Gas Sorption Properties of Isostructural Co-MOFs Containing Dipyridylporphyrin Linkers with Different Substituents at the 10,20-meso-Positions

Two new isostructural 3D dipyridylporphyrin‐based MOFs, [Co(DpyDClP)]6·18H2O (I) and [Co(DpyDCNP)]6·18H2O (II), were prepared and structurally characterized by X‐ray crystallography [DpyDClP: 5,15‐di(4‐pyridyl)‐10,20‐di(4‐chlorophenyl)porphyrin; DpyDCNP: 5,15‐di(4‐pyridyl)‐10,20‐di(4‐cyanophenyl)porphyrin]. They display exactly the same framework structures, notwithstanding different substituents at the 10,20‐meso‐positions of the dipyridylporphyrin backbones. Both substituents, –Cl for I and –CN for II, are completely exposed to the open space of solvent‐free I and II. Therefore, the two MOFs have the same framework structures with distinct pore functionalities. Solvent‐free I and II have solvent‐accessible void volumes of 17.3 and 14.9 %, respectively. The thermal properties of I and II are very similar, but the gas sorption properties strongly depend on the pore dimensions and functionalities. Compound I has a higher uptake of CO2 compared with that of II due to its larger void volume. Particularly, CO2 sorption isotherms at 196 K indicate dramatically different patterns depending on the meso‐substituents. Whereas I shows S‐shape isotherms for CO2 adsorption/desorption at 196 K, II does not. The sorption of N2, H2, and CH4 by the two MOFs was also investigated. Two new isostructural 3D Co–porphyrin MOFs, [Co(L)]6·18H2O (L = DpyDClP and DpyDCNP), possess well‐defined hexagonally arranged micropores, and the pore dimensions and functionalities inside the micropores can be varied systematically.