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The structural characterization of metal-organic frameworks(MOFs) by powder X-ray diffraction can be challenging. Even more difficultare studies of guest solvent or gas molecules inside the MOF pores. Hence, recently we successfully designed several new approaches forstructural investigations of porous MOFs. These methods use structureenvelopes, which can be easily generated from the structure factorsof a few (1-10) of the most intense low index reflections. However, the most interesting results have been found by using differenceenvelope density (DED) analysis. DED can be produced by taking thedifference between observed and calculated structure envelope densities. The generation and analysis of DED maps are straightforward but allowstudying guest molecules in the pores of MOFs by using routine powderX-ray diffraction data. Examples of DED used for studies of solventmolecule location, porosity activation, and gas loading are presentedherein. We show that DED analysis is an important technique in thestudy of host-guest properties in MOFs by providing position, shape, and approximate occupancy of molecules in the MOF pores. [ABSTRACT FROM AUTHOR]

Cocrystallization of 4-nitrophenol(I) with N-methyl substituted aminopyridines,4-N-methylaminopyridine 1, 2-N-methylaminopyridine 2, and 2-N,N-dimethylaminopyridine 3, resultedin three novel adducts 1·2(I), 2·3(I), and 3·3(I), one of which, 2·3(I), wasfound in three polymorphic forms, A, B,and C. The single crystals were grown by slowevaporation from ethanol. The proton transfer from the phenoxy tothe pyridine moieties was registered in all compounds. The adductscomprise pyridinium cations, 4-nitrophenolate anions, and varyingin number neutral 4-nitrophenol molecules. Though the asymmetric hydrogen-bondednetwork involving the −N+H groups of pyridiniumcations and the −C–O–and −C–OHgroups of 4-nitrophenol moieties is registered in the adducts, thedelicate balance of noncovalent interactions that include CH···Ohydrogen bonds and face-to-face stacking interactions between theextended antiparallel arrays of components controls the centrosymmetricpacking. Although three polymorphs of 2·3(I) share several structural common features, they reveal significantdifferences in the conformation of the pyridinium cation, and thehydrogen-bonding patterns. [ABSTRACT FROM AUTHOR]