Instability of some nitrosylruthenium compounds in nitric acid

A trivalent cation of ruthenium species was found in a certain proportion in nitric acid solution of some of the nitrosylruthenium compounds such as nitrosylruthenium trinitrate (RuNO(NO3)3), nitrosylruthenium hydroxide (RuNO(OH)3) and disodium hydroxotetranitronitrosylruthenate (Na2RuNO(NO2)4OHx2H2O). The same species was also observed in nitric acid solution of ruthenium trichloride (RuCl3 3H2O). In order to determine whether the species is the nitrosylruthenium ion (RuNO3+) or the hydrated ruthenium ion (Ru3+), the species was separated from anionic, neutral and other cationic ruthenium ions by cation exchange chromatography. The species adsorbed on the cation exchange column was eluted by 6 N hydrochloric acid or 4 N nitric acid after thorough washing of the column by distilled water. The eluate was evaporated in a vacuum at room temperature. The residues did not show any absorption band in infrared spectrum in the vicinity of 1900 cm-1, characteristic of nitrosylruthenium compound. The determination of nitrogen content by Dumas's method showed that the residue obtained by elution with hydrochloric acid and the cation exchange resin adsorbing the species were free from nitrogen. The results obtained here revealed that the nitrosylruthenium bond, (Ru-NO), which has been considered to be a strong covalent bond, breaks in dilute nitric acid at room temperature. (orig.)