Interaction of Nickel with Carbon Dioxide in [Ni(CO₂)_n]⁻ Clusters Studied by Infrared Spectroscopy

Abstract

We present infrared photodissociation spectra of [Ni(CO2)n](-) clusters (n = 2-8) in the wavenumber region of 1000-2400 cm(-1) using the antisymmetric stretching vibrational modes of the CO2 units in the clusters as structural probes. We use density functional theory to aid in the interpretation of our experimental results. The dominant spectral signatures arise from a core ion composed of a nickel atom and two CO2 ligands bound to the Ni atom in a bidentate fashion, while the rest of the CO2 molecules in the cluster play the role of solvent. Other core structures are observed as well but as minor contributors. The results for [Ni(CO2)n](-) clusters are discussed in the context of other anionic transition- metal complexes with CO2.

Structures of [CoO(CO2)n]− and [NiO(CO2)n]− Clusters Studied by Infrared Spectroscopy

“…It should also be noted that similarly broad features were observed in [Ni(CO 2 ) 2 ] − clusters and attributed to multiphoton effects. 29 It is likely that the broad feature centered at 1825 cm −1 is the result of multiphoton-induced dissociation of isomer A (see Figure 8), but due to the low signal-to-noise ratio, it is difficult to confirm the presence of multiphoton effects for this species.…”

“…16,19−27 We previously studied [Ni(CO 2 ) n ] − and [Co(CO 2 ) n ] − complexes and noticed similar structural behavior for the CO 2 complexes based on these two metals. 28,29 In both cases, [M(CO 2 ) 2 ] − core ions were observed as the dominant core structure where the CO 2 units were both bound in a bidentate fashion (η 2 complexes) to the metal atom. On the basis of these previous results, we would expect similar core structures to exist in both [CoO(CO 2 ) n ] − and [NiO(CO 2 ) n ] − clusters.…”

The interaction of negative charge with carbon dioxide – insight into solvation, speciation and reductive activation from cluster studies

“…It is therefore interesting to understand transition metals in anionic complexes with CO 2 , since these complexes can serve as model systems for the interaction of CO 2 with active sites on supported reduction catalysts. Recent infrared spectroscopic work by Weber and coworkers has focused on the interaction of CO 2 with various metal atoms in singly negatively charged clusters of the form [M(CO 2 ) n À with M = Au, Ag, Cu, Co and Ni [111,[198][199][200][201][202]. This set of studies contrasts two different transition metal families, the coinage metals (Cu, Ag, Au) and first row transition metals (here: Co, Ni, Cu), with copper being a member of both families.…”

“…The interactions of CO 2 with metals that have open d-shells in anionic complexes are fundamentally different in nature from the metalloformate complexes [199,201,202]. The species studied so far (containing Co, Ni or Cu) predominantly form metallate complexes with positively charged metal centres and typically two negatively charged CO 2 ligands that interact with the metal in a bidentate structural motif (see Figure 14).…”

“…However, in most CO 2 -containing metal complexes synthesised in the condensed phase, there is usually no more than one CO 2 ligand bound to the metal centre, and the other coordination positions are filled with bulkier ligands [203]. [199,201,202]. The metal atom is shown in gray, C atoms are black and O atoms are red.…”