TOPOLOGICAL ANALYSIS OF THE ELECTRON-DENSITY DISTRIBUTION OF BIS(DIIMINOSUCCINONITRILO)NICKEL, NI(C4N4H2)(2) - COMPARISON BETWEEN EXPERIMENT AND THEORY

A quantitative description of chemical bonds in bis(diiminosuccinonitr ilo)nickel, Ni(disn)(2), is made in terms of topological properties of electron densities. These properties are obtained both from an X-ray diffraction experiment and from molecular orbital calculations. The as phericity in electron density around the Ni ion is surely observable f rom the Laplacian of the electron density with density accumulation in the d(pi)direction but density depletion along the d sigma (Ni-N) dir ection. On the basis of the topological properties at bond critical po ints, the bonding between Ni and the imino nitrogen atom is classified as mainly a closed-shell interaction but with some covalent character . The bonds within the ligand, disn, are all shared interactions, and the bond order is reflected clearly from the density at the critical p oint, rho(r(c)), The pi-delocalization of the molecule is precisely in dicated by the bond ellipticity and is illustrated by Fermi-hole distr ibution. Atom domains in the molecule are demonstrated. Molecular elec trostatic potential is derived both from experiment and from MO calcul ations. For all the properties, the agreement between experiment and t heory is reasonable.