Investigations of the temperature‐dependent electron paramagnetic resonance spectra and local structures for a cobalt(II) porphyrin complex within a metal–organic framework.

The interaction between an adsorbed CO molecule and the unsaturated coordinated Co2+ center in the metal–organic framework (MOF) PCN‐224 is investigated by analyzing the electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) and the adsorption energies at various temperatures. Six‐ and five‐coordinated octahedral models (four planar N with two and one axial CO molecules, respectively) are constructed to simulate the local structures of the Co2+ centers at different temperatures. Because of the Jahn–Teller effect of the Co2+ centers, the C2–Co–N4 and C–Co–N4 combinations undergo different tetragonal elongation distortions along the C4 axis, characterized by the relative elongation ΔZ and displacement ΔZ′ of Co2+ at different temperatures. Given the agreement between the calculated and experimental EPR parameters, as well as the adsorption properties, the six‐ and five‐coordinated models are regarded as suitable for low‐ and high‐temperature systems, respectively. These studies may be helpful to understand the properties of similar MOFs with adsorbed molecules under the effect of ambient temperature. [ABSTRACT FROM AUTHOR]