A photoelectron spectroscopy and density functional study of di-tantalum boride clusters: Ta2B(x)- (x = 2-5)

The structural and electronic properties for di-tantalum boride clusters Ta(2)B(x)(-) (x = 2-5) were investigated using photoelectron spectroscopy and density functional calculations. The photoelectron spectra for Ta(2)B(x)(-) (x = 2-5) are obtained at several photon energies with rich spectral features. Density functional theory calculations are performed at the BP86 level to search for the global minima of both the anionic and neutral clusters. The calculated vertical electron detachment energies for the global minimum and low-lying isomers are compared with the experimental data. Strong boron-boron bonding is found to dominate the lowest energy structures of Ta(2)B(x)(-) and Ta(2)B(x) (x = 2-5), which are shown to be bipyramidal with the boron atoms forming an equatorial belt around the Ta-Ta dimer. Strong Ta-Ta bonding is observed in Ta(2)B(x)(-) and Ta(2)B(x) for x = 2-4, whereas the Ta-Ta distance is increased significantly in Ta(2)B(5)(-) and Ta(2)B(5).