title: Charge transfer via the dative N-B bond and dihydrogen contacts. Experimental and theoretical electron density studies of four deltahedral boranes.
abstract: In an approach combining high resolution X-ray diffraction at low temperatures with density functional calculations, two closo-borates, B12H12(2-) (1) and B10H10(2-) (2), and two arachno-boranes, B10H12L2 (L = amine (3) or acetonitrile (4)), are studied by means of Atoms In Molecules (AIM) theory and Electron Localizability Indicator (ELI-D). The charge transfer via the dative N-B bonds in the arachno-boranes and via dihydrogen contacts in the closo-borates is quantified. The dative N-B bond in 4 is significantly shorter and stronger than that in 3 and in small N-B Lewis acid base adducts from the literature. It is even shorter in the gas phase than in the crystal environment in contrast to the bond shortening in the crystal generally found for N-B Lewis acid-base adducts. Furthermore, the calculated charge transfer in terms of AIM charges is opposite to the expected N → B direction but still weak as found for all other N-B bonds. The intramolecular charge redistributions due to intermolecular interactions are quantified by the AIM and ELI-D analysis of contact ion pairs. The latter method gives a deeper understanding of delocalization effects in the borane cages as well as in the counterions. Since dihydrogen bonds are rarely found in crystal structures, one focus was directed to the topologies of the large number of 58 experimentally found contacts of this type. The analysis reveals that the electron density at the bond critical point, the corresponding Laplace function, and the curvature along the bond path (λ3) show a behavior that clearly discriminates these interactions from classical hydrogen bonds, confirming earlier theoretical findings.
authors.affiliation: Institut für Chemie und Biochemie/Anorganische Chemie, Freie Universität Berlin, Fabeckstrasse 34-36 and 36a, 14195 Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mebs
authors.forename: Roman
authors.initials: R
authors.lastname: Kalinowski
authors.forename: Simon
authors.initials: S
authors.lastname: Grabowsky
authors.forename: Diana
authors.initials: D
authors.lastname: Förster
authors.forename: Rainer
authors.initials: R
authors.lastname: Kickbusch
authors.forename: Eugen
authors.initials: E
authors.lastname: Justus
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Morgenroth
authors.forename: Carsten
authors.initials: C
authors.lastname: Paulmann
authors.forename: Peter
authors.initials: P
authors.lastname: Luger
authors.forename: Detlef
authors.initials: D
authors.lastname: Gabel
authors.forename: Dieter
authors.initials: D
authors.lastname: Lentz
mesh_terms: D001880:Boranes / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry; D003080:Cold Temperature; D004583:Electrons; D005740:Gases / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry; D058116:Lewis Acids / Q000737:chemistry; D058115:Lewis Bases / Q000737:chemistry; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D011789:Quantum Theory; D055672:Static Electricity; D014961:X-Ray Diffraction
chemical_list: D001880:Boranes; D005740:Gases; D007477:Ions; D058116:Lewis Acids; D058115:Lewis Bases; D003035:Cobalt; D006859:Hydrogen; D009584:Nitrogen