Nitrogen versus carbon in planar pentacoordinate environments supported by Be5Hnrings

Abstract

NBe5Hnn-3 (n = 0-5) (0A-5A) species with a novel planar pentacoordinate nitrogen (ppN) were designed by the isoelectronic substitution of the C atom in planar pentacoordinate carbon (ppC) species CBe5Hnn-4 (n = 0-5) with an N atom. The highly flexible H atoms found in ppC species CBe5H22- and CBe5H3- were fixed upon the nitrogen substitution, as mirrored by the non-flexible H atoms in their ppN analogues NBe5H2- (2A) and NBe5H3 (3A). Moreover, the N atom was found to fit the H-surrounded Be5 rings better than the C atom because the ppC species CBe5H4 and CBe5H5+ adopted non-planar structures due to size-mismatch between the C atom and the H-surrounded Be5 ring, but their ppN analogues NBe5H4+ (4A) and NBe5H52+ (5A) adopted perfect planar structures. The electronic structure analyses revealed that the N atoms in 0A-5A were involved in four doubly occupied orbitals, including three six-center two-electron (6c-2e) σ bonds and one 6c-2e π bond. Therefore, these ppN species not only obey the octet rule, but also possess the interesting σ and π double aromaticity, which contributes to the stabilization. Consequently, 2A, 4A, and 5A are charged kinetically viable global energy minima, and are suitable for the gas phase generation and spectroscopic characterization. This journal is