Structure, magnetism and colour in simple bis(phosphine)nickel(II) dihalide complexes: an experimental and theoretical investigation.

The complex [1,2-bis(di-tert-butylphosphanyl)ethane-κ(2)P,P']diiodidonickel(II), [NiI2(C18H40P2] or (dtbpe-κ(2)P)NiI2, [dtbpe is 1,2-bis(di-tert-butylphosphanyl)ethane], is bright blue-green in the solid state and in solution, but, contrary to the structure predicted for a blue or green nickel(II) bis(phosphine) complex, it is found to be close to square planar in the solid state. The solution structure is deduced to be similar, because the optical spectra measured in solution and in the solid state contain similar absorptions. In solution at room temperature, no (31)P{(1)H} NMR resonance is observed, but the very small solid-state magnetic moment at temperatures down to 4 K indicates that the weak paramagnetism of this nickel(II) complex can be ascribed to temperature independent paramagnetism, and that the complex has no unpaired electrons.