GAS-PHASE REACTIONS OF THE MET-CARS TI8C12-IODIDE(, NB8C12+, AND TI7NBC12+ WITH ACETONE AND METHYL)

Gas phase reactions of the metallocarbohedrenes Ti8C12+, Nb8C12+, and Ti7NbC12+ With two different types of molecules, namely, acetone and m ethyl iodide, are investigated at near thermal energy by employing a l aser-induced plasma source coupled with a triple quadrupole mass spect rometer. Two general types of reactions are observed: molecular associ ations and atom abstraction reactions. in agreement with earlier studi es on the interaction of Ti8C12+ With polar molecules, association rea ctions are found to dominate in the case of acetone. But, the incorpor ation of even one Nh greatly affects the reactivity. For example, the extraction of one and two oxygen atoms from acetone is also observed f or Nb8C12+ and Ti7NbC12+; these products are found to sequentially ass ociate with acetone to form Nb8C12+(O)(1-2)(acetone)(n) and Ti7NbC12+( O)(1-2)(acetone)(n). The reaction involves breaking C=O bonds and form ing M-O bonds, evidently due to the presence of the dipole-induced cha rge center of Nb8C12+ and Ti7NbC12+ Possible reaction mechanisms are p roposed which take into account the electronic structures of Nb8C12+, Ti7NbC12+, and Ti8C12+ In reactions with methyl iodide, all three meta llocarbohedrenes display similar mechanisms, namely, abstraction of io dine atoms. But, there is a gnat enhancement in the number upon the su bstitution of one or more titaniums by niobium atoms. The bonding stre ngth of Ti8C12+-I is determined to be larger than 56 kcal/mol. Conside ring the cagelike structure of metallocarbohedrenes, these results pro vide further insight into the relationship between their reactivities and electronic structures.