Reactivity and structure of dinitrogen complexes of ruthenium(II)

Abstract

The formation of [Ru(NH₃)₅(N₂)]²⁺ from ruthenium(III) trichloride and ammonia by zinc reduction is described. That neither the dinitrogen in the above complex, nor that in the dinuclear complexion, [{Ru(NH₃)₅}₂(N₂)]⁴⁺, can be reduced to ammonia by common reducing agents in aqueous solution is demonstrated by attempts to obtain ¹⁵NH₃ from the corresponding ¹⁵N₂ complexes. It had previously been reported that part of the N₂ in [Ru(NH₃)₅(N₂)]²⁺ could be reduced to ammonia by sodium borohydride in water, but we show now that this erroneous result was caused by the presence of a hydrazine impurty, probably [Ru(NH₃)₅(N₂H₄)]²⁺. The contaminant can be removed from [Ru(NH₃)₅(N₂)]²⁺ by oxidation with mercuric chloride.

The Raman spectrum of [{Ru(NH₃)₅}₂(N₂)][BF₄]₄ shows ν(NN) to be as 2100 cm.^–1, and the complexion is diamagnetic, consistent with the linear structure [(NH₃)₅Ru–NN–Ru(NH₃)₅]⁴⁺.