Theoretical study on the structures and stabilities of silacyclopropylidenoids

Isomeric structures, energies, and properties of silacyclopropylidenoids, C₂H₄SiMX (where M?=?Li or Na and X?=?F, Cl or Br), were studied ab initio at the HF and MP2 levels of theory using the 6-31+G(d,p) and aug-cc-pVTZ basis sets. The calculations indicate that each of C₂H₄SiMXs has three stationary structures: silacyclopropylidenoid (S), tetrahedral (T), and inverted (I). All of the silacyclopropylidenoid (S) forms are energetically more stable than others except that S-LiF is by only 0.7?kcal/mol higher in energy than I-LiF. In contrast, all of the tetrahedral (T) forms are the most unstable ones except for T-NaF. Energy differences between S, T, and I forms range from 0.70 to 8.70?kcal?mol^?1 at the MP2/6-31+G(d,p) level. In addition, the molecular electrostatic potential maps, natural bond orbitals, and frontier molecular orbitals were calculated at the MP2/6-31+G(d,p) level.