A first-principles study on the B5O5+/0 and B5O5- clusters: The boron oxide analogs of C6H5+/0 and CH3Cl

The concept of boronyl (BO) and the BO/H isolobal analogy build an interesting structural link between boron oxide clusters and hydrocarbons. Based upon global-minimum searches and first-principles electronic structural calculations, we present here the perfectly planar C-2 nu B5O5+ (1, (1)A(1)), C-2 nu B5O5 (2, (2)A(1)), and tetrahedral C-s B5O5- (3, (1)A') clusters, which are the global minima of the systems. Structural and molecular orbital analyses indicate that C-2 nu B5O5+ (1) [B3O3(BO)(2)(+)] and C-2 nu B5O5 (2) [B3O3(BO)(2)] feature an aromatic six-membered boroxol (B3O3) ring as the core with two equivalent boronyl terminals, similar to the recently reported boronyl boroxine D-3h B6O6 [B3O3(BO)(3)]; whereas C-s B5O5- (3) [B(BO)(3)(OBO)(-)] is characterized with a tetrahedral B- center, terminated with three BO groups and one OBO unit, similar to the previously predicted boronyl methane T-d B5O4- [B(BO)(4)(-)]. Alternatively, the 1-3 clusters can be viewed as the boron oxide analogs of phenyl cation C6H5+, phenyl radical C6H5, and chloromethane CH3Cl, respectively. Chemical bonding analyses also reveal a dual three-center four-electron (3c-4e) pi hyperbond in C-s B5O5- (3). The infrared absorption spectra of B5O5+ (1), B5O5 (2), and B5O5-(3) and anion photoelectron spectrum of B5O5- (3) are predicted to facilitate their forthcoming experimental characterizations. The present work completes the BnOn+/0/- series for n = 1-6 and enriches the analogous relationship between boron oxides and hydrocarbons. (C) 2015 AIP Publishing LLC.