Nickelkomplexe mit Thioether-Chelatliganden: Elektrochemische Eigenschaften und Kristallstrukturen von [Ni(MeSCH2CH2SMe)2 (NCS)2], [Ni(EtSCH2CH2SEt)2(NCS)2] und [Ni(MeSCH2CH2SMe)2Br2]

Abstract

Abstract Current interest in nickel complexes with sulfur donor ligands as models for the active sites of nickel-containing hydrogenases has prompted us to investigate the structural and electrochemical behaviour of nickel complexes with bifunctional thioether ligands. Crystals of [Ni(MeSCH2CH2SMe)2(NCS)2] (1) and [Ni(EtSCH2CH2SEt)2(NCS)2], (2) are triclinic, space group Pī, Z = 1, 1: a = 7.293(3) Å, b = 7.567(3) Å, c = 8.784(3) Å, α = 72.81(3)°, β = 78.41(3)°, γ = 85.14(3)°; 2: a = 8.611(1) Å, b = 8.101(1) Å, c = 9.163(1) ßrbÅ, α = 66.54(1)°, β = 76.19(1)°, γ = 67.88(1 )ßrb°. [Ni(MeSCH2CH2SMe)2Br2] (3) crystallizes in the monoclinic space group P21/n, a = 6.757(2) A, b = 7.881(2) Å, c = 14.674(4) Å, β = 94.05(2)°, Z = 2. In crystals of 1, 2 and 3 mononuclear neutral complex molecules are observed which have pseudo-octahedral trans-NiS4L2 coordination sites. The cyclovoltammograms of 1 and 3 in MeCN (Ag/AgCl/KCl, 3 mol/l) show only irreversible oxidation waves at +837 mV for 1 and +846 mV for 3, respectively, which are characteristic features of NCS⊖ and Br⊖ ions. In addition, a reduction 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 hydrogenase enzymes.