ROTATIONAL CONFORMERS OF GROUP VI (Cr, Mo, and W) METAL BIS(TOLUENE) $SANDWICH$ COMPLEXES

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Date

2009

Authors

Lee, Jung Sup
Kumari, Sudesh
Yang, Dong-Sheng

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Ohio State University

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Abstract

Transition metal bis(arene) sandwich complexes may adopt eclipsed or staggered conformations due to the aromatic ring rotations about the metal-arene axis., In this study, the group VI (Cr, Mo, and W) metal bis(toluene) complexes are synthesized in a laser-ablation molecular beam source, and their rotational conformers are identified by pulsed-field-ionization zero-electron-kinetic-energy (ZEKE) spectroscopy. For Cr-bis(toluene), the ZEKE spectrum shows three distinctive vibrationless (0-0) transitions between the ground electronic states of the neutral and ionic complexes at 42739(5), 42745(5), and 42805(5) cm−1, corresponding to ionization energies of 180irc, 60irc/120irc, and 0irc rotamers. In addition, the spectrum exhibits metal-toluene bending (164, 180, 196, and 223 cm−1) and stretching (278 and 291 cm−1) frequencies of these rotamers. The ground electronic states of the 0irc and 180irc rotamers are 1A1 (C2v) and 1Ag (C2h) in the neutral form and 2A1 (C2v) and 2Ag (C2h) in the ionized form, respectively. For the 60irc and 120irc rotamers, the ground states of the neutral molecules are 1A (C2), and those of the corresponding ions are 2A (C2). Through the variation of the molecular beam conditions, the eclipsed conformer (0irc) is determined to be more stable than the staggered ones (180irc, 120irc, and 60irc). Similarly, multiple conformers are identified for the Mo and W complexes.

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B.S.~Sohnlein, S.~Li, and D.S.~Yang, J.~Chem.~Phys. 123, 214306 (2005); B.S.~Sohnlein and D.S.~Yang, J.~Chem.~Phys. 124, 134305 (2006)S.Y.~Ketkov, H.L.~Sezle, and F.G.N.~Cloke, Angew.~Chem.~Int.~Ed. 46, 7072 (2007) and references therein.


Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055

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