Electronic Structure and Nature of the Ground State of the Mixed-Valence Dinuclear Tetra(m-1,8-naphthyridine-N,N’)-bis(Halogenonickel) Tetraphenylborate Complexes. Experimental and DFT Characterization

The ground state electronic structure of the mixed-valence systems [Ni2(napy)4X2](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|≈3 cm−1. The iodide derivative was found to be isostructural with the previously reported bromide complex, but not isomorphous. The compound crystallizes in the monoclinic system, space group P21/n, with a=17.240(5), b=26.200(5), c=11.340(5) Å, β=101.320(5)°. 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.