Anion coordination and molecular assembly in C2-substituted thiamine–anion systems: effects of the anion and molecular conformation

Abstract

The compounds (het)(PtCl₆)·2H₂O 1, (het)(HgI₄)·H₂O 2 (het = 2-(α-hydroxyethyl)thiamine) and (hpt)(Hg₂Br₆) 3 (hpt = 2-(α-hydroxypropyl)thiamine) have been prepared and structurally characterized by X-ray crystallography in order to study the influence of the anion and molecular conformation on the formation of supramolecular architectures that adsorb anionic species. Both het and hpt molecules adopt the usual S conformation for C2-substituted thiamine but differ from the F conformation for C2-free thiamine derivatives. Two types of characteristic ligand–anion complexation are observed, being of the forms C(6′)–H⋯anion⋯thiazolium-ring (in 1 and 2) and N(4′1)–H⋯anion⋯thiazolium-ring (in 3). The reaction of het with PtCl₆²⁻ or HgI₄²⁻ gives a 1-D double-chain in 1, consisting of two hydrogen-bonded het chains, which are cross-linked by anions through hydrogen bonding and anion⋯aromatic-ring interactions, or a cationic 3-D framework in 2 formed by the stacking of hydrogen-bonded sheets with anion-and-water-filled channels. In the case of 3, hydrogen-bonded hpt dimers and HgBr₆²⁻ anions form alternate cation–anion columns. A comparison with the cases of C2-free thiamine–anion complexes indicates that the change in molecular conformation results in novel supramolecular assemblies in 1 and 2 and an analogous architecture in 3, which also depends on the nature of the anions.