IR Spectroscopy of M⁺(Acetone) Complexes (M = Mg, Al, Ca):  Cation−Carbonyl Binding Interactions

Abstract

M(+)(acetone) ion-molecule complexes (M = Mg, Al, Ca) are produced in a pulsed molecular beam by laser vaporization and studied with infrared photodissociation spectroscopy in the carbonyl stretch region. All of the spectra exhibit carbonyl stretches that are shifted significantly to lower frequencies than the free-molecule value, consistent with metal cation binding on the oxygen of the carbonyl. Density functional theory is employed to elucidate the shifts and patterns in these spectra. Doublet features are measured for the carbonyl region of Mg(+) and Ca(+) complexes, and these are assigned to Fermi resonances between the symmetric carbonyl stretch and the overtone of the symmetric carbon stretch. The carbonyl stretch red shift is greater for Al(+) than it is for the Mg(+) and Ca(+) complexes. This is attributed to the smaller size of the closed-shell Al(+), which enhances its ability to polarize the carbonyl electrons. Density functional theory correctly predicts the direction of the carbonyl stretch shift and the relative trend for the three metals.

Infrared Spectroscopy of Extreme Coordination: The Carbonyls of U+ and UO2+

“…Our group has recently studied isolated carbonyl ions in the gas phase, where this rule continues to influence coordination even for seven-coordinate species. [24][25][26][27][28] For actinides and lanthanides with f electrons, the corresponding filled s 2 p 6 d 10 f 14 configuration requires 32 electrons, but steric effects preclude the high coordination numbers needed to achieve this. 3,29 However, the d orbitals in actinides are usually less important in bonding, and therefore stable actinide systems often have 22 electrons (e.g., U(C 8 H 8 ) 2 ).…”

“…3,16 Significantly smaller red shifts are seen for cation transition metal complexes, [26][27][28] which exhibit less back-donation because of their positive charge. A blue shift is often observed for "nonclassical" carbonyls 36 with filled d shells such as Au + or Pt + , 24,25 which have essentially no backdonation. The red-shifted C-O stretch of U(CO) 8 + has a frequency comparable to those seen for neutral transition metal carbonyls with significant back-bonding.…”

Intramolecular Ion-Molecule Reactions within Ti+(CH3COCH3)nHeteroclusters: Oxidation Pathway via C=O Bond Activation

“…[1][2][3][4][5][6][7] Among these studies, investigations of gas phase ion/solvent clusters provide a unique and experimentally accessible way to investigate the influence of solvation on the chemical reaction dynamics. Such gas phase studies have enhanced our understanding of the behavior of transition metal ions in the condensed phase.…”

IR spectroscopic characterization of intermediates in a gas-phase ionic reaction: The decarbonylation of Co+(acetophenone)

“…New approaches to spectroscopy of complex gas-phase ions are available which greatly enlarge the possibilities for doing this [11][12][13][14][15][16][17][18][19][20]. In particular, IR spectroscopy over a wide spectral range made possible by a free-electron laser source in combination with capable mass spectrometers gives the opportunity to do IR-spectroscopic characterization of intermediates and products in metal-catalyzed gas-phase reaction sequences [11,12,19].…”