Separation and complexation of palladium(II) with a new soft N-donor ligand 6,6′-bis(5,6-dinonyl-1,2,4-triazin-3-yl)-2,2′-bipyridine (C9-BTBP) in nitric acid medium

Article abstract of DOI:10.1039/c5nj03082j

Soft N-donor bis-triazine ligands developed for the separation of minor actinides (MAs) from lanthanides have been intensively studied for the past two decades. However, the investigation on the recovery and complexation of fission products Pd(ii) with these ligands has rarely been reported to date. Herein, the synthesis, and solvent extraction of Pd(ii) and some typical metals from HNO₃ solutions as well as Pd(ii) complexation with a new soft N-donor ligand C9-BTBP were presented. The C9-BTBP ligand exhibited high extraction capability and high selectivity for Pd(ii) in HNO₃ solution. Both 1:1 and 2:1 Pd(ii)-C9-BTBP complexes were found in solution by a combination of ESI-MS and ¹H NMR titration experiments. A solid binuclear Pd(ii) complex [Pd₂(NO₃)₄·(C9-BTBP)]·2.5H₂O was synthesized and characterized by elemental analysis, DSC-TGA and ¹H NMR. This is the first example that a binuclear Pd(ii) complex with any N-donor bis-triazine ligand has been confirmed both in solution and in the solid state.

Full text of DOI:10.1039/c5nj03082j

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A. Zhang, L. Xu
and G. Lei, New J. Chem., 2016, DOI: 10.1039/C5NJ03082J.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/njc

Page 1 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
Separation and complexation of palladium (II) with a new soft
N-donor ligand 6,6'-bis(5,6-dinonyl-1,2,4-triazin-3-yl)-2,2'
-
bipyridine (C9-BTBP) in nitric acid medium
Anyun Zhang*, Lei Xu, Gaoming Lei
College of Chemical and Biological Engineering, Zhejiang University, No.38 Zheda
Road, Hangzhou 310027, P. R. China
Abstract
Soft N-donor bis-triazine ligands developed for separation of minor actinides (MAs)
from lanthanides have been intensively studied for recent two decades. However, the
investigation on recovery and complexation of fission products Pd(II) with these
ligands has rarely been reported to date. Herein, the synthesis, solvent extraction of
Pd(II) and some typical metals from HNO solutions as well as Pd(II) complexation by
3
a new soft N-donor ligand C9-BTBP were presented. The C9-BTBP ligand exhibited
high extraction capability and high selectivity for Pd(II) in HNO solution. Both the 1:1
3
and 2:1 Pd(II) with C9-BTBP complexes were found in solution by a combination of
1
ESI-MS and H NMR titration experiments. The solid binuclear Pd(II) complex
[
Pd (NO ) ·(C9-BTBP)]·2.5H O was synthesized and characterized by elemental
2 3 4 2
1
analysis, DSC-TGA and H NMR. This is the first example that a binuclear Pd(II)
complex with any N-donor bis-triazine ligands has been confirmed both in solution
and in solid state.
Introduction
Nuclear power has been revived in recent years for its high energy density and low
carbon dioxide emissions. However, how to make the best use of irradiated spent
nuclear fuel and at the same times reduce its long-term radiotoxicity to the
environment has been one of the most important issues nowadays. The well-known
reprocessing process called PUREX (Plutonium Uranium Reduction Extraction) is
developed to separate and recover the uranium, plutonium and neptunium from spent
1
nuclear fuel. The PUREX raffinate, so called the HLW (High Lever Waste) contains
fission or non-fission products, such as the long-lived minor actinides Cm(III) and
Am(III), rare earths, platinum group metals (PGMs), Fe(III), Zr(IV), Mo(VI), Tc(VII) and
heat-emission elements Sr(II) and Cs(I). The removal of these radioactive nuclides,
effective treatment and safe disposal of HLW has been one of the most challenging
1

New Journal of Chemistry
Page 2 of 18
2
View Article Online
DOI: 10.1039/C5NJ03082J
works worldwide. The partitioning and transmutation strategy was proposed to solve
these problems.
As is known, the key step of partitioning and transmutation (P&T) strategy is to
separate the minor actinides (MAs) from lanthanides. This is because lanthanides
have higher neutron capture cross sections compared with actinides which would
significantly reduce the efficiency of the transmutation for actinides. After separation
from lanthanides, MAs can be transmuted to short-lived or stable nuclides by neutron
3
fission. However, this separation is very difficult given the very similar chemical
properties between the trivalent Am(III) and Cm(III) and trivalent lanthanides. Recently,
intensively research focused on the effective separation of the minor actinides (MAs)
4
from lanthanides. Fortunately, it has been reported that the R-BTP, R-BTBP as well
as R-BTPhen type ligands (Fig. 1) exhibit high extraction selectivity toward MAs over
5
lanthanides in highly acidic media.
Fig. 1 N-donor ligands for minor actinides and palladium (II) separation
Unfortunately, when using these soft N-donor bis-triazine ligands to separate MAs
from lanthanides by solvent extraction some other undesired metals are also
6
co-extracted. For example, the ligand CyMe -BTBP has been developed for directly
4
selective extracting radioactive minor actinides from PUREX raffinate in 1-cycle
7
SANEX (Selective Actinide Extraction) process. However, not only Cm(III) and Am(III)
but also some other fission or corrosion products such as Cu, Ni, Zr, Mo, Pd, Ag, and
Cd are co-extracted by CyMe -BTBP. Of which, palladium is reported as one of the
4
107
most abundant transition fission products in HLW. Especially the long-lived Pd(II)
6
has a half-life of about 6.5×10 years and its abundance in spent fuel is about 0.17
kg/ton. If Pd(II) could also be removed from HLW by BTBP type ligands, it will be very
helpful for developing a separation process based on BTBP type ligands that can be
used to simultaneously partition the long-lived minor actinides as well as long-lived
107
Pd from HLW. Furthermore, the effective elimination of Pd can also make the
8
vitrification as a long-term disposal of HLW easier. In our previous work, the R-BTP
ligand had been designed and developed for the separation of the Pd(II) from HNO3
9
solution. The two very successful examples are Non-BTP (2,6-Bis(5,6-dinonyl-1,2,4-
2

