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Gauche, Ortho, Transoid and Anti Conformations of the Tetrasilanes SiMe 3 SiX 2 SiX 2 SiMe 3 (X=H, F, Cl, Br, I): A Computational and Vibrational Spectroscopic Study
Author(s) -
Zink Robert,
Tekautz Günter,
Kleewein Alois,
Hassler Karl
Publication year - 2001
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/1439-7641(20010618)2:6<377::aid-cphc377>3.0.co;2-w
Subject(s) - dihedral angle , raman spectroscopy , chemistry , crystallography , ab initio quantum chemistry methods , ab initio , polar , bond length , line (geometry) , rotation (mathematics) , computational chemistry , potential energy , infrared spectroscopy , molecular physics , atomic physics , molecule , hydrogen bond , physics , crystal structure , geometry , mathematics , organic chemistry , astronomy , optics
The energy profile for rotation around the central Si−Si bonds of the tetrasilanes SiMe 3 SiX 2 SiX 2 SiMe 3 (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 SiMe 3 SiF 2 SiF 2 SiMe 3 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.