Isotope Effects Reveal the Template Influence on the Crystal Growth of a Metal–Halide Network

Crystallization requires the organization of matter into structures with long-range translational order. However, because crystal growth exhibits non-Arrhenius kinetics, it is not possible to apply classical transition state theory to decipher mechanistic details of the crystallization process. With our recently discovered transition zone theory of crystallization, for the first time, it is possible to extract enthalpic and entropic activation parameters for crystal growth from which chemically/physically meaningful mechanistic information is obtained. Here, we measured the respective temperature-dependent crystal growth rates for d0, d1, d9, and d10 isotopomers of the halozeotype CZX-1 to explore how the templating cation impacts the rate of crystal growth. The isotopic dependence of the Kauzmann temperature, T K, and the enthalpic and entropic activation parameters reveal that the mechanism of crystal growth is controlled by both inertial (mass) effects of the template and hydrogen bonding between the template and the metal–halide network. In addition to revealing the role of template–framework interactions for crystal growth of the specific CZX-1 material, this detailed isotope effect study provides an experimental and theoretical framework with which to evaluate details of other condensed-matter reactions.