Solvent-free powder synthesis and MOF-CVD thin films of the large-pore metal-organic framework MAF-6

A simple solvent- and catalyst-free method is presented for the synthesis of the large-pore metal-organic framework (MOF) MAF-6 (RHO-Zn(eIm)(2)) based on the reaction of ZnO with 2-ethylimidazole vapor at temperatures <= 100 degrees C. By translating this method to a chemical vapor deposition (CVD) protocol, crystalline films of a large-pore material could be deposited for the first time entirely from the vapor phase. A combination of positron annihilation lifetime spectroscopy (PALS) and Kr physisorption measurements confirmed the porosity of these MOF-CVD films and the size of the MAF-6 supercages (diameter similar to 2 nm), in close agreement with powder data and calculations. MAF-6 powders and films were further characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), pair distribution function (PDF), and extended X-ray absorption fine structure (EXAFS). The exceptional uptake capacity of MAF-6 in comparison to ZIF-8 is demonstrated by vapor-phase loading of a molecule larger than the ZIF-8 windows.