Exploring cyclohexane/piperazine-urea motifs for spherical halide (X = Cl−/Br−) recognition: effects on anion coordination, photoluminescence, and morphological tunability

Abstract

Numerous approaches to receptor fabrication have been introduced for supramolecular anion recognition, not only for academic purposes but also for their substantial application in environmental and biological fields. We highlight halide (X = Cl⁻/Br⁻) coordination-triggered self-assembly formation using two dipodal receptors, L₁ and L₂. This approach involves several non-covalent interactions, such as N–H_urea⋯X, C–H_phenyl⋯X, and C–H_n-TBA⋯X. Structural aspects of the anion-coordinated supramolecular architectures of L₁ and L₂ (1a, 1b, 2a, 2b) revealed 2 : 1 anion-receptor assembly formation in almost identical fashion, possessing different coordination numbers. Receptor L₁ is composed of cyclohexane-urea motifs, whereas L₂ comprised a piperazine-urea scaffold connected via a propyl spacer, which might be the backbone of the contrasting coordination number of the isostructural anionic ensembles. Solution-state ¹H-NMR and photoluminescence studies corroborated the efficient encapsulation of chloride/bromide via hydrogen bonding interactions. FESEM studies depicted the variations in morphologies in the anion-recognition-triggered self-assembly of the receptors.