A highly porous metal-organic framework: structural transformations of a guest-free MOF depending on activation method and temperature.

A doubly interpenetrating porous metal-organic framework (SNU-77) has been synthesized from the solvothermal reaction of the extended carboxylic acid tris(4'-carboxybiphenyl)amine (H(3)TCBPA) and Zn(NO(3))(2)⋅6H(2)O in N,N-dimethylacetamide (DMA). SNU-77 undergoes single-crystal-to-single-crystal transformations during various activation processes, such as room-temperature evacuation, supercritical CO(2) drying, and high temperature evacuation, to afford SNU-77R, SNU-77S, and SNU-77H, respectively. These guest-free MOFs exhibited different fine structures with different window shapes and different effective window sizes at room temperature. Variable-temperature synchrotron single-crystal X-ray analyses reveal that the guest-free structure is also affected by changes in temperature. Despite the different fine structures, SNU-77R, SNU-77S, and SNU-77H show similar gas sorption properties due to the nonbreathing nature of the framework and an additional structural change upon cooling to cryogenic gas sorption temperature. SNU-77H exhibits a large surface area (BET, 3670 m(2) g(-1)), a large pore volume (1.52 cm(3) g(-1)), and exceptionally high uptake capacities for N(2), H(2), O(2), CO(2), and CH(4) gases.