Ligand substitution, pH dependent deoxygenation, and linkage isomerization reactions of the 2,2′-bipyridinetetranitroruthenate dianion

Daniel A. Freedman, Daron E. Janzen, Jennifer L. Vreeland, Hannah M. Tully, Kent R. Mann

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

The reaction of the [Ru(bpy)(NO2)4]2- (bpy = 2,2′-bipyridine) ion in aqueous solutions produces two different nitrosyl complexes, depending on the pH of the solution. At acidic pH, complex cis, cis-Ru(bpy)(NO2)2(ONO)(NO) was isolated. At neutral or basic pH, [Ru(bpy)(NO2)4]2- reacts to give cis, trans-Ru(bpy)(NO2)2(NO)(OH). Both new complexes were fully characterized by elemental analysis and UV-vis, IR, 1H NMR, and 15N NMR spectroscopy. A single-crystal x-ray structure of cis, trans-Ru(bpy)(NO2)2(NO)(OH) was also obtained. cis,cis-Ru(bpy)(NO2)2(ONO)-(NO) isomerizes in acetone or water solution to give a mixture of the trans, cis-Ru(bpy)(NO2)2(ONO)(NO) and cis,-cis-Ru(bpy)(ONO)2(NO2)(NO) linkage isomers as determined by 1H and 15N NMR spectroscopy. A single-crystal x-ray structure of a solid solution of cis,cis-Ru(bpy)(ONO)2(NO2)(NO)/trans, cis-Ru(bpy)(NO2)2(ONO)(NO) was also obtained. This pair of isomers is the first crystallographically characterized compound with nitro, nitrito, and nitrosyl ligands. The kinetic studies of the Ru-NO2→Ru-NO conversion reactions of [Ru(bpy)(NO2)4]2- in buffered solutions from pH 3 to pH 9 complement previous studies of the reverse reaction. The reactions are first order in [Ru(bpy)(NO2)4]2-. At high pH, the reaction is independent of the concentration of H+ while, at low pH, the reaction is first order in the concentration of H+. The rate determining step of the high pH reaction involves breakage of the Ru-NO2 bond while, at low pH, the mechanism involves a rapid reversible protonation of a NO2 ligand followed by the rate determining loss of hydroxide to produce a nitrosyl ligand.

Original languageEnglish (US)
Pages (from-to)3820-3829
Number of pages10
JournalInorganic chemistry
Volume41
Issue number15
DOIs
StatePublished - Aug 1 2002

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