Dipicolinato complexes of cobalt(II), copper(II) and zinc(II) with thiamine dications

Cobalt(II), copper(II) and zinc(II) dipicolinato complexes having thiamine dication with compositions [HT][CoL2]·5H2O (1), [HT][CuL2]·5H2O (2) and [HT][ZnL2]·5H2O (3) (L = dipicolinato anion, T = thiamine cation) are synthesized, characterized by X-ray diffraction and other spectroscopic techniques. The thiamine part in these complexes exists as divalent cations. The second protonation of thiamine takes place at the less crowded nitrogen atom of the pyrimidine ring. These complexes are stabilized by electrostatic and hydrogen-bonding interactions of –N+–H and –COO− groups along with crystallized water molecules. The complexes are stable in solution as determined by 1H NMR and visible study. The complex 1 has two medicinal components which can be easily separated by controlling pH in aqueous medium. It gets decomposed on treatment with sodium hydroxide at pH > 8 to form neutral complex {[Na2(μ-H2O)3(H2O)3][CoL2]·H2O}2.