SYNTHESIS, X-RAY STRUCTURE, AND SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF NOVEL HETERONUCLEAR RUTHENIUM OSMIUM COMPLEXES WITH AN ASYMMETRIC TRIAZOLATE BRIDGE

The heterodinuclear compounds [(bpy)2Ru(bpt)O5(bpy)2](PF6)3 (RuO5) and [(bpy)2O5(bpt)Ru(bpy)2](PF6)3 (O5Ru), where Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole and bpy = 2,2'-bipyridine, have been prepared and characterized. The crystal and molecular structures of [(Ru(bpy)2)2(bpt)](CF3SO3)3໢4H2O and [(bpy)2Ru(bpt)O5(bpy)2](CF3SO3)34H2O have been determined. The dinuclear ruthenium(II)compound crystallizes in the monoclinic space group P21/c with four molecules in a cell of dimensions a = 13.510 (1) Å, b = 16.110 (2) Å, c = 29.861 (4) Å, β = 99.225 (9)°. Only one of the two possible geometrical isomers of the ruthenium dinuclear compound was found in the crystal structure. The two metal centers are coordinated via N(1) and N(4) of the triazole ring with a Ru(1)-N(1) distance of 2.03 (1) Å and a Ru(2)-N(4) distance of 2.11 (1) Å. The metal-metal distance is 6.184 (2) Å. In [(bpy)2Ru(bpt)O5(bpy)2](CF3SO3)34H2O with Z = 4, P21/c, α = 13.5802 (7) Å, b = 16.247 (2) Å, c = 30.043 (3) Å, β = 100.348 (6)°, ruthenium is coordinated via N(1), whereas osmium binds via N(4) of triazole with similar metal-nitrogen distances as observed for the ruthenium homonuclear compounds. The NMR data revealed that the OsRu isomer has a similar structure, but with the osmium center bound via N(1) and the ruthenium ion coordinated via N(4) of the triazole ring. The electrochemical potentials of the two heterodinuclear compounds are significantly different; for the RuOs compound the oxidation potentials are 0.73 and 1.20 V, while for the OsRu isomer the oxidation potentials arc at 0.65 and 1.30 V vs SCE. These differences in electrochemical behavior between the two isomeric RuOs and OsRu compounds suggest that the N(1) atom of the triazole ring is a better σ-donor than N(4). The mixed-valence dinuclear systems all exhibit rather intense intervalence transition (IT) bands in the near-infrared region, suggesting a moderately strong metal-metal interaction for the bpt systems. A correlation between the energy of the IT bands of the mixed-valence dinuclear complexes and the oxidation potentials has been observed. © 1990, American Chemical Society. All rights reserved.