Molecular and electronic structures of one-electron oxidized Ni-II-(dithiosalicylidenediamine) complexes: Ni-III-thiolate versus Ni-II-thiyl radical states

摘要

The dithiosalicylidenediamine Ni-II complexes [Ni(L)] (R=tBu, R'= CH2C(CH3)(2)CH2 1, R'= C6H4 2; R=H, R'=CH2C(CH3)(2)CH2 3, R'= C6H4 4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R'=CH2C-(CH3)(2)CH2 7, R'=C6H4 8; R=H, R'= CH2C(CH3)(2)CH2 9, R'= C6H4 10) formed by condensation of 2,4-di-R-thiosalicylaldehyde with diamines H,N-R'-NH2 in the presence of Zn-II salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square-planar N2S2 coordination environment and have been characterized by H-1- and C-13 NMR and UV/Vis spectroscopies and by single-crystal X-ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes I and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one-electron oxidation processes, whereas the analogous redox processes for plexes 3 and 4 are not reversible. The one-electron oxidized species, 1(+) and 2(+), can be generated quantitatively either electrochemically or chemically with 70% HClO4. EPR and UV/Vis spectroscopic studies and supporting DFT calculations suggest that the SOMOs of 1(+) and 2(+) possess thiyl radical character, whereas those of 1(py)(2)(+) and 2(py)(2)(+) possess formal Ni-III centers. Species 2(+) dimerizes at low temperature, and an X-ray crystallographic determination of the dimer [(2)(2)]-(ClO4)(2).2CH(2)Cl(2) confirms that this dimerization involves the formation of a S-S bond (S center dot center dot center dot S = 2.202(5) angstrom).