Mixed-Metal Zeolitic Imidazolate Frameworks and their Selective Capture of Wet Carbon Dioxide over Methane

A presynthesized,
square planar copper imidazole complex, [Cu­(imidazole)4]­(NO3)2, was utilized as a precursor in the
synthesis of a new series of zeolitic imidazolate frameworks, termed
ZIF-202, -203, and -204. The structures of all three members were
solved by single-crystal X-ray diffraction analysis, which revealed
ZIF-203 and -204 having successfully integrated square planar units
within the backbones of their respective frameworks. As a result of
this unit, the structures of both ZIF-203 and -204 were found to adopt
unprecedented three-dimensional nets, namely, ntn and thl, respectively. One member of this series, ZIF-204, was
demonstrated to be highly porous, exhibit exceptional stability in
water, and selectively capture CO2 over CH4 under
both dry and wet conditions without any loss in performance over three
cycles. Remarkably, the regeneration of ZIF-204 was performed under
the mild conditions of flowing a pure N2 gas through the
material at ambient temperature.