Sequential bonding of CO molecules to a titanium dimer: A photoelectron velocity-map imaging spectroscopic and theoretical study of Ti2(CO)n− (n = 1-9)

Structural and photoelectron spectroscopic study on the heterotrinuclear nickel-titanium dioxide carbonyl complexes Ni2TiO2(CO) n - (n = 2-4)

Herein, the configurations and intrinsic electronic properties of heteronuclear transition metal dioxide carbonyl anions Ni₂TiO₂(CO) _n ^- (n = 2-4) in the gas phase were investigated using mass spectrometry coupled anionic photoelectron spectroscopy, ab initio calculations, and simulated density-of-state (DOS) spectra. The results clearly show that the binding of electrons is enhanced by the addition of CO. The ground state structures of Ni₂TiO₂(CO) _n ^- (n = 2-4) are characterized to show that three transition metal atoms (one Ti atom and two Ni atoms) forming a quasi-line is favored. The interaction between Ni and C becomes weaker as the cluster size increases. The natural electron configuration shows that the extra electron is enriched on O atoms attached to Ti, and there is strong interaction between Ti and O atoms. This work gives significant insight into the configuration and electronic structures of nickel-titanium dioxide carbonyl anions, which has potential application in adsorption of carbon monoxide on the surfaces/interfaces of alloys.

Photoelectron velocity map imaging spectroscopic and theoretical study of heteronuclear vanadium-nickel carbonyl anions VNi(CO) n - (n = 2-6)

Mass-selected heteronuclear vanadium-nickel carbonyl anions VNi(CO) _n ^- (n = 2-6) were investigated by photoelectron velocity-map imaging spectroscopy and quantum chemical calculations to obtain their chemical bonding and intrinsic electronic structure in the gas phase. The calculated energies (adiabatic detachment energies)/vertical detachment energies (VDEs) match well with experimental values: 1.30/1.49, 1.66/1.95, 2.22/2.48, 2.70/2.89, and 2.95/3.15 eV. The VDE value of VNi(CO) _n ^- increases with an increase of cluster size, implying that the negative electron is stabilized upon the bonding of CO molecules. VNi(CO)₂ ^- consists of one bridging carbonyl and one terminal carbonyl, whose feature is different from MNi(CO)₂ ^- (M = Sc, Y, La, and Ce) with the involvement of one side-on-bonded carbonyl and one terminal CO carbonyl. The building block composed of three bridging carbonyls is favored for VNi(CO)₃ ^-, the structure of which persists up to n = 6. The additional CO ligands are preferentially coordinated in the terminal mode to the Ni atom at n = 4 and then to the V atom at n = 5 and 6. The results obtained in this work would provide a molecular-level understanding about chemisorbed CO molecules on alloy surfaces/interfaces, which is important to understand CO molecule activation processes.

Ligand-Enhanced CO Activation by the Early Lanthanide-Nickel Heterodimers: Photoelectron Velocity-Map Imaging Spectroscopy of LnNi(CO) n- (Ln = La, Ce)

Heterobimetallic lanthanum-nickel and cerium-nickel carbonyls, LnNi(CO) _n^- (Ln = La, Ce; n = 2-5), were generated using a pulsed laser vaporization/supersonic expansion ion source. These compounds were characterized by photoelectron velocity-map imaging spectroscopy and quantum chemical calculations. The binding motif in the most stable isomers of the n = 2 and 3 clusters consists of one side-on-bonded carbonyl. A new building block of two side-on-bonded carbonyls is favored at n = 4, which is retained at n = 5, evidencing the increase of the number of extremely activated CO molecule in the larger clusters. The experimental and theoretical results demonstrate the ligand-enhanced CO activation by the early lanthanide-nickel heterodimers, which would have important implications for the design of alloy catalysts for activation of a molecular ligand.

Probing the bonding of CO to heteronuclear group 4 metal–nickel clusters by photoelectron spectroscopy

MNi(CO)₃⁻ (M = Ti, Zr, Hf) was characterized to be the smallest metal carbonyl with all of the main modes of metal–CO coordination.