A1 Journal article (refereed)
Ion pair complexes and anion binding in the solution of a ditopic receptor (2016)

Mäkelä, T., & Rissanen, K. (2016). Ion pair complexes and anion binding in the solution of a ditopic receptor. Dalton Transactions, 45(15), 6481-6490. https://doi.org/10.1039/C6DT00414H

JYU authors or editors

Mäkelä, Toni
Rissanen, Kari

Publication details

All authors or editors: Mäkelä, Toni; Rissanen, Kari

Journal or series: Dalton Transactions

ISSN: 1477-9226

eISSN: 1477-9234

Publication year: 2016

Volume: 45

Issue number: 15

Pages range: 6481-6490

Publisher: R S C Publications

Publication country: United Kingdom

Publication language: English

DOI: https://doi.org/10.1039/C6DT00414H

Publication open access: Not open

Publication channel open access:

Abstract

The synthesis and crystal structures with alkali halides of a ditopic benzo-15-crown-5 bis-urea receptor L have been presented. In addition, the anion binding properties of L and its alkali metal complexes in solution are presented. A comprehensive single-crystal X-ray crystallographic study of L, all together 13 crystal structures, including the ion pair complexes with NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, and RbI, give a detailed view of how L behaves in the solid-state with different alkali halides depending on the size of the cation and anion. In the solid-state L forms a 1 : 1 complex with a sodium cation and the anion is complexed as a contact (NaCl) or a separate ion pair (NaBr, NaI). With larger potassium and rubidium cations L assembles into a 2 : 1 complex and forms a separated ion pair complex with the anion. Reflecting the crystal structures the L forms a 1 : 1 complex with Na+ in solution, and a 2 : 1 complex with K+, which were verified by Job's plot analysis in 4 : 1 CDCl3/dimethyl sulfoxide. The binding strength of the monomeric [L·Na]+ and the dimeric [2L·K]+ toward chloride, bromide and iodide anions was studied by 1H NMR titrations in 4 : 1 CDCl3/DMSO, and a clear turn-on effect of the cation complexation compared to the neutral receptor L alone (Ka with L for Cl−, Br− and I− being 832, 174 and 32 M−1, respectively) was observed. The monomeric [L·Na]+ binds chloride 9, bromide 8, and iodide 12 times stronger than L, while for the dimeric [2L·K]+ the corresponding increase in binding is 51 (Cl−), 84 (Br−), and 22 (I−) times with the same stoichiometric ratios as observed for the ion pair complexes in the solid-state.

Free keywords: ion pair complexes; anion binding; ditopic receptors

Fields of science: