Relaxation Time Correlation NMR for Mechanochemical in-situ Reaction Monitoring of Metal-Organic Frameworks

We present a new methodology for real-time observation of mechanochemical transformations, based on a magnetic resonance method in which T1-T2* relaxation time correlation maps are used to track the formation of the popular metal-organic framework (MOF) materials Zn-MOF-74 and ZIF-8. This two-dimensional (2D) relaxation correlation measurement is a new method utilizing simple saturation recovery to obtain a T1-T2* spectrum representing different hydrogen environments. The 2D T1-T2* results show a change in signal amplitudes, and their coordinates, within the plots as the reaction progresses, confirming reaction completion. Static solid samples are usually considered difficult to measure because of their short-lived T2* signal and their common non-exponential decay. Using a new processing method, the signal from samples with non-exponential decay was quantified. The importance of key parameters such as the instrument deadtime, the recovery times, and magnetic field strength for the measurement of solids with a short-lived signal is established. This novel magnetic resonance measurement is important since it provides a simple and easy way to analyse an entire solid reaction mixture within its reaction vessel.