A dianionic dinickel(II) complex and its oxidised phenoxyl radical states

The new dianionic dinickel(II) complex [NBu₄] ₂[Ni₂(L)₂] {L^3- = trianionic form of 3,5-di-tert-butyl-2-hydroxy-N-(2-hydroxyethyl)benzamide} has been synthesised and characterised by ¹H, ¹³C NMR and IR spectroscopy, mass spectrometry, elemental analysis and X-ray crystallography. The X-ray structure of [NBu₄]₂[Ni₂(L)₂] ·EtOH·CH₃CN reveals a quasiplanar dinickel(II) dianionic complex, each of the Ni^II ions possessing a NO₃ planar coordination sphere that results from the ligation of L^3- in a NO₂ fashion through the N-amidate, O-phenolate and O-bridging alcoholate donor atoms. The cyclic voltammogram of [Ni₂(L) ₂]^2- reveals two one-electron reversible oxidation processes at relatively low potentials. The EPR and UV/Vis spectroscopic characterisations of the electrochemically generated one-electron- and two-electron-oxidised products are consistent with two ligand-based oxidation processes leading to the formation of relatively stable mono- and diphenoxyl radical complexes, [Ni₂(L^·)(L)]^- and [Ni₂(L^·)₂], respectively.