Metal complexes of sulphur-nitrogen ligands. Synthesis and characterization of palladium(II) complexes of 3-(mercaptomethyl)piperidine

The complexes [Pd(HL)X<inf>2</inf>] [X = Cl (1a) or Br (1b)], [(PdLX)<inf>2</inf>] [X = Cl (2a), Br (2b), or I (2c)], and [Pd<inf>3</inf>L<inf>4</inf>]Cl<inf>2</inf>·2H<inf>2</inf>O (3), where HL and L denote respectively 3-(mercaptomethyl)piperidine in its zwitterionic and anionic forms, have been prepared and characterized. Complex (3) has been shown crystallographically to contain centrosymmetrical trinuclear cations where terminal PdL<inf>2</inf> units, containing cis-S<inf>2</inf>PdN<inf>2</inf> square-planar metal environments, are bound also in a square-planar fashion to a central palladium atom through bridging mercapto groups. The three planar metal environments exhibit equivalent dihedral angles. Complexes (2) exhibit trans mercapto-bridged dimeric structures containing S<inf>2</inf>PdNX square-planar metal centres. Similar sulphur-bridged dimeric structures, with planar S<inf>2</inf>PdX<inf>2</inf> metal environments, are proposed for complexes (1). Complexes (2) and (3) are among the first known chelates of γ-mercaptopiperidines.