Fine-tuning of properties of bismacrocyclic dinuclear cyclidene receptors by N-methylation.

Agnieszka Więckowska 1Renata Bilewicz 1Krzysztof Woźniak 1Jadwiga Szydłowska 1Bohdan Korybut-Daszkiewicz 2

1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
2. Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 44/52, Warszawa 01-224, Poland

Abstract

By changing properties of components of mechanically bonded molecules, one can variate properties of resulting complex structures. Such a tuning of properties can be achieved by severe measures as, for example, replacement of the metal ions, elongation of the aliphatic linkers or change of macrocycles. On the other hand, more subtle changes of properties can be introduced by proper chemical modifications of particular positions of the parent systems. We present the role of N-methylation in controlling the properties of bismacrocyclic substrates used for the construction of more complex molecules.

N-methylated bismacrocyclic Cu and Ni complexes were synthesized and structurally characterised in the solid state. Their properties in the solution were analysed using NMR, ESR spectroscopies and electrochemical methods. Face-to-face biscyclidenes linked via polymethylene chains form rectangular box-like cations. These moieties can host some small guests molecules (water, p-electron donating compounds) and are stabilised by a shell of neighbouring couterions.

For the bismacrocyclic dinuclear complexes containing two nickel or two copper ions, the intramolecular interactions between the metallic centres are strengthened through methylation of the macrocyclic components comparing to the non-methylated species.

Methylation weakens electron acceptor properties of the complexes leading to less effective binding of the p-electron donating guests. It also increases the stability of the lower oxidation states. In the case of the copper complexes both Cu(II)/Cu(I) and Cu(II)/Cu(III) reversible 1 electron transfers are seen in the voltammograms. These changes in properties are interpreted as consequences of steric repulsion between the methyl substituents and the macrocyclic ring.

 

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Presentation: Poster at SMCBS'2005 Workshop, by Agnieszka Więckowska
See On-line Journal of SMCBS'2005 Workshop

Submitted: 2005-08-04 11:44
Revised:   2009-06-07 00:44