Researchers have uncovered the atomic-scale geometry of platinum ions with unprecedented precision within metal organic frameworks (MOFs)—a growing class of porous materials that consist of organic ligands and inorganic components. Due to the immense structural diversity and large surface areas of MOFs, often exceeding the size of a professional football field per gram of material, many uses of MOFs have been discovered in purification, separation, capture, and storage of gases, especially hydrogen, carbon dioxide and methane, as well as applications as catalysts and sensors. These uses critically rely on an atomic-level understanding of the environment of metal ions in MOFs’ structures. Detailed characterization of atomic platinum species supported within the pores of MOFs was obtained using nuclear magnetic resonance (NMR) enhanced by what is known as dynamic nuclear polarization (DNP). Nuclear magnetic resonance (NMR) spectroscopy is a researcher’s equivalent to a physician’s MRI. The main challenge of this research is that 195Pt nuclei yield very wide spectral lines (with breadths reaching 10,000 ppm) imposing an insurmountable sensitivity penalty on traditional NMR spectroscopy. The DNP-enhanced ultra-wideline NMR spectra, which were obtained for the first time, uncovered the atomic-scale geometry of platinum ions with precision not previously available by any means. Undoubtedly, DNP-enhanced ultra-wideline NMR spectroscopy will lead to definite characterization of elusive sites in numerous classes of materials.
Schematic of the Pt atom inside the MOF structure, and its corresponding wideline spectrum acquired using DNP NMR
DNP-Enhanced Ultrawideline Solid-State NMR Spectroscopy: Studies of Platinum in Metal-Organic Frameworks