title: Yes, one can obtain better quality structures from routine X-ray data collection.
abstract: Single-crystal X-ray diffraction structural results for benzidine dihydrochloride, hydrated and protonated N,N,N,N-peri(dimethylamino)naphthalene chloride, triptycene, dichlorodimethyltriptycene and decamethylferrocene have been analysed. A critical discussion of the dependence of structural and thermal parameters on resolution for these compounds is presented. Results of refinements against X-ray data, cut off to different resolutions from the high-resolution data files, are compared to structural models derived from neutron diffraction experiments. The Independent Atom Model (IAM) and the Transferable Aspherical Atom Model (TAAM) are tested. The average differences between the X-ray and neutron structural parameters (with the exception of valence angles defined by H atoms) decrease with the increasing 2θmax angle. The scale of differences between X-ray and neutron geometrical parameters can be significantly reduced when data are collected to the higher, than commonly used, 2θmax diffraction angles (for Mo Kα 2θmax > 65°). The final structural and thermal parameters obtained for the studied compounds using TAAM refinement are in better agreement with the neutron values than the IAM results for all resolutions and all compounds. By using TAAM, it is still possible to obtain accurate results even from low-resolution X-ray data. This is particularly important as TAAM is easy to apply and can routinely be used to improve the quality of structural investigations [Dominiak (2015 ▸). LSDB from UBDB. University of Buffalo, USA]. We can recommend that, in order to obtain more adequate (more accurate and precise) structural and displacement parameters during the IAM model refinement, data should be collected up to the larger diffraction angles, at least, for Mo Kα radiation to 2θmax = 65° (sin θmax/λ < 0.75 Å(-1)). The TAAM approach is a very good option to obtain more adequate results even using data collected to the lower 2θmax angles. Also the results of translation-libration-screw (TLS) analysis and vibrational entropy values are more reliable for 2θmax > 65°.
authors: Biological and Chemical Research Centre, Chemistry Department, University of Warsaw , Żwirki i Wigury 101, 02-089 Warszawa, Poland.
authors: W Fabiola
authors: WF
authors: Sanjuan-Szklarz
authors: Biological and Chemical Research Centre, Chemistry Department, University of Warsaw , Żwirki i Wigury 101, 02-089 Warszawa, Poland.
authors: Anna A
authors: AA
authors: Hoser
authors: Rutherford Appleton Laboratory, ISIS Facility , Chilton, Didcot, Oxfordshire OX11 OQX, UK.
authors: Matthias
authors: M
authors: Gutmann
authors: Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen, Denmark.
authors: Anders Østergaard
authors: AØ
authors: Madsen
authors: Biological and Chemical Research Centre, Chemistry Department, University of Warsaw , Żwirki i Wigury 101, 02-089 Warszawa, Poland.
authors: Krzysztof
authors: K
authors: Woźniak
keywords: TLS analysis; X-ray diffraction results; geometric parameters; independent atom model; precision; transferable aspherical atom model