A theoretical and structural investigation of thiocarbon anions

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 CnSn2- and CnSn (n = 3-6) electron delocalization. Localized molecular orbital contributions to NICS, computed by the individual gauge for localized orbitals method, dissect 7 effects from the a single bonds and lone pair influences. CnSn2- (n = 3-5) structures in D,h Symmetry are minima. Their aromaticity decreases with increasing ring size. C3S32- is both sigma and T aromatic, while C4S42- and C5S52- 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 C6S62- prefers D-2h 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 C6S66- has D-6h minima was confirmed by X-ray structure analysis. Comparisons between thiocarbons and oxocarbons based on dissected NICS analysis show that CnSn2- (n = 3-5) and C6S66- are less aromatic in D-nh symmetry than their oxocarbon analogues.