Small boron clusters are known to be planar, and may be used as ligands to form novel coordination complexes with transition metals. Here we report a combined photoelectron spectroscopy and ab initio study of CoB12− and RhB12- . Photoelectron spectra of the two doped-B12 clusters show similar spectral patterns, suggesting they have similar structures. Global minimum searches reveal that both CoB12− and RhB12− possess half-sandwich-type structures with the quasi-planar B12 moiety coordinating to the metal atom. The B12 ligand is found to have similar structure as the bare B12 cluster with C3v symmetry. Structures with Co or Rh inserted into the quasi-planar boron framework are found to be much higher in energy. Chemical bonding analyses of the two B12 half sandwiches reveal two sets of σ bonds on the boron unit: nine classical two-center-two-electron (2c−2e) σ bonds on the periphery of the B12 unit and four 3c−2e σ bonds within the boron unit. Both σ and π bonds are found between the metal and the B12 ligand: three M−B single σ bonds and one delocalized 4c−2e π bond. The exposed metal sites in these complexes can be further coordinated by other ligands or become reaction centers as model catalysts. We also report a theoretical investigation on the ten-atom boron-carbon mixed clusters CxB10-x− (x = 1-10) with step-by-step substitution of boron by carbon atoms, revealing a molecular wheel to monocyclic ring and linear species structural transition as a function of x upon increasing the number of carbon atoms in the studied series. The C3B7− and C4B6− clusters are found to possess planar distorted wheel-type structures with a single inner boron atom, similar to the experimentally observed CB9− and C2B8−. Going from C5B5− to C9B− inclusive, monocyclic, and ring-like structures are observed as the most stable ones on the PES. The first linear species in the presented series is found for the C10− cluster, which is almost isoenergetic with the one possessing a monocyclic geometry.

Combined photoelectron spectroscopy and ab initio studies of pure, carbon-doped, and transition-metal-doped boron clusters

249th National Meeting (2015)

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