Pyridil bis(N(4)-substituted thiosemicarbazones) have been prepared in which the substituents in place of the NH 2 group in the thiosemicarbazone moieties are piperidinyl (H 2 Plpip), hexamethyleneiminyl (H 2 Plhexim), diethylaminyl (H 2 Pl4DE), and dipropylaminyl (H 2 Pl4DP). IR, electronic, mass, and ESR spectra of their copper(II) complexes are reported. Crystal structure determinations of H 2 Pl4DE and three of the copper(II) complexes of formula [Cu(Plpip)], [Cu(Plhexim)] and [Cu(Pl4DE)] 2´2 [Cu(Pl4DE)], are included. H 2 Pl4DE lacks hydrogen bonding between the thiosemicarbazone moieties, but each moiety is in the Z confi-guration form with hydrogen bonding from the thiosemicarbazone moieties to the pyridyl nitrogen atoms. The crystal used for the structure determination of [Cu(Plhexim)] was isolated from an electrochemical preparation. In all the new compounds the deprotonated ligands are N,N,S,S-tetradentate, coordinating to the copper(II) centre through their azomethine nitrogen atoms and their thiocarbonyl sulfur atoms.