Analysis of Oxygen-Pnictogen Bonding with Full Bond Path Topological Analysis of the Electron Density

A variety of methods are available to investigate the bonding in inorganic compounds. In contrast to wavefunction-based analyses, topological analysis of the electron density affords the advantage of analyzing a physical observable: the electron density. Classical topological analyses of bonding interactions within the atoms in molecules framework typically involve location of a bond path between two atoms and evaluation of a range of real-space functions at the (3, -1) critical point in the electron density that exists on that bond path. We show here that counter-intuitive trends are obtained from the analysis of the electron density (ρ), the Laplacian (∇²ρ), and ellipticity (ε) at the O-E (3, -1) critical points in the coupled-cluster singles doubles electron densities of a series of compounds featuring a range of oxygen-pnictogen bond types: EO⁺, HEO, H₂EOH, H₃EOH⁺, and H₃EO (where E = N, P, As, Sb, or Bi). If, instead, these real-space functions are evaluated along the length of the bond path, the discrepancies in the trends are resolved. We show that robust results are also obtained using electron densities from less computationally demanding density functional theory calculations. The increased computational efficiency allowed us to also investigate organic derivatives of these oxygen-pnictogen-bonded compounds and observe that the trends hold in these instances as well. We anticipate that these results will be of use to inorganic chemists engaged in the synthesis and evaluation of novel bonding interactions, particularly those involving heavy main-group elements.