Arachno, nido, and closo aromatic isomers of the Li6B6H6 molecule

We analyzed chemical bonding in low-lying isomers of the recently computationally predicted B6H6Li6 molecule. According to our calculations the benzene-like B6H6Li6 (D-2h,(1)A(1g)) arachno structure with the planar aromatic B6H66- anion is the most stable one. A nido isomer with two aromatic B6H64- (pentagonal pyramid) and Li-3(+) (triangular) moieties, which can be considered as derived from the global minimum structure through a two-electron intramolecular transfer from B6H66- to three Li+ cations, was found to be 10.7 kcal/mol higher in energy. A closo isomer with three aromatic moieties (octahedral B6H62- and two Li-3(+)) was found to be 31.3 kcal/mol higher in energy than the global minimum. Another isomer with three aromatic moieties (two B3H32- and Li-3(+)) was found to be substantially higher in energy (74.4 kcal/mol). Thus, the intramolecular electron transfers from the highly charged B6H66- anion to cations are not favorable for the B6H6Li6 molecule, even when a formation of three-dimensional aromatic B6H62- anion and two sigma-aromatic Li-3(+) cations occurs in the closo isomer.