Zwitterionic Ru(III) Complexes: Stability of Metal-Ligand Bond and Host-Guest Binding with Cucurbit[7]uril

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Authors

MALALI Sanaz CHYBA Jan KNOR Michal HORNÍ Michal NEČAS Marek NOVOTNÝ Jan MAREK Radek

Year of publication 2020
Type Article in Periodical
Magazine / Source Inorganic Chemistry
MU Faculty or unit

Central European Institute of Technology

Citation
Web DOI: 10.1021/acs.inorgchem.0c01328
Doi http://dx.doi.org/10.1021/acs.inorgchem.0c01328
Keywords ruthenium(III) compound;cucurbit[7]uril;host-guest complex;NMR spectroscopy;paramagnetic;hyperfine shift;spin-dipole contribution
Description A wide range of ruthenium-based coordination compounds have been reported to possess potential as metallodrugs with anticancer or antimetastatic activity. In this work, we synthesized a set of new zwitterionic Ru(III) compounds bearing ligands derived from N-alkyl (R) systems based on pyridine, 4,4'-bipyridine, or 1,4-diazabicyclo[2.2.2]octane (DABCO). The effects of the ligand(s) and their environment on the coordination stability have been investigated. Whereas the [DABCO-R]+ ligand is shown to be easily split out of a negative [RuCl4]- core, positively charged R-pyridine and R-bipyridine ligands form somewhat more stable Ru(III) complexes and can be used as supramolecular anchors for binding with macrocycles. Therefore, supramolecular host-guest assemblies between the stable zwitterionic Ru(III) guests and the cucurbit[7]uril host were investigated and characterized in detail by using NMR spectroscopy and single-crystal X-ray diffraction. Paramagnetic 1H NMR experiments supplemented by relativistic DFT calculations of the structure and hyperfine NMR shifts were performed to determine the host-guest binding modes in solution. In contrast to the intramolecular hyperfine shifts, dominated by the through-bond Fermi-contact mechanism, supramolecular hyperfine shifts were shown to depend on the “through-space” spin-dipole contributions with structural trends being satisfactorily reproduced by a simple point-dipole approximation.
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