Ligand Exchange Dynamics in Aqueous Solution Studied with 2DIR Spectroscopy
- 28 April 2010
- journal article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry B
- Vol. 114 (19), 6693-6702
- https://doi.org/10.1021/jp100833t
Abstract
We have used time-resolved multidimensional vibrational spectroscopy, generally termed 2DIR spectroscopy, to study the equilibrium dynamics of ligand exchange in an aqueous solution containing 3.4 M Mg(ClO4)2 and 1.2 M NaSCN. The sensitivity of the CN stretching frequency of thiocyanate (SCN−) to contact ion pair formation with Mg2+ ions generates distinct spectroscopic signatures for the MgNCS+ contact ion pair and the free SCN−. We have utilized 2DIR spectroscopy to successfully resolve the interconversion between these thiocyanate configurations and measured the MgNCS+ contact ion pair dissociation time constant to be 52 ± 10 ps. We attribute the observed dynamics to perchlorate−thiocyanate anion exchange in the first solvation shell of the Mg2+ cation. Magnesium ions in this concentrated ionic solution will be coordinated by water molecules, as well as perchlorate and thiocyanate ions. While prior studies have observed microsecond residence times for water ligands in the first coordination sphere of Mg2+, our study represents the first experimental observation of anion exchange in the first solvent shell of the Mg2+ cation. We have also used orientational relaxation and spectral diffusion dynamics to quantify the dynamical distinctions between the free anion and the anion in the contact ion pair.Keywords
This publication has 76 references indexed in Scilit:
- Quantitative Characterization of Ion Pairing and Cluster Formation in Strong 1:1 ElectrolytesThe Journal of Physical Chemistry B, 2007
- Ultrafast Carbon-Carbon Single-Bond Rotational Isomerization in Room-Temperature SolutionScience, 2006
- Ultrafast Dynamics of Solute-Solvent Complexation Observed at Thermal Equilibrium in Real TimeScience, 2005
- Chemical exchange 2D IR of hydrogen-bond making and breakingProceedings of the National Academy of Sciences of the United States of America, 2005
- Hydrogen-bond lifetime measured by time-resolved 2D-IR spectroscopy: N-methylacetamide in methanolChemical Physics, 2001
- Kinetic Pathways of Ion Pair Dissociation in WaterThe Journal of Physical Chemistry B, 1999
- Computer simulations of NaCl association in polarizable waterThe Journal of Chemical Physics, 1994
- A theoretical model for SN1 ionic dissociation in solution. 1. Activation free energetics and transition-state structureJournal of the American Chemical Society, 1992
- Friction kernels for the relative dynamics of ion pairs in waterThe Journal of Chemical Physics, 1992
- Dynamical aspects of the sodium(1+)-chloride ion pair association in waterThe Journal of Physical Chemistry, 1992