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

Abstract

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 P2 1 /n; 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-D 2h 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-X high , multipole model, and MO calculations. Bonding densities along N-H, C-C, C-N, CtN 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 d xz , d yz 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.

Theoretical Study of the Reverse Water Gas Shift Reaction on Copper Modified β-Mo2C(001) Surfaces

“…The generalized gradient approximation (GGA) in the form of the Perdew–Burke–Ernzerhof (PBE) functional was used to describe the exchange–correlation term. The double-numerical quality basis set with polarization functions (DNP) , was utilized to expand the wave functions, which was comparable to 6-31G**. , The basis-set superposition error can be minimized by the numerical basis sets . A Fermi smearing of 0.005 hartree was adopted, and a grid of 3 × 3 × 2 Monkhorst–Pack k -points was used for the structural relaxation and transition state (TS) location.…”

Topological Analysis of the Electron Density Distribution of Bis(diiminosuccinonitrilo)nickel, Ni(C4N4H2)2: Comparison between Experiment and Theory

“…Although the exact molecular symmetry in the crystal is C i , the actual geometry can be considered as D 2 h within three standard deviations. The multipole coefficients, P lm , were constrained in D 2 h fashion …”

“…Basis sets of C, N, and H atoms are taken from 6-31G**. The geometry of the molecule is taken to be D 2 h by imposing a C 2 symmetry on the coordinates obtained from X-ray diffraction data …”

“…Charge density distribution of the title compound has been investigated recently through deformation density distribution on a combined experimental and theoretical study brings in a new insight into chemical bonding characterization.…”

Bond Characterization of Metal Squarate Complexes [MII(C4O4)(H2O)4; M = Fe, Co, Ni, Zn]

“…The electron density distribution of transition metal complexes has been investigated extensively using the single-crystal X-ray diffraction method during the last decade. − Systematic studies on the 3d-transition metal complexes are made for the purpose of understanding the trend of electronic structure around the metal ion. The electronic structures of hexaaquametal(II) ions 1-13 are of archetypal importance in understanding metal−ligand (oxygen) bonds.…”