Structural Evolution and Bonding Analysis of Heterotrinuclear Carbonyl Clusters TiNi2(CO)n- (n = 3-5)

A series of heterotrinuclear carbonyl clusters TiNi2(CO)n- (n = 3-5) have been produced by a laser sputtering supersonic cluster ion source and probed by a velocity-map photoelectron imaging spectrometer. Theoretical calculations have been executed to probe the structures and assist the experimental spectral assignments. At n = 3, an intriguing trigonal pyramidal Ti-Ni-Ni-C motif is formed with two μ2-bridging CO ligands and one μ3-bridging CO ligand, which is retained in the most stable structures of larger clusters. For n = 4 and 5, the additional CO ligands are separately bound to each Ni atom in a terminal coordination mode. C-O bond activation is found to increase systematically with the binding motif of metal-CO coordination: terminal < μ2-bridging < μ3-bridging coordination. The present findings elucidate the bonding mechanism in the heteronuclear metal clusters at the molecular level and provide microscopic insights into metal-CO interactions in heterometallic systems.