title: Conformational analysis of 18-azacrown-6 and its bonding with late first transition series divalent metals: insight from DFT combined with NPA and QTAIM analyses.
abstract: Density functional theory calculations, together with quantum theory of atoms in molecules (QTAIM) analyses, have been performed to investigate 18-azacrown-6 complexes of the high-spin late first transition series divalent metal ions in the gas phase and, in some cases, in aqueous solution simulated by a polarizable continuum model. Six intramolecular H-H bonding interactions in the meso-complexes are found to arise from folding of the ligand upon its electrostatic interaction with the metal ions, which are largely absent in the lowest-energy C(2h) conformer of the free ligand. The ligand-to-metal charge transfer obtained from QTAIM analysis, among other things, is found to be an important factor that controls the stability of these complexes. The inter-relationship between the ligand preorganization energy, the zero-point corrected formation energy of the metal complexes, and the H-H bonding pair distances, as well as the dependence of the electron density and the total energy density at the H-H bond critical points on the H-H bonding pair distances, provides a physical basis for understanding and explaining the stabilizing nature of these closed-shell interactions, which are often viewed as steric clashes that lead to complex destabilization.
authors.affiliation: Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, Montréal, Québec, Canada. pradeep@cermm.concordia.ca
authors.forename: Pradeep R
authors.initials: PR
authors.lastname: Varadwaj
authors.forename: Arpita
authors.initials: A
authors.lastname: Varadwaj
authors.forename: Gilles H
authors.initials: GH
authors.lastname: Peslherbe
authors.forename: Helder M
authors.initials: HM
authors.lastname: Marques
mesh_terms: D043844:Crown Ethers / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D043844:Crown Ethers; D008024:Ligands; D009942:Organometallic Compounds; D028561:Transition Elements; C015762:18-crown-6