Structure and aromaticity of B6H5(+) cation: a novel borhydride system containing planar pentacoordinated boron.

A novel structural pattern: two-dimensional, five-membered ring-like boron hydride system B(6)H(5)(+), which contains both planar tetra- and pentacoordinated boron (ptB and ppB) was designed and investigated at [B3LYP, MP2(Full) and CCSD(T,FC)]/6-311+G(d,p) theoretical levels. The results indicate that both degenerate ppB B(6)H(5)(+) configurations A (D(5H),(1)A(1)') and B (C(2nu),(1)A(1)) are energetically favorable, sharing the lowest energy comparison with other isomers considered in this work. The computed considerably large smallest vibrational frequencies [197.5 and 197.4 cm(-1), respectively at MP2 (full) level], HOMO-LUMO energy separations [10.99-11.03 eV computed at MP2 (full) level], and fairly large endothermic dissociation reaction energies suggest they are promising candidate molecules for experimental detection. The detailed molecular orbital analysis, natural bond orbital analysis, magnetic susceptibility anisotropy, and NMR chemical shift analyses confirmed that the two low-energy ppB molecules exhibit strong aromaticities.