Reactions of gases in solution. Part I. Products of the reaction of hydrogen with cobalt(II) cyanide complexes

Abstract

The number and nature of the complexes formed when aqueous solutions of cobalt(II) cyanide complexes react with hydrogen have been investigated. Studies of the equilibria and u.v.–visible spectra in solution show that at least three different complexes may be produced. The main product is shown to be the [Co^III(CN)₅H]^3– ion, which has been isolated in the solid state as the salt Cs₂Na[Co(CN)₅H]. The same ion can be produced by reduction with borohydride or sodium amalgam. The cobalt–hydrogen and –deuterium stretching frequencies are 1860 and 1340 cm.^–1, and bending frequencies 774 and 610 cm.^–1, respectively, in the solid state. Aqueous solutions of the complex show an absorption band at 305–306 mµ(ε_molar∼ 620), as already found by previous workers. A second complex, which is formed in solutions of low cobalt concentration and low ionic strength, contains less than five cyanide groups per cobalt and shows an absorption spectrum with the first d–d band at ∼300 mµ(ε_molar∼ 660); its structure may be [Co^III(CN)₄H₂]. A third complex of possible structure [Co^I(CN)₆] is observed at high cyanide concentrations; its formation from [Co^II(CN)₅H₂O] in the presence of hydrogen obeys an equilibrium involving one additional cyanide group.