Synthesis, spectroscopic characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) dinuclear complexes with di-2-pyridylamine

The syntheses and characterization of a series of dinuclear μ-oxalato copper(II) complexes of the general type [(NN)_{1 or 2}Cu(C₂O₄)Cu(NN)_{1 or 2}]²⁺, where NN=didentate dpyam (di-2-pyridylamine) ligand, are described. The crystal structures of three representative complexes have been determined. The dinuclear-oxalate bridged compounds [Cu(dpyam) ₄(C₂O₄)](ClO₄)₂(H ₂O)₃ (1) and [Cu₂(dpyam)₄(C ₂O₄)](BF₄)₂(H₂O) ₃ (2) crystallize in the non-centrosymmetric triclinic space group P1 which are isomorphous and isostructural. The compound [Cu ₂(dpyam)₂(C₂O₄)(NO₃) ₂((CH₃)₂SO)₂] (3) crystallizes in the centrosymmetric monoclinic space group P1 with all Cu-oxalate contacts in the equatorial plane. All three complexes contain six-coordinate copper centres bridged by planar bis-didentate oxalate groups from the equatorial position of one chromophore to the equatorial position of the other one. Both chromophores in 1 and 2 exhibit the compressed octahedral Cu(II) geometry, while 3 displays an elongated octahedral Cu(II) environment. The IR, ligand field and EPR measurements are in agreement with the structures found. The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a very weak ferromagnetic interaction between the Cu(II) atoms for compound 1 and 2, with a singlet-triplet energy gap (J) of 2.42 and 3.38 cm^-1, for compounds 1 and 2, respectively. Compound 3 has a strong antiferromagnetic interaction with a J of -305.1 cm^-1, in agreement with coplanarity of the magnetic orbitals.