Nickel complexes of tridentate ligands incorporating thioether and triazene-1-oxide functions. Synthesis, structure and metal redox

Abstract

The reaction of nickel(II) acetate with RN(O)NNHC₆H₄SMe (HL¹ : R = Me; HL² : R = Prⁿ; general abbreviation HL) in aqueous ethanol affords [NiL₂] as brown crystalline solids. The X-ray structure of [NiL²₂] is reported. Each ligand acts in the tridentate meridional SNO fashion. The Ni(SNO)₂ coordination sphere is severely distorted from octahedral geometry. The Ni---S distances, 2.519(2) and 2.549(2) Å, constitute the longest nickel(II)---thioether bonds reported so far. Due to low symmetry, the octahedral ν₁ 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^IIIL₂]⁺/[Ni^IIL₂], E_1/2 ≈ 0.75 V (vs S.C.E.). Coulometrically generated [Ni^IIIL₂]⁺ displays rhombic EPR spectra, the g values of the erpendicular components being larger than that of the parallel component corresponding to the (d_z²)¹ ground state.