Methane functionalization by an Ir(III) catalyst supported on a metal–organic framework: an alternative explanation of steric confinement effects

Metal-Organic Frameworks for Greenhouse Gas Applications

Using petrol to supply energy for a car or burning coal to heat a building generates plenty of greenhouse gas (GHG) emissions, including carbon dioxide (CO₂ ), water vapor (H₂ O), methane (CH₄ ), nitrous oxide (N₂ O), ozone (O₃ ), fluorinated gases. These up-and-coming metal-organic frameworks (MOFs) are structurally endowed with rigid inorganic nodes and versatile organic linkers, which have been extensively used in the GHG-related applications to improve the lives and protect the environment. Porous MOF materials and their derivatives have been demonstrated to be competitive and promising candidates for GHG separation, storage and conversions as they shows facile preparation, large porosity, adjustable nanostructure, abundant topology, and tunable physicochemical property. Enormous progress has been made in GHG storage and separation intrinsically stemmed from the different interaction between guest molecule and host framework from MOF itself in the recent five years. Meanwhile, the use of porous MOF materials to transform GHG and the influence of external conditions on the adsorption performance of MOFs for GHG are also enclosed. In this review, it is also highlighted that the existing challenges and future directions are discussed and envisioned in the rational design, facile synthesis and comprehensive utilization of MOFs and their derivatives for practical applications.

Importance of Lattice Constants in QM/MM Calculations on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are crystalline materials with novel physical and chemical properties. Computational simulations have become powerful complements to experiment for understanding catalysis in MOFs and developing new MOFs and their applications. However, due to their relatively large and complex structures, MOFs can be burdensome for fully quantum mechanical calculations. A combined quantum mechanical and molecular mechanical (QM/MM) method that combines the accuracy of fully quantum mechanical methods and the efficiency of MM methods is therefore attractive. In this study, we employ a QM/MM method for the study of two classes of chemical process in a MOF: the conversion of reaction intermediates in an Ir-containing borylation catalyst supported on MOF UiO-67 and the diffusion of a diborylated methane molecule in the pristine UiO-67 framework. We compare the QM/MM results with full-quantum mechanical results on large systems to validate the accuracy of the applied QM/MM method. In the first case, we consider a model of the entire system by partitioning it into subsystems that interact covalently, and in the second case the subsystem interaction is mainly steric. We observe that the QM/MM results agree with the full-quantum mechanical results within an average of 4 kcal/mol in the first case with strong electronic interactions and within an average of 3 kcal/mol in the case with only noncovalent interactions. An important lesson learned from the present study is that the quantitative results are very sensitive to the lattice constants predicted by the MM method used in the QM/MM calculations.

Electronic Structure Modeling of Metal-Organic Frameworks

Owing to their molecular building blocks, yet highly crystalline nature, metal-organic frameworks (MOFs) sit at the interface between molecule and material. Their diverse structures and compositions enable them to be useful materials as catalysts in heterogeneous reactions, electrical conductors in energy storage and transfer applications, chromophores in photoenabled chemical transformations, and beyond. In all cases, density functional theory (DFT) and higher-level methods for electronic structure determination provide valuable quantitative information about the electronic properties that underpin the functions of these frameworks. However, there are only two general modeling approaches in conventional electronic structure software packages: those that treat materials as extended, periodic solids, and those that treat materials as discrete molecules. Each approach has features and benefits; both have been widely employed to understand the emergent chemistry that arises from the formation of the metal-organic interface. This Review canvases these approaches to date, with emphasis placed on the application of electronic structure theory to explore reactivity and electron transfer using periodic, molecular, and embedded models. This includes (i) computational chemistry considerations such as how functional, k-grid, and other model variables are selected to enable insights into MOF properties, (ii) extended solid models that treat MOFs as materials rather than molecules, (iii) the mechanics of cluster extraction and subsequent chemistry enabled by these molecular models, (iv) catalytic studies using both solids and clusters thereof, and (v) embedded, mixed-method approaches, which simulate a fraction of the material using one level of theory and the remainder of the material using another dissimilar theoretical implementation.