Thermal decomposition and IR spectra of Mg(II) compounds with caffeine

Thermogravimetry (TG), differential thermal analysis (DTA), and other analy tical methods have been applied to the investigation of the thermal behavio ur and structure of the compounds Mg(ac)(2)(caf)(2) . 3H(2)O (I) Mg(Clac)(2 )(caf) . 2H(2)O (II), Mg(Cl(2)ac)(2)(caf) . H2O (III) and Mg(Cl(3)ac)(2)(ca f)(2) . 5H(2)O (IV) (ac = CH3COO-, Clac = ClCH2COO-, Cl(2)ac = Cl2CHCOO-, C l(3)ac = Cl3CCOO-, and caf = caffeine). Thermal decomposition of these comp ounds is a multistage process. The compositions of the complexes and the so lid state intermediate and resultant products of thermolysis have been iden tified by means of elemental analysis and complexometric titration. The pos sible scheme of destruction of the complexes is suggested. Heating of the c ompounds first results in a release of water molecules. In complexes I, II, and III the loss of the volatile ligand (caf) occurs (on the TG curves) in one step (- 2caf or caf) and in complex IV in two steps (- caf, - caf). Th e final product of the thermal decomposition was MgO. The thermal stability of the complexes increases in the sequence: I, IV, II, III Caffeine was co ordinated to Mg(II) through the N(9) atom of its heterocyclic ring. IR data suggest a unidentate coordination of carboxylates to magnesium in complexe s I-IV.