Spectroscopic Identification of a Bidentate Binding Motif in the Anionic Magnesium-CO2 Complex ([ClMgCO2]−)

A magnesium complex incorporating a novel metal–CO2 binding motif is spectroscopically identified. Here we show with the help of infrared photodissociation spectroscopy that the complex exists solely in the [ClMg(η2‐O2C)]− form. This bidentate double oxygen metal–CO2 coordination has previously not been observed in neutral nor in charged unimetallic complexes. The antisymmetric CO2 stretching mode in [ClMg(η2‐O2C)]− is found at 1128 cm−1, which is considerably redshifted from the corresponding mode in bare CO2 at 2349 cm−1, suggesting that the CO2 moiety has a considerable negative charge (∼1.8 e−). We also employed electronic structure calculations and kinetic analysis to support the interpretation of the experimental results. Bidentate coordination of CO2: An anionic complex of MgCl− and CO2, [ClMgCO2]−, is formed upon electrospray ionization followed by collision‐induced dissociation. With the help of infrared photodissociation spectroscopy it is shown that the complex exists solely in the double oxygen‐bound [ClMg(η2‐O2C)]− form, a type of CO2 coordination not previously seen in unimetallic complexes.