abstract16
Inorg. Chem., 36 (6), 1048 -1054, 1997. ic961032j S0020-1669(96)01032-4
Copyright © 1997 American Chemical Society
Molecular Structure of Trifluorophosphine Tetraborane(8), B4H8PF3, As Determined in the Gas Phase by Electron Diffraction and ab Initio Computations
Paul T. Brain, David W. H. Rankin,* and Heather E. Robertson
Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, U.K.
Mark A. Fox, Robert Greatrex,* and Alireza Nikrahi
School of Chemistry, University of Leeds, Leeds, LS2 9JT, U.K.
Michael Bühl
Institut für Organische Chemische, Universität Zürich, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland
Received August 22, 1996
Abstract:
The molecular structure of trifluorophosphine tetraborane(8), B4H8PF3, has been studied in the gas phase by electron diffraction. The experimental data can be fitted using a model which represents the gas as consisting solely of the endo conformer with Cs symmetry, the PF3 group staggered with respect to the B(1)-H(1) bond. Important experimental structural parameters (r) are r[B(1)-B(2)] (hinge-wing) = 184.7(9) pm, r[B(1)-B(3)] (hinge-hinge) = 172.2(12) pm, r[B(2)-B(3)] = 179.9(10) pm, r[B(1)-P] = 179.8(9) pm, and r(P-F) (mean) = 152.8(1) pm; B(3)B(1)P = 131.6(11), and the dihedral (“butterfly”) angle between the planes B(1)B(2)B(3) and B(1)B(4)B(3) is 133.9(23). These values agree well with the ab initio (MP2/TZP level) optimized molecular geometry for the endo conformer; at the MP2/TZP//MP2/TZP + ZPE(HF/6-31G*) level, the exo conformer is predicted to represent ca. 2% of the compound vapor, consistent with the experimental 11B NMR solution spectrum. The experimental and theoretical geometries are supported by comparison of the calculated (IGLO) 11B NMR chemical shifts with the experimental NMR data.