Resolving the Structures of Lanthanide-Ligand Complexes with MD and EXAFS (Prof. David Cantu, UN-R)

Title: Resolving the Structures of Lanthanide-Ligand Complexes in Solution with Molecular Dynamics Simulations and Extended X-ray Absorption Fine Structure
Speaker: Prof. David Cantu (University of Nevada, Reno)
Abstract:
The properties and applications of lanthanide-ligand complexes are linked to their coordination structure. Resolving the coordination structure of lanthanide Ln3+ ions in solution is challenging because they can form coordination bonds with ligand, solvent, and anion molecules in dynamic structures. The coordination structures of several Ln-(solvent/anion/ligand) complexes are determined by combining ab initio molecular dynamics (AIMD) simulations and extended X-ray absorption fine structure (EXAFS) spectroscopy. AIMD simulations of Ln-(solvent/anion/ligand) complexes are conducted to predict their solution structures, and theoretical EXAFS spectra are derived using atomic coordinates from the AIMD simulations to generate predicted EXAFS spectra (MD-EXAFS). The MD-EXAFS spectra are directly compared, without fitting, to the measured EXAFS spectra of the same Ln-(solvent/anion/ligand) complex: agreement between MD-EXAFS and EXAFS spectra indicates that the structures in the AIMD simulations are representative of those measured experimentally. The combined AIMD and EXAFS approach was used to resolve the solution structures of Ln3+ aqua ions, Ln-ligand complexes in different protonation states in aqueous solution, and Ln-ligand complexes with different counterions in an organic solvent. Accounting for structural variations in the simulations of the Ln-(solvent/anion/ligand) complexes in solution is crucial to replicate experimental EXAFS spectra.