Interaction of cyanopentaamminechromium(III) with mercuric ion. Electrochemical, spectral and preparative study of adduct formation and linkage isomerism

Abstract

The reaction of Cr(NH 3) 5(CN) 2+ with Hg 2+ was investigated in aqueous medium by various electrochemical techniques, as well as by absorption and emission spectrophotometry. Evidence was found for formation in solution of a stable 2:1 adduct, the polarographic and spectral properties of which indicate linkage isomerization (CrNCHg) of the cyano bridging group. In addition, two solids containing 4:1 and 2:1 Cr:Hg adduct species were isolated and characterized. The kinetics of adduct formation and subsequent Hg 2+promoted CN − aquation were studied by monitoring the phosphorescence of cyanopentaamminechromium(III) end by polarography, respectively. The former reaction obeys the rate law: −d[Cr]/d t= k 1[Cr]+ k 2[Cr] 2, with k 1 independent of the [Hg 2+]:[Cr] ratio in the 5–700 range, and k 2 decreasing as this ratio increases. The aquation rate is independent of both [Hg 2+] and [H 3O +]. The factors affecting the two reaction stages are briefly discussed.