Insights into the Coordination and Extraction of Yttrium(III) Ions with a Phenoxyacetic Acid Ionic-Liquid Extractant

Article abstract of DOI:10.1002/ejic.201601491

Phenoxyacetic acid type extractants such as sec-octylphenoxyacetic acid (CA-12), sec-nonylphenoxyacetic acid (CA-100), and the resulting bifunctional ionic-liquid extractants were developed to separate yttrium from heavy rare-earth elements (REEs). To obtain information on the coordination chemistry of this type of bifunctional ionic-liquid extractant, the CA-12 analogue n-octylphenoxyacetic acid (HOCTPOA) was synthesized, and its structure was characterized by single-crystal X-ray diffraction analysis. Then, a bifunctional ionic-liquid extractant based on HOCTPOA, namely, [N₁₈₈₈][OCTPOA] (N₁₈₈₈ is methyltrioctylammonium) was synthesized. The study of the extraction of yttrium with [N₁₈₈₈][OCTPOA] in chloride media was conducted by IR spectroscopy, log D versus log C slope analysis, ESI-MS, extended X-ray absorption fine structure (EXAFS), and DFT studies. The EXAFS data indicate that a Y^III extraction complex with phenoxyacetic acid formed. Three possible Y^III coordination cations were calculated by the DFT method, and the obtained Y–O bond lengths were comparable to the results from EXAFS fitting. A possible structure for the overall extracted complex was proposed, and this knowledge should contribute to a better understanding of the extraction process with phenoxyacetate-type bifunctional ionic liquids.

Full text of DOI:10.1002/ejic.201601491

A Journal of
Accepted Article
Title: Insight of Coordination and Extraction of Yttrium (III) with a New
Phenoxyacetic Acid Ionic Liquid Extractant
Authors: XIAOQI SUN
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201601491
Link to VoR: http://dx.doi.org/10.1002/ejic.201601491

European Journal of Inorganic Chemistry
10.1002/ejic.201601491
DOI: 10.1002/ejic.201((will be filled in by the editorial staff))
Insight of coordination and extraction of yttrium (III) with a new phenoxyacetic
acid ionic liquid extractant
a
b
b
b
a
a
Xiang-Guang Guo, Ruo-Ou Yang, Yu Gong, Zheng Jiang, Yamin Dong, and Xiaoqi Sun*
Keywords: Rare earth; Ionic liquid; Extraction; Saponification; Coordination chemistry information
Phenoxyacetic acid type extractants such as sec-octyl phenoxyacetic
acid (CA-12), sec-nonyl phenoxyacetic acid (CA-100) and resulting
bifunctional ionic liquid extractants, were developed to separate Y
from heavy rare earth elements (REEs). With the aim of getting the
coordination chemistry information concerning this type of
bifunctional ionic liquid extractants involved in rare earth extraction, a
CA12 analogue n-octyl phenoxyacetic acid (HOCTPOA) was
synthesized and its structure was first characterized by single crystal
X-ray diffraction analysis. Then a bifunctional ionic liquid extractant
based on HOCTPOA, namely, [N1888][OCTPOA] (where N1888 is
methyltrioctyl ammonium) was synthesized. The study on extraction
behavior of yttrium using [N1888][OCTPOA] from chloride media
was conducted through IR, log D versus log C slope analysis, ESI-
MS, EXAFS and DFT studies. X-ray absorption spectroscopy
demonstrates that the Y(III) extraction complex with phenoxyacetic
acid was formed. Three possible Y(III) coordination cation species
were calculated through DFT method and the obtained Y-O bond
distances were comparable to the results from EXAFS fitting. A
possible structure for the overall extracted complex was proposed,
which contributes to getting a better understanding for the extraction
with phenoxyacetate type bifunctional ionic liquid.
Introduction
Solvent extraction based on organic phosphonic acid or
carboxylic acid extractants is the widely used and well-
[
20, 21]
In the periodic table, rare earth elements (REEs) represent a
group of 15 lanthanides, scandium and yttrium, which are
established method to separate REEs.
