Five Stereoactive Orbitals on Silicon: Charge and Spin Localization in the n-Si4Me10(-•) Radical Anion by Trigonal Bipyramidalization.
RIUMP2/def2-TZVPPD calculations show that in addition to its usual conformation with charge and spin delocalized over the Si backbone, the isolated Si4Me10(-•) radical anion also has isomeric conformations with localized charge and spin. A structure with localization on a terminal Si atom has been examined in detail. In vacuum, it is calculated to lie 11.5 kcal/mol higher in energy than the charge-and-spin delocalized conformation, and in water the difference is as little as 1.6 kcal/mol. According to natural orbital and localized orbital analyses, the charge-and-spin-carrying terminal Si atom uses five stereoactive hybrid orbitals in a trigonal bipyramidal geometry. Four are built mostly from 3s and 3p atomic orbitals (AOs) and are used to attach a Si3(CH3)7 and three CH3 groups, whereas the larger equatorial fifth orbital is constructed from 4s and 4p AOs and acts as a nonbonding (radical) hybrid orbital with an occupancy of about 0.65 e.
†Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States.
Matthew K
MK
MacLeod
†Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States.|‡Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám., 2, 166 10 Praha 6, Czech Republic.
Josef
J
Michl
conformational isomerism; oligosilane; pentacoordinate silicon; polaron localization; radical anion; trigonal bipyramidal Si; valence shell expansion