Abstract
Structural analysis of four-coordinate (S = 0) complex [Ni(L-1)(2)] 1 (H2L1 = 4,6-di-tert-butyl-2-(2-benzylthiophenyl)aminophenol) revealed that it has approximately planar NiN2O2 coordination with dangling thioether arms (Mukherjee A and Mukherjee R 2005 Indian J Chem50A 484-490). The two coordinated ligands are in 2-iminobenzosemiquinonate(1-) pi radical (L-ISQ)(center dot-) redox level. Chemical oxidation of 1 by [Fe(eta(5)-C5H5)(2)](PF6) in CH2Cl2 in the air led to oxidation of one of the (L-ISQ)(center dot-) ligands affording a six-coordinate Ni(II) complex [Ni(L-1)(2)](PF6) 2 in mer configuration. The two tridentate ligands are in (L-ISQ)(center dot-) and 2-iminobenzoquinone (L-IBQ)(0) redox level (ligand mixed valency). The Ni-N/O/S distances and ligand backbone metrical parameters led us to assign unambiguously the electronic structure of 1(1+)/2 as [Ni-II{(L-ISQ)(center dot-)}{(L-IBQ)(0)}](1+). The EPR spectral signal of 2 at 120 K exhibits a very large g anisotropy and the magnetic measurement indicates an S = 3/2 ground state. The potential shift observed in going from 1 to coulometrically-generated 1(2+) is marginal. DFT calculations at the CAM-B3LYP level of theory rationalizes the electronic structure of 1, 1(1+) and 1(2+). Time-Dependent (TD)-DFT calculations throw light on the nature of observed absorptions of 1, 1(1+) and 1(2+). Graphic abstract One-electron oxidation of four-coordinate [Ni-II(L-1)(2)] 1 (S = 0) Causes additional coordination by two dangling thioethers affording six-coordinate [Ni-II(L-1)(2)](PF6) 2 (S = 3/2); characterization of 2 has been done by X-ray structural analysis, MOS values, magnetism (ferromagnetic coupling), absorption and EPR spectra, and DFT and TD-DFT calculations.