However, the acidic
extractants are readily to form hydrogen bonded dimers, and
needed to be saponified by acid-base neutralization reactions to
increase their extractabilities and selectivities by breaking the
[
1-6]
critical to high-tech industries and clean technologies. More
and more efforts have been devoted to REEs separation due to
increasing global demand for REEs.[7, 8] As one of the most
common heavy rare earth elements (HREEs), yttrium is widely
used in laser crystal, ceramics, rare earth alloy, and other
functional materials.[9-10] As is known to all, it is difficult to
separate Y(III) from heavy REEs due to their similar ionic
[22]
dimers and eliminating protons. In REEs separation industry,
there are several problems of common saponification and
extraction processes such as large acid, base consumptions and
[23]
millions of tons of waste water produced annually. Therefore,
there is a necessity to develop new methods that selectively
extract REEs in a more economical and environmental friendly
way. Research reveals that ionic liquid (IL) type saponification
is an interesting alternative strategy to overcome the challenges
mentioned above.
3
+
radius (Y : 0.88 Å, Ho: 0.89 Å, Er: 0.88 Å, Tm: 0.87 Å, Yb:
[
11]
0
.86 Å, Lu: 0.85 Å).
Phenoxyacetic acid type extractants such as sec-
octylphenoxyacetic acid (CA-12) and sec-nonylphenoxyacetic
acid (CA-100) developed by Shanghai Institute of Organic
Chemistry are a class of organic ligands which have been found
to be the most promising for the selective extraction of Y from
heavy REEs in recent years. The extraction behavior, kinetics
and possible mechanism of this kind of phenoxyacetic acid type
extractants with rare earth ions were studied by Li et al and
IL-based extraction is a novel form of solvent extraction that
applies ILs instead of VOCs as diluents and/or extractants. ILs
are salts, generally in a liquid form below 100 °C. The
sustainable properties of ILs make them particularly suitable
[
24-26]
for solvent extraction.
Acid-base coupling bifunctional
ionic liquids (ABC-BILs), prepared from functional cations and
anions were applied to the separations of REEs, offering a
promising route to reduce saponification wastewater, increase
[
12-15]
coworkers.
In order to improve the extraction efficiencies
between Y and other rare earth ions, double solvent extraction
system, namely, one extractant is CA12 and the other extractant
is organophosphorus extractants such as C301 and C272 was
investigated and applied to the separation process.[16-19]
[
27]
extractabilities and selectivities. To date, several bifunctional
ILs have been synthesized and used in metal extractions, for
example, Guo et al. synthesized IL extractant for the highly
[
28]
selective extraction and separation of rare earths. Shi et al.
—
[
———————
a] Xiamen Institute of Rare Earth Materials, Haixi Institute,
Chinese Academy of Sciences, Xiamen, 361021, P.R. China
b] Shanghai Institute of Applied Physics, Chinese Academy of
prepared two ILs and evaluated their extraction efficiencies for
the liquid-liquid extraction of lithium ions from aqueous
[
[29]
solution.
Rout et al. synthesized two ILs for liquid-liquid
Sciences, Zhang Heng Road No. 239, Pu Dong New District, PO
Box 918, Shanghai 201204, P. R. China
extraction of Nd(III) from nitric acid medium and pointed out
the possibility to tune the extractability of metal ions and the
[
30-31]
selectivity by a proper choice of the ionic liquid cation.
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201601491
Although several studies about bifunctional ILs in metal ions
extraction were reported, further research into the coordination
chemistry about this kind of extractants behind solvent
extraction was rarely conducted. On the other hand, some
phenoxyacetatic acid based bifunctional IL extractants have
been synthesized and applied to the rare earth separation. Very
recently, the IL type saponification separation processing of
Results and Discussion
2
.1. Structure Description for HOCTPOA
The crystal structure for HOCTPOA has been determined by
single crystal X-ray diffraction analysis, and revealed that the
compound crystallizes in the spacegroup P-1. As shown in
Figure 2, the C-O bond lengths of the carboxylate groups are
[
[
methyltrioctyl ammonium] [sec-octylphenoxy acetate] and
trihexyl(tetradecyl)-phosphonium][sec-octylphenoxy acetate]
1
.2154 and 1.3299 Å, respectively. It is known that organic
for yttrium from other heavy REEs has been developed in our
carboxylic acids readily form dimers through hydrogen bonds,
two equivalent HOCTPOA molecules form acid dimer through
hydrogen bond with the O O distance of 2.7250 Å.
