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.
Highlights
Unlike in the gas phase and in the solution state, reactivity in the solid state is much more limited because molecular/atomic motion is constrained by the 3D arrangement in the crystalline lattice [1].Solid-state reactivity in chemistry is very attractive because the products obtained can be unique since using solution chemistry might result in completely different products
The combination of structural variability, network topology, porosity, coordination bond lability and high temperature in metal organic materials (MOMs) is contributing to the discovery of important structural transformations in MOMs
The availability of single crystals of enough quality to be studied by single crystal XRD after a given thermal process is crucial for understanding the thermal products
Summary
Unlike in the gas phase and in the solution state, reactivity in the solid state is much more limited because molecular/atomic motion is constrained by the 3D arrangement in the crystalline lattice [1]. The observation of the structural transformations induced by heat (i.e., kinetic to thermodynamic products) is very important to understand the reactivity of a given material In such cases, if the thermally induced products can be analyzed by single crystal X-ray diffraction, structure-properties as a function of temperature can be established. To our best knowledge, full structure determination from powder X-ray diffraction data on MOMs describing major structural transformations induced by temperature are still very limited Another scenario that often occurs when thermal reactions are being carried out in MOMs is that in some cases amorphous phases are formed. SCSC published recently, where the interested reader can get an exhaustive description of structural transformations in Organic the solid-state that cover heat as external stimuli [35,36,37,38]
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