Mono-aqua-bridged dinuclear complexes of Cu(II) containing NNO donor Schiff base ligand: hydrogen-bond-mediated exchange coupling

Abstract

Two new mono-aqua-bridged dinuclear Cu (II) complexes of tridentate NNO Schiff bases, [Cu₂(μ-H₂O)L¹₂ (H₂O) ₂](BF₄)₂•2H₂O (1) and [Cu₂ (μ-H₂O)L²₂ (H₂O) ₂](BF₄)₂•2H₂O (2) where HL¹ = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol and HL² = 2-[(2-dimethylamino-ethylimino)-methyl]-phenol were synthesized. Both the complexes were characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. For both the complexes each Cu (II) ion is in a square-pyramidal environment being bonded to three atoms from the tridentate NNO Schiff base and a terminal H₂O molecule in the equatorial plane; a second H₂O ligand acts as a bridge between the two Cu (II) centres through the axial positions. Hydrogen bonds between the terminal H₂O ligand and the Schiff base of the adjacent centre complete the intra-dimer linkages. Variable-temperature (4–300 K) magnetic susceptibility measurement shows the presence of significant antiferromagnetic coupling for both the complexes (J = −12.2 and −12.5 cm⁻¹, respectively for 1 and 2), mediated mainly through the intra-dimer H-bonds.