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Thermal Decomposition and IR Spectra of Mg(II) Compounds with Caffeine

S. C. Mojumdar, M. Melník, and E. Jóna

Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava



Abstract: Thermogravimetry (TG), differential thermal analysis (DTA), and other analytical methods have been applied to the investigation of the thermal behaviour and structure of the compounds Mg(ac)2(caf)2 . 3H2O (I) Mg(Clac)2(caf) . 2H2O (II), Mg(Cl2ac)2(caf) . H2O (III) and Mg(Cl3(ac)2(caf)2 . 5H2O (IV) (ac = CH3COO-, Clac = ClCH2COO-, Cl2ac = Cl2CHCOO-, Cl3ac = Cl3CCOO-, and caf = caffeine). Thermal decomposition of these compounds is a multistage process. The compositions of the complexes and the solid state intermediate and resultant products of thermolysis have been identified by means of elemental analysis and complexometric titration. The possible scheme of destruction of the complexes is suggested. Heating of the compounds 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). The final product of the thermal decomposition was MgO. The thermal stability of the complexes increases in the sequence: I, IV, II, III Caffeine was coordinated to Mg(II) through the N(9) atom of its heterocyclic ring. IR data suggest a unidentate coordination of carboxylates to magnesium in complexes I-IV.

Full paper in Portable Document Format: 535a309.pdf


Chemical Papers 53 (5) 309–314 (1999)

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