Spectrochemistry of solutions. Part 16. A Raman spectroscopic study of the complexation of mercury(II) by cyanide ligands in liquid ammonia at 293 K

Abstract

The pattern of complexation of Hg(CN)₂ by CN^– ligands in liquid ammonia has been examined. Steps involve straightforward replacements of NH₃ by CN^– on the Hg(CN)₂(NH₃)₂ species through [Hg(CN)₃(NH₃)]^– to [Hg(CN)₄]^2– with no change in the tetrahedral geometry around the Hg^II centre. No higher complexes are found. The geometry of complexation differs from that observed in both water and methanol solutions where addition of CN^– converts linear Hg(CN)₂ to tetrahedral [Hg(CN)⁴]^2–. Band assignments of the symmetric and antisymmetric v(CN) stretching vibrations have been made for the complexes as follows: Hg(CN)₂(NH₃)₂, 2 164 (sym), 2 161 (antisym); [Hg(CN)₃(NH₃)]^–, 2 148 (sym), 2 145 (antisym); [Hg(CN)₄]^2–, 2 139 (sym), 2 134 cm^–1(antisym).