[M(C6Li6)2]n− (M = Nb, Ta, Mo and W; n = 1, 0): Sandwich complexes containing star-like hexalithiobenzenes

The structural, electronic and aromatic properties of novel sandwich complexes [M(C6Li6)2]n− (M = Nb, Ta, Mo and W; n = 1, 0) containing star-like hexalithiobenzenes have been investigated by both density functional theory (DFT) and ab initio theory calculations in this work. These sandwich complexes with the staggered D6d symmetry structures are all true minimum with singlet electron state, while the D6h symmetry conformations are the transition states on the potential energy surface with one imaginary vibration frequency. The effective d-π coordination interactions between the partially filled 4d (or 5d) orbitals of transition-metal atoms and the delocalized π orbitals of the C6Li6 maintain the stabilities of these novel sandwich complexes. The centered metal of these novel sandwich complexes meet well with the 18-electron requirements. The negative NICS values for the C6Li6 ligands clearly indicated that these complexes are all aromatic in nature. The infrared (IR) spectra of these complexes have been simulated to facilitate the future experiment. These novel sandwich complexes turn out to be strongly thermodynamically favored in the gas phases and may be targeted in future experiments to expand the domain of sandwich complexes.