REACTION PRODUCTS OF LASER ABLATED EARLY TRANSITION METALS WITH BENZENE MOLECULES IN CONDENSING ARGON
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Date
2004
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Ohio State University
Abstract
Early transition metal atoms, produced by laser ablation, are reacted with benzene vapor diluted in argon during co-deposited onto a low temperature CsI window. The resulting reaction products are trapped and the $M(C_{6}H_{6})$ and $M(C_{6}H_{6})_{2}$ complexes are identified by benzene isotopic studies $(C_{6}H_{6}$, $^{13}C_{6}H_{6}$, $C^{6}D^{6})$. Density Functional Theory (DFT) frequency calculations are used to confirm the assignments. Calculated ground state energies predict these reaction energetically favorable. The $M(C_{6}H_{6})$ and $M(C_{6}H_{6})_{2}$ products have $C_{6v}$ and $D_{6h}$ symmetries respectively. Based on the observed aromatic C-C breathing mode frequency shifts, the metal-carbon bond strengths are shown to increase down a group (from vanadium to tantalum) and decrease from left to right along a period (from scandium to chromium). These trends indicate that back donation of electrons from the metal d orbitals to the unoccupied $\pi^{\ast}$ orbitals of benzene is the primary electronic interaction responsible for the bonding in these molecules. Analogous experiments in progress with $C_{60}$ give similar product complexes.
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Author Institution: Department of Chemistry, University of Virginia