Supramolecular forces and their interplay in stabilizing complexes of organic anions: tuning binding selectivity in water

Abstract

How do different supramolecular forces contribute to the stabilization of complexes of organic anions in water? Oftentimes, when debating such a theme, we refer to broad concepts like positive or negative cooperative effects; the focus of the present work is rather on their interplay, i.e. on the way different kinds of stabilizing interactions (salt bridges, H-bonds, anion–π interactions, π–π stacking, solvent effects, etc.) dialogue among themselves. What happens if we tune the strengths of salt bridges by altering the basicity of the anion? What if we change the geometry of the charged group? How does shifting towards more hydrophilic or hydrophobic anions impact the stability of complexes in water? What happens in the solid state? Will aromatic anions go for a π–π stacking or an anion–π interaction mode and do they all behave in the same manner? Does the host/guest size make any difference? What if we play with regiochemistry: will one of the isomers be selectively recognized? Here we present a case study featuring the tetrazine-based ligands L1 and L2 and a series of selected organic anions; potentiometric, NMR, and XRD data and in silico simulations are employed to render such a complex picture.