Characterization of metal-carbon clusters in the gas phase using Fourier transform mass spectrometry

Yong Gwan Byun, Purdue University

Abstract

The metallo-carbohedrenes, $\rm M\sb8C\sb{12}\sp+,$ (M = V, Nb) are studied using a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer coupled to a compact supersonic source. Their reactions with water, ammonia, ROH $\rm(R=CH\sb3,\ C\sb2H\sb5,\ C\sb3H\sb7,\ C\sb4H\sb9),$ and $\rm CH\sb3X$ (X = Cl, Br, I) are reported. For polar molecules, sequential attachment reactions occur leading to the initial build-up of the products $\rm M\sb8C\sb{12}L\sb4\sp+.\ M\sb8C\sb{12}L\sb{5-7}\sp+$ peaks for ammonia and alcohols have also been observed, but they grow in slowly. These results provide evidence that the geometric structure of both $\rm M\sb8C\sb{12}\sp+$ species is the theoretically calculated more stable T$\rm\sb{d}$ or D$\rm\sb{2d}$ symmetry with two sets of metals, as opposed to the $\rm T\sb{h}$ symmetry with all 8 equivalent metals. The results from this study are compared to those of other met-cars. $\rm Nb\sb6C\sb7\sp+$ and $\rm V\sb{14}C\sb{12/13}\sp+$ are studied using a FTICR mass spectrometer coupled to a compact supersonic source. The reactions of $\rm Nb\sb6C\sb7\sp+$ with $\rm H\sb2O,\ NH\sb3,\ CH\sb3OH,\ CH\sb3CN,\ and\ C\sb6H\sb6$ are reported. For each of these ligands, sequential attachment reactions occur leading to the initial truncation products $\rm Nb\sb6C\sb7L\sb4\sp+.$ A measurement of the relative rate constants for the sequential addition reactions of $\rm CH\sb3OH,$ for example, demonstrates quantitatively that addition of the fifth $\rm CH\sb3OH$ is very slow compared to the first four additions. The optimized structure of $\rm Nb\sb6C\sb7\sp+$ using ab initio calculations in which four of the six niobium atoms are equivalent, but different from the other two, is consistent with the experimental results. The reactions of $\rm V\sb{14}C\sb{12/13}\sp+$ with $\rm H\sb2O\ and\ CH\sb3CN$ are also reported. Sequential reactions with up to 8 H$\sb2$O molecules result in the formation of $\rm V\sb{14}C\sb{12,13}(OH)\sb2(H\sb2O)\sb6\sp+\ and\ V\sb{14}C\sb{13}(OH)\sb4(H\sb2O)\sb4\sp+$ by loss of H$\sb2$ or attachment of H$\sb2$O. Both ions are observed to attach up to 8 CH$\sb3$CN molecules. These results provide evidence for the proposed 3 x 3 x 3 cubic structure of $\rm V\sb{14}C\sb{13}\sp+$ where the 8 metals in the corners are the active binding sites. The similarity of the reactivity of $\rm V\sb{14}C\sb{12}\sp+$ suggests an analogous structure.

Degree

Ph.D.

Advisors

Freiser, Purdue University.

Subject Area

Analytical chemistry|Chemistry

COinS