4.1 Article

Azulene revisited: solid-state structure, invariom modeling and lattice-energy minimization of a classical example of disorder

出版社

INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S2052520618010120

关键词

azulene; invariom modeling; lattice-energy minimization; disorder; DFT calculations

资金

  1. Deutsche Forschungsgemeinschaft [DI 921/3-1, 921/3-2, FA 9649/1-1]
  2. Major National Research Facilities Program (Commonwealth of Australia)
  3. Australian Research Council
  4. Australian Department of Education, Science and Training
  5. Alexander von Humboldt-Stiftung

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The molecular and solid-state structure of azulene both raise fundamental questions. Therefore, the disordered crystal structure of azulene was re-refined with invariom non-spherical atomic scattering factors from new single-crystal X-ray diffraction data with a resolution of d = 0.45 angstrom. An unconstrained refinement results in a molecular geometry with C-s symmetry. Refinements constrained to fulfill C-2v symmetry, as observed in the gas phase and in high-level ab initio calculations, lead to similar figures of merit and residual densities as unconstrained ones. Such models are consistent with the structures from microwave spectroscopy and electron diffraction, albeit they are not the same. It is shown that for the disorder present in azulene, the invariom model describes valence electron density as successfully as it does for non-disordered structures, although the disorder still leads to high correlations mainly between positional parameters. Lattice-energy minimizations on a variety of ordered model structures using dispersion-corrected DFT calculations reveal that the local deviations from the average structure are small. Despite the molecular dipole moment there is no significant molecular ordering in any spatial direction. A superposition of all ordered model structures leads to a calculated average structure, which explains not only the experimental determined atomic coordinates, but also the apparently unusual experimental anisotropic displacement parameters.

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