Coordination chemistry of 2-hydroxymethylbenzimidazole complexes with copper(II) and cadmium(II) ions: Similarities and differences

The new Cu(II) and Cd(II) complexes of the biologically relevant ligand 2-hydroxymethylbenzimidazole: [CdL2(NO3)2] 1, ([CuL2(NO3)](NO3)(H2O) 2, [CdL3](NO3)2L(EtOH)0.253, mer-[CuL3](NO3)2(H2O)(i-PrOH) 4 have been synthesized and characterized by elemental analyses, UV–Vis, IR, Raman, EPR, NMR, X-ray diffraction and magnetic measurements. X-ray studies have confirmed a bidentate fashion of coordination of the 2-CH2OHBIm to the Cd(II) as well to Cu(II) ions. This results in the formulation of a five-membered chelate ring in which both N(imidazole) and O(hydroxymethyl) donors of ligand are involved. A comparison of Cu(II) 4 and Cd(II) 3 model complexes shows that both metals may form complexes which exhibit identical structures (distorted octahedral) forming chromophores of the MN3O3 type. On the contrary, the polyhedra of metal complexes containing two ligands are different. The copper complex 2 is a five-coordinated with tetragonal pyramid as coordination polyhedron (CuN2O3) but cadmium forms an eight-coordinated (CdN2O6) complex 1. Weak C–H⋯π type interactions which were extracted from X-ray data of 1 were confirmed by the 13C NMR method. The IR data indicated that Cd(II) is a considerably better acceptor (Lewis acid) than Cu(II) ion for the N, O-donor ligand. The similarities and differences revealed in the coordination behaviour of Cu(II) and Cd(II) towards N, O-donor ligand should be treated as a test on possibility of the copper(II) ions to be displaced by cadmium(II), for example, in the intracellular sites.

The new Cu(II) and Cd(II) complexes of the biologically relevant ligand 2-hydroxymethylbenzimidazole have been synthesized and characterized by UV–Vis, IR, Raman, EPR, NMR and X-ray. The polyhedra of metal complexes containing two ligands are different. The copper complex is a five-coordinated (tetragonal pyramid) but cadmium forms an eight-coordinated (CdN2O6) complex.Figure optionsDownload as PowerPoint slide