Insight into Fast Nucleation and Growth of Zeolitic Imidazolate Framework-71 by In Situ Static Light Scattering at Variable Temperature and Kinetic Modeling

Zeolitic imidazolate frameworks (ZIFs) represent an important subclass of porous metal organic frameworks (MOFs). The present work continues a previous study on ZIF-71 nanocrystal formation at room temperature (<i>Cryst. Growth Des.</i> <b>2016</b>, 16, 2002–2010), which proposed a four-step formation process. It introduces a kinetic nucleation and growth model, which satisfactorily reproduces in situ time-resolved static light scattering data measured at room temperature in the previous work and at variable temperatures in the present work. Successful fitting can only be achieved with a precursor reaction being put before particle nucleation. The kinetic analysis provides rate constants for the precursor reaction, for particle nucleation, and for particle growth via monomer addition, and the equilibrium concentration of nonconsumed matter at the end of reaction. The rate constants of the precursor reaction and the nucleation process increase with temperature, which is counterintuitive if compared to classical nucleation theory as it suggests a decrease of the nucleation rate with temperature. In fact, ZIF-71 formation deviates from classical nucleation in that a precursor reaction to produce active “monomers” precedes the formation of amorphous particles that subsequently transform into the crystalline ZIF phase