Cyclic (H2O)6 confined hexameric host–guest assemblies and aerial CO2 fixation by electron-rich neutral urea/thiourea scaffolds

Abstract

One of the supreme anion binding building blocks exhibiting strong interplay among topology, complementarity and coordination over the last two decades is the tris(2-aminoethyl)amine skeleton. However, recognition of anions/hydrated anions within the self-assemblies of simplest phenyl-based tris(oxyurea/thiourea) neutral ligands has been underexplored from 1995 and more challenging, mainly because of the lack of π-acidic or electron-withdrawing substituents in aryl terminals, especially in the solid state. Herein, two simple tris(oxyurea) (L₁) and tris(thiourea) (L₂) electron-rich scaffolds are reported with comparatively less acidic terminal aromatic functionalization but still capable of trapping chair-shaped cyclic water hexamer within the infrequent fluoride encapsulated hexameric L₁ core as well as divalent carbonate anion encapsulated dimeric capsular cage of L₂via hydroxide ion induced aerial CO₂ fixation. Moreover, L₁ shows large dihydrogen phosphate dimer [(H₂PO₄⁻)₂] bound neutral dimeric pseudo-capsular assembly, while the thiourea analogue L₂ exhibits chloride and acetate bound unimolecular capsular assembly and divalent sulfate bound dimeric cage via hydrogen-bonding activated proton transfer reaction.