Photoelectron imaging spectroscopic signatures of CO activation by the heterotrinuclear titanium-nickel clusters

A series of heterotrinuclear Ti2Ni(CO)n– (n = 6–9) carbonyls have been generated via a laser vaporization supersonic cluster source and characterized by mass-selected photoelectron velocity-map imaging spectroscopy. Quantum chemical calculations have been carried out to identify the structures and understand the experimental spectral features. The results indicate that a building block of Ti-Ti-Ni-C four-membered ring with the C atom bonded to Ti, Ti, and Ni is dominated in the n = 6–8 complexes, whereas a structural motif of Ti-Ti-Ni triangle core is preferred in n = 9. These complexes are found to be capable of simultaneously accommodating all the main modes of metal-CO coordination (i.e., terminal, bridging, and side-on modes), where the corresponding mode points to the weak, moderate, high CO bond activation, respectively. The number of CO ligands for a specific bonding mode varies with the cluster size. These findings have important implications for molecular-level understanding of the interaction of CO with alloy surfaces/interfaces and tuning the appropriate CO activation via the selection of different metals.