Solid-state NMR spectroscopy: An advancing tool to analyse structure and properties of metal-organic frameworks

Metal-organic frameworks (MOFs) find increasing interest due to their outstanding properties like extremely high porosity, structural variability, and various possibilities for functionalization. Their overall structure is usually determined by diffraction techniques. However, diffraction is often not sensitive for subtle local structure changes and ordering effects as well as dynamics and flexibility effects. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy is sensitive for short range interactions and thus complementary to diffraction techniques. Novel methodical advances make ssNMR experiments increasingly suitable to tackle the above mentioned problems and challenges. NMR spectroscopy also allows to study host-guest interactions between the MOF lattice and adsorbed guest species. Understanding the underlying mechanisms and interactions is particularly important with respect to applications such as gas and liquids separation processes, gas storage, and others. Special in-situ NMR experiments allow to investigate properties and functions of MOFs under controlled and application-relevant conditions. The present minireview explains the potential of various solid-state and in-situ NMR techniques and illustrates their application to MOFs by highlighting selected examples from the recent literature.