Factors Influencing the Magnitude of Alpha-13C Hyperfine Couplings in Cyclosilane Anion Radicals

摘要

Considerations of hyperfine coupling constants (hfsc) in the ESR spectra of cyclopolysilane anion radicals (R2Si)n(-) lead to a representation of the singly occupied molecular orbital (SOMO) as a linear combination of Si-C Sigma* and symmetry-adapted Si-Si sigma* hybrid orbitals. The atomic orbital contributions to these hybrid orbitals are believed to be principally silicon 3P sub x, 3P sub y and 3p sub z and carbon 2s, 2P sub x 2P sub y and 2p sub z. A simple perturbation approach is used to rationalize the values of 13C hfssc measured for substituted cyclopentasilanes Me9Si5R(-) compared to the value observed for (Me2Si) 5(-), in terms of altered mixing of the Si-Si sigma* and Si-C Sigma orbitals. (Reprints).