Charge Density and Bonding in Bis(diiminosuccinonitrilo)nickel, Ni(C4N4H2)2: A Combined Experimental and Theoretical Study

A combined experimental and theoretical charge density study is made on the compound bis(diiminosuccinonitrilo)nickel, Ni(s-disn)2. It is investigated experimentally by an accurate X-ray diffraction measurement on a single crystal of the compound at 110 K and theoretically by various molecular orbital calculations. The crystal belongs to monoclinic crystal system, space group P21/n; a = 3.639(1), b = 8.743(1), c = 15.948(1) A, β = 94.74(1)°, Z = 2. The molecule is planar with pseudo-D2h symmetry stacked along the a axis. Single-point MO calculations are performed using EHMO, ab initio, and density functional methods. Deformation densities are produced via conventional X−Xhigh, multipole model, and MO calculations. Bonding densities along N−H, C−C, C−N, C⋮N bonds, and lone-pair electron densities are clearly demonstrated and are in excellent agreement between experiment and theory. The bonding density between the coordinated nitrogen atom of the ligand and the nickel atom indicates a certain degree of dati...