Page 3 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
triazi-ne-3-yl)-pyridine) and BD-BTP (2,6-bis(5,6-dibutyl--1,2,-triazine-3-yl)pyridine)
which exhibit high separation factor of Pd(II) from other typical metals in HNO3
solution. However, the investigation on recovery and complexation of fission products
Pd(II) with BTBP type ligands has not been reported to date.
In order to investigate the separation and complexation behavior of palladium
with RBTBP type ligands, a new ligand 6,6'-bis(5,6-dinonyl-1,2,4- triazin-3-yl)-2,2'
-
bipyridine (C9-BTBP, Fig. 2) was synthesized and characterized. Its extraction
properties for Pd(II) over some typical metals in HNO solution was studied. To strip
3
the Pd(II) from loaded organic phases, thiourea was selected as the strippant and the
stripping conditions were optimized. Importantly, the formation of complexes between
Pd(II) and C9-BTBP both in solution and solid state were investigated.
Fig. 2 Synthesis route of C9-BTBP.
Results and discussion
Effect of contact time on extraction
The extraction capability and selectivity of an extractant towards target metals strongly
relies on the strength of the chemical complexation ability between them. Based on
10
the Pearson’s HSAB (hard / soft acids and bases) principle , the ligand C9-BTBP
containing eight soft nitrogen atoms can be considered as a soft base. In contrast, the
Pd(II) with the unoccupied p orbit, can therefore be considered as a typical soft Lewis
acid. The HSAB principle tells us that the hard acids tend to form strong chemical
11
bonds with hard bases and the soft acids tend to form strong bonds with soft bases.
Therefore, it is predicted that the stable complex can be formed between Pd(II) and
the ligand C9-BTBP and it will have a strong extraction ability toward Pd(II).
3

New Journal of Chemistry
Page 4 of 18
View Article Online
DOI: 10.1039/C5NJ03082J
To investigate the extraction properties of C9-BTBP, the effect of contact time on the
extraction of Pd(II) and the other typical elements Na(I), K(I), Rb(I), Cs(I), Sr(II),Ba(II),
Ru(III), and Fe(III) from 2.0 M HNO solution by C9-BTBP in chloroform was studied.
3
As shown in Fig. 3, C9-BTBP exhibited excellent extraction ability and high selectivity
for Pd(II) over other tested metals. The D value of Pd(II) was larger than 45 even after
30 minutes of contact and higher than 1000 after the extraction equilibrium was
reached. These results indirectly confirmed the above prediction that the soft base
C9-BTBP would have a strong coordination ability with Pd(II).
Fig. 3 Distribution ratio as a function of contact time (Aqueous phase, Na(I), K(I), Rb(I),
-4
Cs(I), Sr(II),Ba(II), Ru(III), Fe(III) and Pd(II) (5.0×10 M each) in 2.0 M HNO . Organic
3
-3
phase, 1.0×10 M C9-BTBP dissolved in chloroform. T=298K, A/O=1.0).
Conversely, the ligand showed weak or no extraction efficiency for other tested
elements such as Na(I), K(I), Rb(I), Cs(I), Sr(II), Ba(II), Ru(III) and Fe(III). Based on
the HSAB principle, the metals such as Na(I), K(I), Fe(III) and Sr(II) are the hard acids
which can only form the stable complexes with the hard bases. So they exhibited
weak or no affinity with the soft base C9-BTBP. On the other hand, Ru(III), Ba(II), Rb(I),
and Cs(I) are regarded as the borderline or the transition acids, so they are
unmatched with the soft base C9-BTBP. Thus the D values of them were very smaller
than that of Pd. Consequently, the presence of these metals in HLW solution will have
no adverse impact on the removal of Pd(II) by C9-BTBP..
On the other hand, with contact time increasing, the extraction of Pd increased
within the initial 80 minutes and then kept constant indicating that the extraction
equilibrium was reached. Similar with CyMe -BTBP type ligands, which showed slow
4
12
extraction rates for Am(III) , the ligand C9-BTBP also exhibited slow extraction
kinetics for Pd(II). As is reported, one main reason may be responsible for this slow
4b
extraction rate. Prior to complexation with Pd(II), a conformation change of ligand
C9-BTBP from its thermodynamically stable trans-conformation to its less-favored
4

