Effect of ion-ligand binding on ion pairing dynamics studied by two-dimensional infrared spectroscopy
- Authors
- Kwon, YoungAh; Lee, Junho; Park, Sungnam
- Issue Date
- 7-5월-2017
- Publisher
- ROYAL SOC CHEMISTRY
- Citation
- PHYSICAL CHEMISTRY CHEMICAL PHYSICS, v.19, no.17, pp.10889 - 10897
- Indexed
- SCIE
SCOPUS
- Journal Title
- PHYSICAL CHEMISTRY CHEMICAL PHYSICS
- Volume
- 19
- Number
- 17
- Start Page
- 10889
- End Page
- 10897
- URI
- https://scholar.korea.ac.kr/handle/2021.sw.korea/83479
- DOI
- 10.1039/c6cp08852j
- ISSN
- 1463-9076
- Abstract
- Cation-specific ion pairing dynamics between M+ (M = Ag or Cu) and SCN- in N, N-dimethylthioformamide (DMTF) are studied by probing the nitrile (CN) stretching vibration. The SCN- ion, which is an ambidentate ligand, readily associates with cations to form two different types of contact ion pairs (CIPs) (i.e., M-SCN or M-NCS) and its CN stretching frequency is significantly blue-shifted so that free SCN- and CIPs can be well-distinguished in the FTIR spectra. Interestingly, Ag+ ions prefer the formation of Ag-SCN in DMTF (Ag+ + SCN reversible arrow Ag-SCN) but Cu+ ions form Cu-NCS (Cu+ + SCN reversible arrow Cu-NCS). We have studied the effect of ion-ligand binding on the ion pairing equilibria and dynamics in great detail by using FTIR, IR pump-probe (IR PP), and two-dimensional infrared (2DIR) spectroscopy combined with quantum chemical calculations. First, our quantum chemical calculations corroborate that Ag-SCN and Cu-NCS of the two possible CIP configurations (M-SCN or M-NCS) are energetically stable and favored in DMTF. Second, the thermodynamic properties (DH and DS) of ion pairing equilibria are determined by temperature-dependent FTIR experiments. Finally, IR PP and 2DIR experiments are used to measure the association and dissociation rate constants. The ion pairing dynamics between Cu+ and SCN- are found to occur on much faster timescales than those between Ag+ and SCN-. Our current results provide important insights into understanding the effect of ion-ligand binding on the ion pairing equilibria and dynamics in polar solvents.
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