THIOETHER-LIGATED NICKEL - SYNTHESIS, X-RAY CRYSTAL-STRUCTURE AND REDOX BEHAVIOR OF COMPLEXES OF HEXADENTATE LIGANDS INCORPORATING THIOETHER AND TRIAZENE-1-OXIDE FUNCTIONS

The hexadentate ligands RN(O)NNHC6H4S(CH2)3SC6H4NHN(O)NR (H-2L1: R = Me; H-2L2: R = Prn; general abbreviation H-2L) and their nickel(II) complexes, [NiL1] and [NiL2]+, have been synthesized. The X-ray structure of [NiL1] has revealed the presence of a severely distorted NiN2O2S2 coordination sphere with longer than normal Ni-S distances: 2.494(4) and 2.526(3) angstrom. The low symmetry of the ligand field is reflected in large splittings of octahedral v1 and v2 bands. In dichloromethane solution the nickel(III)-nickel(II) redox couple is observable cyclic voltammetrically and the E1/2 values are: [NiL1]+ = 0.74 and [NiL2] = 0.75 V (vs SCE). Frozen (77 K) solutions of the electrogenerated nickel(III) species display rhombic EPR spectra: g1 = 2.195, g2 = 2.145, g3 = 2.038 for [NiL1]+; g1 = 2.199, g2 = 2.138, g3 = 2.035 for [NiL2]+. The g1 and g2 parameters for each complex can be considered as split components of g(perpendicular-to) of the idealized geometry affording the inequality g(perpendicular-to) > g(parallel-to), which corresponds to an effective axial elongation and (d(z)2)1 ground state.