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

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, [Cu 2 (BIM) 2 (C 2 O 4 ) 2 ]·4H 2 O ( 1 ) (BIM = bis(2-imidazolyl)methane) and [Cu 2 (BIK) 2 (C 2 O 4 ) 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 μ 1,1,2 -oxalato is observed, a μ 1,2,3 -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 d x 2 -y 2 d x 2 - y 2 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 (2 J  = −0.33(1) cm −1 for compound 1 and 2 J  = −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.