NICKEL-COMPLEXES WITH CHELATING THIOETHER LIGANDS - ELECTROCHEMICAL PROPERTIES AND CRYSTAL-STRUCTURES OF [NI(MESCH(2)CH(2)SME)(2)(NCS)(2)],[NI(ETSCH(2)CH(2)SET)(2)(NCS)(2)] AND [NI(MESCH(2)CH(2)SME)(2)BR-2]

Current interest in nickel complexes with sulfur donor ligands as mode ls for the active sites of nickel-containing hydrogenases has prompted us to investigate the structural and electrochemical behaviour of nic kel complexes with bifunctional thioether ligands. Crystals of [Ni(MeS CH(2)CH(2)SMe)(2)(NCS)(2)] (1) and [Ni(EtSCH(2)CH(2)SEt)(2)(NCS)(2)] ( 2) are triclinic, space group P1, Z = 1, 1: a = 7.293(3) Angstrom, b = 7.567(3) Angstrom, c = 8.784(3) Angstrom, alpha = 72.81(3)degrees, be ta = 78.41(3)degrees, gamma = 85.14(3)degrees; 2: a = 8.611(1) Angstro m, b = 8.101(1) Angstrom, c = 9.163(1) beta rb Angstrom, alpha = 66.54 (1)degrees, beta = 76.19(1)degrees, gamma = 67.88(1)beta rb degrees. [ Ni(MeSCH(2)CH(2)SMe)(2)Br-2] (3) crystallizes in the monoclinic space group P2(1)/n, a = 6.757(2) Angstrom, b = 7.881(2) Angstrom, c = 14.67 4(4) Angstrom, beta = 94.05(2)degrees, Z = 2. In crystals of 1, 2 and 3 mononuclear neutral complex molecules are observed which have pseudo -octahedral rmns-NiS(4)L(2) coordination sites. The cyclovoltammograms of 1 and 3 in MeCN (Ag/AgCl/KCl, 3 mol/l) show only irreversible oxid ation waves at +837 mV for 1 and +846 mV for 3, respectively, which ar e characteristic features of NCS- and Br- ions. In addition, a reducti on wave at +393 mV is observed in 3. No redox response is found in the potential region between -700 and +100 mV which is used by the NiFe h ydrogenase enzymes.