NITROXIDE COMPLEXES OF DIRUTHENIUM(II,II) CARBOXYLATES - STRUCTURAL AND MAGNETIC-PROPERTIES

The bis adduct of Tempo (2,2,6,6-tetramethylpiperidine-N-oxyl) with diruthenium (II,II) tetrakis(trifluoroacetate) has been prepared and characterized by x-ray diffraction at room and low (201 K) temperatures. It is a centrosymmetric complex in which the free radical ligands are axially bound. Its magnetic properties were studied in the 5-300 K temperature range and compared to those of the bis-THF dimetal precursor and to those of the diruthenium(II,II) tetrakis(perfluorobenzoate) bis-Tempo derivative. These properties were interpreted considering a large zero-field splitting within the dimetal core and nitroxyl-nitroxyl and diruthenium-nitroxyl exchange interactions. In the two bis-Tempo adducts the exchange interaction between the free radical and the dimetal center is antiferromagnetic and large (almost-equal-to 300 cm-1). It was not possible to assess the presence of internitroxyl coupling through the metal-metal double bond. Relevant crystallographic parameters at room temperature are as follows: triclinic system, space group P1BAR, a = 8.779(2) angstrom, b = 10.728(3) angstrom, c = 11.597(3) angstrom, alpha = 107.1(1)-degrees,beta = 103.3(1)-degrees, gamma = 107.2(1)-degrees, Z = 2.