Complexes of Zn2+, Cd2+, and Hg2+ with 2-(α-Hydroxybenzyl)thiamine Monophosphate Chloride

• Published in: Inorganic chemistry 1996-10, Vol.35 (22), p.6513-6519
• Main Authors: Dodi, Katerina, Gerothanassis, Ioannis P, Hadjiliadis, Nick, Schreiber, Andre, Bau, Robert, Butler, Ian S, Barrie, Patrick J
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic950758x

The binding sites of Zn2+, Cd2+, and Hg2+ in complexes with 2-(α-hydroxybenzyl)thiamine monophosphate chloride, (LH)+Cl-, have been investigated in the solid state [2-(α-hydroxybenzyl)thiamin monophosphate chloride monoprotonated at the phosphate group and protonated at N1‘ is denoted as (LH)+Cl-; therefore, the ligand monoprotonated at the phosphate group and deprotonated at N1‘ is L]. Complexes of formulae MLCl2, M(LH)Cl3, and (MCl4)2-(LH)2 + (M = Zn2+, Cd2+, and Hg2+) were isolated in aqueous and methanolic solutions, depending on pH. The crystal structure of the complex of formula HgL2Cl2 was solved, together with that of the free ligand (LH)+Cl-, by X-ray crystallography. HgL2Cl2 crystallizes in C2/c, with a = 32.968(6) Å, b = 7.477(2) Å, c = 21.471(4) Å, β = 118.19(1)°, V = 4665(2) Å3, and Z = 4. (LH)+Cl- crystallizes in Cc, with a = 10.951(3) Å, b = 17.579(4) Å, c = 13.373(3) Å, β = 105.36(2)°, V = 2482.4(10) Å3, and Z = 4. Mercury(II) binds to the N(1‘) of the pyrimidine ring. Both ligands are in the S conformation [ΦT = −98.1(9)° and ΦP = 176.1(10)° for HgL2Cl2 and ΦT = 104.1(5)° and ΦP = 171.9(6)° for (LH)+Cl-]. 31P and 13C NMR spectra, together with vibrational spectra (IR/Raman), are used to deduce the binding sites of the metal and the protonation states of the ligand at various pH values. It is found that solid-state 31P NMR spectroscopy is particularly useful in characterizing these complexes as the 31P shielding tensors are sensitive to the state of the phosphate group. On the other hand, the 31P NMR spectra indicate that direct bonding between Zn2+ and Cd2+ to the phosphate can occur under certain preparation conditions. Solid-state 13C NMR and vibrational (IR/Raman) spectroscopic results are also in agreement with the other techniques.