David Keen

Abstract:

The field of metal–organic frameworks (MOFs) has rapidly evolved from disconnected examples of multi-dimensional coordination polymers into an expansive collection of functional materials containing over 100,000 structures. Because any material’s chemical structure dictates its function, a robust structural understanding is a crucial prerequisite for the optimization of a material’s physical properties and its effective deployment towards an application. This is especially true for MOFs, which frequently demonstrate multiple possible structures from a single metal-ligand combination. Without proper identification, these phase distributions confuse analysis and hinder applicability of the material(s). Conversely, when well-understood, phase multiplicity serves to increase the number of available structures (and functions) within an established chemical window. Thus, control over phase distributions in MOF systems is a critical aspect of their analysis and utility.In this work, a luminescent ligand based on the tetraphenylethene (TPE) molecule is used as a foundation to generate three distinct MOF systems, which are analyzed for their essential structures and functional properties. All three TPE-based systems are found to demonstrate various degrees of phase multiplicity; while some distributions depend solely on the initial synthetic conditions to generate distinct framework isomers, others undergo dynamic and reversible phase transformations according to their post-synthetic treatments. These structural aspects are characterized in detail, and mechanistic explanations are presented that can be applied to broad design principles towards phase-controlled MOF systems

Abstract:

Methylammonium lead iodide crystallises in three phases. The high-temperature phase is cubic with a high degree of orientational disorder of the molecular ions. The intermediate phase shows progressive alignment of the molecules, but still with disorder.

Abstract:

Abstract The topology of amorphous materials can be affected by mechanical forces during compression or milling, which can induce material densification. Here, we show that densified amorphous silica (SiO2) fabricated by cold compression of siliceous zeolite (SZ) is permanently densified, unlike densified glassy SiO2 (GS) fabricated by cold compression although the X-ray diffraction data and density of the former are identical to those of the latter. Moreover, the topology of the densified amorphous SiO2 fabricated from SZ retains that of crystalline SZ, whereas the densified GS relaxes to pristine GS after thermal annealing. These results indicate that it is possible to design new functional amorphous materials by tuning the topology of the initial zeolitic crystalline phases