Hexaammineruthenium III Tribromide

Hexaammineruthenium(II) dichloride (1 g.) (see Note 5 above) is oxidized with bromine water, as described above in Sec. C. After oxidation solid sodium bromide is dissolved in the neutral solution until the product [Ru(NH3)6]Br3 forms as a yellow powder. The product is collected and redissolved in water (5 ml.) and reprecipitated by the addition of sodium bromide. The product is washed finally with ethanol. Yield is 1 g. Anal. Caled. for [Ru(NII3)0]Br3 N,. 19.0%. Found N, 18.8%. 

Nitrogen is determined by the Kjeldahl method using Devarda s alloy. The complex and the alloy are placed in a standard Kjeldahl apparatus and the ammonia distilled off from a 7.5 M sodium hydroxide solution into 2% boric acid. The ammonia is titrated with standard hydrochloric acid using bromocresol green-methyl red as indicator. 

The yellow hexaammineruthenium(II) cation is a moderately strong reducing agent and will, for example, reduce hydrogen chloride, mercuric chloride, gold(III) chloride,1 and the hexa-amminecobalt(III) cation.6 The dry complexes are stable for a matter of weeks, especially when kept cold, but in aqueous solution decomposition is more rapid. 

The yellow pentaammine complex of ruthenium(III) chloride crystallizes as octahedral crystals. It is a stable compound and exists in hydrochloric acid solution over a wide range of acid concentrations. The pale yellow hexaammine complex of ruthenium(III) is soluble in water and an excellent starting material for further ruthenium(III) compounds.5 

The infrared spectra of the complexes have been recorded, and assignments have been made.2 The Ru(II) and Ru(III) ammines are readily distinguished by their infrared absorptions around 1300 cm.-1. 

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