Compounds of cobalt(II), copper(II) and zinc with malic acid and imidazole

Synthesis and investigation of properties of mixed ligand complexes (MLC) of "life metals " (Fe, Zn, Cu, Mn, Mo and Co) with biologically active ligands are particular interested for theoretical, coordinational, applied chemistry, biology and medicine. In this work the compounds of cobalt(II), copper(II) and zinc with malic acid C ₄H ₆O ₅ (H ₂Ma1a1) and imidazole C ₃H ₄N ₂ (Im) were investigated in forms of solid salts and complex compounds in solution. Zinc and copper(II) malates were synthesized by interaction with their carbonates and malic acid followed by extraction from water solution (pH 4.5-5.0) by acetone; cobalt(II) malate was synthesized from concentrated water solution of cobalt(II) chloride and malic acid (pH 4.5-5.0). The MLC were synthesized from solid salts of cobalt(II), copper(II) and zinc malates with general composition MMa1at · 3H ₂O and from Im solution at pH 6.5-8.7 (at this pH the neutral imidazole molecule is dominated) according to reaction: Ma1at (s) + xIm = MIm _xMa1at. The sediments of cobalt and zinc imidasolmalates were precipitated from water solution; the copper(II) biligand salt is extracted by acetone. The composition of synthesized MLC is MIm _xMa1at • nH ₂O (x = 1, 3; n = 0-3), was established by chemical, thermal and thermogravimetric analyzes. The thermo-gravimetric analysis data of biligand salts confirm the salts composition and allow to suppose the mechanism of their thermal decomposition. The prevalence of complexes [MIm ₂] +, [MMa1at] in water solution of double systems (pH 6.5-7.3) was demonstrated by method of isomolar series. In triple systems (pH 6.8) the stage complex formation with overlapping areas of dominance complexes were observed; the stability constants of the MLC [MImMa1at] and [MIm ₂Ma1at] were determined at ionic strength 0.3. The inner sphere ligands compatibility and greater stability of biligand complex compared with monoligand ones were demonstrated. According to IR data of the salts, primary ligands and EAS (electronic absorption spectra) of single, double and triple systems water solutions pyridine nitrogen of imidazole and oxygen of carboxilic groups of malic acid take part in the formation of a bond with d-metal cations.

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