Hydrated anion glued capsular and non-capsular assembly of a tripodal host: Solid state recognition of bromide–water [Br5–(H2O)6]5− and iodide–water [I2–(H2O)4]2− clusters in cationic tripodal receptor

Abstract

Herein, we describe a flexible polyammonium tripodal (N4 unit) receptor for hydrated anions. Multiple protonation sites increased the degree of protonation and allowed to study binding of multiple anions towards the receptor in aqueous medium. All three arms are projected in the same direction in the protonated receptor and formed bowl shaped conformation. Whereas the free receptor L occupied an orientation in between open and bowl shaped conformation. We observe anion or anion–water assisted capsular and non-capsular assembled supramolecular structures stabilized by several H-bonding interactions. We show fluoride–water and chloride ion belt induced bimolecular capsular assemblies in complexes 1 and 3. On the other hand, we establish chloride–water, bromide–water and iodide–water templated non-capsular aggregations of the protonated receptor in complexes 2, 4 and 5. Most interestingly, a long chain fluoride–water cluster [F₇–(H₂O)₈]⁷⁻ in capsular complex 1, unique extended bromide–water [Br₅–(H₂O)₆]⁵⁻ and discrete iodide–water [I₂–(H₂O)₄]²⁻ clusters in non-capsular complexes 4 and 5 are also examined structurally. All supramolecular complexes are characterized by FTIR, NMR, TGA-DSC and X-ray analysis.