Neutral metal−benzene complexes, M n (benzene) m (M = Sc to Cu), are produced for all of the 3d transition metals in the gas phase by using the laser vaporization method. These species are characterized by mass spectrometry, photoionization spectroscopy, and chemical probe experiments. Depending on the metal, there are two types of structures for M n (benzene) m :  multiple-decker sandwich structures and metal clusters fully covered with benzene molecules (rice-ball structures). The former sandwich structure is characteristic of the complexes for early transition metals (Sc−V), whereas the latter is formed for late transition metals (Fe−Ni). Electronic structures of M1(benzene) x (x = 1, 2) complexes are investigated through systematic measurements of ionization energies (E i's).

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Cobalt-benzene clusters, Co,,(benzene),,,, were synthesized by the reaction of laser-vaporized C o atoms with benzene vapor. The clusters exhibit magic-number behavior not only at m = n + 1 (n = 1-3) but also at (n-m) = (3-3), (4-4), (5-4), (6-4), (7-4), (8-5), and (9-6). Observed magic-number behavior and ionization energies are consistently explained by assuming the structure of the clusters to be multiple-decker sandwiches for n-m (m = n + 1, n = 1 -3) and to be an n atom metal cluster coated by m benzene molecules for iz-m ( n 2 4). In this paper, we will present the properties of Co,,(benzene),,, clusters from the viewpoints of mass distribution, reactivity, and ionization energies. The structure and formation mechanism of the Co,,(benzene),,, clusters will also be discussed.

Transition metal (Sc, Ti, V, and Cr)-C 60 binary clusters were produced in the gas phase by a two-laser vaporization method. In the mass spectra of cationic M n (C 60 ) 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 C 60 are alternately stacked. Clusters with composition (4, 4) + and (5, 5) + are presumed to be ring structures. For Cr n (C 60 ) m + , however, a Cr atom is surrounded by three C 60 , 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 (C 60 ) m and a chemical probe method using CO, O 2 , and C 2 H 4 as reactants gave information concerning the geometrical and electronic structures.

Organometallic lanthanide complexes of Ln n (C8H8) m (Ln = lanthanide metals of Ce, Nd, Eu, Ho, and Yb; C8H8 = 1,3,5,7-cyclooctatetraene) were produced by a combination of laser vaporization and molecular beam methods. The complexes having (n, m) = (n, n + 1) for n = 1−5 were prominently produced as magic numbers in the mass spectra. Using mass spectrometry, photoionization spectroscopy, and photoelectron spectroscopy, it is concluded that these magic-numbered complexes form multiple decker sandwich structures in which Ln atoms and C8H8 molecules are alternately piled up. The obtained spectroscopic data show that these sandwich complexes are formed through ionic bonds and are charge transfer complexes, where the Ln atoms are multiply charged cations of Ln k + (k = 2 and 3) and C8H8 molecules are multiply charged anions.