Sana, M.
Decrem, M.
Leroy, Georges
[UCL]
Nguyen, MT.
Vanquickenborne, LG.
A theoretical analysis of the classical and non-classical silicon radical cations, H(n)SiX(.+)C with X = N, O, F, P, S and Cl has been carried out. Heats of formation of the ions considered have been determined using ab initio molecular orbital (MO) calculations at the UMP4/6-31 + G(2df, p) level with UMP2/6-31G(d, p) optimized geometries plus vibrational and thermal corrections. No classical halogen radical cations (H3Si-X(.+) with X = F and Cl) could be found. In other cases, non-classical ions (H2Si-XH(n-2) (.+)) are consistently more stable than their classical counterparts (Hn-1SiH+ + I). The difference in stability between both isomers depends on the nature of X: it is large with N and O, but rather small with P and S. Interconversion between both isomeric forms has also been investigated. When X is a second-row atom, the energy of the transition structure for the 1,2-hydrogen shift is close to that of the fragments Hn-1SIH+ + H. When X is a third-row atom, the barrier height increases, but remains smaller than the dissociation energy. The potential-energy surface of the H,SiN'+ ions is reported in detail. Overall it has been shown that silicon-containing non-classical radical cations do not have a formal separation of both charge and radical centres as is the case in carbon analogues. Therefore they cannot properly be described as 'distonic radical cations' under the currently accepted definition.
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| Bibliographic reference |
Sana, M. ; Decrem, M. ; Leroy, Georges ; Nguyen, MT. ; Vanquickenborne, LG.. Classical and Nonclassical Silicon Radical Cations - H(n)six(center-dot+) Species (x=n, O, F, P, S and Cl). In: Journal of the Chemical Society. Faraday Transactions, Vol. 90, no. 23, p. 3505-3511 (1994) |
| Permanent URL |
http://hdl.handle.net/2078.1/48563 |
