Evidence from Ion Chromatography Experiments That Met-Cars Are Hollow Cage Clusters

Abstract

Ion chromatography studies were performed to assess various models proposed for the structure of M(8)C(12) species, the met-cars. A laser desorption source was used to make a sequence of titanium-carbon clusters centered around Ti(8)C(12)(+). The Ti(8)C(12)(+) was determined to be a hollow cage cluster, with the dodechadron structure originally propposed termined to be a hollow cage cluster, with the dodecahedron structure originally proposed giving the best fit to experiment; cubic structures could be excluded. Collisional breakup of Ti(8)C(12)(+) yielded only Ti(7)C(12)(+) under the experimental conditions described herein, and modeling indicated that the cage structure was retained. Both Ti(8)C(11)(+) and Ti(8)C(13)(+) were made by the cluster source, and again, dodecahedral-type cage structures were consistent with experiment. The extra carbon atom in Ti(8)C(13)(+) was attached exohedrally to a single titanium atom. No evidence for an endohedral species was found.

Vibrational Spectroscopy of Gas-Phase Metal-Carbide Clusters and Nanocrystals

“…Chemisorption reactivity studies have suggested either eight or four equivalent metal atoms on the surface depending on conditions [13,14], while negative ion photoelectron spectra are consistent with the orbital occupation expected for the T d structure [15,16]. Ion mobility measurements determined that the structure is approximately spherical but could not distinguish between the proposed symmetries [17]. The M 14 C 13 cluster was suggested to have a 3 3 3 3 3 nanocrystalline cubic structure [7,8], which is supported by theory [12,18].…”

Predicted infrared and Raman spectra for neutralTi8C12isomers

“…Other geometries have also been proposed including structures belonging to the C 3v point group 10,11,12,13 . Comparison of the drift time of mass selected Ti 8 C + 12 with calculated mobilities for various structures reinforces the proposed hollow cage structures instead of more closely packed cubic structures 14,15 .…”

Experimental and Theoretical Studies of Nb6C70/+

“…The results were consistent with a dodecahedral-type hollow cage-like structure. 14 Recently, we reported on the gas-phase chemistry of M 8 C 12 + (M ) V, Nb), and this study provided support for the theoretically proposed low-energy T d or D 2d structure, [15][16][17] as opposed to the more symmetric T h structure originally proposed. 1 For metal-carbon (metal ) Ti, V, Nb) clusters, [18][19][20][21] two types of stoichiometries are especially abundant, those corresponding to cubic crystallites (e.g., M 14 C 13 and fcc fragments such as M n C n , n ) 4, 6, or 9) and metallo-carbohedrenes (M 8 C 12 ).…”