Formation and structures of transition metal-C₆₀ clusters

Transition metal (Sc, Ti, V, and Cr)-C₆₀ binary clusters were produced in the gas phase by a two-laser vaporization method. In the mass spectra of cationic M_n(C₆₀)_m⁺, for M = Sc, Ti, and V, clusters having the composition of (n, m) = (1, 1)⁺, (1, 2)⁺, (2, 3)⁺, (3, 4)⁺, (4, 4)⁺, and (5, 5)⁺ were predominantly produced. The peaks having (n, n + 1)⁺ compositions are explicable in terms of multiple dumbbell structures, in which metal atoms and C₆₀ are alternately stacked. Clusters with composition (4, 4)⁺ and (5, 5)⁺ are presumed to be ring structures. For Cr_n(C₆₀)_m⁺, however, a Cr atom is surrounded by three C₆₀, forming a tricapped structure, and the structure acts as a unit for larger stable clusters of (2, 4)⁺, (3, 4)⁺, and (4, 4)⁺. Ionization energy measurements for neutral M_n(C₆₀)_m and a chemical probe method using CO, O₂, and C₂H₄ as reactants gave information concerning the geometrical and electronic structures.