Structure and magnetism of an exchange coupled system: An NMR approach

A binuclear copper(II) complex [Cu2L(OH)](C1O4)2·2H2O has been synthesized and characterized by X-ray crystallography and1H-NMR studies. The crystal structure shows that the bridging angles between Cu(l)-O(l)-Cu(2) and Cu(l)-O(2)-Cu(2) are 98.9(2)° and 102.2(2)° respectively. The Cu(l)-Cu(2) distance is 3.0097(12)Å. This indicates that the interaction between the two copper atoms is antiferromagnetic in nature. The geometry around Cu(l) is distorted square-pyramid with one water molecule occupying the axial fifth position, whereas, the geometry around Cu(2) is distorted square-planar with weak interactions of one of the perchlorate anion. There are eight molecules present in the unit cell. There is an interdimer interaction between the dimers. The temperature-dependent1H-NMR chemical shift studies have been performed on six different protons of this complex which reveals that the exchange coupling constant (- 2J) is same for all protons (208 ± 1 cm-1). However, the hyperfine coupling constant (A′) was found to be different in magnitude as well as in sign. We also report solvent dependent NMR properties. © 1995 Indian Academy of Sciences.