IR Photodissociation Spectroscopy and Theory of Au+(CO)n Complexes: Nonclassical Carbonyls in the Gas Phase

J. Velasquez III, University of Georgia
Bosiljka Njegic, Iowa State University
Mark S. Gordon, Iowa State University
M. A. Duncan, University of Georgia

Reprinted (adapted) with permission from Journal of Physical Chemistry A 112 (2008), 1907, doi:10.1021/jp711099u. Copyright 2008 American Chemical Society.

Abstract

Au+(CO)n complexes are produced in the gas phase via pulsed laser vaporization, expanded in a supersonic jet, and detected with a reflectron time-of-flight mass spectrometer. Complexes up to n = 12 are observed, with mass channels corresponding to the n = 2 and n = 4 showing enhanced intensity. To investigate coordination and structure, individual complexes are mass-selected and probed with infrared photodissociation spectroscopy. Spectra in the carbonyl stretching region are measured for the n = 3−7 species, but no photodissociation is observed for n = 1, 2 due to the strong metal cation-ligand binding. The carbonyl stretch in these systems is blue-shifted 50−100 cm-1 with respect to the free CO vibration (2143 cm-1), providing evidence that these species are so-called “nonclassical” metal carbonyls. Theory at the MP2 and CCSD(T) levels provides structures for these complexes and predicted spectra to compare to the experiment. Excellent agreement is obtained between experiment and theory, establishing that the n = 3 complex is trigonal planar and the n = 4 complex is tetrahedral.