Page 5 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
cis-conformation was required (see Fig. 4). That is, the configure change of this
procedure slows the extraction rates for Pd(II) by C9-BTBP. This argument can be
proven by the trans-conformation of the free RBTBP type ligands and the
cis-conformation of their complexes with some metals that have been determined by
5c
X-ray crystallographic analysis in solid state.
Fig.4 The conformation change of C9-BTBP.
Effect of HNO concentration on extraction
3
As is well known, HLW is a highly nitric acid solution, which means that the selected
13
ligands must have good extraction ability for Pd(II) even in 3-4 M HNO solution.
3
Therefore, the effect of HNO concentration from 0.4 M to 6.0 M on the extraction of
3
Na(I), K(I), Rb(I), Cs(I), Sr(II), Ba(II), Ru(III), Fe(III) and Pd(II) was investigated and
the results were shown in Fig. 5.
Fig. 5 Distribution ratio as a function of HNO concentration (Aqueous phase, Na(I),
3
-4
K(I), Rb(I), Cs(I), Sr(II),Ba(II), Ru(III), Fe(III) and Pd(II) (5.0×10 M each) in different
-3
HNO concentration. Organic phase, 1.0×10 M C9-BTBP dissolved in chloroform,
3
contact time: 120 min, T=298K, A/O=1.0.).
The largest D value for Pd(II) was observed (D >1100) in optimum 2.0 M HNO
Pd
3
solution. Indeed, when the HNO concentration was higher than 3.0 M, the D was
3
Pd
still larger than 450 indicating that an effective extraction could still be achieved even
in 3.0 M HNO solution if desired. Meanwhile, the amount of other tested metals
3
extracted was very small, resulting in the separation factors between Pd(II) and other
5

New Journal of Chemistry
Page 6 of 18
3
View Article Online
DOI: 10.1039/C5NJ03082J
metals larger than 10 . These results demonstrated that C9-BTBP was capable of
separation for Pd(II) over other tested metals with high selectivity.
14
Similar to R-BTP type ligands , the extraction of Pd(II) by C9-BTBP (see Fig.5)
underwent a quickly increase until the maximum was reached at 2.0 M HNO and then
3
a slowly decrease was observed from 2.0 M to 6.0 M HNO . This could be explained
3
by competitive reaction of metal cations and HNO for R-BTBP molecules. That is,
3
except for complexation with Pd(II), the ligand C9-BTBP as a base will also be
protonated in HNO solution. The following two equations illustrated both the positive
3
(
Eq(a)) and negative (Eq(b)) effects on the extraction of Pd(II) by C9-BTBP. In other
words, the positive effect was dominant when the concentration of HNO was lower
3
than 2.0 M. However, the decrease of Pd(II) extraction in excess of 2.0 M HNO was
3
probably due to the protonation of the ligand. Further studies are needed to
investigate in terms of the co-extraction behavior of HNO by R-BTBP ligands.
3
-
2+
(
(
a) 2NO + Pd + C9-BTBP ↔ Pd(NO ) ·C9-BTBP
3 3 2
b) HNO + C9-BTBP ↔ HNO ·C9-BTBP
3
3
Stripping behavior of Pd(II)
To recover the Pd(II) as well as make the ligands reusable in further extraction cycles,
the back-extraction of Pd(II) from loaded organic phases was required. Thiourea was
used for stripping of Pd in this work because it is widely used as an effective strippant
14, 15
for the back-extraction of Pd(II) from organic phase.
The loaded organic phases
were brought into contact with thiourea solution of different concentrations (1.0~10
mM) in 0.1 M HNO solutions and the results were presented in Fig. 6a. A Pd(II)
3
stripping efficiency of more than 99.5% was achieved when the concentration of
thiourea was 5 mM in 0.1 M HNO3 solution. Further increasing the thiourea
concentration, the stripping efficiency of Pd(II) no longer increased. So the optimized
thiourea concentration in 0.1 M HNO solution was determined as 5mM.
3
Fig.6 (a) Back-extraction of Pd(II) with thiourea of different concentrations in 0.1M
HNO ; (b) back-extraction of Pd(II) with 0.005 M thiourea in HNO of different
3
3
concentrations; contact time: 120 min, T=298K, A/O=1.0.
6

Page 7 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
Then the stripping behavior of Pd(II) by thiourea as a function of HNO3
concentration was investigated. As shown in Fig. 6b, the HNO concentration had an
3
significant effect on the recovery of Pd(II) by thiourea and the optimized HNO3
concentration was 0.3 M, under which condition almost 100% Pd(II) was stripped from
the loaded organic phase.
Effect of temperature on extraction
The extraction of Pd(II) and Na(I), K(I), Rb(I), Cs(I), Sr(II),Ba(II), Ru(III), Fe(III) from
2
.0 M HNO by C9-BTBP in chloroform under different temperatures was studied. As
3
presented in Fig. 7, the extraction of Pd(II) decreased gradually with an increase of
temperature from 298 K to 318 K, indicating that the extraction of Pd(II) from HNO3
into CHCl was an exothermic process. That is, increasing the temperature was
3
unfavorable for the Pd(II) extraction, thus the best temperature in Pd(II) separation by
C9-BTBP appeared to be at room temperature or at 298K. The extraction of other
tested metals by C9-BTBP, however, exhibited small change with temperature
increasing from 298 K to 318 K.
Fig. 7 Distribution ratios as a function of extraction temperature (Aqueous phase,
-4
Na(I), K(I), Rb(I), Cs(I), Sr(II), Ba(II), Ru(III), Fe(III) and Pd(II) (5.0×10 M each) in 2.0
-3
M HNO . Organic phase, 1.0×10 M C9-BTBP dissolved in chloroform, contact time:
3
120 min, T=298K, A/O=1.0).
Extraction mechanism
ESI-MS (electrospray ionization mass spectrometry) is considered as an effective
16
technique to investigate the composition of the RBTBP complexes in solution . The
results of the ESI-MS of organic phases after extraction for Pd(II) were shown in Fig.8.
L:M ratios stand for the relative molar concentration of the C9-BTBP in organic
phases and that in aqueous phases (where L=C9-BTBP, M=Pd). In the case of
L:M=0.5, the most abundant peak (m/z=923.6-926.6) corresponding to the 1:1 type
7

