Novel homoleptic bis-o-semiquinonato nickel complexes

A number of square-planar bis-o-semiquinonato nickel complexes were obtained by the reaction of tetracarbonylnickel(0) with the derivatives of 3,6-di-tert-butyl-benzoquinone-1,2. Structural investigation of two complexes having annulated rings (N,N′-piperazino- and O,O′-1,2-ethanediolato-) in 4,5-back positions of quinonato ring detected square-planar molecular geometry. All complexes were studied by 1H NMR, NIR-IR spectroscopy, magnetic susceptibility. Each compound has intensive absorption band in NIR-region which is attributed to b1u → b∗3g (in D2h point symmetry) ligand based transition. Magnetic measurements indicate only one complex (with O,O′-1,2-ethanediolato – substituent) having magnetic moment corresponding to two noninteracting unpaired electrons (2.45 μB). Magnetic moments of the other complexes are essentially lower and correspond to so-called singlet diradical character of complexes. So, in general, the order of frontier orbitals does not depend on the electronic properties of substituents in o-semiquinonato ligands with one mentioned exception.