Chemical bonding in hypervalent molecules revised.: Application of the Atoms in Molecules Theory to Y3 X and Y3 XZ (Y = H or CH3; X = N, P or As; Z = O or S) compounds

Atoms in Molecules Theory has been applied to analyze bonding properties, in potentially hypervalent pnicogen (N, P or As)-chalcogen(O or S) bonds within the framework of three plausible models: (i) one sigma bond and two pi back-bonds (negative hyperconjugation), (ii) one sigma bond and three pi back-bonds, and (iii) three Omega (banana) bonds. The topological analyses (based upon the electron charge density (rho(r)), its Laplacian (del(2)rho(r)), bond ellipticity, etc.) ana the charges were consistent with a highly polarized sigma bond, with;bond strength dependent on the electrostatic interactions. The equilibrium geometries were optimized by both density functional theory with a hybrid functional (B3LYP) and by ab initio methods at the MP2(full) level, using the 6-311G basis set augmented by polarization and/or diffuse functions.