N-methylation of macrobicycles reduces encapsulation ability.
Sofia Derossi1, David T Farrell, Charles J Harding
1Chemistry Department, Loughborough University, Loughborough, UKLE11 3TU.
Dalton Transactions (Cambridge, England : 2003)
|May 2, 2007
Summary
N-methylation of octa-azacryptands prevents copper(II) coordination. However, carbonate complexes uniquely bind two copper ions within the cavity using both oxygen and nitrogen donors.
Area of Science:
- Coordination Chemistry
- Supramolecular Chemistry
Background:
- Octa-azacryptands are macrocyclic ligands with potential N-donor sites.
- N-methylation can influence the conformational flexibility and coordination behavior of ligands.
Purpose of the Study:
- To investigate the effect of N-methylation on the coordination properties of octa-azacryptands with copper(II).
- To explore the structural features of copper(II) complexes formed with these modified cryptands and anionic guests.
Main Methods:
- Synthesis and characterization of N-methylated octa-azacryptands.
- X-ray crystallography to determine the structures of copper(II) complexes.
- Spectroscopic methods to analyze coordination modes.
Main Results:
- N-methylation restricts the conformational flexibility of octa-azacryptands, limiting the use of all nitrogen donors for coordination.
- This often leads to exogenous coordination in the presence of other donors.
- A unique exception was observed with carbonate complexes, which successfully sequestered two copper(II) ions within the cavity.
Conclusions:
- The "basket-shaped" cavity of octa-azacryptands can accommodate two copper(II) ions when coordinated by carbonate anions.
- The carbonate anion, through its two O-donors and the cryptand's three N-donors, facilitates this unique binuclear complex formation.
- N-methylation significantly impacts the coordination chemistry of octa-azacryptands, creating specific binding environments.
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