Nitrosoruthenium nitrite-nitrate complexes in aqueous and nitric acid solutions as probed by 15N NMR

Aqueous and nitric acid solutions of Na₂[Ru¹⁵NO(¹⁵NO₂)₄OH] in the concentration range $c_{H^{15} NO_3 }$ = 0–3.3 mol/L have been studied by ¹⁵N NMR, dominating complex species have been identified, and the equilibrium constants for the nitrate ion incorporation into the inner coordination sphere of nitrosoruthenium have been estimated. The equilibration time for such equilibria is no more than 2 h at room temperature. In addition to the nitro complexes, isomeric nitritonitronitrosoruthenium compounds have been identified in solutions. In weak acidic solutions at $c_{HNO_3 }$ < 0.25 mol/L, nitro and nitritonitro complexes containing four and three coordinated nitrite ions predominate. At the HNO₃ concentration 0.4–1.7 mol/L, the vast majority of ruthenium presents in solution as fac-dinitronitrosoruthenium complexes containing coordinated water molecules and nitrate ions. In solutions with $c_{HNO_3 }$ > 1.5 mol/L, the fractions of dinitro- and mononitronitrosoruthenium complexes are comparable. In strong nitric acid solutions ( $c_{H^{15} NO_3 }$ = 10 mol/L) kept for three years in contact with air, nitro complexes are absent, and mononitrato- and dinitratoaquanitrosoruthenium complexes are dominating.