Building Up a Hexacopper(II)-Pyrazolate/Oxamate Magnetic Complex with Rare Ethane-1,2-Dioxide (–OCH2CH2O–) as a Bridge Between Copper(II) Units

The synthesis, structural, and magnetic characterization of a novel neutral copper(II) hexanuclear complex [Cu6(en)4(OCH2CH2O)2(pyox)4]·3eg·en·12H2O (1) was investigated [en = ethylenediamine, eg = ethylene glycol, and H2pyox = 4-(1H-pyrazole-4-yl)phenylene-N-oxamic acid]. The crystal structure of 1, obtained by the single-crystal X-ray diffraction technique, revealed that the hexacopper(II) complex is built from two linear tricopper(II) complex subunits. Each subunit contains two [Cu(en)]2+ moieties connected to a [Cu(OCH2CH2O)] unit by two pyox2− ligands acting as μ-κN:κN′ bridges, as well as a [OCH2CH2O]2− ligand, which is ultimately found in the μ3-κO,O′:κO:κO′ coordination form. The subunits are connected via the amide portion of the pyox2− ligand, linked to copper atoms in the other subunit. They occupy the apical coordination positions, leading the trinuclear copper(II) segments to be almost perpendicular. The structural, chemical, and spectroscopic characterizations evidenced that ethylene glycol acted both as a solvent and a reactant upon deprotonation, forming the –OCH2CH2O– ligand due to the basic crystallization environment. DC magnetic studies revealed a strong antiferromagnetic interaction between the copper atoms within the trinuclear subunits, influenced by alkoxide and pyrazolate bridging ligands. Our findings offer new insights into the structural and magnetic properties of copper(II) complexes, enhancing the understanding of metal–ligand interactions in supramolecular chemistry.