Unexpected assembly of a tetranuclear copper(II) complex bridged by glyoximate groups

The tetranuclear copper(II) complex of composition [Cu4(dmg)2(Hdmg)2(H2dmg)2(H2O)3](ClO4)2·3H2O (H2dmg=dimethylglyoxime) has been synthesized and its crystal structure was determined by single-crystal X-ray diffraction analysis. The structure consists of one Hdmg−/dmg2−-bridged tetranuclear cation [Cu4(dmg)2(Hdmg)2(H2dmg)2(H2O)3]2+, two uncoordinated perchlorate anions and three crystallization water molecules. The tetranuclear cation can be described as two Hdmg−/dmg2−-bridged dimers: {[Cu(dmg)(Hdmg)(H2O)][Cu(H2dmg)(H2O)]}+ and {[Cu(dmg)(Hdmg)][Cu(H2dmg )(H2O)]}+, which are linked through the oxime group (Hdmg−) of the former dimer. The H2dmg ligands in the cation co-ordinate to the copper ion as capping ligands. The geometry around each copper atom is a distorted square pyramid. The IR and UV–Vis spectra have been investigated.