Toward Understanding the Thermodynamic Viability of Zeolites and Related Frameworks through a Simple Topological Model

Framework materials (e.g., zeolites, metallophosphates, chalcogenides, and metal organic frameworks) are widely used as catalysts, adsorbents, and ion exchangers. Although many different frameworks have been synthesized (or found in nature), numerous applications still call for frameworks with larger pores, lower framework densities, and/or higher specific absorption volumes than currently available. Thus, research into synthesizing novel framework materials with one or more of the desired properties has been extensively pursued in recent years, often however with no prior knowledge regarding their synthetic viability. In this study, we show how the decomposition of an archetypal class of framework materials (zeolites) into polyhedral tiles and the analysis of the face-size distribution obtained (using topological descriptors and periodic atomistic calculations on both synthesized and hypothetical frameworks) can lead to definite predictions regarding the thermodynamic viability of their synthesis. Moreover, it is demonstrated that pore size and framework density cannot be varied freely, but that they, at least for frameworks corresponding to simple tilings, are intimately connected to the thermodynamic viability of the framework's synthesis through its topology. These new insights allow us not only to rationalize the thermodynamic viability of a range of desirable (but as yet unmade) frameworks but also to begin to understand the physical and topological boundaries which inherently limit attempts to synthesize frameworks with ever-larger pores and lower framework densities. Although the methodology is validated for all-silica frameworks, the mode of investigation, due to its generality and nonreliance on specific geometric/chemical details, should be applicable to framework materials in general.