Spectrochemistry of solutions. Part 25. Cyano-complexation of nickel(II), palladium(II) and platinum(II) in liquid ammonia

Abstract

A vibrational spectroscopic study of cyano-ligation of Ni^II, Pd^II and Pt^II in liquid NH₃ has been performed. Only [Ni(CN)₄]^2– and [Ni(NH₃)₆]²⁺ are observed in the Ni^II–CN^––NH₃ system. In the Pt^II–CN^––NH₃ system [Pt(CN)₄]^2–, trans-[Pt(NH₃)₂(CN)₂] and [Pt(NH₃)₆]²⁺ exist in equilibrium. In contrast, the Pd^II–CN^––NH₃ system slowly equilibrates (1–3 d) to mixtures containing [Pd(NH₃)₆]²⁺, [Pd(NH₃)₃(CN)]⁺, cis-[Pd(NH₃)₂(CN)₂], [Pd(NH₃)(CN)₃]^– and [Pd(CN)₄]^2–, but not trans-[Pd(NH₃)₂(CN)₂]. Infrared and Raman frequencies have been recorded. In all three systems ion pairs, in which the alkali-metal co-cation M interacts with square-planar [M′(CN)₄]^2– through one of its CN^– ligands, have been identified as stable species: [M⁺⋯^–NC·M′(CN)₃]^–. In liquid NH₃, cyano-complexes of Pd^IV and Pt^IV are immediately reduced to Pd^II and Pt^II.