Subject Number : S－16－MS－1039
Support Type : Technical support (except the training)
Proposal Title (English) : Dynamic property of polyiodides in room-temperature ionic liquids
Username (English) : H. Abe1), M. Aono1) and T. Kiyotani2)
Affiliation (English) :1) Dept. of Mater. Sci. & Eng., National Defense Academy, 2) Showa Pharmaceutical Univ.

1. Summary
Polyiodides, Im-, were formed in room-temperature ionic liquids (RTILs). The RTILs were 1-alkyl-3-methylimidazolium iodide, [Cnmim][I] (n = 1, 2, 3, 4, 6, and 12). By 127I-NMR, the local environments of only polyiodides were extracted by changing n, m, and the temperature. Doublet/triplet peak splitting of pure [Cnmim][I] (n = 3, 4, and 6) occurred at low temperature. In [Cnmim][Im] (n = 2 and 4), the effect of polyiodides was clarified from the chemical shifts and peak splitting in the NMR spectra.

2. Experimental
A 600 MHz NMR spectrometer (JNM-ECA600, JEOL Co.) was used to investigate the behaviors of the I- anion and polyiodides (Im-). (CD3)2CO, acetone-d6 (99.96 atom% D, Sigma-Aldrich Co.), was dissolved in the RTILs was used as the reference. For comparison, the 127I-NMR of 0.1 M KI–D2O solution was measured.Temperature range for 127I-NMR was -20 to 50 ºC.

3. Results and Discussion
The chemical shifts of pure [Cnmim][I] (n = 3, 4, and 6) were obviously deshielded compared with the solid group. The difference in the chemical shift of [C4mim][I] originates from the specific orientational order and the bond length between C4mim+ and I-, which are predicted by DFT and MD. [C4mim][Im] (liquid-type) were measured at a fixed temperature of 40 ºC. An interesting point regarding [C2mim][Im] (solid-type) is that a multi-step peak splitting is induced by adding iodine. Doublet and triplet peaks appeared in the NMR spectrum at m = 2 and m = 5, respectively. Because peak splitting in pure [C2mim][I] was not observed even at low temperature, peak splitting on the m scale is regarded as a polyiodide-inherent property. Above m = 5, triplet peaks mean that the hopping process of iodide between polyiodides becomes more complicated. In contrast, [C4mim][Im] has a different peak splitting on the m plot (Fig. 1). At m = 8, a third peak appeared in the [C4mim][Im] system. From the NMR peak splitting of the [Cnmim][Im] system, we confirm that the crossover points of the viscosity, density, and conductivity at around m = 4 are related to the coexistence of strongly and loosely bound iodides.

4. Others
N/A

5. Publication/Presentation
(1) H. Abe, M. Aono, T. Kiyotanib and S. Tsuzuki, Phys. Chem. Chem. Phys. Vol. 18 (2016) p.p. 32337-32344.
(2) H. Abe, M. Aono, T. Kiyotanib and S. Tsuzuki, The Physical Society of Japan Meeting, 2017/03/18

6. Patent
N/A