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

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(1') 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 (5-gamma) 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: C15H17N4OS4Zn (1), monoclinic, space group P2(1)/a, a = 17.764(5), b = 12.484(2), c = 12.104(2) angstrom, beta = 125.46(2)-degrees, V = 2186.4(9) angstrom-3, Z = 4, and R = 0.043 for 2076 observed reflections (F(o) > 3-sigma-(F(o))); C15H17CdN7OS4 (2), triclinic, space group PBAR1, a = 8.118(4), b = 10.076(4), c = 14.174(5) angstrom, alpha = 94.32(3), beta = 85.88(3), gamma = 111.49(4)-degrees, V = 1075(2) angstrom-3, Z = 2, and R = 0.072 for 3940 reflections (F(o) > 3-sigma-(F(o))).