Fe(CN) 5ampy 3- (ampy = 4-aminopyridine) complex was unstable at pH ? 4 with respect to the dissociation due to the protonations of the complex. The first protonation on the 4-aminopyridine ligand at pK a = 3.2 resulted in a ? 150-fold increase in rate of dissociation as compared to that of the complex in the neutral solution. However, further protonation of the complex on the cyanide ligand at pK a = 1.5 increased the rate only slightly. The large increase in the rate constant of dissociation for Fe(CN) 5ampyH 2- complex suggests that in the transition state the proton is likely shifted from the amino group and becomes coordinated to a pair of dπ electrons directed at the face of the coordinated octahedron.
Relation:
Journal of the Chinese Chemical Society Volume 48, Issue 5, 2001, Pages 849-853
