Deuterated Water Effect in a Room Temperature Ionic Liquid: N,N-Diethyl-N-methyl-N-2-methoxyethyl Ammonium Tetrafluoroborate

Hiroshi Abe,^*,† Yusuke Imai,^† Takahiro Takekiyo,^‡ and Yukihiro Yoshimura<sup>‡

†</sup>Department of Materials and Science and Engineering, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan
^‡Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan

J. Phys. Chem. B 114, pp. 2834-2839 (2010).

Abstract

A deuterated water effect in the room temperature ionic liquid (RTIL) N,N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF₄], is observed in its crystal domain structures; crystallization temperature, T_c; crystal superstructures; and volume contractions. The above effect, seen in [DEME][BF₄]-0.9 mol % H₂O mixtures, is reduced in 1.0 mol % 0.75H₂O・ 0.25D₂O and 0.9 mol % 0.5H₂O・ 0.5D₂O mixtures and is completely suppressed in 1.3 mol % D₂O mixtures. Interestingly, T_c decreased systemically with D substitutions of water. In contrast to the crystal state, it was found that there is no difference between H₂O and D₂O mixtures in the liquid state, on the basis of X-ray diffraction patterns. At around 80-90 mol % H₂O, the intermolecular correlation of [DEME][BF₄] as a local structure changes to that of bulk water.

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	Figure 1. X-ray diffraction patterns in [DEME][BF4]-x mol % H2O mixtures at room temperature.
	Figure 2. H2O and D2O concentration dependences of Q position at the maximum intensity, Qmax, of X-ray diffraction patterns (Figure 1). Qmax values increase drastically above 90 mol % H2O and D2O.
	Figure 3. (a) X-ray diffraction intensity of pure [DEME][BF4] in electron units per molecule. Solid curve reveals calculated Σi{fi(Q)}2 + RΣiIi comp(Q). (b) Weighted structure function of pure [DEME][BF4].
	Figure 4. Radial distribution function of [DEME][BF4]-x mol % H2O mixtures. At 90 mol % H2O as a crossover point from the [DEME][BF4] network to a bulk water one, molecular correlation visibly decreases.
	Figure 5. X-ray diffraction patterns at -80 °C of (a) [DEME]-[BF4]-0.9 mol % H2O, (b) -1.0 mol % 0.75H2O・ 0.25D2O, (c) -0.9 mol % 0.5H2O・ 0.5D2O, and (d) -1.3 mol % D2O. Closed squares show the aO′ × bO′ × 2cO′ modulated lattice, and open triangles show the 2aO′ × bO′ × 2cO′ modulated one. Open circles and closed circles are calculated positions of the orthorhombic lattices, aO′ × bO′ × cO′ and aO × bO × cO, respectively.
	Figure 6. Crystallization temperature in 1 mol % (1-y)H2O・ yD2O mixtures. With increasing y, Tc visibly decreases.
	Figure 7. Rocking curves at -80 °C of (a) [DEME][BF4]-0.9 mol% H2O, (b) -1.0 mol % 0.75H2O・ 0.25D2O, (c) -0.9 mol % 0.5H2O・ 0.5D2O, and (d) -1.3 mol % D2O.
	Figure 8. A bonding scheme of (a) H2O and (b) D2O in crystal. In protonated water, “on-centering” is preferred, whereas “off-centering” occurs in deuterated water. The atomic distance between oxygens, dOO, varies depending on the interaction.
	Figure 9. Optimized structures of the BF4--n(H2O) (n= 1-4) complex using the B3LYP/6-311++G(d,p) basis set. Green, brown, gray, and red represent the boron, fluorine, hydrogen, and oxygen atoms. In the case of the BF4--2H2O complex, the BF4- anion takes two arrangement patterns with two water molecules; one is a linear arrangement (b-1) and another is a perpendicular arrangement (b-2). The former is energetically more stable than the latter (ΔE=1.6 kJ/mol).
	Figure 10. Nearly free hydrogen bond band of water mapping in the liquid and solid states. NFHB is selectively observed in the Raman spectra, where NFHB reveals the OH oscillator which does not form a hydrogen bonding network among water molecules, as in pure bulk water.

