Quantum Theory of Atoms In Molecules Analysis of NH/O Hydrogen Bonds of Glycine Complexes with a Water Molecule

Abstract

Quantum Theory of Atoms In Molecules (QTAIM) analysis was performed for NH/O hydrogen bonds of various glycine transition metal complexes. The dependencies of the CCSD(T)/CBS interaction energy values and hydrogen bond distances on QTAIM parameters at the corresponding bond critical point were analyzed. Values of electron densities ρ(rb) range from 0.0224 to 0.0344 au, Laplacians of electron densities ∇2ρ(rb) are all positive, total energy densities H(rb) are approximately zero, and the ratios of kinetic and potential energy densities [-G(rb)/V(rb)] are close to 1.0. For complexes with the same charge, hydrogen bonds with stronger interaction energies have higher ρ(rb) and ∇2ρ(rb), and lower H(rb) and [-G(rb)/V(rb)]. Almost all charged complexes have negative H(rb) values, which was shown to be a indicator of covalent character of the hydrogen bond. Linear regressions between hydrogen bond distances and any of the QTAIM parameters have very high correlation coefficient: 0.994, 0.993, 0.968, and 0.995 for ρ(rb), ∇2ρ(rb), H(rb), and [-G(rb)/V(rb)], respectively