INTERACTION OF CYANOPENTAAMMINECHROMIUM(III) WITH MERCURIC ION - ELECTROCHEMICAL, SPECTRAL AND PREPARATIVE STUDY OF ADDUCT FORMATION AND LINKAGE ISOMERISM

The reaction of Cr(NH3)5(CN)2+ with Hg2+ was investigated in aqueous m edium by various electrochemical techniques, as well as by absorption and emission spectrophotometry. Evidence was found for formation in so lution of a stable 2:1 adduct, the polarographic and spectral properti es of which indicate linkage isomerization (Cr-NC-Hg) of the cyano bri dging group. In addition, two solids containing 4:1 and 2:1 Cr:Hg addu ct species were isolated and characterized. The kinetics of adduct for mation and subsequent Hg2+-promoted CN- aquation were studied by monit oring the phosphorescence of cyanopentaamminechromium(III) and by pola rography, respectively. The former reaction obeys the rate law: -d[Cr] /dt=k1[Cr]+k2[Cr]2, with k1 independent of the [Hg2+]:[Cr] ratio in th e 5-700 range, and k2 decreasing as this ratio increases. The aquation rate is independent of both [Hg2+] and [H3O+]. The factors affecting the two reaction stages are briefly discussed.