Ligand exchange dynamics in aqueous solution studied with 2DIR spectroscopy

Sungnam Park, Minbiao Ji, Kelly J. Gaffney

Research output: Contribution to journalArticle

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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.

Original languageEnglish
Pages (from-to)6693-6702
Number of pages10
JournalJournal of Physical Chemistry B
Volume114
Issue number19
DOIs
Publication statusPublished - 2010 May 20

Fingerprint

Ion exchange
Ligands
Spectroscopy
Ions
aqueous solutions
ligands
Anions
spectroscopy
Negative ions
ions
anions
perchlorates
Cations
Positive ions
Vibrational spectroscopy
Water
cations
Solvation
Magnesium
Stretching

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

Ligand exchange dynamics in aqueous solution studied with 2DIR spectroscopy. / Park, Sungnam; Ji, Minbiao; Gaffney, Kelly J.

In: Journal of Physical Chemistry B, Vol. 114, No. 19, 20.05.2010, p. 6693-6702.

Research output: Contribution to journalArticle

Park, Sungnam ; Ji, Minbiao ; Gaffney, Kelly J. / Ligand exchange dynamics in aqueous solution studied with 2DIR spectroscopy. In: Journal of Physical Chemistry B. 2010 ; Vol. 114, No. 19. pp. 6693-6702.
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