CO Binding at a Four-Coordinate Cobaltous Porphyrin Site in a Metal-Organic Framework: Structural, EPR, and Gas Adsorption Analysis

The variable-temperature CO binding at a four coordinate cobaltous porphyrin complex within a metal organic framework is investigated using a combined array of infrared, X-ray diffraction, EPR, and CO adsorption analysis. Single-crystal X-ray diffraction experiments provide the first crystallographically characterized example of a noniron first row transition metal porphyrin carbonyl adduct. Variable temperature electron paramagnetic resonance spectroscopy supports the structural observation and reveals conversion of the dicarbonyl complex to a monocarbonyl species as temperature is increased. Finally, CO adsorption analysis data enable quantification of the Co-CO interaction, providing a binding enthalpy of h(ads) = 29(2) kJ/mol. This value is nearly twice that observed for 0(2) binding in the same compound and is attributed to a stronger a interaction for Co and CO vs 0(2): These results demonstrate the ability of MOFs to enable a thorough investigation of CO binding in metalloporphyrins.