Insight and control of the crystal growth of zeolitic imidazolate framework ZIF-67 by atomic force microscopy and mass spectrometry

Combination of electrospray ionization mass spectrometry (ESI-MS) and in situ atomic force microscopy (AFM) are applied to provide the first nanoscopic study of the crystal growth of zeolitic imidazolate framework ZIF-67. ZIF-67 is found to form through a process of nucleation and spreading of metastable unenclosed substeps to form stable surface steps of the enclosed framework structure and demonstrates that isostructural MOFs, ZIF-67 and ZIF-8, undergo identical crystal growth mechanisms. The information on the crystal growth species obtained from the AFM experiments correlates well with the solution species identified by ESI-MS indicating that the species involved in the growth under low supersaturation conditions are methylimidazole/methylimidazolate, monomeric nonmethylimidazole/methylimidazolate complexed Co2+ ions and monomeric complexed [Co(methylimidazole/methylimidazolate)1-2] ions. Combination of the use of low supersaturation growth solutions and in situ AFM has also allowed the successful ext...