New Journal of Chemistry
Page 8 of 18
2+
+ +
View Article Online
DOI: 10.1039/C5NJ03082J
Pd(II) complex [L+Pd -H ] was found in Fig.8a and Fig.8b,. In addition, another peak
2+
-
3
+
locating at m/z=986.5 was assigned to the 1:1 type complex of [L+Pd +NO ] .
Similar 1:1 Pd(II)-BTBP complexes have also been reported in CyMe -BTBP type
4
16
ligand. What’s more, this type of complexes were also observed in cases of L:M=
1:1 and 1:2. As shown in Fig. 8c and 8d, the peak of m/z=1049.5 was ascribed to the
2+
-
3
+ +
formation of complexes of [L+Pd +2NO +H ] . It is worth mentioning that a peak at
2+
-
3
+
m/z=1270.9 were assigned to the 2:1 type Pd(II) complexes [L+2Pd +3NO +3H O] ,
2
indicating that the binuclear complexes of Pd(II) with BTBP type molecules were
formed in solution. Further investigations about this 2:1 Pd-BTBP complex were
shown on the following solid state Pd complex study section.
In addition, the peaks locating at m/z=1660.7 corresponded to the complexes of
+
+
[
2L+Na ] , indicating that some free C9-BTBP molecules were present as dimers in
solution. Usually, the decomposition and rearrangement of the ligand molecular during
the ionization were very common in the ESI-MS tests. A peak locating at m/z=1468.6
+
was assigned to the complex [2L-C N H ] and a possible fragmentation of
10
2
19
+
C9-BTBP in complex [2L-C N H ] was shown in Fig 9.
10
2
19
Fig. 8 Positive ESI-MS of loaded organic phases after extraction, contact time: 120
min, T=298K, A/O=1.0; Organic phase 1.0 mM C9-BTBP in chloroform; aqueous
phase: 2.0 M HNO containing Pd with different concentrations (a) 2.0 mM Pd, L/M=
3
0.5, (b) the enlargement of a in the range of m/z=800~1000, (c) 1.0 mM Pd, L/M= 1.0,
(
d) 0.5 mM Pd, L/M= 2.0; L/M = C9-BTBP equivalents.
8

Page 9 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
+
Fig. 9 A possible fragmentation of C9-BTBP in [2L-C N H ] complexes.
10
2
19
1
H NMR titrations of C9-BTBP with Pd(II) nitrate were carried out to elucidate the
coordination chemistry of Pd(II) with BTBP type ligands in solution. A mixture of
1
CDCl /CD CN (3/7, v/v) was used for H NMR titration due to the poor solubility of
3
3
1
Pd(NO ) in CDCl . The results of the H NMR titrations were shown in Fig. 10 and Fig.
3
2
3
1
1
1 respectively and the selected protons and nitrogen atoms for illustrating the H
NMR titration spectra were presented in Fig. 12.
1
Fig. 10 H NMR titration spectra (0-9.0 ppm) of 10.0 mM C9-BTBP with various
equivalents of Pd(NO ) in CDCl -CD CN (3/7, v/v), M/L=Pd equivalents.
3
2
3
3
18
The rate exchange of ligand C9-BTBP was not slow enough on the NMR
1
time-scale to allow the observation of different H NMR peaks for free C9-BTBP and
19
the complex. Also the rate exchange of ligand was not high enough on the NMR
time-scale that more than three broadening peaks were found for protons H1, H2 and
H3 (Fig. 11, M/L = 0.4). That is, the moderate rate of ligand exchange led to the large
1
broadening peaks in the H NMR spectra (Fig. 11, 0 <M/L<1.0).
1
Further, in the H NMR spectrum of free C9-BTBP, the H4 and H5 exhibited two
independent triplets due to the different chemical environments of them. However,
with an increase of Pd(II) amounts, these two triplets shifted downfield and overlapped.
This change indicated that the two Pd-N bonds were most likely formed between two
nitrogen atoms N2/N2` and Pd(II), which resulted in the much more similar chemical
9

