Interactions between thiamine and large anions. Crystal structures of (H-thiamine)[Pt-II(SCN)(4)] center dot 3H(2)O and (H-thiamine)[Pt-IV(SCN)(6)] center dot H2O

The reaction of thiamine with (K2PtCl4)-Cl-II and with (PtCl4)-Cl-IV in the presence of excess NaSCN in aqueous solution gave thiamine salts, (H-thiam ine)[Pt(SCN)(4)]. 3H(2)O (1) and (H-thiamine)[Pt(SCN)(6)]. H2O (2), respect ively, structures of which have been determined by X-ray diffraction. The t hiamine molecule adopts the usual F conformation in each salt. In 1, [Pt(SC N)(4)](2-) ions act as large planar spacers in the crystal lattice and inte ract scarcely with thiamine, except for a hydrogen bonding with the termina l hydroxy O(5 gamma). Instead, water molecules form two types of host-guest -like interactions with the pyrimidine and the thiazolium moieties of a thi amine molecule, one being a C(2)-H...water...pyrimidine bridge and the othe r being an N(4'alpha)-H...water...thiazolium bridge. In 2, despite the much larger ion size, octahedral [Pt(SCN)(6)](2-) ions form a C(2)-H... anion.. .pyrimidine bridge and an N(4'alpha)-H...anion...thiazolium bridge. An addi tional hydrogen bonding between the anion and the terminal O(5 gamma) of th iamine creates a hydrogen-bonded macrocyclic ring {thiaminium-[Pt(SCN)(6)]( 2-)}(2), a supramolecule. (C) 1999 Elsevier Science S.A. All rights reserve d.