A tetranuclear copper(II) complex: crystal structure, assembly, EPR, electrochemistry and magnetism

A tetranuclear copper(II) complex, [Cu2L]2(ClO4)2 4H2O (1), where H3L = N,N'-bis(4-(3'-formyl-5'-chlorosalicyclidene)iminoethyl)-4-chloro-2,6-bimethyliminophenol, has been synthesized and structurally characterized by ES-MS, IR and X-ray crystallography. The complex is a dimer of two dinuclear copper(II) acylic enantiomorph subunits ([Cu2L]ClO4 2H2O), held together by -, coordination and hydrogen bond interactions. The Cu-Cu separation in each subunit, bridged by one phenoxide, is 3.228 , and the shortest distance of Cu-Cu between the two subunits is 3.252 . There are two crystallographically unique copper(II) environments, one (Cu1) is square-based pyramidal with O3N2 donor set, another (Cu2) square planar with O2N2 donor set. The cyclic voltammogram of the complex shows that it undergoes two stepwise reduction processes, Epc = -0.707 and -0.850 V, respectively. Magnetic measurements in the 2-300 K range indicate strong antiferromagnetic interactions between Cu(II) ions in each subunit with the exchange constant J = -211(2) cm-1. The observation has been rationalized on the basis of the effective magnetic pathway.