[
32-34]
laboratory.
Simplification of reciprocating saponification
procedures, avoidance of saponification wastewater and
stripping by distilled water are economical and sustainable
futures of IL type saponification over common saponification.
Also, the IL extractants for synergistic extraction in
impregnated resin was studied and revealed higher distribution
coefficients and synergistic enhancement coefficients for
…
[
35]
REEs.
Chen et al. prepared a novel polymer inclusion
membrane composed of bifunctional IL and investigated the
preconcentration and separation of heavy rare earth element
[
36]
(HREE) Lutetium (Lu) from dilute solution.
The
regeneration of the IL after metal extraction was investigated,
which implies that bifunctional IL extractants may be applied in
a
future continuous and sustainable process for metal
[
37]
extraction.
Figure 2. Crystal structure for HOCTPOA and hydrogen-
bonded dimer fromed by two equivalent molecules.
IR analysis
As shown in Figure 3, IR spectrum analysis was performed to
compare HOCTPOA, [N1888][OCTPOA] and [N1888][OCTPOA]
3
+
loaded with Y . The disappearance of stretching vibration for
−
1
C=O group observed at ca. 1717 cm
indicated the
-
deprotonation of the carboxylate group. The changes of COO
from 1607 cm before extraction to 1610 cm after extraction
reveals the interactions between the carboxylate group and Y
-
1
-1
3
+
[
33]
ions.
Figure 1. The structures of CA-12, HOCTPOA and
[
N1888][OCTPOA].
Study on coordination chemistry is important to metal ions
extraction, as it can provide an explanation for the strengths and
selectivities shown by the extractants.[38-41] Peter A. Tasker
pointed out that the extraction of metal ions can be achieved
through inner-sphere, outer-sphere interactions between
extractants and metal species.[42] To our knowledge, the
coordination behavior between Y and phenoxyacetic acid
extractant together with resulting ABC-BIL was not studied to
date. In this paper, the metal extraction for the rare earth ion
Y(III) by a bifunctional IL methyltrioctyl ammonium n-octyl
phenoxyacetic acid ([N1888][OCTPOA]) from chloride media
was discussed. This allows a better understanding of the
mechanism for the extraction of metal ions from the aqueous
with this type of ILs. Structures of CA12, HOCTPOA and
Figure 3. IR spectra of (1) HOCTPOA; (2) [N1888][OCTPOA];
(3) 0.4 mol/L [N1888][OCTPOA] loaded with YCl3.
[
N1888][OCTPOA] are shown in Figure 1.
Effect of aqueous pH on Y(III) extraction
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201601491
The effect of extractant concentration on Y(III) extraction
was also investigated, and the result is shown in Figure 5. It
showed that the extraction efficiency for Y(III) increased with
the increasing of the extractants concentration in
[
N
1888][OCTPOA] extraction systems. The log D against log
C
[N1888][OCTPOA] showed linear slopes close to 1, which indicates
that the stoichiometry of [N1888][OCTPOA] to Y(III) in the
organic phase is about 1.
ESI-MS studies
Electrospray ionization (ESI) is a very promising tool for the
analysis of IL, metal organic complexes that allows the sample
molecules to be transferred directly from the solution to the gas
phase by generating charged ions without disrupting metal-
[
43]
ligand bonds.
Figure 4. Effect of aqueous phase acidity on the extraction
efficiency of Y(III). [Y(III)] = 0.0093 mol/L, [N1888][OCTPOA]
=
0.015 mol/L.
As shown in Figure 4, the effect of aqueous pH on the
extraction behavior was investigated and the extraction
efficiencies of Y(III) were measured at different pH values. The
extraction efficiencies of Y(III) increase as the aqueous pH
values increase, when the pH values are between 3.5 and 5.0,
there are relative higher and stable efficiencies for Y(III) ions.
