title: Ab initio studies on isomers of macropolyhedral borane ions [B20H18]n (n = 0, -2, -4).
abstract: Various isomers of macropolyhedral borane ions [B20H18]n (n = 0, -2, -4) are investigated by using the density functional theory methods at RB3LYP/6-31+G* and RB3LYP/6-31G* levels to obtain the optimized geometries, harmonic vibrational frequencies, electron structures, and the stability order. The calculated results show that optimized bond lengths are consistent with the available experimental values and the natural populations, taking [a2 -B20H18]4- (4) as an example, are also in agreement with NMR spectra. The calculated vibrational frequencies are all real, so all of these isomers could be stable, among which [a2 -B20H18]2- (3) and [a2 -B20H18]0 (7) are considered for the first time in this paper. On the basis of the contour maps of molecular orbitals, the delocalized characteristic of molecular orbitals and the possible redox mechanism of these ions are also discussed. Moreover, the analysis on counting of skeletal bonding electrons shows that the isomers (1)-(6) obey the electronic requirement predicted by the mno rule, whereas the newly predicted isomer (7) does not match the mno rule.
authors.affiliation: State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Mingyu
authors.initials: M
authors.lastname: Zhang
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Baoguo
authors.initials: B
authors.lastname: Chen
authors.forename: Chia-Chung
authors.initials: CC
authors.lastname: Sun