83781-30-0Relevant articles and documents
Lay, Peter A.,Magnuson, Roy H.,Sen, J.,Taube, Henry
, p. 7658 - 7659 (1982)
Pyrazine-bridged complexes. Synthesis of and spectroscopic studies on binuclear pyrazine complexes of osmium, ruthenium, and rhodium ammines
Lay, Peter A.,Magnuson, Roy H.,Taube, Henry
, p. 2364 - 2371 (2008/10/08)
The compound [(NH3)5Os(pz)Os(NH3)5]Cl6 is obtained (~40% yield) by the reaction of pyrazine (pz) with a small excess of [Os(NH3)5(OSO2CF3)](CF 3SO3)2 in dry acetone for 8 days and, more conveniently, by the reaction of [Os(NH3)5(pz)]2+ with [Os(NH3)5(OSO2CF3)]2+ in acetone. The best method of preparation of the binuclear ion involves the in situ generation of [Os(NH3)5(pz)]2+ by reducing a mixture of [Os(NH3)5(OSO2CF3)]2+ and pz (2:1 molar mixture) in a weakly coordinating solvent. The comproportionation constant, 1.0 × 1013 (0.1 M HCl, 22°C), obtained from electrochemical measurements (E°(6+/5+) = 0.32 V and E°(5+/4+) = -0.44 V vs NHE) is 7 orders of magnitude greater than that observed for the ruthenium analogue. The mixed-valence ion is thought to be delocalized, since the transitions arising from the effects of spin-orbit coupling on the ground electronic state, which are observed for all mononuclear and binuclear Os(III) complexes (1500-2100 nm), are absent. Instead, intense electronic transitions (ε ~(3-4) × 103 M-1 cm-1) are present in the normal-IR region (3000-3400 cm-1), which have been assigned the spin-orbit transitions of the delocalized complex. The very low intensity of the symmetric pyrazine mode in the IR spectrum (1600 cm-1) is also consistent with a symmetric delocalized description. The synthesis and properties of the binuclear complexes [(NH3)4(N2)Os(pz)Os(NH3) 5]n+ (n = 4, 5, 6), [(NH3)4(Cl)Os(pz)Os(NH3)5] m+ (m = 3, 4, 5), [(NH3)5Os(pz)Rh(NH3)5]m+ (m = 6, 5), and [(NH3)5Rh(pz)Rh(NH3)5]6+ are also described, in addition to improved syntheses of the binuclear Ru2 and RuRh complexes. The mixed-valence ion [(NH3)4(Cl)Os(pz)Os(NH3)5] 4+ has spectral properties similar to those of [(NH3)5Os(pz)Os(NH3)5]5+ and is believed to possess an electronic structure close to the delocalized description. By contrast, [(NH3)4(N2)Os(pz)Os(NH3) 5]5+ has properties typical of a valence-localized species. The [(NH3)5Rh(pz)Rh(NH3)5]5+ ion is very unstable and rapidly decomposes to form [Rh(NH3)5(pz)]3+ and an uncharacterized product. The species [(NH3)5Os(pz)Rh(NH3)5]5+ also is unstable and appears to undergo a slow intramolecular reduction of Rh(III) by Os(II).