Effect of Extractant Concentration
Figure 6. ESI positive and negative ion mass spectrum of the
organic phase after extraction equilibrium.
As ESI-MS was effectively used for the analysis of the
extraction complex in the solvent extraction, here we tried to
use this method to analyze the formed complex between the
3
+
rare earth Y ions and IL extractants [N1888][OCTPOA].
However, it is difficult to identify the extraction complex
despite trying our best, which may be due to the fact that the
relatively low percent [N1888][OCTPOA] IL extractants
participation in forming extraction complexes compared to
phosphorus extractants with rare earth ions and large quantities
of molecular aggregate of IL. How to separate the extraction
complexes from ILs may be a possible way to identify the
Figure 5. Effect of [N1888][OCTPOA] concentration on the
extraction of Y(III). Organic phase: 0.01-0.055 mol/L
[N
1888][OCTPOA] in heptane. Aqueous phase: 0.0093 mol/L complex with further research. Studies revealed that ILs tend to
YCl
3
; pH = 3.83. O/A = 1:1.
form molecular aggregates under the vacuum condition in the
mass spectrometer, the major m/z peaks were molecular
aggregates of anions and cations from the ESI-MS analysis. As
shown in Figure 6, in the positive mode, the m/z peak at 368.4
As the IL extractants are diluted in organic solutions and the
interactions are relatively weak electrostatic or hydrogen bond
actions, which is weaker than coordination action of
phenoxyacetic acid between Y(III) ions, so the IL extractants in
molecular diluents can be treated as free extractants concerning
this extraction system.
+
correspond to the single cation [N1888] , while the m/z peaks at
+
771.8 and 1000.0 to the aggregates of two [N1888] cations, with
-
-
one Cl and one [OCTPOA] , respectively.
3
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European Journal of Inorganic Chemistry
10.1002/ejic.201601491
The observed m/z peak at 263.1 was the anion of n-octyl
As the EXAFS technique can give precise mean metal-
oxygen bond distances, but not very accurate coordination
numbers, we tried to optimize the several possible coordination
species. The most stable species of rare earth ions including
lanthanide and yttrium cations in solution are found typically in
the trivalent oxidation state that allow their diversified
phenoxyacetic acid, and the peak found at 666.5 was the
-
+
-
aggregate of one [OCTPOA] , one [N1888] and one Cl . The
major m/z peak at 894.7 correspond to the aggregation in the
-
+
form of two [OCTPOA] and one [N1888] cation. In previous
studies, extraction of the metal cation via a negative complex
2
−
2-
[46]
(
e.g., ZnCl
4
, PdCl
4
) always proceeds via the cation of the IL
coordination number with 7-9 most common in solutions.
[
44]
by the uptake of a negatively charged metal complexes.
Therefore, to investigate the possible species, three different
Y(III) complexes with coordinated water molecules 5-7, i.e.,
However this usually occurs at high acid conditions (low pH)
2
+
2+
and high chloride concentrations. Negative metal complex such
[Y(OCTPOA)(H
[Y(OCTPOA)(H
2
O)
O)
5
] ,
]
[Y(OCTPOA)(H
2
O)
6
]
and
-
2+
as YCl
4
was not found after an inspection on the negative
2
7
were taken into account and optimized
mode of ESI-MS spectrum as in dilute chloride solutions.
at the B3LYP/6-31G(d,p)/RECP level of theory. The optimized
structures of Y(III) species and structural parameters such as Y-
EXAFS Analysis and DFT Calculation of Y(III) Species
In order to obtain the coordination chemistry information
involved in solvent extraction such as coordinating atoms, the
bond distances between metal ions and neighboring
coordination atoms, EXAFS analysis on the organic phase after
O bond distances are shown in Figure 8 and Table 1. The Y-O
average bond lengths in these species are 2.28, 2.30 and 2.34 Å,
while the obtained Y-O average distances are 2.38, 2.42 and
2.47 Å, respectively. We can see that the results from DFT
calculations are comparable to the data from the fitting of
EXAFS analysis.
c
w
Table 1 Fitting Results Deduced from Y K-edge EXAFS
Spectra from the organic phase
2
3
2
Shell
CN
R(Å)
0
σ *10 (Å ) ΔE (eV) R factor
Y-O
1
2
2.0±0.2 2.26±0.04 3.0±0.3
6.0±0.7 2.38±0.04 4.2±0.4
-1.8±0.8
Y-O
-1.8±0.8 0.010
2
*
CN = Coordination number, R = Bond length, σ = Debye-
0 0
Waller factor, ΔE = E shift.
