Palladium(II) and platinum(II) complexes of 2-hydroxy acetophenone N(4)-ethylthiosemicarbazone – crystal structure and description of bonding properties

Reaction of H2PtCl4 and K2PdCl4 with 2-hydroxyacetophenone N(4)-ethylthiosemicarbazone, H2Ap4Et, afforded [Pt(Ap4Et)(H2Ap4Et)] and [Pd(Ap4Et)(H2Ap4Et)]. Their crystal and molecular structures are reported and represent the first 1:2 thiosemicarbazone complexes with ligands having both different formal charge and denticity. The dianion, Ap4Et2−, coordinates in a planar conformation to palladium(II) or platinum(II) via the phenolato O, imine N and thiolato S atoms, while the neutral molecule exhibits monodentate coordination by the thione S atom. Intra-, intermolecular hydrogen bonds and C–H⋯π contacts lead to aggregation and a supramolecular assembly. Electronic, IR, and NMR spectral data, as well as electrochemical measurements, are included. The pKa values of the poorly water soluble H2Ap4Et were obtained spectrophotometrically in aqueous solutions of constant ionic strength.