Metal ion interactions with vitamin B1. Crystal structures of Zn(thiamine)(SCN) 3 having a metal-base bond and Cd(thiamine)(SCN) 3 having a metal-hydroxyethyl bond

Abstract

The crystal structures of Zn(thiamine)(SCN) 3 ( 1) and Cd(thiamine)(SCN) 3 ( 2) have been determined by X-ray diffraction methods. The zinc complex 1 forms a discrete structure in which the tetrahedral Zn(II) ion is bonded by the pyrimidine ring nitrogen N(I′) and three thiocyanato ligands through nitrogen atoms. The cadmium complex 2 forms a polymeric structure with the octahedral Cd(II) ion bonded by the lateral hydroxyethyl oxygen O (5γ) of thiamine and five thiocyanato ligands, one terminal and the others bridging ones. Each thiamine ligand in 1 and 2 adopts the usually observed F conformation. A thiocyanato ligand bridges between the thiazolium and the pyrimidine rings of the same thiamine molecule through a C(2)-H…SCN − hydrogen bond and an SCN −…pyrimidine ring electrostatic contact; this is a factor that affects the F conformation of thiamine. This anion-bridge is also emphasized as a substrate fixation model. Crystal data: C 15H 17N 4OS 4Zn ( 1), monoclinic, space group P2 1/ a, a = 17.764(5), b = 12.484(2), c = 12.104(2) Å, β = 125.46(2)°, V = 2186.4(9) Å 3, Z= 4, and R = 0.043 for 2076 observed reflections ( F o>3σ( F o)); C 15H 17CdN 7OS 4 ( 2), triclinic, space group P 1 , a = 8.118(4), b = 10.076(4), c = 14.174(5) Å, α = 94.32(3), β = 85.88(3), γ = 111.49(4)°, V = 1075(2) Å 3, Z=2, and R = 0.072 for 3940 reflections ( F o>3σ( F o)).