During the course of studying the dehydrogenation reactions of hydrocarbons by titanium atoms, ions, and clusters, an exceptionally stable and abundant cluster which contains 8 titaniums and 12 carbons was discovered. "Titration" reactions with ND(3) reveal the uptake of eight molecules, pointing to the fact that the titanium atoms are at exposed positions of similar coordination. A dodecahedral structure of T(h) point group symmetry is proposed to account for the unusual stability of this molecular cluster. The Ti(8)C(12)(+) dodecahedron has 12 pentagonal rings and each of the rings is formed by two titanium and three carbon atoms, where each titanium is bound to three carbons. Based on the model, it is expected that neutral Ti(8)C(12) would be a stable metallo-carbododecahedral molecule and may comprise one member of a new class of molecules, namely metallo-carbohedrenes.

Reactivities and collision-induced dissociation of vanadium oxide cluster cations are investigated using a triple quadrupole mass spectrometer coupled with a laser vaporization source. The dominant peaks in the mass distribution correspond to cluster ions with stoichiometries of (VO 2 ) n (V 2 O 5 ) m (O 2 ) q + . Collision-induced dissociation studies of the vanadium oxide species V 2 O 4-6 + , V 3 O 6-9 + , V 4 O 8-10 + , V 5 O 11-13 + , V 6 O 13-15 + , and V 7 O 16-18 + show that VO 2 , VO 3 , and V 2 O 5 units are the main building blocks for most of these clusters. The reaction pathways observed for these vanadium oxide clusters include molecular association, cracking, dehydration, and oxygenation of the neutral hydrocarbons with the reactivities of specific clusters differing from species to species. For example, V 3 O 7 + is very efficient in the dehydrogenation of 1,3-butadiene and in the cracking of 1-butene. On the other hand, V 3 O 6 + produces only molecular association products with these same reactants. To help explain these differences in reactivity, calculations on the molecular structure of some of these cluster ions were also undertaken, and the findings are presented.

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A new method of forming Met-Car−ligand complexes, Ti8C12 +(M) n (M = halogens, π-bonding molecules, and polar molecules, n = 1−8) is reported which involves the direct interaction of titanium with mixtures of methane and selected reactant gases. The results show that the formation of Ti8C12 in the plasma is kinetically and thermodynamically favored over other reaction processes. Through an examination of Met-Car−ligand complexes, various reaction mechanisms of Ti8C12 + are identified and characterized, namely oxidation, complexation, and ion−dipole interaction. Oxidation of Ti8C12 + occurs when Met-Cars react with halogen-containing molecules through valence electron donation from Ti8C12 + to the halogen atoms. When Ti8C12 + interacts with π-bonding molecules, the findings are consistent with the formation of “surface complexes” comprised of the ligand binding across two of the metal atoms in the pentagonal ring of Ti8C12 + through d−π interaction. In these cases, the cluster size distributions in the mass spectra of the reaction products exhibit truncation at Ti8C12 +(M)4. By contrast, ion−dipole interactions lead to the formation of Ti8C12 +(M)1-8 (M denoting polar molecules), which is consistent with previous findings showing that polar molecules bond to each metal site. The product distribution of Ti8C12 + with butanol at various pressures provides new evidence which serves to resolve controversies in the literature regarding observed truncations and their implications concerning the geometric structure of Ti8C12 +; the findings are supportive of the originally proposed Th symmetry. Furthermore, the further reaction of Ti8C12 +(I) with methanol, which gives the product distribution truncation at Ti8C12 +(I)(CH3OH)7, indicates that the titration method is a useful tool to probe the cluster structures in these systems.

Niobium oxide cluster ions are produced by a laser-induced plasma source. The cluster distribution, collision-induced dissociation (CID), and cluster reactivities are studied using a triple-quadrupole mass spectrometer. CID experiments on the cluster ions Nb3O7 - 9 +, Nb4O9 - 11 +, and Nb5O12 + reveal that their building blocks are Nb2O5, NbO2 +, NbO3, Nb3O7 +, O, and O2, whereby the cluster stoichiometry is assigned to have the general form (NbO3) m (NbO2) n (O)0 - 4 +. The trends in the ionization potentials of these species are estimated in terms of the CID fragments produced. Nb3O8 - 9 + and Nb4O11 + cluster ions evidently form via the adsorption of one oxygen atom or molecule onto the cluster surface. Nb3O7 +, Nb4O9 +, and Nb5O12 + have strong reactivities to abstract an oxygen atom from oxygen-containing molecules and adsorb small hydrocarbons at near thermal energies. In particular, the reactivity of the oxygen atom or molecule in the oxide clusters Nb3O8 - 9 + and Nb4O11 + is consistent with our suggestions that it has a radical oxygen character.