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References

(1) Earle, M. J.; Seddon, K. R. Pure Appl. Chem. 2000, 72, 1391.
Cooper, E. R.; Andrews, C. D.; Wheatley, P. S.; Webb, P. B.; Wormald,P.; Morris, R. E. Nature 2004, 430, 101.
Earle, M. J.; Esperanca, J. M. S. S.; Gilea, M. A.; Lopes, J. N. C.; Rebelo, L. P. N.; Magee, J. W.; Seddon,K. R.; Widegren, J. A. Nature 2006, 439, 831.
(2) Sato, T.; Masuda, G.; Takagi, K. Electrochim. Acta 2004, 49, 3603.
(3) Imai, Y.; Abe, H.; Goto, T.; Yoshimura, Y.; Kushiyama, S.; Matsumoto, H. J. Phys. Chem. B 2008, 112, 9841.
(4) Imai, Y.; Abe, H.; Yoshimura, Y. J. Phys. Chem. B 2009, 113, 2013.
(5) Abe, H.; Imai, Y.; Goto, T.; Yoshimura, Y.; Aono, M.; Takekiyo, T.; Matsumoto, H.; Arai, T. Metal. Mater. Trans. A 2009, in press.
(6) Imai, Y.; Abe, H.; Goto, T.; Yoshimura, Y.; Michishita, Y.; Matsumoto, H. Chem. Phys. 2008, 352, 224.
(7) Abe, H.; Yoshimura, Y.; Imai, Y.; Goto, T.; Matsumoto, H. J. Mol. Liq. 2009, 150, 16.
(8) Yoshimura, Y.; Goto, T.; Abe, H.; Imai, Y. J. Phys. Chem. B 2009, 113, 8091.
(9) Takekiyo, T.; Imai, Y.; Abe, H.; Yoshimura, Y. in preparation.
(10) Koval, S.; Kohanoff, J.; Migoni, R. L.; Tosatti, E. Phys. Rev. Lett. 2002, 89, 187602.
(11) Koval, S.; Kohanoff, J.; Lasave, J.; Colizzi, G.; Migoni, R. L. Phys. Rev. B 2005, 71, 184102.
(12) Lasave, J.; Koval, S.; Dalal, N. S.; Migoni, R. L. Phys. Rev. B 2005, 72, 104104.
(13) Liu, A.; Lu, Z.; Wang, J.; Yao, L.; Li, Y.; Yan, H. J. Am. Chem. Soc. 2008, 130, 2428.
(14) Abe, H.; Yamamoto, K.; Matsuoka, S.; Matsuo, Y. J. Phys.: Condens. Matter 2007, 19, 466201.
(15) Nishikawa, K.; Iijima, T. Bull. Chem. Soc. Jpn. 1984, 57, 1750.
(16) Katayanagi, H.; Hayashi, S.; Hamaguchi, H.; Nishikawa, K. Chem. Phys. Lett. 2004, 392, 460.
(17) Zhang, L.; Xu, Z.; Wang, Y.; Li, H. J. Phys. Chem. B 2008, 112, 6411.
(18) Danten, Y.; Cabaco, M. I.; Besnard, M. J. Mol. Liq., in press.
(19) Frish, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montogomery, J. A.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J. W.; Petersson, G. A.; Ayala, P. Y., Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavechari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayaakkara, A.; Gonzalez, C.; Challacombe, M. P.; Gill, M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. GAUSSIAN 03, Gaussian, Inc.: Pittsburgh, PA, 2003.
(20) Becke, A. D. Phys. Rev. A 1998, 38, 3098.
(21) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785.
(22) Fujii, K.; Soejima, Y.; Kyoshoin, Y.; Fukuda, S.; Kanzaki, R.; Umebayashi, Y.; Yamaguchi, T.; Ishiguro, S.; Takamuku, T. J. Phys. Chem. B 2008, 112, 4329.
(23) Deetlefs, M.; Hardacre, C.; Nieuwenhuyzen, M.; Sheppard, O.; Soper, A. K. J. Phys. Chem. B 2005, 109, 1593.
(24) Takekiyo T.; Yoshimura, Y.; Imai, Y.; Abe, H. In preparation.

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ab@nda.ac.jp

Department of Materials Science and Engineering
National Defense Academy

Last Modified: April 1, 2009