2
extraction was conducted. The Fourier transformed k χ(k)
EXAFS data and its fitting curves are shown as the solid and
dashed line in Figure 7.
As shown in Table 1, EXAFS analysis reveals that there are
two kinds of inner sphere coordination oxygen atoms with Y3+
ions, one is with relatively shorter Y-O average distance 2.26 Å,
which can be ascribed to the oxygen atoms form the
phenoxyacetic acid with Y3+ ions. The other with relatively
longer average bond distance 2.38 Å is from the coordination
3
+
oxygen atoms of water molecules with Y ions, which is
consistent with former studies.[45]
Figure 8. Optimum structures of Y(III) species (a)
2
+
2+
[
[
Y(OCTPOA)(H
Y(OCTPOA)(H
2
O)
O)
5
] , (b) [Y(OCTPOA)(H
2
O)
6
]
and (c)
2
+
2
7
] .
The ion association mechanism of phenoxyacetic acid type
IL extractants for REEs(III) extraction in chloride media
medium has been pointed out when the [N1888][CA-100],
[N1888][CA-12] and [P6,6,6,14][CA12] were used as extractants in
organic diluents. The final extraction equations (1), (2) and (3)
with ionic extractants were written as follows:
Figure 7. Fourier transform EXAFS spectra of Y-OCTPOA
[32-34]
2
-1
complex octn. k : ∆k = 3.0 – 11.0Å , ∆r=1.1 – 3.0 Å, from
2
fitting Y-O nearest neighbors in Y
were 0.81.
2 3 o
O values obtained for S
4
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European Journal of Inorganic Chemistry
10.1002/ejic.201601491
sphere as charge balance ions. As the ESI-MS analysis revealed,
-
the Cl might exist in the form of the molecular aggregate such
+
-
-
as one [N1888] , one OCTPOA and one Cl ion and also on. It is
a fact that bifunctional IL extractants can have different
extraction behavior compared to conventional organic
compounds, both cations and anions have distinct influence on
the extraction properties of IL extractants. Studies in our case
revealed that Y(III) ions were extracted into organic phase
through the coordination to phenoxyacetate anion, while one
In this article, our effort was made to provide insights into
the extraction complex structure related to the phenoxyacetic
acid bifunctional IL extractants. Based on the former studies,
the combination of IR analysis, log D versus log C slope and
-
role of the amine cation played was dragging the Cl to organic
3
+
phase to maintain charge balance. As coordination chemistry
concerning IL extraction with metal ions was also important
and less reported in this insight, our research contributes to
getting a better understanding on extraction process about this
type of IL extractant from a different view.
EXAFS analysis, we can conclude that each Y ion is
-
coordinated by about one OCTPOA to form complex cation
-
with charge balanced Cl anions. As water is a particularly
strong ligand and large hydration energy of REE ions, the Y3+
ion is more readily to be coordinated by oxygen atoms from
-
water molecules rather than Cl anions in conventional
molecular solvents.[47,48] Thus the Cl anion, which is co-
-
Conclusions
extracted into the organic phase with IL in the form of
-
+
-
In conclusion, a new phenoxyacetic acid type bifunctional IL
extractant was synthesized and its extraction behaviour with
molecular aggregates such as Cl …[N1888] …[OCTPOA] and
so on, interacts with coordination cation through outer sphere
actions.