New Journal of Chemistry
Page 10 of 18
View Article Online
DOI: 10.1039/C5NJ03082J
environments of H4 and H5 in Pd complex than that in free ligand. Meanwhile, with
Pd(II) contents increasing, the chemical shifts of protons (H1, H2 and H3) of pyridine
rings also significantly changed and the two peaks of H1 and H3 exhibited upfield.
Conversely, the resonance peak related to proton H2 showed a big chemical
downfield shift of 0.39 ppm upon addition of 1.0 equivalents of Pd(II). These changes
provided evidence for the formation of two Pd-N bonds between two nitrogen atoms
N4/N4` and Pd(II). Based on the above analysis, the four nitrogen atoms N2, N2`, N4
and N4` (see Fig.12) in C9-BTBP were confirmed to bound with Pd and a typical
square-planar geometry Pd(II) complex was formed.
1
Fig. 11 The enlargement of partial H NMR titration spectra (2.8-9.0 ppm) of 10.0 mM
C9-BTBP with various equivalents of Pd(II) in CDCl /CD CN (3/7, v/v).
3
3
Fig. 12 Structure of C9-BTBP molecular and the selected protons and nitrogen atoms.
1
Furthermore, the results of H NMR titrations spectra indicated that the C9-BTBP
initially formed only the 1:1 Pd-C9-BTBP complexes in solution, since transformation
to a new single complex was complete after addition of 1.0 equivalents of Pd(II). The
only 1:1 Pd-C9-BTBP complexes found in ESI-MS (M/L=0.5, 1.0) study demonstrated
this argument. Subsequent formation of small amounts of 2:1 Pd-C9-BTBP
complexes was proposed since the appearance of three new class peaks upon
10

Page 11 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
addition of excess amount of Pd in solution (labeled red lines, Fig. 11). The existence
2+
-
3
+
of this type complex was supported by the peak of [L+2Pd +3NO +3H O] observed
2
in ESI-MS study (Fig. 8c) and the formation of 2:1 solid complex
1
[
Pd (NO ) ·(L)]·2.5H O which was characterized by elemental analysis and H NMR in
2
3 4
2
the following parts. Based on the typical square-planar geometries of Pd(II)
-
complexes, four NO 3 were presumed to bound with Pd(II) in 2:1 Pd-C9-BTBP
complex. Consequently, two structures of 1:1 and 2:1 Pd-C9-BTBP complexes were
proposed and shown in Fig. 13, respectively.
Fig. 13 Possible structures of the 1:1 and 2:1 Pd(II)-C9-BTBP complexes,
stands
-
for NO .
3
It should be noted that the ESI-MS (Fig. 8d) tests were performed under the
identical conditions with the liquid / liquid solvent extraction experiments, where
L:M=2:1 (M:L=0.5). In this case, only 1:1 type Pd-C9-BTBP complexes were found
1
both in ESI-MS and H NMR titration studies. Therefore, the extraction mechanism of
Pd(II) by C9-BTBP/CHCl is illustrated in Fig. 14.
3
Fig. 14 The extraction mechanism of Pd(II) from HNO solution by C9-BTBP in
3
chloroform.
Solid Pd(II) complex study.
In order to elucidate the composition of the complexes in solid state, the solid Pd(II)
with C9-BTBP complex was synthesized and characterized by elemental analysis,
11

New Journal of Chemistry
Page 12 of 18
View Article Online
1
DSC-TGA， H NMR. However, attempts to obtain the crystals of complex sui
D
ta
O
b
I:
l
1
e
0.1
f
039/C5NJ03082J
or
X-ray diffraction failed. Found: C, 47.63; H, 6.18; N, 12.19; requires C, 47.36; H, 6.57;
N, 12.69. Formula of the complex: [Pd (NO ) ·(L)]·2.5H O, L stands for C9-BTBP. This
2
3 4
2
results demonstrated that the complex was a binuclear structure in solid state.
Fig. 15 (a) TGA-DSC curves of 2:1 Pd-C9-BTBP complex under nitrogen atmosphere
◦
with a heating rate of 10 C/ min; (b) the possible decomposition fragments and
processes of the 2:1 bis-complex of Pd in nitrogen atmosphere.
The thermal decomposition processes of the complex were investigated by TGA
analysis under nitrogen atmosphere. As shown in Fig.15a, the first stage occurred
◦
from 0 to 100 C with the mass loss of 3.7%, corresponding to the loss of water (calc.
◦
3
.5%). Subsequent mass loss of 23.8% occurred at 100–280 C, which was assigned
to the loss of two C N H (calc. 25.0%) fragments from the complex molecular. The
10
2
19
same loss of C N H moiety from the C9-BTBP molecular was also observed in
10
2
19
◦
ESI-MS study (Fig. 8). The last stage occurred from 280 to 700 C with the mass loss
of 23.3% which was in agreement with the loss of two C NH (calc. 23.3%). The final
10
19
residues were palladium salts and carbides. Based on the above analysis, the thermal
decomposition processes of [Pd (NO ) ·(L)]·2.5H O were occurred in three steps
2
3 4
2
which could be elucidated with the scheme as presented in Fig.15b.
1
In addition, the solid Pd-C9-BTBP complex was characterized by H NMR in CDCl
3
1
solution (ESI, Fig. S4). A comparison of H NMR spectra of ligand C9-BTBP, solid 2:1
Pd complex and C9-BTBP titration with 2.0 equivalents of Pd(II) in CDCl /CD CN (3/7,
3
3
v/v) solution was shown in Fig.16. The relative strength of two class peaks
corresponding to H2 and H3 (labeled red font) in spectrum of the solid Pd complex
was much stronger than that of C9-BTBP (see Fig.16b and a). According to the above
1
H NMR titration analysis, these two sets of peaks were assigned to the protons in
binuclear Pd(II) complexes. In addition, the overlapped peaks of H1 and H3 (black
font) corresponding to 1:1 Pd-C9-BTBP complex were observed, which suggested
that part of 2:1 type complex was transformed to 1:1 type in solution.
12

