Nickel(II) and zinc(II) dimonensinates: Single crystal X-ray structure, spectral properties and bactericidal activity

Mononuclear transition metal complexes of the polyether ionophorous antibiotic monensin (monensic acid, MonH) with nickel(II) and zinc(II) were prepared and characterized using single crystal X-ray diffraction and spectral methods. Monensin complexes crystallize as [Ni(Mon)2(H2O)2]·H2O·5MeCN (1) and [Zn(Mon)2(H2O)2]·H2O·4.5MeCN (2), respectively, in the monoclinic space group P21. Compounds 1 and 2 consist of two monoanionic monensic acid ligands (monensinates) bound in a bidentate coordination mode to the transition metal ion. The metal center is placed in an octahedral environment with monensin anions occupying the equatorial plane of complexes via oxygens of carboxylate and hydroxyl groups located at the both ends of ionophore molecule. The strongly folded antibiotic anions are supported by intramolecular H-bonds, most of them originating from the two aqua ligands attached to the metal(II) ions in axial positions and completing their 6-fold coordination. The bioactivity assay reveals that the presence of divalent metal ion in the monensin complexes influences the biological properties of the ligand and should be taken into account when discussing its mode of action.