New dinuclear copper complexes incorporating bis(imidazolyl) based ligands and bidentate–monodentate oxalate bridges. Crystal structure and magnetic properties of [Cu2(BIM)2(C2O4)2]·4H2O and [Cu2(BIK)2(C2O4)2] (BIM = bis(2-imidazolyl)methane), BIK = bis(2-imidazolyl)ketone). Exploring magneto-structural correlations

Abstract

This paper reports the synthesis, X-ray crystal structure and magnetic characterization of two novel copper(II) dinuclear compounds including bis(imidazolyl) ligands and oxalate anions, [Cu2(BIM)2(C2O4)2]·4H2O (1) (BIM=bis(2-imidazolyl)methane) and [Cu2(BIK)2(C2O4)2] (2) (BIK=bis(2-imidazolyl)ketone). The oxalate anion acts as bidentate–monodentate in both cases, although it exhibits different coordination bridging modes: whereas in compound 1 a μ1,1,2-oxalato is observed, a μ1,2,3-oxalato is found in compound 2. In both cases, the 3D framework is held together by a combination of H-bonding and aromatic-aromatic interactions provided by the convenient structural features of BIM and BIK ligands and oxalate. EPR spectra are indicative of an essentially dx2-y2 ground state for the copper(II) ions in both compounds. Magnetic susceptibility measurements reveal the existence of weak antiferromagnetic exchange interactions between the copper(II) ions (2J=−0.33(1)cm−1 for compound 1 and 2J=−1.45 (1)cm−1 for compound 2. Finally, the reported values of the singlet–triplet gap are compared with those observed in related copper(II) compounds with bidentate–monodentate out-of-plane oxalato bridges.