Tetrahydrosalen Uranyl(VI) Complexes: Crystal Structures and Solution Binding Study

Article abstract of DOI:10.1002/ejic.201701401

A pair of uranyl complexes incorporating tetrahydrosalen and N,N-dimethyltetrahydrosalen ligands are synthesized and studied. These new ligands, with saturated secondary and tertiary amines, exhibit higher chemostability than the prototype Schiff base (sa

Full text of DOI:10.1002/ejic.201701401

A Journal of
Accepted Article
Title: Tetrahydrosalen Uranyl(VI) Complexes: Crystal Structures and
Solution Binding Study
Authors: Xiao Zhao, Di Zhang, Yu Ren, Shunsen Chen, and Dahui
Zhao
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10.1002/ejic.201701401
European Journal of Inorganic Chemistry
FULL PAPER
Tetrahydrosalen Uranyl(VI) Complexes: Crystal Structures and
Solution Binding Study
Xiao Zhao,[a] Di Zhang,[a] Yu Ren,[b] Shusen Chen,[b] and Dahui Zhao*[a]
Abstract: A pair of uranyl complexes incorporating tetrahydrosalen
and N,N-dimethyltetrahydrosalen ligands are synthesized and
studied. Compared to the prototype Schiff-base (salen) structure,
these new ligands with saturated secondary and tertiary amines
exhibit higher chemo-stability, especially under acidic conditions. As
shown by the X-ray crystallography, the coordination geometry of
Hence, a number of salicyladehyde-derived 4 or 5 dentate Schiff
bases,[12] particularly some salen and salophen derivatives, were
previously studied and found to form stable complexes with
uranyl ion,[13] because they offer both hard O and soft N
coordinating sites with suitable steric and electronic
properties.[1,14,15] Besides offering valuable experimental data for
uranium in these new complexes is a distorted pentagonal bipyramid, fundamental studies on the reactivity and coordination properties
with the (dimethyl)tetrahydrosalen wrapped around the equatorial
of uranyl ion, in recent years the complexation chemistry of
uranyl with salen- and salophen-type ligands has also been
investigated to explore their unique optical, magnetic, catalytic
functions and anion recognition capabilities.[16-21] Moreover, by
virtue of the facile and cost-effective synthesis procedures,
various salen-type scaffolds have been investigated as ligand-
design platforms for developing uranium adsorbents and nuclear
fuel recycling extractants.[22]
Although most uranyl complexes comprising Schiff-base
ligands are relatively stable in neutral to basic aqueous solutions
and in the solid state, the C=N bonds are well known to be labile
and susceptible to exchange[23,24] and hydrolysis reactions under
acidic conditions.[25-27] Previously, both transamination and
hydrolysis were observed with the Schiff-base ligands in uranyl
complexes.[28,29] The mechanism of hydrolysis was suggested to
involve an intermediate of carbinolamine [–NH–CH(OH)–],
formed by addition of water to the imine group, followed by C–N
bond cleavage in the N-protonated form.[29,30] This property
basically precludes the Schiff-base type chelating ligands from
applications as uranyl adsorbents, because material degradation
inevitable results from the hydrolysis of Schiff-bases under the
acidic conditions.
2+
plane of UO2
. Interestingly, UO2([H4]-salen) comprising the
tetrahydrosalen ligand forms a dimer structure in the crystals, with
two subunits held together by sharing one of the two phenoxy
oxygen atoms from each subunits. Whereas, UO2([H2Me2]-salen)
with the N,N-dimethyltetrahydrosalen ligand is in the monomer state,
with a solvent molecule coordinated to uranium to complete the
penta-coordination configuration. Moreover, as revealed by the
UV−vis spectrometry using the colorimetry method, these
hydrogenated salen ligands exhibited comparable or even higher
binding affinity toward uranyl than the prototype Schiff-base salen
ligand in weakly basic solution.
Introduction
The coordination chemistry of uranium deserves great attention
not only for the fundamental research interests in the element
reactivity, coordination properties and bonding interactions with
various ligands,[1-3] relevant study results are also useful to
exploring potential applications of uranyl complexes as catalysts
and sensors,[4] as well as to the technologies for extracting,
seperating and concentrating uranium.[5-10] The design and
identification of new chelating ligands that can bind to uranyl
with high affinity and high selectivity are of particular importance.
The linear uranyl dication (UO22+) is the most common form
of uranium in the majority of known uranium compounds. With
two chemically inert oxygen atoms taking the axial positions, the
Figure 1. The chemical structures of salen, tetrahydrosalen ([H4]-salen) and
N,N-dimethyltetrahydrosalen ([H2Me2]-salen) ligands.
