A Novel Network Structure of Organometallic Clusters in the Gas Phase

In the gas phase, novel network structures were found in organometallic clusters between metal atoms produced by laser ablation and organic ligand molecules. For 3d metal-benzene, M_nBz_m, two kinds of structures of multiple sandwich and rice-ball were formed, depending on the metal elements. Early transition metals (ME) of Sc, Ti, and V form the multiple-decker sandwich structure of (n, m) = (n, n + 1) in which metal atoms and benzene are alternately piled up, while late transition metals (M_L) of Fe, Co, and Ni form the rice-ball structure in which central metal clusters were fully covered by benzene molecules. The ionization energy of M_E-Bz drops significantly with increasing layers, which can be explained by delocalization of d electrons along the molecular axis. M-C₆₀ binary clusters were also generated by a two-laser vaporization method; M_E-C₆₀ clusters efficiently form a chain or a ring structure consisting of a dumbbell unit, in which metal atoms and C₆₀ are alternately connected. For M_L-C₆₀ clusters, however, the metal atom is tricapped by C₆₀ and a face-centered tetrahedron structure is formed at (n, m) = (4, 4). A similar multiple-decker sandwich structure is formed also between lanthanide metal atoms (Ln) and an organic ligand of cyclooctatetraene (COT). The Ln-COT cluster is a charge transferred cluster consisting of positively charged Ln and negatively charged COT. Their electronic structure is fairly ionic and is localized around each metal atom. These novel structures of organometallic clusters should inspire new thoughts in material science because it is hoped that the regular arrangement of metal ions can introduce useful properties such as electroconductivity and magnetism.