PREPARATION, CHEMICAL CHARACTERIZATION AND THERMAL STUDY OF 2-AMINOPYRIDINIUM SALTS OF SQUARE-PLANAR 1,2-DITHIOOXALATO-S,S' METAL-COMPLEXES (M=NI-II, PD-II AND PT-II)

Reaction of an aqueous solution of 2-aminopyridinium chloride with the appropriate K-2[M(S2C2O2)(2)] Salt yielded microcrystalline powders of three complexes of the formulae (HC5H6N2)(2)[Ni(S2C2O2)(2)] (1), (HC5H6N2)(2)[Pd(S2C2O2)(2)] (2) and (HC5H6N2)(2) [Pt(S2C2O2)(2)] (3), which were characterized by elemental analysis, IR and UV-vis spectroscopies, thermal analysis (TG, DTG and DTA) and X-ray powder diffraction techniques. The IR and UV-vis spectra support the presence of the aromatic cation and the complex anions. Single crystals of 1 were grown in silica hydrogel at room temperature employing test tubes. However, this compound is not stable on X-ray exposure and only the unit cell parameters were determined. The three compounds are isostructural, and crystallize in the monoclinic space group C2/c with Z = 8. Thermal studies give evidence that the mechanism and the final solid products are strongly influenced by the atmospheric conditions. The final decomposition products were identified by elemental analysis and the X-ray powder diffraction technique. In an argon-oxygen atmosphere, thermal degradation led to a mixture of nickel sulphides, oxides and sulphate for 1, metallic palladium and palladium(II) oxide for 2, and platinum(0) for 3. Thermal decompositions in an inert atmosphere yielded nickel(II) sulphide, a mixture of Pd-PdS and metallic platinum, respectively.