Orientational Order of Linkers Controls ZIF-8 Crystallization.

Zeolitic imidazolate framework-8 (ZIF-8) crystallizes through an amorphous intermediate, but the molecular events that trigger nucleation within this disordered phase have remained elusive. Here we introduce a dynamic-binding, implicit-solvent force field for the ionic building units of ZIF-8 that enables unbiased microsecond-scale molecular dynamics of the full crystallization pathway─from solvated monomers to a 10 nm ZIF-8 nanocrystal. Our simulations reproduce the experimentally observed multistep pathway: monomers and oligomers phase-separate into a solute-rich amorphous network with liquid-like dynamics, lower density, and predominantly three-coordinated Zn. Whereas crystalline ZIF-8 is defined by sterically constrained, near-tetrahedral Zn(mIm)4 nodes, the amorphous network sustains a broad distribution of coordination environments and linker orientations. Nucleation occurs within this disordered phase through collective rearrangements that anneal misconfigured Zn(mIm)4 nodes and couple linker rotational fluctuations to topological reorganization, locking in the four-connected framework. Crystal growth proceeds by the same defect-annealing mechanism. These results identify linker configurational dynamics as key for ZIF-8 nucleation, and provide a molecular foundation for understanding multistep MOF crystallization.