A new class of metal cyano-complexes. Part I. Preparation and nature of the copper complex

Abstract

A study of the reaction between Cu²⁺ and CN^– ions in aqueous solution has shown that at a CN/Cu molar ratio of 4, and pH 7·3, the solution is coloured pink, and on further addition of Cu²⁺ the colour intensifies to deep wine red, at pH 5·7, below which CuCN is precipitated. The effect of concentration of reagents, pH, temperature, and time of standing on the stability of colour has been studied. The coloured solution exhibits an absorption band at 511 mµ and the coloration is attributed to the formation of a dicyano-monocyanogen complex ion, [Cu(CN)₂NCCN]^–. The colour could also be produced by passing pure (CN)₂ gas in a solution containing mainly Cu(CN)₂^– and prepared from CuCN + KCN. On standing, the complex polymerises to a dark brown solid which is highly resistant to chemical attack but decomposes on heating, giving (CN)₂ gas. The evidence for the co-ordination of cyanogen has been inferred from infrared spectra, and the results of chemical analysis of the sodium salt agree well with the formula Na[Cu(CN)₂NCCN],4H₂O. The effect of thermal treatment has also been studied by differential thermal analysis.