Exploitingin situNMR to monitor the formation of a metal-organic framework

Abstract

The formation processes of metal-organic frameworks are becoming more widely researched usingin situtechniques, although there remains a scarcity of NMR studies in this field. In this work, the synthesis of framework MFM-500(Ni) has been investigated using anin situNMR strategy that provides information on the time-evolution of the reaction and crystallization process. In ourin situNMR study of MFM-500(Ni) formation, liquid-phase1H NMR data recorded as a function of time at fixed temperatures (between 60 and 100 °C) afford qualitative information on the solution-phase processes and quantitative information on the kinetics of crystallization, allowing the activation energies for nucleation (61.4 ± 9.7 kJ mol−1) and growth (72.9 ± 8.6 kJ mol−1) to be determined.Ex situsmall-angle X-ray scattering studies (at 80 °C) provide complementary nanoscale information on the rapid self-assembly prior to MOF crystallization andin situpowder X-ray diffraction confirms that the only crystalline phase present during the reaction (at 90 °C) is phase-pure MFM-500(Ni). This work demonstrates thatin situNMR experiments can shed new light on MOF synthesis, opening up the technique to provide better understanding of how MOFs are formed.