Current nucleation models propose manifold options for the formation of crystalline materials. Exploring and distinguishing between different crystallization pathways on the molecular level however remain a challenge, especially for complex porous materials. These usually consist of large unit cells with an ordered framework and pore components and often nucleate in complex, multiphasic synthesis media, restricting in-depth characterization. This work shows how aluminosilicate speciation during crystallization can be documented in detail in monophasic hydrated silicate ionic liquids (HSILs). The observations reveal that zeolites can form via supramolecular organization of ion-paired prenucleation clusters, consisting of aluminosilicate anions, ion-paired to alkali cations, and imply that zeolite crystallization from HSILs can be described within the spectrum of modern nucleation theory.

A guideline for zeolite phase selection in inorganic synthesis media is proposed, based on a systematic exploration of synthesis from inorganic media using liquid Na+, K+, and Cs+ aluminosilicate. Although the Si/Al ratio of the zeolites is a continuous function of the synthesis conditions, boundaries between topologies are sharp. The here-derived phase selection criterion relates the obtained zeolite topology to the Si/Al ratio imposed by the synthesis medium. For a given Si/Al ratio, the framework with the highest occupation of topologically available cation sites is favored. The large number of published zeolite syntheses supporting the observation provides strong indication that the concept is applicable in a larger context. The proposed criterion explains how minor variations in the composition of inorganic synthesis media induce the commonly occurring, abrupt changes in topology. It highlights underlying reasons causing the strict demarcation of stability fields of the as-synthesized zeolites experimentally observed in inorganic synthesis.