An Open-Shell Superatom Cluster Ta 10 - 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, Ta 10 - exhibits prominent mass abundance indicative of its unique inertness. DFT calculation results revealed a D 4 d bipyramidal prolate structure of the most stable Ta 10 - , which was verified by photoelectron spectroscopy experiments. The calculations also unveiled that Ta 10 - 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 Ta 8 - moiety.