FURTHER INVESTIGATION OF MOLECULAR, MAGNETIC, AND ELECTRONIC-STRUCTURES OF 2-HYDROXYPYRIDINATE COMPLEXES OF DIRUTHENIUM(II)

Another new Ru2(xhp)4 type compound, Ru2(fhp)4(thf) (fhp- = 6-fluoro-2-hydroxypyridinate), has been reported from Ru2- (O2CCH3)4 and characterized by X-ray crystallography and magnetic susceptibility measurements from ca. 5 to ca. 300 K. Dark brown Ru2(fhp)4(thf) crystallizes in space group P2(1)2(1)2(1) with a = 16.392 (4) angstrom, b = 17.161 (5) angstrom, c = 9.148 (2) angstrom, V = 2573 (1) angstrom-3, and Z = 4. The structure determined has Ru-Ru = 2.274 (1) angstrom and a polar ligand arrangement placing all like atoms (i.e., N's or O's) on the same metal centers. The magnetic behavior is identical with those previously describe for three other 2-hydroxypyridinate complexes and is thus consistent with a ground state derived from a (pi*)2(delta*)2 configuration, which is also required by the Ru-Ru bond length. A (pi*)3(delta*) configuration is explicitly excluded as a possible ground-state configuration for all carboxylate and hydroxypyridinate complexes of diruthenium(II) on the basis of an analysis that leads to a prediction of qualitatively different behavior of the effective magnetic moments as a function of temperature. SCF-X-alpha calculations provide quantitative support for the (pi*)2(delta*)2 configuration. A singlet-triplet Boltzmann distribution based on (pi*)4 and (pi*)3 (delta*) configurations also fails to have the type of temperature dependence in accord with experiment.