Reactivity of Hydrated Monovalent Cobalt (I) Toward Nitrous Oxide in the Gas Phase

Cobalt ions solvated in nanoscale water droplets in the phase provides the media for the investigation of the chemistry of cobalt metal in rarely occurred +1 oxidation state. The successive hydration of Co⁺ in water clusters and the redox reaction of Co⁺(H₂O)_n with N₂O have been studied theoretically using M06/DFT methods with 6-311++g(d,p) basis set. The 3d⁸-electron configuration allow Co⁺ to possess different electronic states, with the triplet state being over 100 kJ/mol lower-lying than the singlet and quintet states for all cluster sizes studied (n ≤ 12). The core structure and coordination number for the ground state hydrated cobalt complexes, Co⁺(H₂O)_n (n = 2–12), have been examined. We observed that the monovalent Co⁺ is directly bound with four water molecules for cluster sizes n = 4 – 9. However, for larger clusters, n = 10–12, the lowest energy isomer has six coordinated structure and the remaining water molecules occupied the second solvation shell, which forms two or more hydrogen bonds with the first solvation shell. N₂O can react with the Co⁺ center either through N- or O-coordination, forming ONNCo⁺(H₂O)_n or NNOCo⁺(H₂O)_n, respectively. The former is preferentially formed for clusters containing up to eight water, while the latter formed larger n. In agreement with a previous experimental result, we found that the redox reaction between Co⁺(H₂O)_n and N₂O followed by the formation of [CoOH]⁺(H₂O)_n and [CoO]⁺(H₂O)_n is size dependent and the reaction takes place in the cobalt water clusters containing at least five water molecules.