Developing rapid room-temperature
synthesis is key to sustainable
manufacturing of metal–organic frameworks (MOFs). Using layered
compounds such as hydroxy double salts (HDSs) as precursors significantly
promotes the reaction kinetics and lowers the required synthesis temperature.
However, limited understanding of the reaction mechanism impedes the
further exploration of new routes for MOF synthesis. Here, we report
for the first time the use of combined in-situ synchrotron X-ray diffraction
and X-ray absorption spectroscopy to monitor the dynamic processes
to form MOFs in solution. The conversion from a (Zn,Co) HDS to a mixed-metal
zeolitic imidazolate framework-8 (mmZIF-8) was chosen as our model
reaction. Time-resolved diffraction patterns exclude the presence
of intercalated HDS structures with altered d-spacing
and any other crystalline intermediate phase during the synthesis.
The activation energies of nucleation and growth were found as 25.5
± 2.5 and 64.0 ± 7.9 kJ·mol–1, respectively.
In addition, we captured the evolution of local structures from mixed
coordination states in the HDS to tetrahedral coordination in the
mmZIF-8. Furthermore, two possible reaction pathways were proposed
to account for the fast conversion from HDS to mmZIF-8. The fundamental
understanding towards the HDS-based synthesis obtained in this work
is expected to guide future development of new fabrication methods
for MOF materials.