Conformational flexibility of hybrid [3]- and [4]-rotaxanes

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  • External authors:
  • Selena J. Lockyer
  • Selina Nawaz
  • Adam Brookfield
  • Alistair J. Fielding
  • Inigo J. Vitorica-yrezabal
  • Grigore A. Timco
  • Neil A Burton

Abstract

The synthesis, structures and properties of [4]- and [3]-rotaxane complexes are reported where [2]rotaxanes, formed from het-erometallic {Cr7Ni} rings, are bound to a fluoride-centered {CrNi2} triangle. The compounds have been characterized by sin-gle crystal X-ray diffraction and have the formulae [CrNi2(F)(O2CtBu)6]{(BH)[Cr7NiF8(O2CtBu)16]}3 (3) and [CrNi2(F)(O2CtBu)6(THF)]{(BH)[Cr7NiF8(O2CtBu)16]}2 (4); where B = py-CH2CH2NHCH2C6H4SCH3. The [4]rotaxane 3 is an isosceles triangle of three [2]rotaxanes bound to the central triangle while the [3]rotaxane 4 contains only two [2]rotaxanes bound to the central triangle. Studies of the behavior of 3 and 4 in solution by small angle X-ray scattering (SAXS) and atomistic molecular dynamic simulations (AMDS) show that the structure of 3 is similar to that found in the crystal but that 4 has a different conformation to the crystal. C.w. and pulsed EPR spectroscopy were used to study the structures present and demonstrate that in frozen solutions (at 5 K) 4 forms more extended molecules than 3 and with a wider range of confor-mations.

Bibliographical metadata

Original languageEnglish
JournalJournal of the American Chemical Society
Early online date21 Aug 2020
DOIs
Publication statusE-pub ahead of print - 21 Aug 2020

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