Studies of Met-Car adducts: Ti8C12+(M)(n) (M=halogens, pi-bonding molecules, and polar molecules)

A new method of forming Met-Car-ligand complexes, Ti8C12+(M)(n) (M = halogens, pi-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 iondipole 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 pi-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-pi 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 T-h 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.