Thermal Reactivity in Metal Organic Materials (MOMs): From Single-Crystal-to-Single-Crystal Reactions and Beyond

Abstract

Thermal treatment is important in the solid-state chemistry of metal organic materials (MOMs) because it can create unexpected new structures with unique properties and applications that otherwise in the solution state are very difficult or impossible to achieve. Additionally, high-temperature solid-state reactivity provide insights to better understand chemical processes taking place in the solid-state. This review article describes relevant thermally induced solid-state reactions in metal organic materials, which include metal organic frameworks (MOFs)/coordination polymers (CPs), and second coordination sphere adducts (SSCs). High temperature solid-state reactivity can occur in a single-crystal-to-single crystal manner (SCSC) usually for cases where there is small atomic motion, allowing full structural characterization by single crystal X-ray diffraction (SC-XRD) analysis. However, for the cases in which the structural transformations are severe, often the crystallinity of the metal-organic material is damaged, and this happens in a crystal-to-polycrystalline manner. For such cases, in the absence of suitable single crystals, structural characterization has to be carried out using ab initio powder X-ray diffraction analysis or pair distribution function (PDF) analysis when the product is amorphous. In this article, relevant thermally induced SCSC reactions and crystal-to-polycrystalline reactions in MOMs that involve significant structural transformations as a result of the molecular/atomic motion are described. Thermal reactivity focusing on cleavage and formation of coordination and covalent bonds, crystalline-to-amorphous-to-crystalline transformations, host–guest behavior and dehydrochlorination reactions in MOFs and SSCs will be discussed.

A Merry Dance Across the π-Cloud: Tracking the Transformation of a 2,7-Substituted Dihydropyrene Through a Thermally Stimulated Single-Crystal-to-Single-Crystal Reaction

“…While SC-SC transformations in a range of materials are known, the one we have observed in a crystal of 8 appears to be unique. The topological postulate states that “reactions in crystals occur with minimum atomic and molecular motion.” In essence, the reactants, transition states, and products “must fit within a reaction cavity formed by their close packed nearest neighbors.” Some seminal observations include the observation of photochemical [2 + 2] cycloadditions in the crystalline form, − phase transitions − within the pores of metal–organic frameworks (MOFs) used as catalyst supports, − and the reorganization of bonds within MOFs. , There are also extant examples where molecular crystals react with external reagents such as oxygen and other small molecules . The structural origin of the SC-SC transformation was examined by in situ variable-temperature single-crystal X-ray diffraction.…”

Kinetic Trapping of 2,4,6-Tris(4-pyridyl)benzene and ZnI 2 into M 12 L 8 poly-[n]-catenanes using unconventional self-assembling processes

“…Another important aspect is that kinetic products tend to be dynamic and hence can perform guest exchange/inclusion reactions, but also can undergo further transformations towards more stable structures upon external stimuli (i.e., upon heating) following crystal-to-amorphous-to-crystal transformations. 33 Thus, the crystallization process has a direct effect on the nal structure formed and is therefore very important to gain control. The ability to direct at will the product formed in a chemical reaction has a crucial role both in the chemical synthesis and material sciences.…”

ZIF-L to ZIF-8 Transformation: Morphology and Structure Controls

“…As stated previously, ZIF-L is metastable due to the existence of unterminated coordination bonds. Thus, it can be used as a starting material for synthesizing a ZIF-8 that has a similar structure ( Figure 1 a) via ZIF-L-to-ZIF-8 transformation [ 17 ]. Here, leaf-shaped ZIF-L particles ( Figure 1 b) were exposed to a 333K pure solvent containing a 2:1 ( v / v ) DMAc/H 2 O mixture.…”

“…Numerous investigations have attempted to regulate the morphology of MOFs by tuning the synthesis condition. (e.g., However, there is no technique that can be broadly applied to metal-organic frameworks, and there is a fundamental lack of understanding of inclusion of additives [ 3 ], pH control [ 16 ], and synthesis solvent control [ 17 ]). how to stimulate the formation of crystals with a target shape.…”