The Structure and Chemical Bonding in the N2-CuX and N2•••XCu (X = F, Cl, Br) Systems Studied by Means of the Molecular Orbital and Quantum Chemical Topology Methods

Ab initio studies carried out at the MP2(full)/6-311+G(2df) and MP2(full)/aug-cc-pVTZ-PP computational levels reveals that dinitrogen (N-2) and cuprous halides (CuX, X = F, Cl, Br) form three types of systems with the side-on and end-on coordination of N-2: N N-CuX (C-infinity nu), N-2-CuX (C-2 nu) stabilized by the donor-acceptor bonds and weak van der Waals complexes N-2 center dot center dot center dot XCu (C-2 nu) with dominant dispersive forces. An electron density transfer between the N-2 and CuX depends on type of the N-2 coordination and a comparison of the NPA charges yields the [N N](delta+) -[CuX](delta-) and [N-2](delta-) -[CuX](delta+) formula. According to the NBO analysis, the Cu-N coordinate bonds are governed by predominant LPN2 ->sigma*(Cu-X) ''2e-delocalization'' in the most stable N N-CuX systems, meanwhile back donation LPCu ->pi*(N-N) prevails in less stable N-2-CuX molecules. A topological analysis of the electron density (AIM) presents single BCP between the Cu and N nuclei in the N N-CuX, two BCPs corresponding to two donor-acceptor Cu-N bonds in the N-2-CuX and single BCP between electron density maximum of the N N bond and halogen nucleus in the van der Waals complexes N-2 center dot center dot center dot XCu. In all systems values of the Laplacian del(2)rho(r)(r(BCP)) are positive and they decrease following a trend of the complex stability i.e. N N-CuX (C-infinity nu) > N-2-CuX (C-2 nu) > N-2 center dot center dot center dot XCu (C-2v). A topological analysis of the electron localization function (ELF) reveals strongly ionic bond in isolated CuF and a contribution of covalent character in the Cu-Cl and Cu-Br bonds. The donor-acceptor bonds Cu-N are characterized by bonding disynaptic basins V(Cu,N) with attractors localized at positions corresponding to slightly distorted lone pairs V(N) in isolated N-2. In the N N-CuX systems, there were no creation of any new bonding attractors in regions where classically the donor-acceptor bonds are expected and there is no sign of typical covalent bond Cu-N with the bonding pair. Calculations carried out for the N N-CuX reveal small polarization of the electron density in the N N bond, which is reflected by the bond polarity index beine in range of 0.14 (F) to 0.11 (Cl). (c) 2008 Wiley Periodicals, Inc.