Orientational Order of Linkers Controls ZIF-8 Crystallization

Zeolitic imidazolate framework-8 (ZIF-8) crystallizes through an amorphous intermediate, but the molecular events that triggers 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.