Electronic substitution effects on anion coordination of a tripodal thiourea receptor: evidences of deprotonation of oxy-anions in solid and solution

Abstract

Two simple tris(2-aminoethyl)amine (tren)-based electron-donating p-methyl (L₁) and p-methoxy (L₂)-substituted tris-thioureas have been extensively studied with various anions. The X-ray diffraction studies reveal that in the case of both receptors L₁ and L₂, halide anions (F⁻ , Cl⁻  and Br⁻ ) are encapsulated into the tripodal cavity of the receptors with 1:1 stoichiometry and anions such as and form dimeric capsular assemblies of the receptors with 1:2 stoichiometry. The solution-state binding and encapsulation of anions have also been confirmed by ¹H NMR titration and 2D NOESY NMR experiments. The ¹H NMR titration experiments show that receptor L₁ is able to deprotonate , and in solution, which was further verified with the addition of tetrabutylammonium hydroxide. On the other hand, receptor L₂ failed to deprotonate the hydrogenated oxy-anions in solution.

Keywords::

• tripodal receptor
• thiourea
• anion encapsulation
• crystal structure
• deprotonation of oxy-anions

Acknowledgements

G.D. acknowledges the Council of Scientific and Industrial Research (EMR/01/3664/12) and Department of Science and Technology (DST), New Delhi, India for financial support, CIF and IIT Guwahati for providing instrument facilities and DST FIST for single crystal X-ray diffraction facility. A.G acknowledges IIT Guwahati, India, for research fellowship.

Notes

^1. Mercury 2.3, Supplied with Cambridge Structural Database; CCDC, Cambridge, 2007. Lied with Cambridge Structural Database, CCDC, Cambridge, UK, 2007.