Porous organic cage CC2 and CC3 crystals: nucleation and growth studies

Abstract

Porous organic cages (POCs) represent a novel type of microporous crystals with highly desirable properties, such as uniform micropores, high surface areas, and thermal and chemical stability, making them suitable candidates for diverse functional applications. Their unique structure and distinctive solid state molecular packing differentiate POCs from conventional porous crystals, such as zeolites, metal organic frameworks, and covalent organic frameworks. POCs are made of covalently bonded organic cages that assemble into crystalline microporous materials displaying three-dimensional connectivity and uniform pore size. POCs are typically synthesized via cycloimination reactions. Depending on the amine and trialdehyde employed, distinctive cages can be formed. Due to their regular crystalline structure with unimodal limiting pore sizes, POCs have found applications in the fields of separations, catalysis, adsorption, among others.About a decade has passed since the first report on the successful synthesis of POCs and almost nothing is known about the onset of POC nucleation. Since the events in the early stages of POC formation are pivotal in determining the course of crystallization, a fundamental understanding of these phenomena (nucleation, crystallization, and growth) is highly important in order to improve their structural, textural and morphological properties.In this work, we explore the crystallization and formation of two prototypical porous organic cages, CC3 and CC2. We followed the structural evolution of these crystals as a function of synthesis time and explored new synthetic approaches of these crystals in order to gain a fundamental understanding of how these crystals grow, and how this relates to their structure-function relationship. This research may lead to the use of these intriguing materials in a broader set of applications by providing alternative synthetic routes which can tailor their structural, compositional, morphological, and textural properties.