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Crown ethers and their supramolecular derivatives are well-known chelators and scavengers for a variety of cations, most notably heavier alkali and alkaline-earth ions. Although they are widely used in synthetic chemistry, available crystal structures of uncoordinated and solvent-free crown ethers regularly suffer from disorder. In this study, we present the X-ray crystal structure analysis of well-ordered solvent-free crystals of dibenzo-21-crown-7 (systematic name: dibenzo[ b, k]-1,4,7,10,13,16,19-heptaoxacycloheneicosa-2,11-diene, C22H28O7). Because of the quality of the crystal and diffraction data, we have chosen invarioms, in addition to standard independent spherical atoms, for modelling and briefly discuss the different refinement results. The electrostatic potential, which is directly deducible from the invariom model, and the Hirshfeld surface are analysed and complemented with interaction-energy computations to characterize intermolecular contacts. The boat-like molecules stack along the a axis and are arranged as dimers of chains, which assemble as rows to form a three-dimensional structure. Dispersive C-H...H-C and C-H...π interactions dominate, but nonclassical hydrogen bonds are present and reflect the overall rather weak electrostatic influence. A fingerprint plot of the Hirshfeld surface summarizes and visualizes the intermolecular interactions. The insight gained into the crystal structure of dibenzo-21-crown-7 not only demonstrates the power of invariom refinement, Hirshfeld surface analysis and interaction-energy computation, but also hints at favourable conditions for crystallizing solvent-free crown ethers. [ABSTRACT FROM AUTHOR]

Two new polymorphs of the phase-change material sodium acetate were characterized by single-crystal X-ray diffraction. A tetragonal form was found first. It converted to a orthorhombic form after measurement of a single crystal of the tetragonal form at 100 K and subsequent warming to ambient temperature. Hirshfeld surface fingerprint plots show the different packing environments of the two new compared to the two known orthorhombic polymorphs Forms I and II. The accuracy and precision of the structures were improved compared to conventional independent atom model refinement through the use of aspherical scattering factors of the invariom database. We think that the layered nature of all sodium acetate forms, and the thereby limited (“quantized”) availability of vibrational modes, is related to the phenomenon of supersaturation, which is connected to its phase-change properties.

Two new polymorphs of the phase-change material sodium acetate were characterized by single-crystal X-ray diffraction. A tetragonal form was found first. It converted to a orthorhombic form after measurement of a single crystal of the tetragonal form at 100 K and subsequent warming to ambient temperature. Hirshfeld surface fingerprint plots show the different packing environments of the two new compared to the two known orthorhombic polymorphs Forms I and II. The accuracy and precision of the structures were improved compared to conventional independent atom model refinement through the use of aspherical scattering factors of the invariom database. We think that the layered nature of all sodium acetate forms, and the thereby limited (“quantized”) availability of vibrational modes, is related to the phenomenon of supersaturation, which is connected to its phase-change properties. [ABSTRACT FROM AUTHOR]