The formation of the complex pentacyano(3‐pyrazincarboxylate)ferrate(II) in various water‐cosolvent mixtures

Abstract

Abstract This article presents the kinetic of formation of pentacyano(3‐pyrazincarboxylate)ferrate(II) from pyrazincarboxylate and pentacyanoaquoferrate(II) ions in various isodielectric water‐cosolvent mixtures at 298 K. The rate law is in the form d [Fe(CN) 5 (3‐pzCO 2 ) 4− ]/ dt = 𝓀 f [Fe(CN) 5 H 2 O −3 ] [pzCO 2 − ]. Plots of log(𝓀 f /dm 3 mol −1 s −1 ) vs. D (where D m is the bulk dielectric constant of the medium) and log(𝓀 f /dm 3 mol −1 s −1 ) vs. the Grunwald‐Winstein parameter are nonlinear for some of the mixtures and to each mixture corresponds a different behavior in respect to the above parameters. The plots of log(𝓀 f /dm 3 mol −1 s −1 ) vs. the mol fraction of water are straight lines over the entire composition range studied, except for the water‐methanol mixture. It is evident that the solvation phenomenon plays a dominant role and that the rate of formation is mediated by the dual solvent vectors, the overall basicity and acidity of the solvent mixtures.