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Trisilaallene and the Relative Stability of Si3H4 Isomers Monica Kosa, Miriam Karni,* and Yitzhak Apeloig*

Summary: Trisilaallene and the Relative Stability of Si3H4 Isomers
Monica Kosa, Miriam Karni,* and Yitzhak Apeloig*
Department of Chemistry and the Lise Meitner, MinerVa Center for Computational
Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
Received June 17, 2005
Abstract: A theoretical quantum-mechanical study of trisilaallene, H2SidSidSiH2, and of 15
other Si3H4 isomers was carried out using ab initio and DFT methods with a variety of basis
sets. Values given below are at B3LYP/6-31G(d,p). Unlike H2CdCdCH2 which is linear, H2-
SidSidSiH2 is highly bent at the central silicon atom, with a SiSiSi bending angle of 69.4. The
SidSi bond length is 2.269 , longer than a regular SidSi double bond (2.179 ) but shorter
than a Si-Si single bond (2.351 ). The distance between the terminal silicon atoms is 2.583
, significantly longer than a Si-Si single bond. The geometry and electronic properties of H2-
SidSidSiH2 are similar to those of the corresponding trisilacyclopropylidene, which is only 2.7
kcal/mol higher in energy. A barrier of only 0.1 kcal/mol separates trisilacyclopropylidene and
trisilaallene which can be described as bond-stretch isomers. Sixteen minima were located on
the Si3H4 PES, most of them within a narrow energy range of ca. 10 kcal/mol. Six of the Si3H4
isomers are analogous to the classic C3H4 minima structures; however, the other Si3H4 isomers
do not have carbon analogues, and they are characterized by hydrogen-bridged structures.
The chemistry of compounds containing multiple bonds to


Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology


Collections: Chemistry