Magnetism and EPR Studies of Binuclear Ruthenium Hydride Binuclear Species Bearing Redox-Active Ligands.

Abstract

The binuclear complex {[N3]Ru(H)}2(μ-η1:η1-N2) ([N3] = 2,6-(ArylN═CMe)2C5H3N and Aryl = mesityl or xylyl) contains two formally Ru(I), d7 centers linked by a bridging dinitrogen ligand, although the odd electrons are substantially delocalized onto the redox non-innocent pincer ligands. The complex exhibits paramagnetic behavior in solution, but is diamagnetic in the solid state. This difference is attributed to intermolecular "π-stacking" observed in the solid state, which essentially couples unpaired electrons on each half of the complex to form delocalized 22-center-2-electron covalent bonds. Introduction of a bulky t-butyl group on the ligand pyridine ring prevents this intermolecular association and allows further investigation of the magnetic behavior and electronic structure of the binuclear species. The interaction of the unpaired electrons in the two halves of the complex has been probed with magnetic susceptibility and perpendicular and parallel mode EPR measurements, revealing a weakly antiferromagnetically coupled system with a thermally accessible triplet excited state. In addition, the mixed valent, S = 1/2, {[N3]Ru(H)}(μ-η1:η1-N2){[N3]Ru} system has also been observed via perpendicular mode EPR and was used to quantify the growth of the thermally accessible triplet state of the dihydride complex using parallel mode EPR.