- The ion-molecule reactions of the Cr(CO)5-anion with molecular oxygen are described. the Cr(CO)5-anion reacts with 02to produce the Cr(CO)3O2-and Cr(CO)3O-anions. the Cr(CO)3O2-anion reacts with neutral Cr(CO)6to reform Cr(CO)5-; whereas, the Cr(CO)3O-anion reacts with 02to form CrO3-The rate of reaction of Cr(CO)5-shows an unusual temperature dependence. the temperature-dependent reaction rate is attributed to the formation of a high-spin state of Cr(CO)5by thermal decomposition of Cr(CO)6. the mechanism of the reaction of Cr(CO)5-with oxygen is probed by (1802) isotopic labeling. the proton and electron affinities of the Cr(CO)3O2-, Cr(CO)3O-, and CrO3-anions are measured by using the bracketing method. In addition, the structures of the various anions are probed by using collision-induced dissociation (CID) methods, and the relative abundance of the CID fragment ions is used to estimate relative ligand binding energies for CO and 02. 1987, American Chemical Society. All rights reserved.