (on the TG curves) in one step(-2na, -2py and -2caf) and in complex III in two steps (-pic, -p ic). The final product of the thermal decomposition was MgO. The thermal st ability of the complexes can be ordered in the sequence: IV <I < III < II. Nicotinamide, pyridine, gamma -picoline and caffeine were co-ordinated to M g(II) through the N atom of the respective heterocyclic ring. IR data sugge sted a unidentate co-ordination of carboxylates to Mg(II) in complexes I-IV .