High-electron-density C6H6 units:: Stable ten-π-electron benzene complexes

The first stable benzene molecule with ten pi electrons is predicted. Stability is achieved through barium atoms acting as an electron-donating "matrix" to C6H6 in the inverted sandwich complex [Ba-2(C6H6)]. The his(barium)benzene complex has been computed at the density functional level of theory by using the hybrid functional mPW1PW91. Ab initio calculations were performed by using the coupled-cluster expansion, CCSD(T). Nucleus independent chemical shift (NICS) indices imply distinct aromatic character in the benzene ring of bis-(barium)benzene. The D-6h-symmetric structure with a (1)A(1g) electronic ground state represents a thermochemically stable, aromatic benzene molecule with four excess it electrons, stabilised by two barium ions. A possible molecular wire, built up from Ba end-capped thorium-benzene "sandwiches", is discussed.