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- Acetic acid (1)
- Beta-cyclodextrin (1)
- Crystal structures (1)
- DFT (1)
- Energetic Materials (1)
- Formic acid (1)
- Hydrogen bond (1)
- Inclusion complex (1)
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Organisationseinheit der BAM
ß-Cyclodextrin (ßCD)-formic acid (1) and ß-CDacetic acid (2) inclusion complexes crystallizeas ß-CD...0.3HCOOH...7.7H2O and ß-CD...0.4CH3COOH...7.7H2O in themonoclinic space group P21 with comparable unit cell constants. Anisotropic refinement of atomic parameters against X-ray diffractiondata with Fo 2 > 2 (Fo 2) (986/8563 and 991/8358) converged at R-factors of 0.051 and 0.054 for 1 and 2,respectively. In both complexes, the ß-CD molecularconformation, hydration pattern and crystal packing are similar,but the inclusion geometries of the guest molecules are different.The ß-CD macrocycles adopt a ``round'' conformationstabilized by intramolecular, interglucose O3(n)...O2(n + 1)hydrogen bonds and their O6H groups are systematically hydratedby water molecules. In the asymmetric unit, each complex contains one ß-CD, 0.3 formic acid (or 0.4 acetic acid), and 7.7 water moleculesthat are distributed over 9 positions. Water sites located in the ß-CD cavity hydrogen bond to the guest molecule. In thecrystal lattice, ß-CD molecules are packed in a typical ``herringbone'' fashion. In 1, the formic acid (occupancy 0.3) is entirely included in the ß-CD cavity such that its C atom is shifted from the O4-plane center to the ß-CD O6-side by 2.90 Å and C=O, C-O bonds point to this side. In 2, the acetic acid (occupancy 0.4) is completely embedded in the ß-CD cavity, in which the carboxylic C atom is displaced from the O4-plane centerto the ß-CD O6-side by 0.87 Å; the C=O bond directsto the ß-CD O6-side and makes an angle of 15°to the ß-CD molecular axis. Furthermore, bothdimethyl-ß-CD-acetic acid and ß-CD-acetic acidcomplexes form a cage structure, showing that the small guestsenclosed entirely in the cavity either in ß-CD or indimethyl--CD do not affect the packing of the host macrocycles.
Highly anharmonic thermal vibrations may serve as a source of structural instabilities resulting in phase transitions, chemical reactions and even the mechanical disintegration of a material. Ab initio calculations model thermal motion within a harmonic or sometimes quasi-harmonic approximation and must be complimented by experimental data on temperature-dependent vibrational frequencies. Here multi-temperature atomic displacement parameters (ADPs), derived from a single-crystal synchrotron diffraction experiment, are used to characterize low-frequency lattice vibrations in the alpha-FOX-7 layered structure. It is shown that despite the limited quality of the data, the extracted frequencies are reasonably close to those derived from inelastic scattering, Raman measurements and density functional theory (DFT) calculations. Vibrational anharmonicity is parameterized by the Grüneisen parameters, which are found to be very different for in-layer and out-of-layer vibrations.