Electronic structure and nature of the ground state of the mixed-valence binuclear tetra(μ-1,8-naphthyridine-Ν,Ν′)-bis(halogenonickel) tetraphenylborate complexes:: Experimental and DFT characterization

The ground state electronic structure of the mixed-valence systems [Ni-2(napy)(4)X-2](BPh4) (napy=1,8-naphthyridine; X = Cl, Br, I) was studied with combined experimental (X-ray diffraction, temperature dependence of the magnetic susceptibility, and high-field EPR spectroscopy) and theoretical (DFT) methods. The zero-field splitting (zfs) ground S=3/2 spin state is axial with \ D \ approximate to 3 cm(-1). The iodide derivative found to be isostructural with the previously reported bromide complex, but not isomorphous. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a = 17.240(5), b = 26.200(5), c = 11.340(5) (A) over circle, beta = 101.320(5)degrees. DFT calculations were performed on the S = 3/2 state to characterize the ground state potential energy surface as a function of the nuclear displacements. The molecules can thus be classified as Class III mixed-valence compounds with a computed delocalization parameter, B = 3716, 3583, and 3261 cm(-1) for the Cl, Br, and I derivatives, respectively.