3
+
Y
ions was studied. Based on the information obtained from
the IR, ESI-MS, log D versus log C slope analysis and EXAFS
analysis, the whole extraction complex was deduced to be a
large coordination ion complex. The structural parameters Y-O
bond distances obtained from DFT calculations for three
possible Y coordination cation species were comparable to the
EXAFS fitting results. The studies tried to provide useful
information for an improved understanding of the fundamental
aspects of the Y(III) extraction with phenoxyacetic acid type
bifunctional ILs extractants, which contributes to developing
the sustainable and efficient separation technology based on IL
type saponification strategy for REEs.
Experimental Section
Reagents and Instruments: Trioctylmethylammonium bromide
([N1888]Br) was purchased from Yixing Kai Lida Chemical Co.,
Ltd (China). An anion-exchange resin (Dowex Monosphere 550A
OH)) was obtained from the Dow Chemical Company. H and 13C
1
(
nuclear magnetic resonance (NMR) spectra of the octyl
phenoxyacetic acid and its ABC-BILs were obtained in CDCl with
3
an AV III-500 Bruker spectrometer. The extracting phases were
prepared by dissolving the extractants in heptane. The yttrium
oxide was purchased from Fujian Changting Golden Dragon Rare-
3
Earth Co., Ltd (China). Stock solutions of YCl were prepared by
dissolving yttrium oxide (>99.99%) in concentrated hydrochloric
acid and diluted with distilled water. Thermo scientific iCAP 6500
series plasma-atomic emission spectroscopy (ICP-AES) was used
to determine the concentrations of REEs of aqueous phase in
extraction procedure. IR spectra were measured with a Nicolet
iS50 spectrometer, when the IR measurement was conducted, the
solution of 0.012 mol/L Y(III) in organic phase was used.
Electrospray ionization mass spectrometry (ESI-MS) was
Figure 9. Proposed structure of extraction complex between
3
+
[
N1888][OCTPOA] and Y ions.
As shown in Figure 9, the possible extraction complex
structure in solution was proposed, the water molecules might
be to fulfill the more coordination number of Y3+ ions. The
whole extraction complex may be a large coordination ion
complex. The coordination main part i.e., the inner
performed on a Finnigan LCQ mass spectrometer using CH
mobile phase.
3
CN as
Synthesis of 4-Octyl Phenoxyacetic Acid (HOCTPOA): A
solution of 0.01 mole of the 4-octyl phenol, 0.02 mole of KOH
in 30 ml of ethanol was heated to boiling. The appropriate
bromocarboxylic acid (2.06 g, 0.01 mole), dissolved in 30 ml of
3
+
coordination sphere of Y ion was fulfilled by two oxygen
atoms from the carboxylic acid and other oxygen atoms from
-
coordinated water molecules, while the Cl ions lie in the outer
5
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European Journal of Inorganic Chemistry
10.1002/ejic.201601491
ethanol, was added dropwise, the resulting solution was heated
under reflux overnight. The reaction mixture was cooled,
acidified with dilute HCl, and concentrated under reduced
pressure. The residue was extracted with ether, and after being
dried, the ether was removed to give a waxy residue. The
product was recrystallized from petroleum ether to afford 0.8 g
EDTA titration. The organic phase was separated for EXAFS
analysis.
X-ray absorption fine structure (XAFS) data at the Y K-edge
was collected in fluorescence mode on BL14W at the Shanghai
Synchrotron Radiation Facility (SSRF, China). The electron
beam energy is 3.5 GeV, and the mean stored current is 200
mA. The source of BL14W is a 38-pole wiggler device with
maximum magnetic field of 1.2 T. The station was operated
with a Si (111) double crystal monochromator. The extended
XAFS (EXAFS) signals were extracted from the absorption
1
HOCTPOA as white crystals. (mp 91-92 ºC) H NMR δ (500
MHz, CDCl
2
3
) 0.88 (t, 3H), 1.25-1.27 (m, 10 H), 1.55-1.57 (m,
H), 2.55 (t, 2H), 4.65 (s, 2H), 6.85 (d, 2H), 7.11 (d, 2H). 13
C
NMR (500 MHz, CDCl
3
): 172.50, 155.33, 136.82, 129.50 (2C),
1
2
14.52 (2C), 65.10, 35.05, 31.88, 31.62, 29.47, 29.26 (2C), raw data by using the IFEFFIT package.[49]
2.67, 14.10. Anal. calcd for C16
H
24
O
3
(%): C, 72.69; H, 9.15;
General procedures for X-ray crystallography
Found: C, 72.38; H, 9.63.
