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The stepwise ligation patterns for the complexation by CNof Znz+, Cd2+ and Hg2+ in liquid ammonia solutions have been established from analyses of the infrared and Raman spectra of M"/CN-mixtures between 295 and 21 3 K. All the cyano-complexes are soluble and complexation, complete at the 4 : l stage for all three metal cations, proceeds by direct replacement of the solvating NH, by CN-on tetrahedrally co-ordinated Zn2+ and Hg2+. Cyano-ligation of Cd2+ is quite different with octahedral 1 : 1 and 2:l complexes, followed by a change to tetrahedral 3 : l and 4 : l complexes. There is no evidence for multinuclear complex formation, and mononuclear complexation is strong for all three metals; no uncomplexed CN-is present until the solution composition exceeds [CN-]/[M"] = 4.0: 1. Stable outer-sphere complexes (or ion associates) form between the 4 : 1 complexes and the Na+ cocation, viz. [Na+ -NC-M(CN),], and there is some evidence f c similar

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