Layered Porphyrin Coordination Polymers Based on Zinc···Nitro Recognition: Reversible Intercalation of Nitrobenzene

A new coordination synthon, Zn···NO2 recognition, is used in the synthesis of a layered porphyrin coordination polymer
(Zn-5,15-di(4-nitrophenyl)-10,20-di(p-tolyl)-porphyrin, 1-Zn) with 44 topology. This solid is thermally stable and incorporates nitrobenzene
molecules between the layers to form 1-Zn−PhNO2. The Zn···NO2 recognition exists in 1-Zn and 1-Zn−PhNO2; it is formed by coordination
bonding between a Zn2+ ion embedded in a porphyrin core and one of the O-atoms of the nitro group. The structure of 1-Zn−PhNO2 is
also layered and contains 44 networks such as those found in 1-Zn. The two structures, however, differ significantly in several intra- and
interlayer parameters. Despite these differences, removal of nitrobenzene from the crystals of 1-Zn−PhNO2 yields crystalline 1-Zn. When
soaked in nitrobenzene, these desolvated 1-Zn crystals yield crystalline 1-Zn−PhNO2. These reversible solid-to-solid transformations
demonstrate the robustness of Zn···NO2 recognition in holding the 44 networks together in the solid state.