Thermal analysis of dithiomalonamide complexes

Dithiomalonamide [H₂A, CH₂(CSNH₂)₂] and 2,2-dimethyldithiomalonamide [H₂B, C(CH₃)₂(CSNH₂)₂] can act as bidentate ligands and form stable, cationic 1∶2 complexes with general formula M₂(H₂L)₂X₂ [M=Ni²⁺, Pd²⁺, Pt²⁺;X=C1, Br, I; H₂L=H₂A, H₂B] in strong acidic medium. An elaborate thermal study is presented, based on results from elemental analyses and vibrational studies (IR and Raman spectroscopy). The H₂A complexes start to decompose by releasing two HX molecules whereafter a stable intermediate M(HA)₂ is formed. The H₂B complexes degrade in a different way; the metal-sulphur bond is broken and the ligand is expelled as a whole. Influences of the metal ion and of the halogenide counterions are investigated.