Determination of the Preassembled Nucleating Units That Are Critical for the Crystal Growth of the Metal-Organic Framework CdIF-4

Identifying the form and role of the chemical species that traverse the stages of crystallization is critical to understanding the formation process of coordination polymers. Herein, we report the combined use of in situ atomic force microscopy and mass spectrometry to identify preformed, complex, cadmium 2-ethylimidazole containing solution species in the growth solution of the cadmium 2-ethylimidazolate metal–organic framework CdIF-4, and show that they are critical in the surface nucleation for the crystal growth of this material. Surface nucleation appears to be instigated by these [Cd_x(CH₃CO₂)_y(C₅H₇N₂/C₅H₈N₂)_z]-containing solution species and not by sole addition of the ligand molecules. The CH₃CO₂⁻ or Cd(CH₃CO₂)₂ groups of the former are substituted subsequently as the framework growth proceeds. Our greater understanding of such solution species and their role in crystallization will guide future syntheses of designed functional coordination polymers.