linear uranyl dication typically prefers
a (nearly) planar
pentadentate coordinating motif around its equatorial plane.[11]
In order to circumvent this problem of acid sensitivity of
Schiff-base ligands,
tetrahydrosalen ([H4]-salen) and N,N-dimethyltetrahydrosalen
[H2Me2]-salen, Figure 1), were synthesized, derived from N,N’-
ethylenebis(salicylidenimine) (salen), and their binding
properties with uranyl ion were studied. Apparently, these
new molecules containing saturated secondary and tertiary
amine moieties are basically inert to hydrolysis and more stable
compared to corresponding Schiff-base analogues.[31] By
examining their binding affinities to UO22+ ion, here we show that
a
pair of new chelating ligands,
[a]
X. Zhao, D. Zhang, Prof. D. Zhao
Beijing National Laboratory for Molecular Sciences (BNLMS),
Department of Applied Chemistry, Centre for Soft Matter Science
and Engineering, Key Lab of Polymer Chemistry & Physics of
Ministry of Education, College of Chemistry, Peking University
Beijing 100871, China
E-mail: dhzhao@pku.edu.cn
http://www.chem.pku.edu.cn/zhaodh/index.htm
R. Yu, Dr. S. Chen
(
[b]
Beijing Research Institute of Chemical Engineering and Metallurgy,
Beijing, 101149, China
both tetrahydrosalen and N,N-dimethyltetrahydrosalen are
Supporting information for this article is given via a link at the end of
the document.
2+
highly competent chelating ligands for binding UO2
,
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10.1002/ejic.201701401
European Journal of Inorganic Chemistry
FULL PAPER
exhibiting comparably or even higher binding abilities than salen.
Such desirable properties render these tetrahydrosalen
derivatives potentially useful binding motifs to be incorporated in
the future design of uranium adsorbant materials.
that the O=U=O moiety was slightly bent toward the direction
opposite to the coordinating water molecule. The bond lengths
of U(1)-O(4) and U(1)-O(5) [2.226(8) and 2.323(9) Å] were
reasonably shorter compared to those of U(1)-N(1) and U(1)-N(2)
[2.649(8) and 2.62(1) Å].[35]
Results and Discussion
Syntheses of the ligands and uranyl complexes
Molecules [H4]-salen and [H2Me2]-salen were both prepared
using the readily available Schiff-base molecule salen as the
starting material (Supporting information). Using similar
procedures as the previously reported,[28] tetrahydrosalen ([H4]-
salen) was first obtained by reducing salen with NaBH4 in nearly
quantitative yield. Subsequently, the N-methylation was realized
by reacting [H4]-salen with an excess of formaldehyde to form an
imine intermediate, followed by reduction with NaBH4. A high
yield of [H2Me2]-salen (98%) was achieved over the two steps.
Figure 2. ORTEP drawing of the crystal structure of UO2([H2Me2]-salen)
(thermal ellipsoids are drawn at the 50% probability level; non-coordinating
acetonitrile molecules are not shown; hydrogen atoms are shown in white,
nitrogen in blue, oxygen in red, and uranium in green).
Subsequently, complexes UO2([H4]-salen) and UO2([H2Me2]-
salen) were obtained by mixing the corresponding ligand ([H4]-
salen or [H2Me2]-salen) with a stoichiometric amount of uranyl
nitrate hexahydrate[17] in methanol solution at room temperature,
with decent yields offered in the range of 80-90% (Scheme 2).
Table 1. Selected bond lengths [Å] of uranyl complex UO2([H2Me2]-salen).
The chemical structures of UO2([H4]-salen) and UO2([H2Me2]-
Bond parameters
U1 N1
Cal.[a]
2.690
2.687
1.785
1.789
2.200
2.281
2.569
Exp.
salen) were confirmed by 1H & 13C NMR spectroscopy and mass
spectrometry. Besides the tetradentate ligand of [H4]-salen or
[H2Me2]-salen, an additional coordinating ligand is presumably
present, the identity of which is dependent on the solvent. FT-IR
analyses (Figure S1, SI) were subsequently conducted to
further characterize the structures of the obtained uranyl
complexes. In the IR spectra, a new band, attributed to the
asymmetric stretching vibrations of O=U=O, was observed at
900 and 885 cm−1 with uranyl complexes of UO2([H4]-salen) and
2.649(8)
2.62(1)
1.787(7)
1.794(8)
2.226(8)
2.323(9)
2.469(8)
U1 N2
U1 O1
U1 O2
U1 O3
UO2(
[H2Me2]-salen), respectively.[37]
U1 O4
Crystal structures
U1 O5
Red colored crystals suitable for X-ray diffraction of
UO2([H2Me2]-salen) were first obtained by slow evaporation of
[a] Optimized structure obtained with the B3LYP method.
an acetonitrile solution maintained at about 4 °C. The molecular
structure determined by the X-ray diffraction analysis is shown in
Figure 2, with the selected crystallographic data listed in Table 1.
