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

A series of heterotrinuclear Ti_(2)Ni(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 C-O 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.