Molecular and electronic structures of one-electron oxidized NiII–(dithiosalicylidenediamine) complexes: NiIII–thiolate versus NiII–thiyl radical states

The dithiosalicylidenediamine NiII complexes [Ni(L)] (R=tBu, R′=CH2C(CH3)2CH2 1, R′=C6H4 2; R=H, R′=CH2C(CH3)2CH2 3, R′=C6H4 4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R′=CH2C(CH3)2CH2 7, R′=C6H4 8; R=H, R′=CH2C(CH3)2CH2 9, R′=C6H4 10) formed by condensation of 2,4‐di‐R‐thiosalicylaldehyde with diamines H2N‐R′‐NH2 in the presence of ZnII salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square‐planar N2S2 coordination environment and have been characterized by 1H‐ and 13C NMR and UV/Vis spectroscopies and by single‐crystal X‐ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes 1 and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one‐electron oxidation processes, whereas the analogous redox processes for complexes 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 NiIII centers. Species 2+ dimerizes at low temperature, and an X‐ray crystallographic determination of the dimer [(2)2](ClO4)2⋅2 CH2Cl2 confirms that this dimerization involves the formation of a S-S bond (S⋅⋅⋅S=2.202(5) Å)