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Ligand Steric Interactions Modulate Multidentate Ligand Exchange Pathways: Kinetics of Nickel(II) Ion Capture from
Nathan E Boland1, Alan T Stone1
1Department of Environmental Health and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
Inorganic Chemistry
|August 15, 2022
Summary
Steric bulk in chelating agents influences metal ion exchange pathways. Increased bulk favors disjunctive pathways, altering reaction rates and environmental metal speciation predictions.
Area of Science:
- Environmental Chemistry
- Coordination Chemistry
- Chemical Kinetics
Background:
- Multidentate ligand exchange reactions control metal ion speciation in aquatic systems.
- Predicting kinetic behavior is challenging due to complex reaction mechanisms.
Purpose of the Study:
- To investigate the impact of steric interactions between ligands on metal-chelate exchange pathways.
- To elucidate how N-substituent bulk in iminodiacetate ligands affects reaction kinetics.
Main Methods:
- Utilized capillary electrophoresis to monitor ligand exchange reactions.
- Employed kinetic modeling to analyze reaction pathways and rates.
- Studied nickel(II) complexes with various N-substituted iminodiacetate ligands (IDA, MIDA, BIDA) and CDTA.
Main Results:
- Exchange reactions proceed via parallel adjunctive and disjunctive pathways.
- Increased steric bulk of N-substituents shifts product formation towards the disjunctive pathway.
- Pathway shifts result in nonlinear effects on overall reaction rates and ligand concentration dependence.
Conclusions:
- Steric hindrance plays a critical role in directing ligand exchange mechanisms.
- Understanding these pathways is crucial for predicting dynamic metal ion speciation in the environment.
- The adjunctive-disjunctive paradigm provides clarity for complex kinetic behaviors.
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