Abstract
Rotaxanes as well as catenanes are known as potential building blocks of molecular machines. The nanohoop [2]rotaxane investigated is composed of a macrocycle derived from a [6]cycloparaphenylene (CCP, designated as a carbon nanohoop), where one of the six para-linked phenyl rings is replaced by a 2,6-substituted pyridyl ring. This macrocycle is mechanically interlocked with a thread, a linear rod-shaped diyne fragment sitting in the cavity of the macrocycle. Two bulky 3,5-di-t-butyl-phenyl rests as end groups keep the thread fixed. The interplay between macrocycle and thread was examined by means of the electron density distribution (EDD) obtained by application of the invariom formalism, relying on X-ray diffraction data collected earlier. The so-obtained EDD was subjected to topological analysis using the QTAIM formalism. Moreover, molecular Hirshfeld and electrostatic potential (ESP) surfaces were calculated. The 73 C–C bonds were analysed in terms of bond topological properties. For the 46 single and the 22 aromatic bonds, the analysis gave average bond orders of 1.03 and 1.61. The five C–C bonds in the diyne fragment can clearly be distinguished into three types: formal triple bonds with bond orders above 3.0, arene bonds with bond orders of 1.6 and finally bond orders of 1.3 in the adjacent C–C bonds, which indicate a considerable electron delocalization in this fragment. Mapping the ED onto the Hirshfeld surfaces of the macrocycle and the thread does not show strong signals. This shows that in between the molecules only weak non-covalent interactions are present. The electrostatic potentials (ESPs) were mapped onto molecular EDD isosurfaces. For all phenyl rings, small regions of negative ESP are visible on the delocalized π systems. A potential gradient between the mostly positive ESP of the macrocycle and the diyne region of the thread exist, which can be considered the dominant force to hold this rotaxane together.
Dedicated to Professor Dr. Karl Fischer, Saarbrücken, on the occasion of his 95th birthday.
Author contribution: The authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: None declared.
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.
References
1. Gil-Ramirez, G., Leigh, D. A., Stephens, A. J. Angew. Chem. Int. Ed. 2005, 54, 6110–6150.10.1002/anie.201411619Search in Google Scholar PubMed PubMed Central
2. Press release of the Nobel Committee. 2016, http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2016/press.html, see also Leigh D. A. Angew. Chem. Int. Ed. 2016, 55, 14506–14508.10.1002/anie.201609841Search in Google Scholar PubMed
3. Luger, P., Dittrich, B., Mebs, S., Slawin, A. M. Z., Leigh, D. A. Z. Naturforsch. 2018, 73b, 677–687; https://doi.org/10.1515/znb-2018-0179.Search in Google Scholar
4. Van Raden, J. M., White, B. M., Zakharov, L. N., Jasti, R. Angew. Chem. Int. Ed. 2019, 58, 7341–7345.10.1002/anie.201901984Search in Google Scholar PubMed
5. Allen, F. H. Acta Crystallogr. 2002, B58, 380–388; https://doi.org/10.1107/s0108768102003890.Search in Google Scholar PubMed
6. Groom, C. R., Bruno, I. J., Lightfood, M. P., Ward, S. C.. Acta Crystallogr. 2016, B72, 171–179; https://doi.org/10.1107/s2052520616003954.Search in Google Scholar
7. Dittrich, B., Koritsanszky, T., Luger, P. Angew. Chem. Int. Ed. 2004, 43, 2718–2721; https://doi.org/10.1002/anie.200353596.Search in Google Scholar PubMed
8. Dittrich, B., Hübschle, C. B., Pröpper, K., Dietrich, F., Stolper, T., Holstein, J. J. Acta Crystallogr. 2013, B69, 91–104; https://doi.org/10.1107/s2052519213002285.Search in Google Scholar PubMed
9. Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J., Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466–470; https://doi.org/10.1107/s0021889807067908.Search in Google Scholar
10. Keller, E., Pierrard, J. S. Schakal99; Albert-Ludwigs University: Freiburg (Germany), 1999.Search in Google Scholar
11. Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122; https://doi.org/10.1107/s0108767307043930.Search in Google Scholar PubMed
12. Bader, R. F. W. Atoms in Molecules – A Quantum Theory; Clarendon Press: Oxford, 1994.Search in Google Scholar
13. Luger, P., Messerschmidt, M., Scheins, S., Wagner, A. Acta Crystallogr. 2004, A60, 390–396; https://doi.org/10.1107/s0108767304014825.Search in Google Scholar
14. Bader, R. F. W. Theor. Chem. Acc. 2001, 105, 276–284.10.1007/s002140000233Search in Google Scholar
15. Volkov, A., Gatti, C., Abramov, Y., Coppens, P. Acta Crystallogr. 2000, A56, 252–258; https://doi.org/10.1107/s0108767300001628.Search in Google Scholar
16. Volkov, A., Macchi, P., Farrugia, L. J., Gatti, C., Mallinson, P. R., Richter, T., Koritsánszky, T. XD2006 – A Computer Program for Multipole Refinement, Topological Analysis of Charge Densities and Evaluation of Intermolecular Energies from Experimental and Theoretical Structure Factors; University of Buffalo: Buffalo, NY (USA), 2006. University of Milano: Milano (Italy); University of Glasgow: Glasgow, Scotland (U.K.); CNRISTM: Milano (Italy); Middle Tennessee State University: Murfreesboro, TN (USA).Search in Google Scholar
17. Hübschle, C. B., Luger, P. J. Appl. Crystallogr. 2006, 39, 901–904; https://doi.org/10.1107/s0021889806041859.Search in Google Scholar
18. McKinnon, J. J., Mitchell, A. S., Spackman, M. A. Chem. Eur. J. 1998, 4, 2136–2141.10.1002/(SICI)1521-3765(19981102)4:11<2136::AID-CHEM2136>3.0.CO;2-GSearch in Google Scholar
19. Spackman, M. A., McKinnon, J. J., Jayatilaka, D. CrystEngComm 2008, 10, 377–388.Search in Google Scholar
20. Volkov, A., King, H. F., Coppens, P., Farrugia, L. J. Acta Crystallogr. 2006, A62, 400–408; https://doi.org/10.1107/s0108767306026298.Search in Google Scholar
21. Hübschle, C. B., Luger, P., Dittrich, B. J. Appl. Crystallogr. 2007, 40, 623–627; https://doi.org/10.1107/s0021889807016524.Search in Google Scholar
Supplementary Material
The online version of this article offers supplementary material (https://doi.org/10.1515/znb-2020-0170).
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