Examinando por Materia "HYDROGEN-BONDS"

Mostrando 1 - 2 de 2
  • No hay miniatura disponible
    Ítem
    (H 3N-BH 3) 4: The ammonia borane tetramer
    (ROYAL SOC CHEMISTRY, 2012-01-01) Guerra, Doris; David, Jorge; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    For this special edition of PCCP dealing with prediction of new molecules using quantum mechanical methods, we propose a structure for (H 3N-BH 3) 4, the isolated ammonia borane tetramer in gas phase, for which there are no experimental reports. The structure, belonging to the S 4 point group, was found at the MP2/6-311++G(d,p) level of theory; the total energy was computed at the CCSD(T) level including BSSE correction, affording a binding energy of 40.1 kcal mol -1. The tetramer is stabilized by a network of dihydrogen bonds. We study the stabilizing interactions via QTAIM, obtaining eight N-H d+? d-H-B bonding interactions characterized as hydrogen bonds by application of the Koch-Popelier rules; in addition, two highly controversial B-H d-? d-H-B interactions are also predicted by a topological analysis of the electron density. This journal is © 2012 the Owner Societies.
  • No hay miniatura disponible
    Ítem
    Spanning QTAIM topology phase diagrams of water isomers W4, W5 and W6
    (ROYAL SOC CHEMISTRY, 2011-01-01) Jenkins, Samantha; Restrepo, Albeiro; David, Jorge; Yin, Dulin; Kirk, Steven R.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    Structural and chemical properties of the small water clusters W 4, W5 and W6 are investigated with the theory of atoms and molecules (QTAIM). For the W4, W5 and W 6 clusters, nine, fourteen and twenty-seven conformers, respectively, have been analyzed. For the W4, W5 and W6 clusters one, two and three of these structures, respectively, have not been reported before. We then proceed to extend the W4, W5 and W6 water cluster topology space using QTAIM; the PoincaréHopf topological sum rules are applied to create rules to identify the spanning set of conformer topologies, this includes finding three, ten and eight new distinct topologies that satisfy the PoincaréHopf relation for W4, W5 and W6 respectively. The topological stability of degenerate solutions to the PoincaréHopf relation is compared by evaluating the proximity to rupturing of critical points of the gradient vector field of the charge density. We introduce a QTAIM topology space to replace the inconsistent use of Euclidean geometry to determine whether a cluster is 1-, 2- or 3-D. We show from the topology of the charge density that the conformers of the W 4, W5 clusters are more energetically stable in less compact, planar forms, conversely the conformers of W6 are more energetically stable with compact 3-D topologies. Quantifying the degree of covalent character in the hydrogen bonding for the W4, W5 and W6 clusters independently verifies this finding. Differences in simple rules for the number of hydrogen bonds obeying the BernalFowler ice rules between W4, W5 and W6 reflect the transition from 2-D to 3-D structures being more energetically stable. In addition, we identify a new class of OO bonding interactions that are up to 48% longer than the inter-nuclear separation and appear to be failed hydrogen bonds. © 2011 the Owner Societies.