Probing the properties of size dependence and correlation for tantalum clusters: geometry, stability, vibrational spectra, magnetism, and electronic structure

An Open-Shell Superatom Cluster Ta10- with Enhanced Stability by United d-d π Bonds and d-Orbital Superatomic States

We carried out a comprehensive study on the gas-phase reactions of Ta_n^- (n = 5-27) with nitrogen using a customized reflection time-of-flight mass spectrometer coupled with a velocity map imaging apparatus (Re-TOFMS-VMI). Among the studied tantalum clusters, Ta₁₀^- exhibits prominent mass abundance indicative of its unique inertness. DFT calculation results revealed a D_4d bipyramidal prolate structure of the most stable Ta₁₀^-, which was verified by photoelectron spectroscopy experiments. The calculations also unveiled that Ta₁₀^- has the largest HOMO-LUMO gap and second-order difference of binding energy among the studied clusters. This is associated with its well-organized superatomic orbitals, which consist of both 6s and 5d orbitals of tantalum atoms, allowing for splitting of superatomic 1D and 2P orbitals and an enlarged gap between the singly occupied molecular orbital (SOMO) and unoccupied β counterpart, which brings forth stabilization energy pertaining to Jahn-Teller distortion. Also, the SOMO exhibits a united d-d π orbital pattern that embraces the central Ta₈^- moiety.

Structures of Small Tantalum Cluster Anions: Experiment and Theory

We present a study of the structural evolution of tantalum cluster anions Ta_n^-, 6 ≤ n ≤ 13 using a combination of trapped ion electron diffraction (TIED) experiments with a variety of electronic structure methods. A genetic algorithm has been employed to establish a set of likely structures for each cluster, their geometries and energetics have been studied by density functional theory (DFT), random phase approximation, and two-component (2C) DFT methods, which include spin-orbit coupling. We find octahedral structures for Ta₆^- and Ta₈^- as well as structures based on the pentagonal bipyramid (Ta₇^- and Ta₉^-). Ta₁₀^--Ta₁₂^- are defective icosahedral structures and Ta₁₃^- is a distorted icosahedron. For most clusters, we find a good agreement between the theoretically predicted ground-state structures, especially those determined by the 2C method and the TIED results.