Synthesis, structure, and magnetic properties of lanthanide(III) complexes incorporating a tris-chelate cobalt(III) complex as a metalloligand

A series of CoIII–LnIII–CoIII trinuclear complexes [Ln{Co(Hmtimn)3}2](NO3)3 were prepared by following a simple one-pot synthesis method, mixing an unsymmetrical bidentate ligand 2-(2-imidazolinyl)-6-methoxypheol (H2mtimn) with Co(NO3)2·6H2O and LnX3· 6H2O (where Ln = La, Ce, Pr, Nd, Gd or Dy and X = NO3− or Cl−) in methanolic solution in the presence of triethylamine in air. In the reaction mixture, this leads to the in situ formation of a tris-chelate CoIII metalloligand unit, which can coordinate LnIII ions through the interactions of phenolato- and methoxy-O donors. X-ray structural analysis revealed that the CoIII metalloligand functions as a rigid tripodal ligand to coordinate to a LnIII ion by six oxygen donors. The two metalloligands in the complex exhibit homochiral aggregation (ΔΔ or ΛΛ) upon coordination to the LnIII ion. The coordination of the central LnIII ion was found to be a distorted icosahedral geometry. Magnetic susceptibility measurements reveal that both cobalt and central lanthanide ions exist in trivalent states.