STRUCTURAL AND MAGNETIC-PROPERTIES OF A BIS(NITROXYL) BINUCLEAR COPPER(II) COMPLEX

Bis(µ-ethoxo)bis[(1-oxy-2,2,6,6-tetramethylpiperidin-4-yl)pivaloylacetato]dicopper(II), a bis(nitroxyl)dicopper complex, has been prepared. Its crystal and molecular structures have been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P21/n with two molecules in a unit cell of dimensions a = 12.073 (3) Å, b = 11.510 (2) Å, c = 14.781 (2) Å, and β = 101.47 (2)°. The Cu2O2 core is planar, and the Cu-Cu separation is 2.974 (2) Å. The coordination geometry around each copper ion is roughly square pyramidal with axially bound nitroxyl ligands. Significant parameters of the coordinated nitroxide include Cu-O = 3.036 (4) Å. On the basis of metal-metal and metal-nitroxyl distances, the magnetic data are discussed in terms of four S = ½ spin units involving two copper(II) ions of one molecule and two nitroxyl groups of neighboring molecules. It is found that the two copper ions are strongly antiferromagnetically coupled, J = −538 K, while the copper-nitroxyl interaction is ferromagnetic, j = +12 K. These results are of use in rationalizing magnetostructural correlations in metal-nitroxyl adducts and show that binuclear complexes might be used in the design of high-spin molecular species. © 1990, American Chemical Society. All rights reserved.