Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

7C, 10B/2004G299

Coordination property of the Ni−Phenolic Oxime−Organophosphoric acidcomplexes in solution
Hirokazu NARITA*1, Mikiya TANAKA1, Tsuyoshi YAITA2, Yoshihiro OKAMOTO2
Research Institute for Environmental Management Technology, National Institute of Advanced
Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan
2
Quantum Beam Science Directorate, Japan Atomic Energy Research Institute, Koto 1-1-1, Sayo,Hyogo 679-5148, Japan
1Introduction
The rate of Ni(II) extraction with LIX84I (2-hydroxy5-nonylacetophenone oxime) is significantly accelerated
by adding a small amount of D2EHPA (bis(2-ethylhexyl)
phosphoric acid) [1]; however, the detailed role of
D2EHPA remains unclear. In this study, we investigated
the structure of the extracted complexes in theNi−LIX84I−D2EHPA extraction system, and the effect ofthe D2EHPA addition on the extraction rate and thecoordination geometry of Ni(II) by XAFS measurements.
Experimental
The Ni−LIX84I−D2EHPA solution complexes wereprepared by solvent extraction: LIX84I and/or D2EHPA
in n-dodecane−NiSO4 solution adjusted to the appropriate
pH value using NaOH solution. All of the XAFS spectra
were measured in transmission mode at the BL-7C and10B in the KEK-PF. The experimental data were analyzed
by WinXAS Ver. 3.0 [2] and fit using theoretical phaseand amplitudes calculated from the program FEFF 8 [3].
Results and Discussion
The variation in the Ni(II) coordination structure withthe addition of D2EHPA to LIX84I was investigated bychanging the molar ratio of [D2EHPA]/[LIX84I] (0 (NiL), 0.1, 0.2, 0.5, 1, [LIX84I] = 0 (Ni-D);[D2EHPA]+[LIX84I] = 0.6 M; [Ni]org = 0.1 M) in theorganic phase during the extraction. Figures 1A and 1B
3show the Ni K-edge XANES and the FTs of the k weighted EXAFS spectra of the Ni−LIX84I−D2EHPA
system, respectively. In Fig. 1A, the peak corresponding
to 1s→4pz transition (~8339 eV) decreases with anincrease in the D2EHPA concentration, while the peakaround 8349 eV increases. This means that the Ni(II)coordination changes from square-planar to octahedral [4].
In Fig. 1B, with the increasing D2EHPA concentration,
the peak around 1.5 Å relating to the Ni-O/N correlationin the square-planar Ni-L complex (N: 4.1(6), r: 1.85(2)Å) shrinks, and the intensity of a new peak at ~1.7 Åincreases. The peak position (~1.7 Å) is similar to that of
the first shell in the Ni-D complex (N: 5.6(9), r: 2.04(2)Å). Therefore, this new peak can be assigned to thecorrelation in the inner coordination sphere of anoctahedral complex. This is consistent with the XANES
result.
In the 0.5 M LIX84I system, the Ni(II) extraction isvery slow. In contrast, the addition of D2EHPA (0.5 M
LIX84I−0.05 M D2EHPA system) accelerates theextraction; the shaking time to obtain the nearly 100%
extraction is reduced from 80 min to 40 min. However,the XAFS spectra are virtually the same between twosamples; thus, the extracted complexes consist mainly ofthe Ni-L complex. Taking into account the large
difference in the extraction rates between two systems
and the predominance of the Ni-L complex in theextracted complexes, the acceleration effect would not
result from the formation of the complexes that can be
rapidly extracted. Therefore, D2EHPA can play the roleof a phase transfer catalyst in the Ni(II)−LIX84I system.
References[1] M. Tanaka et al., Shigen-to-Sozai, 120, 440 (2004).
[2] T. Ressler, J. Synch. Rad., 5, 118 (1998).
[3] A. L. Ankudinov et al., Phys. Rev. B 58, 7565 (1998).
[4] R. A. Scott, Physica B 158, 84 (1989).
* hirokazu-narita@aist.go.jp

3Fig. 1 (A) Ni K-edge XANES spectra and (B) the FTs of the k -weighted EXAFS spectra of the Ni-L, Ni-D andNi−LIX84I−D2EHPA solution ([D2EHPA]/[LIX84I] = 0.1-1). The phase shifts are not corrected.

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