MoCoC- Bimetallic Anion Mediates Room-Temperature Conversion of Four NH3 to Five H2 Molecules.

Ammonia (NH3) decomposition is critical for a zero-carbon hydrogen economy. While gas-phase transition metal cations have been extensively studied as ideal model systems, the reactivity of anions remains largely unexplored. Herein, we report that the heteronuclear metal anion MoCoC- exhibits exceptional reactivity, sequentially activating four NH3 molecules and releasing five H2 molecules. The first two NH3 molecules are completely decomposed, releasing all six hydrogen atoms as three H2 to form MoCoCN2 -. The third and fourth NH3 molecules each release one additional H2, yielding the final product MoCoCN2(NH)2 -. Density functional theory calculations were employed to elucidate the decomposition mechanisms of the first two NH3 molecules. In the first step, which generates H2 and MoCoCNH-, bond state switching between Mo and Co facilitates the activation of H atoms in NH3, while the C atom in the cluster provides additional electron density. In the subsequent reaction with the second NH3 molecule, two H2 molecules are released, leading to MoCoCN2 -. In this step, Mo and Co act as hydrogen shuttles and electron donors for N─H bond activation. This study on MoCo-based anions for NH3 decomposition provides a theoretical foundation for elucidating the mechanism of condensed-phase MoCo catalysts in NH3 decomposition.