A novel metal-thiamine complex with a cyclic dimer formed by metal-bridged two thiamine ligands. Crystal structure of [Mn(thiamine)Cl 2(H 2O)] 2[thiamine] 2Cl 4·2H 2O

Abstract

The crystal structure of [Mn(thiamine)Cl 2(H 2O)] 2[thiamine] 2Cl 4·2H 2O has been determined by X-ray diffraction methods. The compound contains a cyclic dimer of a complex cation with two thiamine ligands bridged by two Mn(II) ions across a crystallographic center of symmetry. Each Mn(II) is coordinated by two chloride atoms, a water molecule, a N(1′) atom of the pyrimidine from a thiamine and an O(53) atom of the hydroxyethyl side chain from another thiamine. There are two free-base thiamine molecules related by a center of symmetry in the unit cell, which form a base-pair through the hydrogen bonds. Both the independent thiamine molecules in the asymmetric unit assume the common F conformation with φ T=10.0(9) and 3.6(10) and φ P=85.6(7) and 79.6(7), respectively. The compound provides a possible model for a metal-bridged enzyme-coenzyme complex in thiamine catalysis. Crystallographic data: triclinic, space group P 1 , a=12.441(4), b=13.572(4), c=11.267(3) Å, α=103.15(2), β=89.03(3), γ=115.64(2)°, Z=1, D calc=1.524 g cm −3, and R=0.050 for 3019 observed reflections with I>3σ( I).