An Ag(i)-linked bis-calix[4]pyrrole molecular capsule and its selective recognition of fluoride anions†

Abstract

A well-defined “four-wall” capsule () was constructed based on the coordination-driven self-assembly of a tetratopic pyridine-functionalized calix[4]pyrrole cavitand with four stabilizing pyridine⋯Ag⁺⋯pyridine coordination bonds in N,N-dimethylformamide (DMF). Capsule was characterized by means of various techniques, including ¹H nuclear magnetic resonance (NMR) spectroscopy, diffusion ordered NMR spectroscopy (DOSY), electrospray ionization mass spectrometry (ESI-MS), and single crystal X-ray diffraction analyses. The tetra-α-meso-pyridyl extended calix[4]pyrrole ligand and the corresponding dimeric capsule were found to selectively recognize the fluoride anion over other halide anions (chloride, bromide, and iodide anions) in DMF. Cavitand was found to bind and release Ag⁺via a fast equilibrium exchange process on the NMR timescale, whereas the fluoride binding of both and capsule found to be slow on the NMR timescale. The transformation among multiple molecular states, viz. monomeric form , capsule , and their corresponding fluoride-bound complexes F⁻⊂ and 2F⁻⊂, could be modulated by the addition of silver, fluoride, and chloride ions.