Page 13 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
1
Fig. 16 (a) partial H NMR spectra of 10.0 mM C9-BTBP with 2.0 equivalents of Pd(II)
1
in CDCl /CD CN (3/7, v/v); (b) partial H NMR spectrum (400 MHz, CDCl , 298K) of solid
3
3
3
Pd(II) complex in CDCl and (c) ligand C9-BTBP in CDCl .
3
3
1
The solid Pd(II) complex and H NMR titration studies demonstrated the presence
binuclear complex of Pd with C9-BTBP both in solid state and in solution. The specific
structure of this type of complex deserves to be further determined in our laboratory.
Conclusions
The recovery and complexation of Pd(II) from some typical metals in highly nitric acid
medium was achieved by a new ligand C9-BTBP. The C9-BTBP/CHCl system
3
exhibited high extraction capability and high selectivity for Pd(II) over other tested
metals in HNO solution whereas the extraction kinetics was relatively slow. Both the
3
1:1 and 2:1 Pd to C9-BTBP complexes were found in solution, while the Pd with
C9-BTBP complex in solid state was 2:1 type. The thermal decomposition processes
of the complex were proposed based on the results of TGA-DSC.
This is the first report on the binuclear Pd(II) complexes formed with BTBP type
molecules. More comprehensive studies of structures of Pd(II) complexes with these
multi-dentate N-donor ligands needs to be further investigated. To elucidate the
coordination mechanism between these soft N-donor ligands and some fission
products co-existent with MAs in HLW is very important for the partitioning of minor
actinides. The outcome of this work is very valuable for understanding the mechanism
of complexation of Pd(II) with RBTBP type ligands.
Experimental
General methods
13

New Journal of Chemistry
Page 14 of 18
View Article Online
DOI: 10.1039/C5NJ03082J
The ruthenium nitrosyl nitrate solution with 1.5% (w/v) of Ru(III) was from Alfa-Aeser.
Palladium(II) nitrate solution with 5.0% (w/w) of Pd(II) was from Shanxi Kaida
II
II
Chemical Engineering Co.,Ltd. China. The Fe(NO ) ·9H 0, M (NO ) (M =Ba and Sr)
3
3
2
3 2
I
I
and alkali metals nitrates M(NO ) (M=Na, K, Rb and Cs) tested were of analytical
3
grade. All the nitric acid solutions used were made by diluting concentrated HNO with
3
deionized water. The concentrations of all the tested elements were about 0.5 mM. All
the other reagents were of analytical grade and used without further purification
except for anhydrous ether which was dried with P O and zeolite. NMR spectra were
2
5
performed with a Bruker Avance DMX 400 spectrophotometer or a Bruker Avance 500
spectrophotometer. FT-IR spectra were taken on a Bruker Vector 22 FT-IR
spectrometer. The electrospray ionization mass spectra (ESI-MS) were collected on a
Varian 500-ES Model instruments or a Bruker Esquire 3000 Plus spectrometer.
Elemental analyses were performed with Thermo Finnigan Italia S.P.A EA 1112 CHNS
elemental analyzer. The DSC-TGA curves were recorded on TA SDTQ600 thermal
analyzer. The concentrations of all the tested elements in the aqueous phases were
determined by the Atomic Absorption Spectrometer (AA 240).
Synthesis of 6,6'-bis(5,6-dinonyl-1,2,4-triazin-3-yl)-2,2'-bipyridine (C9-BTBP)
To obtain the C9-BTBP two intermediates were synthesized in advance as shown in
Figure 2. One was icosane-10,11-dione obtained by the reaction of decanoate ethyl
with sodium, followed by acidification with H SO (55%, w/w), and oxidation with
2
4
copper(II) acetate. Treating the 2,2’-bipyridine with hydrogen peroxide (30%, w/w), the
2
0
2
,2’-bipyridine dioxide was obtained. Followed by the reaction of 2,2’- bipyridine
21
dioxide with benzoyl chloride and trimethylsilyl cyanide, 6,6’-dicyano-2,2’- bipyridyl
was synthesized. Then 6,6’-dicyano-2,2’-bipyridyl was reacted with hydrazine hydrate
(
98%, w/w) in ethanol solution and the mixture was stirred at room temperature for 17
22
days to get the compound 2,2'-Bipyridine-6,6'-dicarboxbisamidrazone.
A suspension of 2,2'-Bipyridine-6,6'-dicarboxbisami-drazone (2.60 g, 9.62 mmol)
in a mixture of triethylamine (12.5 mL) and THF (450 mL) was added with
icosane-10,11-dione (6.60 g, 21.3 mmol). The mixture was stirred and heated under
reflux for 3 days. The heavy black oil was obtained after removing the solvent by the
rotary evaporation and the mixture was purified by column chromatography (ethyl
acetate-petroleum ether, 1:3, v/v). Then, the solid obtained was recrystallized with
ethanol and allowed to dry in the vacuum oven to afford the C9-BTBP as a yellow
◦
-1
solid (2.7g, 34 %). Mp 79.2 C; IR (neat) cm : 2923, 2853, 1575, 1517, 1462, 1384,
-1
1
1
270, 1079, 784, 634 cm ; H NMR (400 MHz, CDCl ): δ 8.99 (d, J = 7.8 Hz, 2H;
3
-
ArH), 8.59 (d, J = 7.6 Hz, 2H; -ArH), 8.08 (t, J = 7.8 Hz, 2H; -ArH), 3.08 (t, J = 7.8 Hz,
H; -CH ), 2.95 (t, J = 7.8 Hz, 4H; -CH ), 1.9 (m, 8H, -CH ), 1.41 (m, 48H, -CH ), 0.88
4
2
2
2
2
14

