MERCURY(II)-PROMOTED FORMATION AND AQUATION OF LINKAGE ISOMERS OF TRANS-DICYANOTETRAAMMINECHROMIUM(III) - A POLAROGRAPHIC AND SPECTRAL STUDY

Polarography and spectrophotometry reveal various interactions between trans-Cr(NH3)(4)(CN)(2)(+) and Hg2+ in acidic aqueous solution. There is evidence for formation of two trinuclear adducts with Cr:Hg propor tions of 2:1 and 1:2, accompanied by linkage isomerization (Cr-NC-Hg) of the cyanide bridging groups. These processes are followed by Hg2+-i nduced aquation of CN-. The six Cr(III) species occurring in the react ion sequence are identified by their half-wave reduction potentials. T he trans configuration of the final aquation product, Cr(NH3)(4)(H2O)( 2)(3+), indicates complete stereoretention during all the reactions, c onsistent with the observed stoichiometry of Cr-Hg association which d iffers from that of a cis-dicyano analogue. The linkage isomerization of trans-Cr(NH3)(4)(CN)(2)(+) is much faster than that of trans-Cr(NH3 )(4)(H2O)(CN)(2)(+), while the rates of the respective Hg2+-promoted a quation reactions are the same, denoting trans effects of CN- in the f ormer process but not in the fatter.