Planar pi-aromatic C-3h B6H3+ and pi-antiaromatic C-2h B8H2: boron hydride analogues of D-3h C3H3+ and D-2h C4H4
Based upon extensive density functional theory and wave function theory calculations performed in this work, we predict the existence of the perfectly planar triangle C-3h B6H (3) (+) (1, (1)A') and the double-chain stripe C-2h B8H2 (9, (1)A(g)) which are the ground states of the systems and the inorganic analogues of cyclopropene cation D-3h C3H (3) (+) and cyclobutadiene D-2h C4H4, respectively. Detailed adaptive natural density partitioning (AdNDP) analyses indicate that C-3h B6H (3) (+) is pi plus sigma doubly aromatic with two delocalized pi-electrons and six delocalized sigma-electrons formally conforming to the 4n + 2 aromatic rule, while C-2h B8H2 is pi antiaromatic and sigma aromatic with four delocalized pi-electrons and ten delocalized sigma-electrons. The perfectly planar C-2h B8H4 (5, (1)A(g)) also proves to be pi antiaromatic analogous to D-2h C4H4, but it appears to be a local minimum about 50 kJ mol(-1) less stable than the three dimensional C-s B8H4 (6, (1)A'). AdNDP, nucleus independent chemical shifts (NICS) and electron localization function (ELF) analyses indicate that these boron hydride clusters form islands of both sigma- and pi-aromaticities and are overall aromatic in nature in ELF aromatic criteria.
aromaticity adndp boron hydride clusters dft electronic structures geometrical structures