title: Gauche, ortho, transoid and anti conformations of the tetrasilanes SiMe3SiX2SiX2SiMe3 (X=H, F, Cl, Br, I): a computational and vibrational spectroscopic study.
abstract: The energy profile for rotation around the central Si-Si bonds of the tetrasilanes SiMe3SiX2SiX2SiMe3 (X=H, F, Cl, Br and I) were examined by ab initio calculations and temperature-dependent Raman spectroscopy. Ethanelike intrinsic barriers to rotation were found for X=H, Cl, Br and I. MP2 calculations predict for SiMe3SiF2SiF2SiMe3 the existence of a gauche minimum with backbone dihedral angle ω≈64° and a twisted minimum with ω≈115°, as shown in the picture (solid line=HF, dashed line=MP2). The curious 115° local minium can be accounted for by a unique intrinsic barrier to rotation superimposed by electrostatic interactions involving strongly polar SiF bonds.
authors.affiliation: Institut für Anorganische Chemie, Technische Universität, Graz, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Zink
authors.forename: G
authors.initials: G
authors.lastname: Tekautz
authors.forename: A
authors.initials: A
authors.lastname: Kleewein
authors.forename: K
authors.initials: K
authors.lastname: Hassler