Spectral and structural studies of metal complexes of 1-phenylglyoxal bis { {N (3) -diethylthiosemicarbazone} }

Nickel (II) , copper (II) and palladium (II) complexes of 1-phenylglyoxal bis {N (3) -diethylthiosemicarbazone} , H₂Pg4DE, have been prepared, studied spectroscopically and their crystal structures solved. H₂Pg4DE and the three complexes have been characterized by IR, electronic, ¹H NMR (Ni, Pd) and ESR (Cu) spectra. Upon formation of these complexes, loss of the N (2) H hydrogens from both thiosemicarbazone moieties occurs, and the ligands coordinate to the metal centers as dianionic, tetradentate N₂S₂ ligands. The nickel (II) and copper (II) complexes, [M (Pg4DE) ] , coordinate in the expected 5-5-5-chelate ring system, but [Pd (Pg4DE) ] coordinates with 5-6-4-membered chelate rings. The thiosemicarbazone moiety attached to the phenyl keto carbon in [Pd (Pg4DE) ] forms the 4-membered chelate ring coordinating via N (2) rather than the azomethine nitrogen, N (1) .