Analysis of two catenanes based on electron densities from invariom refinement and results from DFT calculations
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Catenanes are of considerable interest as potential building blocks for molecular machines. The simplest catenanes, Hopf links, consist of two macrocycles that are mechanically interlocked. This unusual architecture cannot be opened without breaking at least one covalent bond. Based on these structural characteristics, unusual properties on Hirshfeld or electrostatic potential surfaces could be expected. For a comparison of their structural and electronic properties, the electron densities (EDs) of two catenanes, coded H22 and H4L7 in the original papers, were examined after application of the invariom formalism, relying on X-ray diffraction data collected earlier. The obtained electron density distributions were subjected to an analysis using the QTAIM formalism to yield bond and atomic properties. Moreover, molecular Hirshfeld surfaces and electrostatic potentials (ESP) were calculated. There are different types of intra- and intermolecular interactions in these two catenanes. In addition to classical N-H···N and C-H···O hydrogen bonds, various types of π···π interactions in H22 and in H4L7 exist. Most of them are verified by local ED concentrations visible on the corresponding Hirshfeld surfaces, except for the parallel π···π interactions in H22, which are either too weak or too diffuse to generate an ED signal on the Hirshfeld surface between the contributing aromatic rings. The electrostatic potentials (ESPs) were calculated and displayed on molecular surfaces. The interaction in the cavity of one macrocycle with the penetrated fragment of the second one was examined and it was found that corresponding to the above-mentioned contacts attractive and repulsive interactions exist. Additionally the ED was examined using results of density functional calculations, including non-covalent interaction index (NCI) and electron localizability indicator (ELI-D) surface analysis, complementing experimental findings.
Luger , P , Dittrich , B , Mebs , S , Slawin , A M Z & Leigh , D A 2018 , ' Analysis of two catenanes based on electron densities from invariom refinement and results from DFT calculations ' , Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences , vol. 73 , no. 10 , pp. 677-687 . https://doi.org/10.1515/znb-2018-0179
Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences
Copyright © 2018 Walter de Gruyter GmbH, Berlin/Boston. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1515/znb-2018-0179
DescriptionThe authors are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support by project DI 921/6-1.
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