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The binding sites of Zn2+, Cd2+, and Hg2+ in complexes with 2-(alpha-hydroxybenzyl)thiamine monophosphate chloride, (LH)Cl-+(-), have been investigated in the solid state [2-(alpha-hydroxybenzyl)thiamin monophosphate chloride monoprotonated at the phosphate group and protonated at N-1' is denoted as (LH)Cl-+(-); therefore, the ligand monoprotonated at the phosphate group and deprotonated at N-1' is L]. Complexes of formulae MLCl(2), M(LH)Cl-3, and (MCl(4))(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 HgL(2)Cl(2) was solved, together with that of the free ligand (LH)Cl-+(-), by X-ray crystallography. HgL(2)Cl(2) crystallizes in C2/c, with a = 32.968(6) Angstrom, b = 7.477(2) Angstrom, c = 21.471(4) Angstrom, beta = 118.19(1)degrees, V = 4665(2) Angstrom(3), and Z = 4. (LH)Cl-+(-) crystallizes in Cc, with a = 10.951(3) Angstrom, b = 17.579(4) Angstrom, c = 13.373(3) Angstrom, beta = 105.36(2)degrees, V = 2482.4(10) Angstrom(3), and Z = 4. Mercury(II) binds to the N(1') of the pyrimidine ring. Both ligands are in the S conformation [Phi(T) = -98.1(9)degrees and Phi(P) = 176.1(10)degrees for HgL(2)Cl(2) and Phi(T) = 104.1(5)degrees and Phi(P) = 171.9(6)degrees for (LH)Cl-+(-)]. P-31 and C-13 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 P-31 NMR spectroscopy is particularly useful in characterizing these complexes as the P-31 shielding tensors are sensitive to the state of the phosphate group. On the other hand, the P-31 NMR spectra indicate that direct bonding between Zn2+ and Cd2+ to the phosphate can occur under certain preparation conditions. Solid-state C-13 NMR and vibrational (IR/Raman) spectroscopic results are also in agreement with the other techniques. Inorg Chem |
