Metal-Dependent Adsorption Mechanism in Perfluorinated MIL-140A Metal–Organic Frameworks

Perfluorinated metal–organic frameworks (MOFs) with MIL-140A topology display metal-dependent adsorption behavior: while the CeIV analogue [F4_MIL-140A(Ce)] exhibits step-shaped CO2 adsorption isotherms and strong affinity for H2O, both associated with a concerted structural rearrangement of the linkers, the ZrIV counterpart [F4_MIL-140A(Zr)] shows a classical type I CO2 isotherm with a lower adsorption capacity and only weak affinity for H2O. A multitechnique approach, including solid-state nuclear magnetic resonance spectroscopy, in situ infrared spectroscopy, and variable temperature powder X-ray diffraction, provided clear evidence that this contrasting behavior arises from the absence of an open metal site on ZrIV and the inability of ZrIV to adopt an octacoordinated geometry, which prevent the establishment of strong metal-guest interactions.