Interactions between thiamine and large anions. Crystal structures of (H-thiamine)[Pt(SCN)4] · 3H2O and (H-thiamine)[Pt(SCN)6] · H2O

The reaction of thiamine with K₂Pt^IICl₄ and with Pt^IVCl₄ in the presence of excess NaSCN in aqueous solution gave thiamine salts, (H-thiamine)[Pt(SCN)₄] · 3H₂O (1) and (H-thiamine)[Pt(SCN)₆] · H₂O (2), respectively, structures of which have been determined by X-ray diffraction. The thiamine molecule adopts the usual F conformation in each salt. In 1, [Pt(SCN)₄]²⁻ ions act as large planar spacers in the crystal lattice and interact scarcely with thiamine, except for a hydrogen bonding with the terminal hydroxy O(5γ). Instead, water molecules form two types of host–guest-like interactions with the pyrimidine and the thiazolium moieties of a thiamine molecule, one being a C(2)–Hwaterpyrimidine bridge and the other being an N(4′)–Hwaterthiazolium bridge. In 2, despite the much larger ion size, octahedral [Pt(SCN)₆]²⁻ ions form a C(2)–Hanionpyrimidine bridge and an N(4′)–Hanionthiazolium bridge. An additional hydrogen bonding between the anion and the terminal O(5γ) of thiamine creates a hydrogen-bonded macrocyclic ring {thiaminium–[Pt(SCN)₆]²⁻}₂, a supramolecule.