83781-30-0Relevant academic research and scientific papers
Syntheses of pentaammineosmium(III) and -osmium(II) complexes: Pentaammine(trifluoromethanesulfonato-O)osmium(III)
Lay, Peter A.,Magnuson, Roy H.,Taube, Henry
, p. 3001 - 3007 (2008/10/08)
The triflato complex [Os(NH3)5(OSO2CF3)](CF 3SO3)2 is prepared in 95-100% yield by either the Br2 or O2 oxidation of [Os(NH3)5(N2)]Cl2 in neat CF3SO3H or the substitution reaction of [Os(NH3)5Cl]Cl2 in neat CF3SO3H. Solvation rates are rather rapid in comparison to those of other Os(III) complexes, with kobs = 8.8 × 10-4 s-1 at 25°C in 1 M aqueous CF3SO3H. The solvation rate constants have been recorded for a number of solvents; however, basic solvents cause disproportionation reactions, which limits the range of solvents in which this reaction can be studied. In the case of [Os(NH3)5(acetone)]3+, a second first-order reaction is observed, which is believed to involve the condensation of acetone with an ammine ligand. A large variety of pentaammmeosmium(III) complexes can be prepared either by the direct reaction of the triflato complex with the neat ligand or by the use of relatively labile solvent complexes as intermediates. These reactions are not suitable for basic ligands because of the disproportionation problems. Complexes with many anionic ligands are prepared readily by heating the triflato complex in aqueous solutions of HX or acidified NaX solutions. The osmium(II) analogues are prepared readily from the reduction of the osmium(III) complexes. The shifts in the Os(III/II) redox potentials of the complexes containing the π-acid ligands compared to [Os(NH3)6]3+/2+ are more positive than the corresponding shifts in the ruthenium analogues. This indicates the greater extent of π-back-bonding for Os(II), as compared to Ru(II). The reactivity patterns of the Os(III) and Ru(III) complexes also indicate that π-back-bonding is significant for Os(III), but not for Ru(III). The [Os(NH3)5(acetone)]3+/2+ and [Os(NH3)5(dmso)]3+/2+ complexes exhibit oxidation-state-dependent linkage isomerization reactions. The electronic absorption spectra of both the Os(III) and Os(II) complexes with π-acid ligands are dominated by MLCT transitions, which occur at lower energies for the former. The electronic transitions that occur within the t2 subset of the 5d orbitals are observed in the near-IR region. They are due to the effects of spin-orbit coupling on the t25 electronic configuration and are an order of magnitude more intense for the complexes with π-acid or π-base ligands than those where the ligand shows little or no tendency to π-bond.
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).
