Polyhedron Vol. 12, No. 19, pp. 232>2329, 1993 Printed in Great Britain 0277-5387/93 W.oO+.OO 0 1993 Pergamon Press Ltd zyxwvutsr NICKEL COMPLEXES OF TRIDENTATE LIGANDS INCORPORATING THIOETHER AND TRIAZENEl-OXIDE FUNCTIONS. SYNTHESIS, STRUCTURE AND METAL REDOX SOMA KARMAKAR, SURANJAN BHANJA CHOUDHURY, DEBASHIS RAY aod ANIMESH CHAKRAVORTY* Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR (Received 20 April 1993 ; accepted 3 June 1993) Abstract-The reaction of nickel(I1) acetate with RN(0)NNHC6H,SMe (HL’ : R = Me; HL’ : R = Pr” ; general abbreviation HL) in aqueous ethanol affords BiL,] as brown crystalline solids. The X-ray structure of [NiL22] is reported. Each ligand acts in the tridentate meridional SNO fashion. The Ni(SN0)2 coordination sphere is severely distorted from octahedral geometry. The Ni-S distances, 2.519(2) and 2.549(2) A, constitute the longest nickel(II)-thioether bonds reported so far. Due to low symmetry, the octahedral v, band of the complexes are split into components lying at ca 1400 and 1000 nm. The complexes display quasireversible cyclic voltammograms corresponding to the metal redox couple [Ni”‘L2]+/[Ni”L2], E1,2 N 0.75 V (vs S.C.E.). Coulometrically generated [Ni”‘L2]+ displays rhombic EPR spectra, the g values of the perpendicular components being larger than that of the parallel component corresponding to the (dg)’ ground state. This work forms part of our programme on the syn- thesis, structure and redox behaviour of nickel(I1) complexes incorporating thioether ligation. l-4 The nickel(IIkthioether link is intrinsically weak5-7 and we have used polydentate ligation as the stabilizing principle. Ligands having both thioether and triazene-l-oxide functions are well-suited’ for nickel(I1) binding and we have recently reported the case of hexadentate coordination zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (1).4 In this concluding study on the thioether triazene-l-oxide complexes we examine the case of tridentate ligands, which have two disadvantages compared with hexadentate ligands : diminished chelate effect and potentially easier dissociation of the terminally placed thioether site. Nevertheless, complexes of coordination type 2 have, however, been isolated and one of these has been structurally characterized. Redox activity of nickel-sulphur complexes are of bioinorganic interest. 9, lo The present complexes are oxidisable in solution affording EPR-active nickel(II1) species. 2325 M aterials *Author to whom correspondence should be addressed. 2-Methylthioaniline was prepared by methy- lating 2-aminothiophenol by methyl iodide in alka- line media. The hydroxylamines were made by reduction of the corresponding nitro compounds.’ ’ All reagents used were of commercial grade. Tetra- ethylammonium perchlorate and pure dichlo- romethane for electrochemical and spectroscopic work were obtained as before. I2 & 09 S SJ EXPERIMENTAL