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

摘要

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)(C2O4)(2)]center dot 4H(2)O (1) (BIM = bis(2-imidazolyl)methane) and [Cu-2(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 mu(1,1,2)-oxalato is observed, a mu(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 dx(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 (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. (C) 2016 Elsevier Ltd. All rights reserved.