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.