title: The structure of arachno-[B6H11]-, at -25 degrees C in (CD3)2O, is resolved via the ab initio/IGLO-GIAO/NMR procedure.
abstract: The arachno-[B6H11]- solution structure at -25 degrees C was clarified as fluxional compound 2 by applying the ab initio/IGLO/NMR method. The anion 2 can be derived from arachno-B6H12, 1, by the removal of the B2/B3 bridging hydrogen (2). No minimum on the potential energy surface could be found for an asymmetric complex, a, between [B5H8]- and BH3, which had been proposed originally. A Cs-symmetric [mu-(BH3)B5H8]- complex, A, only 3.2 kcal mol-1 higher in energy than 2, is the intermediate in the fluxional rearrangement observed on the NMR time scale. The transition structure [D] connecting 2 (Erel = 0.0) and A (Erel = 3.2) has a relative energy of 9.7 kcal mol-1. The elimination of both a and A as "most stable structure" candidates of arachno-[B6H11]- reinforces the early geometrical bonding systematics for boranes and carboranes.
authors.affiliation: Institut für Organische Chemie, Universität Erlangen-Nürnberg, Erlangen D-91054, Germany. hofmann2@zopyros.ccqc.uga.edu
authors.forename: M
authors.initials: M
authors.lastname: Hofmann
authors.forename: P
authors.initials: P
authors.lastname: von R Schleyer
authors.forename: R E
authors.initials: RE
authors.lastname: Williams