Page 15 of 18
New Journal of Chemistry
+
-
View Article Online
DOI: 10.1039/C5NJ03082J
(
m, 12H, -CH ) ppm; ESI-MS: m/z=841.7 [M + Na] , 817.7 [M - H] ; elemental analysis
3
calcd (%) for C H N (M = 819.26): C, 76.23; H, 10.09; N, 13.68; found: C, 76.03; H,
52
82
8
r
10.19; N, 13.67.
Synthesis of the solid Pd(II) complex of C9-BTBP
C9-BTBP (0.12 mmol 100.0 mg) was dissolved in ethanol (10.0 mL). To this solution
was added with the concentrated nitric acid (65%, w/w) to obtain the 2.0 M HNO3
solution. Then palladium (II) nitrate (0.25 mmol 588.8 mg) in HNO solution was
3
added to the solution dropwise over 10 min. After stirring at room temperature for 2
hours, the insoluble orange solid was filtered, washed with ethanol and 2.0 M HNO to
3
obtain the complex as an orange solid (50.0 mg, 31%).
Liquid / liquid solvent extraction experiments
-3
In extraction experiments performed, 1.0×10 M C9-BTBP in CHCl was used as the
3
-4
organic phases. The aqueous phases were 5.0×10 M of Na(I), K(I), Rb(I), Cs(I), Sr(II),
Ba(II), Ru(III), Fe(III) and Pd(II) in HNO of different concentrations (0.4-6.0 M). Equal
3
aqueous phases (5.0 mL each) were pre-equilibrated with the same volumes of CHCl3
and the organic phases were pre-equilibrated with nitric acid (5.0 mL each) of the
same concentration without adding any tested elements. Then equal amounts of
organic phases (5.0 mL each) and aqueous phases were mixed by vigorous shaking
(
120 rpm) with TAITEC MM-10 model oscillation box in 25 mL glass flask for 120 min
at 298 K. In preliminary experiments, it was found that a contacting time of 120 min
was enough to reach the extraction equilibrium. After centrifugation, the
concentrations of all the tested elements in the aqueous phases were determined by
the Atomic Absorption Spectrometer. The distribution ratios (D) were calculated as the
ratios of the concentrations of the tested metals in the organic to those in the aqueous
phases. It should be noted that the solvent extraction experiments were repeated
three times for each point we obtained.
Back extraction experiments
-3
To optimize the stripping conditions, a solution of 1.0×10 M C9-BTBP in HCCl
3
(
pre-equilibrated with 2.0 M nitric acid, A/O=1) was loaded with Pd(II) from 2.0 M
HNO aqueous phase. Then the loaded organic phases (1.0 mL each) were brought
3
into contact with the equal volume of thiourea of different concentrations in HNO3
solution.
15

New Journal of Chemistry
Page 16 of 18
View Article Online
DOI: 10.1039/C5NJ03082J
Acknowledgments
We would like to acknowledge the financial support from National Natural
Science Foundation of China under contracts No. 20871103 and 21376210.
Notes and references
1
2
D. D. Sood, S. K. J. Patil, Radioanal. Nucl. Chem., 1996, 203, 547.
a) M. Salvatores, Nucl. Eng. Des., 2005, 235, 805-816; b) M. Salvatores, G.
Palmiotti, Nucl. Phys., 2011, 66, 144-166.
3
4
a) E.D. Collins, J.P. Renier, Proc. Int. Conf. (Global 2005). 9–13 Oct., 2005, Japan, p.
2
35; b) M. Jeswani, A. Furnham, Nucl. Eng., 2003, 42(9), 263-277.
a) A. Bremer, D.M. Whittaker, C.A. Sharrad, A. Geist, P.J. Panak, Dalton. T., 2014,
3, 2684-2694; b) F.W. Lewis, L.M. Harwood, M.J. Hudson, M.G.B. Drew, J.F.
4
Desreux, G. Vidick, N. Bouslimani, G. Modolo, A. Wilden, M. Sypula, J. Am. Chem.
Soc., 2011, 133 13093-13102.
5
a) C.L. Xiao, C.Z. Wang, L.Y. Yuan, B. Li, H. He, S. Wang, Y.L. Zhao, Z.F. Chai, W.Q.
Shi, Inorg. Chem., 2014, 53, 1712-1720; b) L. M. Harwood, D. M. Laventine, A.
Afsar, M. J. Hudson, Heterocycles., 2012, 86 1419; c) M.R.S. Foreman, M.J.
Hudson, M.G.B. Drew, C. Hill, C. Madic, Dalton. T., 2006, 13, 1645; d) D.M.
Whittaker, T.L. Griffiths, M. Helliwell, A.N. Swinburne, L.S. Natrajan, F.W. Lewis,
L.M. Harwood, S.A. Parry, C.A. Sharrad, Inorg. Chem., 2013, 52, 3429-3444; e)
M.J. Hudson, L.M. Harwood, D.M. Laventine, F.W. Lewis, Inorg. Chem., 2013,
52(7), 3414-3428; f) F.W. Lewis, M.J. Hudson, L.M. Harwood, Chem. Inform.,
2012. 43(5), 24; g) P.J. Panak, A. Geist, Chem. Rev., 2013, 113(2), 1199-1236.
6
a) M.R.S. Foreman, M.J. Hudson, A. Geist, C. Madic, M. Weigl, Solvent. Extr. Ion
Exc., 2005, 23, 645-662; b) C. Hill, D. Guillaneux, B. Laurence, C. Madic, J. Nucl.
Sci. Technol., 2002, 39, 309-312. c) E. Aneheim, C. Ekberg, M.R. Foreman,
Hydrometallurgy., 2012, 115, 71-76. d) F.W. Lewis, L.M. Harwood, M.J. Hudson, P.
Distler, J. John, K. Stamberg, A. Núñez, H. Galán, A.G. Espartero, Eur. J. Org.
Chem., 2012, 2012, 1509-1519; e) A. Wilden, C. Schreinemachers, M. Sypula, G.
Modolo, Solvent. Extr. Ion. Exch., 2011, 29(2), 190-212.
7
a) D. Magnusson, A. Geist, A. Wilden and G. Modolo, Solvent. Extr. Ion. Exch., 2013,
31, 1–11; b) A. Wilden, G. Modolo, C. Schreinemachers, F. Sadowski, S. Lange,
16

