Hexa-, Hepta-, and Octacoordinate Boronium Ions:(1) BH(6)(+), BH(7)(2+), and BH(8)(3+).

The parent hexa-, hepta-, and octacoordinate boronium ions, BH(6)(+) (1), BH(7)(2+) (4), and BH(8)(3+) (6), respectively, were found as stable minima by ab initio MP2/6-31G and QCISD(T)/6-311G level of calculations. The C(2)(v)() symmetrical structure 1 with two 3c-2e bonds and C(3)(v)() symmetrical structure 4 with three 3c-2e bonds are isostructural with their isoelectronic carbon analogues CH(6)(2+) and CH(7)(3+), respectively. Eight hydrogen atoms of T(d)() symmetrical structure 6 are bonded to the boron atom by four 3c-2e bonds. The protonation of BH(5) to form BH(6)(+) was found to be strongly exothermic. The reaction of BH(4)(+) (3) and H(2) might be a suitable way to generate BH(6)(+) (1) in the gas phase.