Abstract
The persilylated Si(3)-Si(7) analogues of the C(3)-C(7) aromatic molecules and ions with all hydrogen or all fluorine atoms at silicon have been calculated at high levels of theory, up to MP2/aug-cc-pVTZ for all species and CCSD/6-311++G** for Si(3) and Si(4) species, both in the gas phase and in a polar solvent (water). The aromaticity of the calculated species was estimated using structural, energetic, and NMR criteria. (SiF)(3)(+) cations are more aromatic than (SiH)(3)(+) by the NICS (nuclear-independent chemoical shift) but less aromatic by the ASE (aromatic stabilization energy) criterion. Dications (SiX)(4)(2+) are planar (X = H) or slightly puckered (X = F); the ASE decreases by 4-5 kcal/mol upon going from gas to solution, or from X = H to X = F. Dianions (SiX)(4)(2-)are nonplanar and antiaromatic. The ASE for the slightly distorted-from-planarity anion Si(5)H(5)(-) is ~53 kcal/mol, vs. 85 kcal/mol for its carbon analogue. The structure of Si(6)X(6) molecules strongly depends on the level of calculations. The NICS and ASE values have been calculated for planar Si(6)H(6) and (SiH)(7)(+) but not for strongly distorted Si(6)F(6) and (SiF)(7)(+) species.