Bond Length and Local Energy Density Property Connections for Non-Transition-Metal Oxide-Bonded Interactions

Abstract

For a variety of molecules and earth materials, the theoretical local kinetic energy density, G(rc), increases and the local potential energy density, V(rc), decreases as the M−O bond lengths (M = first- and second-row metal atoms bonded to O) decrease and the electron density, ρ(rc), accumulates at the bond critical points, rc. Despite the claim that the local kinetic energy density per electronic charge, G(rc)/ρ(rc), classifies bonded interactions as shared interactions when less than unity and closed-shell when greater, the ratio was found to increase from 0.5 to 2.5 au as the local electronic energy density, H(rc) = G(rc) + V(rc), decreases and becomes progressively more negative. The ratio appears to be a measure of the character of a given M−O bonded interaction, the greater the ratio, the larger the value of ρ(rc), the smaller the coordination number of the M atom and the more shared the bonded interaction. H(rc)/ρ(rc) versus G(rc)/ρ(rc) scatter diagrams categorize the M−O bonded interactions into domains with the local electronic energy density per electron charge, H(rc)/ρ(rc), tending to decrease as the electronegativity differences for the bonded pairs of atoms decrease. The values of G(rc) and V(rc), estimated with a gradient-corrected electron gas theory expression and the local virial theorem, are in good agreement with theoretical values, particularly for the bonded interactions involving second-row M atoms. The agreement is poorer for shared C−O and N−O bonded interactions.