title: A theoretical and structural investigation of thiocarbon anions.
abstract: Density functional theory energies, geometries, and population analyses as well as nucleus-independent chemical shifts (NICS) have been used to investigate the structural and magnetic evidence for cyclic CnSn(2-) and CnSn (n = 3-6) electron delocalization. Localized molecular orbital contributions to NICS, computed by the individual gauge for localized orbitals method, dissect pi effects from the sigma single bonds and lone pair influences. CnSn(2-) (n = 3-5) structures in Dnh symmetry are minima. Their aromaticity decreases with increasing ring size. C3S3(2-) is both sigma and pi aromatic, while C4S4(2-) and C5S5(2-) are much less aromatic. NICS(0)pi, the C-C(pi) contribution to NICS(0) (i.e., at the ring center), decreases gradually with ring size. In contrast, cyclic C6S6(2-) prefers D2h symmetry due to the balance between aromaticity, strain energy, and the S-S bond energies and is as aromatic as benzene. The theoretical prediction that C6S6(6-) has D6h minima was confirmed by X-ray structure analysis. Comparisons between thiocarbons and oxocarbons based on dissected NICS analysis show that CnSn(2-) (n = 3-5) and C6S6(6-) are less aromatic in Dnh symmetry than their oxocarbon analogues.
authors: Computational Chemistry Annex, The University of Georgia, Athens, GA 30602-2525, USA. zhongfang.chen@chemie.uni-erlangen.de
authors: Zhongfang
authors: Z
authors: Chen
authors: Liam R
authors: LR
authors: Sutton
authors: Damian
authors: D
authors: Moran
authors: Andreas
authors: A
authors: Hirsch
authors: Walter
authors: W
authors: Thiel
authors: Paul von Ragué
authors: Pv
authors: Schleyer