Superior Reactivity of Molybdenum-Sulfur Cluster Anions Mo 5 S 2 - and Mo 5 S 3 - toward Dinitrogen.

Inspired by the fact that Mo is a key element in biological nitrogenase, a series of gas-phase Mo x S y - cluster anions are prepared and their reactivity toward N 2 is investigated by the combination of mass spectrometry, photoelectron imaging spectroscopy, and density functional theory calculations. The Mo 5 S 2 - and Mo 5 S 3 - 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 Mo 5 S 2 - and Mo 5 S 3 - . The large dissociative adsorption energy of N 2 and the favorable entrance channel for initial N 2 approaching are proposed as two decisive factors for the superior reactivity of Mo 5 S 2 - and Mo 5 S 3 - . Besides, the modulation of S ligands on the reactivity of metal centers with N 2 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.