Characterization of Intermediate Oxidation States in CO₂ Activation

Abstract

Redox chemistry during the activation of carbon dioxide involves changing the charge state in a CO molecular unit. However, such changes are usually not well described by integer formal charges, and one can think of COO functional units as being in intermediate oxidation states. In this article, we discuss the properties of CO and CO-based functional units in various charge states. Besides covering isolated CO and its ions, we describe the CO-based ionic species formate, oxalate, and carbonate. Finally, we provide an overview of CO-based functional groups and ligands in clusters and metal-organic complexes.

Infrared Multiple Photon Dissociation Spectroscopy of Hydrated Cobalt Anions Doped with Carbon Dioxide CoCO2(H2O)n−, n=1–10, in the C−O Stretch Region

“…Cationic metal–CO 2 complexes M + (CO 2 ) n (M=Mg, Al, Si, V, Fe, Co, Ni, Rh, Ir) have been extensively investigated in the past decades, and also anionic species M − (CO 2 ) n (M=Ti, Mn, Fe, Co, Ni, Cu, Ag, Au, Sn, Bi) have received considerable attention, foremost by the group of Weber . Generally, the anionic CO 2 − stretching vibrations shift to the red compared to neutral CO 2 vibrations . CO 2 as a ligand was also investigated as metal oxides, NbO 2 + (CO 2 ) n and TaO 2 + (CO 2 ) n by Mackenzie and co‐workers .…”

“…The electrochemical route of activation involves the carbon dioxide radical anion CO 2 − as a short‐lived intermediate . It is well known that CO 2 − is metastable and undergoes autodetachment with a measured lifetime of up to milliseconds . This has been repeatedly confirmed by quantum chemical calculations .…”

“…This has been repeatedly confirmed by quantum chemical calculations . In interaction with a rare gas matrix or a solvation shell such as (CO 2 ) n −[6, 11, 12] or CO 2 (H 2 O) n − , the radical anion is stabilized . The same is true in a salt environment where the interaction with positive charge centers is responsible for the stabilization .…”

“…The same is true in a salt environment where the interaction with positive charge centers is responsible for the stabilization . In the interaction of CO 2 with metal ions, electron transfer from the metal to the electrophilic carbon atom can occur spontaneously, leading to complexes of the metal center with CO 2 − . When a single bond is formed between the metal and the carbon atom, as observed for example, with the nickel group, coinage metal, or bismuth anions, the excess charge in this metalloformate η 1 ‐(C) complex, MCO 2 − , is delocalized over the whole molecular ion …”

“…Vibrational spectroscopy is a powerful method for structural analysis in the gas phase . Vibrational spectra of Co n + (CH 3 OH) 3 ( n= 1–3) were measured by IR photodissociation spectroscopy .…”