IR-spectroscopic characterization of acetophenone complexes with Fe+, Co+, and Ni+ using free-electron-laser IRMPD

The gas-phase complexes M+(acet)(2), where M is Fe, Co, or Ni and acet is acetophenone, were studied spectroscopically by infrared multiple-photon dissociation (IRMPD) supported by density functional (DFT) computations. The FELIX free electron laser was used to give tunable radiation from similar to 500 to 2200 cm(-1). The spectra were interpreted to determine the metal-ion binding sites on the ligands (oxygen (O) or ring ( R)) and to see if rearrangement of the ligand(s) to toluene plus CO occurred. For Ni+, O binding was found to predominate (similar to the previously studied Cr+ case), with less than similar to 10% of R-bound ligands in the population. For Co+, a roughly equal mixture of R-bound and O-bound ligands was present; based on the computed thermochemistry, the OR complex was considered likely to predominate. Fe+ complexes appeared largely O-bound, but with clear evidence for some R-binding. The exceptionally large extent of R binding for Co+ highlights the special affinity of this metal ion for aromatic ring ligands. In contrast, the predominant O binding for Ni+ emphasizes the especially high metal-ion affinity of the O site of acetophenone compared with other ligands such as anisole where R binding of Ni+ predominates. The spectra did not indicate significant intracomplex rearrangement of ligands to toluene plus CO, and in particular for the Co+ case the absence of a metal-bound C O stretching peak near 2100 cm(-1) strongly ruled out such a rearrangement.