Novel silicon nanorings: Persilacyclacenes at DFT

Structures, energies, and aromatic characters are compared and contrasted for a series of [n]persilacyclacenes with n = 6-12: Si24H12, Si28H14, Si32H16,Si36H18, Si40H20, and Si48H24, respectively, at B3LYP levels (n, number of fused benzenoid rings). These are a brand of silicon nanorings that bear a resemblance to the shortest zig-zag silicon nanotubes (SiNTs), henceforth referred to as SiNRs. The NBO results show nearly SP2 -hybridization for virtually all Si atoms of our SiNRs. This is in contrast to most reports where Sp(3) -hybridization is proposed for typical SiNTs. Comparison between the optimized SiNRs and their corresponding planar (polyacenic) forms shows longer bond lengths for the former, due to their curvatures. Except for sterically hindered Si-24,H-12 (n = 6), all even SiNRs (n = 8, 10, and 12), are more aromatic than the odd ones (n = 7, 9, and 11). Such a higher aromaticity is witnessed inside, outside, and on the surface of the scrutinized SiNRs. Also, except for Si44H22 (n = 11), the energy gaps (Delta EHOMO-LUMO) for the odd set of SiNRs, as well as the even set, appear inversely proportional to their corresponding diameters, per se. Except for the sterically hindered SiNRs with n = 6 or 7, all the even SiNRs enjoy a higher stability (aromaticity) and conductivity for showing lower Delta EHOMO-LUMO than the odd ones. Evidently, the ideal diameter for persilacyclacenes (SiNRs) studied is from 0.92 to 1.42 nm, corresponding to n = 8-12, respectively. Higher than 1.42 nm causes structural disorders while lower than 0.92 brings about bond localization due to the high-steric effects. (c) 2007 Wiley Periodicals, Inc.