Carbon Dioxide Activation at Metal Centers: Evolution of Charge Transfer from Mg (.+) to CO(2) in [MgCO(2)(H(2)O)(n)](.+), n=0–8

We investigate activation of carbon dioxide by singly charged hydrated magnesium cations Mg (.+)(H(2)O)(n), through infrared multiple photon dissociation (IRMPD) spectroscopy combined with quantum chemical calculations. The spectra of [MgCO(2)(H(2)O)(n)](.+) in the 1250–4000 cm(−1) region show a sharp transition from n=2 to n=3 for the position of the CO(2) antisymmetric stretching mode. This is evidence for the activation of CO(2) via charge transfer from Mg (.+) to CO(2) for n≥3, while smaller clusters feature linear CO(2) coordinated end‐on to the metal center. Starting with n=5, we see a further conformational change, with CO(2) (.−) coordination to Mg(2+) gradually shifting from bidentate to monodentate, consistent with preferential hexa‐coordination of Mg(2+). Our results reveal in detail how hydration promotes CO(2) activation by charge transfer at metal centers.