Synthesis of [N1888][OCTPOA]: A solution of [N1888]OH in 20
Crystals for single-crystal X-ray analysis were obtained for n-
octyl phenoxyacetic acid as described in the synthesis
ml methanol was prepared from 0.269 g of [N1888]Br (0.6
procedure. The data was collected using
a
graphite
mmol) using a Dowex Monosphere 550A (OH) anion exchange monochromated Mo-Kα radiation (λ = 0.71073 Å) on a Bruker
resin. 0.1586 g of octyl phenoxyacetic acid (0. 6 mmol) was
added to the [N1888]OH solution. The mixture was then stirred
at room temperature for 6 h until the solution became neutral.
The methanol and water were distilled off with a IKA RV10
rotary evaporator, and the product was dried at 70 ºC under
AXS-KAPPA APEX II diffractometer. Cell parameters were
retrieved using Bruker SMART software and refined using
Bruker SAINT on all observed reflections. The structures were
solved and refined using direct methods the SHELXTL
[
50]
software package.
CCDC 1497757 contains the
vacuum for 12 h to yield [N1888][OCTPOA] as a yellow viscous
supplementary crystallographic data for this paper.
DFT Calculation Details
1
liquid (0.35 g, yield: 92.3%). H NMR δ (400 MHz, CDCl
3
)
0
2
.85-0.88 (t, 12 H), 1.24-1.29 (m, 40 H), 1.55-1.57 (m, 8H),
.48 (t, 2H), 3.20 (s, 3H), 3.21-3.25 (m, 6H) 4.40 (s, 2H), 6.83
The calculation for structural optimization of proposed Y-
complex was carried out with the Gaussian 09 program using
Dell PowerEdge T630, 2 CPU Intel E5-2640 V32.6 GHz, 32
1
3
(d,2H), 7.00 (d, 2H). C NMR (500 MHz, CDCl
3
): 173.38,
[
51]
1
4
2
1
1
57.14, 134.40, 128.91 (2C), 114.58 (2C), 67.92, 61.26 (3C),
8.69, 35.10, 31.9, 31.8, 31.64 (3C), 29.70 (3C), 29.50, 29.37,
9.29, 29.13 (3C), 29.01 (3C), 26.31 (3C), 22.67, 22.57 (3C)
GB RAM computational sources.
The geometric
configuration of Y(III) species was optimized in the gas phase
using the B3LYP hybrid exchange-correlation functional, viz.,
Becke’s three-parameter exchange functional (B) and the Lee-
Yang-Parr correlation (LYP) functional, and a 6-31G(d, p)
4.09, 14.03 (3C). Anal. calcd for C41
3
H77NO (%): C, 77.91; H,
2.28; N: 2.22 Found: C, 77.38; H, 11.96; N, 2.98
[
52, 53]
Extraction Procedure
basis set for C, H, O atoms.
While the quasi-relativistic
Extraction experiments were performed by contacting equal
volumes of organic phase with aqueous solution for 30 min in a
vibrating mixer at 30 °C. The concentration of the REEs in the
aqueous phase was determined using ICP-OES after
effective core potentials (RECPs) of Dolg et al. (ECP28MWB)
[
54]
was used for Y. The optimized geometry was confirmed to
be the minimum energy point with no imaginary vibrations by
vibrational frequency analysis.
centrifugation at 2500 rpm for 5 min. All the concentration Acknowledgments
values of the REEs in extraction procedure were measured in
duplicate and the uncertainty was within 5%. The extraction
This work was supported by National Natural Science
efficiency (E), distribution ratio (D) were defined as follows:
Foundation of China (21571179), ‘Hundreds Talents Program’
from Chinese Academy of Sciences, Science and Technology
Major Project of the Fujian Province, China (2015HZ0101).
[
M ] [M ]a
(4)
t
E% 
100%
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M ]t
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