Structure and Conformations of Cyclopentasilane, Si5H10

Three different conformations of cyclopentasilane, Si 5 H 10, have been analyzed in detail using ab initio and density functional methods at the HF/B2, MP2/B2, CCSD/6-31G*, and B3LYP/B2 levels of theory. While the envelope ( C s ) and the twist ( C 2 ) forms have essentially the same energy, the planar form ( D 5 h ) is ca. 1.3−2.9 kcal mol -1 less stable. The averaged computed Si−Si bond length of 2.356 Å (for C s and C 2, each) is ca. 0.02 Å larger than the r e value of 2.332 Å derived from an electron diffraction study.