Author: Jiang GD, Yang Q, Wei GP, Li ZY, He SG.

Abstract: Inspired by the fact that Mo is a key element in biological nitrogenase, a series of gas-phase Mo_<i>x</i>S_<i>y</i>^- cluster anions are prepared and their reactivity toward N₂ is investigated by the combination of mass spectrometry, photoelectron imaging spectroscopy, and density functional theory calculations. The Mo₅S₂^- and Mo₅S₃^- cluster anions show remarkable reactivity compared with the anionic species reported previously. The spectroscopic results in conjunction with theoretical analysis reveal that a facile cleavage of N≡N bonds takes place on Mo₅S₂^- and Mo₅S₃^-. The large dissociative adsorption energy of N₂ and the favorable entrance channel for initial N₂ approaching are proposed as two decisive factors for the superior reactivity of Mo₅S₂^- and Mo₅S₃^-. Besides, the modulation of S ligands on the reactivity of metal centers with N₂ is proposed. The highly reactive metal-sulfur species may be obtained by the coordination of two to three sulfur atoms to bare metal clusters so that an appropriate combination of electronic structures and charge distributions can be achieved.