Two bis-urea type receptors were synthesized containing a polyether bridge and two 4-nitrophenyl groups as chromogenic units, R1 and R2. Molecular recognition studies of receptors towards different tetraalkylammonium and alkali metal salts were carried out in DMSO by UV-Vis and 1 H-NMR spectroscopy. The receptors were found to have high affinity for diverse anions and ion-pairs, showing the highest affinities towards the tetramethylammonium and sodium salts. The cation binding ability of the receptors was evidenced by means 1 H NMR, mass spectrometric ESI + studies and the crystal structures of some precursors. Additionally, the molecular modelling at the DFT level of the tetramethylammonium acetate complexes illustrates the potential ion-pair binding ability of the receptors: the anion is recognized through strong hydrogen bonds from the NH─ groups from the two urea sites, while the cation is bound by a combination of cation─π, C-H···O and C-H···π interactions.
Bibliographical noteFunding Information:
This work was supported by the Consejo Nacional de Ciencia y Tecnología [CB-239581,Red Temática de Química Supramolecular 281251,Sabbatical grant 121614].
This work was supported by the “Consejo Nacional de Ciencia y Tecnología (CONACyT)” under a graduate Grant (for PJGV and REEP), under a sabbatical Grant (number 121614), under Grants CB-239581 and 281251 (“Red Temática de Química Supramolecular”) and under an equipment grant INFR-2014-01-225455 (for the single crystal X-ray diffractometer). Finally, access to the X-ray facilities of the Chemical Research Center at Morelos State University (LANEM) is gratefully acknowledged.
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- anion recognition
- heteroditopic receptor
- ion-pair recognition
- polyether bridge