Charge density and bonding in bis(diiminosuccinonitrilo)nickel, Ni(C4N4H2)2: A combined experimental and theoretical study

Chi-Shen Lee, Tsong Song Hwang, Yu Wang*, Shie Ming Peng, Ching Shan Hwang

*Corresponding author for this work

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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 P21ln; a = 3.639(1), b = 8.743(1), c = 15.948(1) Å, 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 dative bond through the donation of nitrogen lone pair electrons to the metal center. The redistribution in electron density around the nickel atom is substantial with electron density depletion along the σ-direction but electron density surplus along the π-direction, which conforms to the crystal field theory. The agreement in deformation density between experiment and theory around nickel atom is reasonably good. Bonding type in the s-disn ligand was further analyzed with orbital wave functions, the complete π-electron delocalization of the ligand is incorporated with the dxz, dyz orbitals of the Ni atom. Three Lewis structures are deduced from the ab initio MO calculation; they are exactly the same as expected by valence bond theory. The resonance between three Lewis structures represents the π-electron delocalization of the molecule. Comparisons between experiment and theory are made on electron density distribution, net atomic charges of the molecule, and d-orbital occupancies of the Ni atom.

Original languageEnglish
Pages (from-to)2934-2941
Number of pages8
JournalJournal of physical chemistry
Issue number8
StatePublished - 22 Feb 1996

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