Page 17 of 18
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ03082J
M. Sypula, D. Magnusson, A. Geist, F. W. Lewis, L. M. Harwood and M. J. Hudson,
Solvent. Extr. Ion Exch., 2013, 31, 519–537.
8
Kolarik, Z, E. V. Renard, Platin. Met. Rev., 2003, 47, 74-87.
a) G. Rizvi, J. Mathur, M. Murali, R. Iyer, Sep. Sci. Technol., 1996, 31 1805-1816.
b) A.Y. Zhang, Y.P. Zhu, Z.F. Chai, J. Chem. Eng. Data., 2012, 57, 1267-1273.
0 T.L. Ho, Chem. Rev., 1975, 75, 1-20.
9
1
11 R.G. Pearson, J. Am. Chem. Soc., 1963, 85, 3533-3539.
12 A. Geist, C. Hill, G. Modolo, M. R. St. J. Foreman, M. Weigl, K. Gompper, M. J.
Hudson, Solvent. Extr. Ion. Exch., 2006, 24(4), 463-483.
13 M. Hudson, J. Phys., 2003., 53, A305-A311.
14 M. Weigl, A. Geist, U. Müllich, K. Gompper, Solvent. Extr. Ion. Exc., 2006, 24,
845-860.
1
5 M. Mohan Raj, A. Dharmaraja, K. Panchanatheswaran, K.A. Venkatesan, T.G.
Srinivasan, P.R. Vasudeva Rao, Hydrometallurgy., 2006, 84, 118-124.
6 a) T. Retegan, L. Berthon, C. Ekberg, A. Fermvik, G. Skarnemark, N. Zorz,
Solvent. Extr. Ion. Exc., 2009, 27, 663-682. b) L. Berthon, N. Zorz, B. Gannaz, S.
Lagrave, T. Retegan, A. Fermvik, C. Ekberg, IOP Conference Series: Materials
Science and Engineering., 2010.
1
1
7 E. Aneheim, B. Grüner, C. Ekberg, M.R. Foreman, Z. Hájková, E.
Löfström-Engdahl, M.G. Drew, M.J. Hudson, Polyhedron., 2013, 50, 154-163.
8 D. F. Evans, C. Y. Wong, J. Chem. Soc., Dalton Trans., 1992, 431, 2009-2012.
9 C. Srivanavit, J. I. Zink, J. J. Dechter, J. Am. Chem. Soc., 1977, 99, 5876-5881.
0 A.Y. Zhang, Y.P. Zhu, Z.F. Chai, AIChE. J., 2010, 56, 3074-3083.
1
1
2
2
2
1 P. Simpson, A. Vinciguerra, J.V. Quagliano, Inorg. Chem., 1963, 2, 282-286.
2 Y. Ohshiro H. Kikuta. Research Institute for Science and Technology., 1997, 9, .
29-32.
17

New Journal of Chemistry
Page 18 of 18
View Article Online
DOI: 10.1039/C5NJ03082J
New Journal of Chemistry (NJ-ART-11-2015-003082)
Separation and complexation of palladium (II) with a new soft
N-donor ligand 6,6'-bis(5,6-dinonyl-1,2,4-triazin-3-yl)-2,2'-bipyridine
(
C9-BTBP) in nitric acid medium
*
Anyun Zhang , Lei Xu, Gaoming Lei
College of Chemical and Biological Engineering, Zhejiang University, No.38 Zheda
Road, Hangzhou 310027, P. R. China
Graphical Abstract
1
Both the 1:1 and 2:1 Pd to C9-BTBP complexes were found in solution by H
NMR titration.
*
Corresponding author. Anyun Zhang. E-mail: zhangay@zju.edu.cn (A. Zhang)