Syntheses and luminescent properties of tetrahedral nickel(0) complexes

Tetrahedral nickel(0) complexes [NiL(4)], [Ni(dppe)(2)] and [Ni(CO)(2)(SbPh(3))(2)] (L=AsPh(3), SbPh(3), P(OPh)(3), dppe=1,2-bis (diphenylphosphino)ethane) were prepared by reduction of NiCl2 . 6H(2)O with NaBH4 under N-2 or CO atmosphere in the presence of the ligand. The complex [Ni(SbPh(3))(4)] was also obtained by electrolysis at -1.3 V (Ag/Ag+), under a platinum gauze, of the system NiCl2 . 6H(2)O/SbPh(3) (molar ratio=1:4). These complexes, both in the solid state and in solution, show an orange emission at room temperature, when excited with UV radiation. A qualitative molecular orbital diagram for the [NiL(4)] complexes is proposed. Electronic absorption spectra of the complexes show bands near 400 nm assigned as MLCT pi(2e)*<--d(2t2). A (1)A(1)<--T-3(1) transition is suggested for the emission observed in these systems. Lifetimes in microsecond range were estimated from time-resolved emission spectra. Spectroscopic properties of the free ligands have also been investigated.