A Porous 4-Fold-Interpenetrated Chiral Framework Exhibiting Vapochromism, Single-Crystal-to-Single-Crystal Solvent Exchange, Gas Sorption, and a Poisoning Effect

The synthesis and characterization of a 4-fold-interpenetrated pseudodiamond metal-organic framework (MOF), Co-II(pybz)(2)center dot 2DMF [pybz = 4-(4-pyridyl)benzoate], are reported. N,N-Dimethylformamide (DMF) of the channels can be removed to give the porous framework, and it can also be exchanged for methanol, ethanol, benzene, and cyclohexane. It is a rare example of a stable MOF based on a single octahedral building unit. The single-crystal structures of Co-II(pybz)(2)center dot 2DMF, Co-II(pybz)(2), Co-II(pybz)(2)center dot 4MeOH, and Co-II(pybz)(2)center dot 2.5EtOH have been successfully determined. In all of them, the framework is marginally modified and contains a highly distorted and strained octahedral node of cobalt with two pyridine nitrogen atoms and two chelate carboxylate groups. In air, the crystals of Co-II(pybz)(2)center dot 2DMF readily change color from claret red to light pink. Thermogravimetric analysis and Raman spectroscopy indicate a change in coordination, where the carboxylate becomes monodentate and an additional two water molecules are coordinated to each cobalt atom. In a dry solvent, this transformation does not take place. Tests show that Co-II(pybz)(2) may be a more efficient drying agent than silica gel and anhydrous CuSO4. The desolvated Co-II(pybz)(2) can absorb several gases such as CO2, N-2, H-2, and CH4 and also vapors of methanol, ethanol, benzene, and cyclohexane. If Co-II(pybz)(2) is exposed to air and followed by reactivation, its sorption capacity is considerably reduced, which we associate with a poisoning effect. Because of the long distance between the cobalt atoms in the structure, the magnetic properties are those of a paramagnet.