Thiocyanate complexes of d-metals: Influence of concentration of kncs and nh4cl on a type of coordination of scn- ions by FTIR spectrometry

Abstract

By IR spectrometry thiocyanates aqueous solutions of divalent cations of cadmium, mercury, nickel, manganese, iron, zinc and cobalt were studied. It was found that cadmium (II), mercury (II), nickel (II), iron (II) thiocyanate ions coordinated by type thiocyanate, zinc (II) - according to the type isothiocyanate; cobalt (II) and manganese (II) coordination mode change depending on the concentration of potassium thiocyanate in a solution. These results are consistent with the theory of hard and soft acids and bases. Co2+ ions are intermediate acids, so they can coordinate with SCN- into two types; Zn2+ ions, although they belong to intermediate acids but have a strong affinity to nitrogen atoms, so thiocyanate group coordinated through nitrogen with Zn2+. Cations Hg2+ and Cd2+ are typical soft acids, so only coordinated SCN- ions through sulfur (as a mild base). Mn2+ ions can coordinate SCN- by two types. The effect of additives of the ammonium chloride ions on thiocyanate ions (0.5 mol/l) coordination with cobalt (II) ions was studie. With the increasing concentration of ammonium chloride in a solution a change occurs of coordination type with thiocyanate to isothiocyanate. It has been suggested that the increase in the concentration of potassium thiocyanate leads to the increase in the proportion of Co(NCS)4 2- and reduce the proportion of «free» water (unrelated with ions in the solution). Therefore, SCN- ions in the case Mn2+ and Co2+ oriented so that the hydrophobic sulfur atoms are external ones.