Ligand Steric Interactions Modulate Multidentate Ligand Exchange Pathways: Kinetics of Nickel(II) Ion Capture from N-Substituted IDA Complexes by CDTA.

Exchange reactions between multidentate ligands (also known as chelating agents) contribute to kinetic control of metal ion speciation in aquatic environments. However, the complexity of the stepwise reaction mechanism complicates predictions of kinetic behavior (rates, rate laws, and mechanisms). Clarity is achieved with the adjunctive-semijunctive-disjunctive paradigm, which categorizes multidentate ligand exchange pathways along a continuum according to the decreasing ease of forming intermediate mixed-ligand ternary complexes.

Effects of calcium on the kinetics of a model disjunctive ligand exchange reaction: implications for dynamic trace metal ion speciation.

Trace metal ion speciation in natural waters is often under kinetic control due to slow exchange reactions involving multidentate ligands (both natural and anthropogenic) and constituent ions (e.g. calcium).