Examination of the microstructure of metal-organic frameworks (MOFs) after postsynthetic exchange (PSE) reveals that the exchanged ligand is concentrated at the edges of the crystal and decreases in concentration with crystal depth, resulting in a core-shell arrangement. Diffusion studies of the carboxylate ligand into MOF-5 indicate that diffusion is limiting to the exchange process and may ultimately be responsible for the observed core-shell structure. Examination of PSE in UMCM-8 and single crystals of UiO-66 shows a similar trend, illustrating the applicability of PSE as a method for the creation of core-shell MOFs.

Metal-organic frameworks (MOFs) are being increasingly studied as scaffolds and supports for catalysis. The solid-state structures of MOFs, combined with their high porosity, suggest that MOFs may possess advantages shared by both heterogeneous and homogeneous catalysts, with few of the shortcomings of either. Herein, efforts to create single-site catalytic metal centers appended to the organic ligand struts of MOFs will be discussed. Reactions important for advanced energy applications, such as H2 production and CO2 reduction, will be highlighted. Examining how these active sites can be introduced, their performance, and their existing limitations should provide direction for design of the next generation of MOF-based catalysts for energy-relevant, small-molecule transformations. Finally, the introduction of second-sphere interactions (e.g., hydrogen bonding via squaramide groups) as a possible route to enhancing the activity of these metal centers is reported.

Metal-organic frameworks (MOFs) are crystalline, hybrid materials that consist of inorganic connecting nodes and organic linker molecules. MOFs are attractive materials for applications in gas adsorption, [1] separations, [2] catalysis, [3] and other technologies [4] because of their high porosity, thermal stability, and chemical tunability. The ability to utilize different organic ligands in MOFs is particularly advantageous, as it allows for the introduction of a wider variety of functional groups into the pores of the MOF when compared to other porous, crystalline solids. The use of postsynthetic modification (PSM) has provided broader access to functional groups within MOFs. [5,6] Both solvothermal and PSM routes have demonstrated that multifunctional or "multivariate" MOFs can be prepared, with more than one functional group displayed within the MOF pores. [7][8][9][10][11][12][13] In these multifunctional MOF materials, the relative abundance of different ligands (and hence different functional groups) can be controlled, but not the distribution nor spatial orientation of the functional groups with respect to each other. To truly achieve the next level of tailored, multi-purpose materials, [14] control over the relative position of different functional groups would be required. Herein, we describe the first class of bifunctional MOF "ligand regioisomers" and show that even these subtle changes can result in materials with dramatically different physical properties.Recently, framework isomers of MOFs have been classified into three major groups: interpenetrated, conformational, and orientation isomers-which all describe different structures comprised of the same ligand and metal ion composition.[15] These isomers tend to have different properties from each other, albeit sometimes minor. MOFs derived from different ligands are referred to as "ligand-originated isomers". Although many different ligands have been investigated for MOF formation, we are unaware of any systematic studies of ligand-originated isomers that arise from differences is regiochemical isomerism in a multifunctional ligand. In the studies presented here, the first MOF regioisomers are described and it is found that these regioisomers manifest themselves as distinct conformational isomers with notably different physical properties. Furthermore, these studies are the first to control the position of targeted functional groups in a porous, crystalline material.We chose a previously unreported class of bifunctional amino-halo benzene dicarboxylates (NH 2 X-BDC, where X = Cl, Br, or I) as the building blocks for MOF regioisomers. Independently, amino and halide groups are well-known in MOFs, [5,16] and PSM routes for both amino and halide groups have been reported, [13] leaving open the possibility of PSM on MOF regioisomers. The target ligands were synthesized by halogenation of dimethyl-2-amino terephthalate (1) using Nhalosuccinimides (NCS, N-chlorosuccinimide; NBS, N-bromosuccinimide; NIS, N-iodosuccinimide; Table 1 and Scheme S1 in the Sup...

Herein, we utilize a new, squaramide-based ligand, combined with a postsynthetic exchange (PSE) synthetic approach to prepare a series of Cu(ii)-squaramide MOFs that are active catalysts for the Friedel-Crafts reaction.