Nitrogen adsorption on Nb₂C₆H₄⁺ cations: the important role of benzyne (ortho-C₆H₄)

N-2 adsorption is a prerequisite for activation and transformation. Time-of-flight mass spectrometry experiments show that the Nb2C6H4+ cation, resulting from the gas-phase reaction of Nb-2(+) with C6H6, is more favorable for N-2 adsorption than Nb+ and Nb-2(+) cations. Density functional theory calculations reveal the effect of the ortho-C6H4 ligand on N-2 adsorption. In Nb2C6H4+, interactions between the Nb-4d and C-2p orbitals enable the Nb-2(+) cation to form coordination bonds with the ortho-C6H4 ligand. Although the ortho-C6H4 ligand in Nb2C6H4+ is not directly involved in the reaction, its presence increases the polarity of the cluster and brings the highest occupied molecular orbital (HOMO) closer to the lowest occupied molecular orbital (LUMO) of N-2, thereby increasing the N-2 adsorption energy, which effectively facilitates N-2 adsorption and activation. This study provides fundamental insights into the mechanisms of N-2 adsorption in "transition metal-organic ligand" systems.