Competing but Coexisting: Sulfate-and Potassium-Induced Supramolecular Motifs in Squaramide-Based Receptor Complexes

Abstract

We explore the coexistence and interplay of two distinct supramolecular motifs within a single receptor molecule combining squaramide and benzo-15-crown-5 ether domains. These heteroditopic systems display a dual recognition behavior, forming either sandwich-type potassium complexes or 4:1 sulfate assemblies, depending on the ions present. Through 1H NMR titrations, NMR diffusion analysis, and 2D NMR experiments, we reveal that these motifs do not simply compete but can coexist and cooperate, generating higher-order assemblies stabilized by simultaneous cation–anion interactions. When both K⁺ and SO₄²⁻ are present, the receptor adopts a new tetrameric structure (4L·2K⁺·SO₄²⁻), reflected by distinct NMR signals and a nearly 40% drop in diffusion coefficients. Dynamic light scattering measurements show a remarkable increase in hydrodynamic diameter—from 190 nm for sulfate-only species to over 340 nm in mixed-ion systems—demonstrating ion-induced cooperative aggregation. X-ray crystallography confirms that potassium sulfate drives orthogonal dimer–dimer association, producing extended 3D networks. Extraction experiments verify that such assemblies persist under realistic conditions, confirming their structural robustness and functional potential. These findings highlight how integrating two complementary recognition motifs within one receptor enables controllable transitions between competitive and cooperative binding modes, offering new strategies for the design of multifunctional ion-pair receptors and adaptive supramolecular architectures