Under such crystal-growth conditions (i.e., in acetonitrile)
Similar to UO2([H2Me2]-salen), red crystals [H4]-salen were
also grown from the acetonitrile solution. Upon X-ray diffraction
analysis the obtained crystal was nonetheless found to contain
complex UO2([H2Me2]-salen) was found to contain one equilvant
the dimer form of UO2([H2Me2]-salen). Representative bond
of water molecule as the auxilary ligand. As shown by the crystal
structure, this complex had a pentagonal-bipyramidal geometry,
with two nitrogen and three oxygen (two from [H2Me2]-salen and
one from water molecule) atoms surrounding the equatorial
plane of the linear [O=U=O]2+. Namely, the uranyl cation was
included into the tetradentate cavity of the [H2Me2]-salen, and
the two methyl groups on the tertiary amines were flanked on
the opposite side of the coordinating plane, as a trans-
length data are listed in Table 2. As shown in Figure 3, in the
UO2([H4]-salen) dimer both of the subunits exhibit pentagonal-
bipyramidal geometry, and the two bipyramids share an edge of
the pentagon with each other. Namely, one of the phenoxy
oxygen atoms from each of subunit is coordinating to both two
uranium atoms. The bond lengths between the uranium centre
and the bridging oxygen atoms are 2.39-2.43 Å, which are
perceivably longer than those between the non-bridging oxygen
and uranium. Our repeated attempts at obtaining monomeric
UO2([H4]-salen) crystals in different solvents all ended in vain.
configuration. Hence,
exhibited by UO2 [H2Me2]-salen). The axial O=U=O bond lengths
in complex UO2
a chiral pseudo-C2 symmetry was
(
(
[H2Me2]-salen) were 1.787(7) and 1.794(8) Å,
which were the typical values for uranyl complexes.[34] A bond
angle of 175.4(3)° was measured for O(1)-U(1)-O(2), indicating
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10.1002/ejic.201701401
European Journal of Inorganic Chemistry
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U1 O2
U1 O3
U1 O4
U1 O7
U2 N3
U2 N4
U2 O4
U2 O5
U2 O6
U2 O7
U2 O8
1.786
2.195
2.446
2.431
2.664
2.708
2.440
1.787
1.782
2.445
2.190
1.787(4)
2.211(5)
2.385(5)
2.430(4)
2.560(7)
2.612(6)
2.411(4)
1.808(5)
1.791(4)
2.429(4)
2.153(5)
Figure 3. ORTEP drawing of the crystal structure of UO2([H4]-salen) (thermal
ellipsoids are drawn at the 50% probability level; non-coordinating acetonitrile
molecules are not shown; hydrogen atoms are shown in white, nitrogen in blue,
oxygen in red, and uranium in green).
Uranyl binding property study
[a] Optimized structure obtained with the B3LYP method.
The binding capabilities of the newly designed ligands to
uranyl ion in solution are the basis for their application as
the uranium adsorbents. Hence, relevant properties of [H4]-
salen and [H2Me2]-salen were subsequently evaluated using
the colorimetry method via solution titration. For comparison,
the behaviour of salen was also examined under the same
conditions. Because the ligands were not sufficiently
soluble in aqueous or alcohol solvents, the titration
experiments were carried out at 25 °C in pyridine, which
was selected to be the solvent for providing suitable
solubility for the ligands and complexes under weakly basic
condition. The colorimetric process was monitored by the
UV-vis spectrophotometry. Upon the addition of
UO2(NO3)2·6H2O, the colour of the [H4]-salen and [H2Me2]-
salen solutions (at ca. 5 × 10-5 M) was gradually changed
from colourless to orange. In the meanwhile, the UV-vis
absorption spectrum was observed to experience notable
changes with an increasing concentration of uranium ion.
New absorption bands emerged around 385 and 475 nm,
ascribable to the LMCT transitions of the uranium
complexes.[2] These absorption bands were found to grow
continuously when the uranyl ion was present at a sub-
stoichiometric amount. However, after the concentration of
uranyl ion reached one equivalent to the ligand molecule,
nearly no further change was detected with the band
intensity (Figures 4 and 5). Hence, a stoichiometric ratio of
1:1 was indicated for both complexes UO2([H4]-salen) and
UO2([H2Me2]-salen) when binding with the uranyl ion under
these conditions.
Subsequently, quantitative analyses were conducted to
assess the binding abilities of these ligands to uranyl ion
under the applied conditions. By fitting the experimental
data to a mathematic equation (Eq. 1, SI) employed in
previous studies[37] to describe the 1:1 binding systems, the
extinction data of both UO2([H4]-salen) and UO2([H2Me2]-
salen) at various concentration of UO22+were well fitted to
the 1:1 complexation model (Figure 4b and 5b), and the
apparent binding constants (K) under the given conditions
(in pyridine) were estimated to be (2.3 ± 0.6) × 107 and (1.6
±
0.6)
×
107 M-1 for [H4]-salen and
[H2Me2]-salen,
respectively. Remarkably, these values were quite
comparable, or even slightly higher, than that of salen [K =
(1.3 ± 0.4) × 107 M-1, Figure S2] obtained under the same
conditions (Table 3). These results clearly indicated that
[H4]-salen and [H2Me2]-salen were competent or even better
2+
chelating ligands to UO2
than salen. The enhanced
binding affinity observed was very likely benefitted from to
the higher basicity (better electron donating ability) of the
saturated amine groups compared to the imine (C=N)
moieties in salen. The binding ability difference between
[H4]-salen and [H2Me2]-salen was tentatively attributed to the
smaller steric hindrance experienced by the secondary
amine groups in the former. The additional entropy cost
caused by the two N-methyl groups in [H2Me2]-salen might
have contributed to the minor binding constant difference as
well.
Table 3. Binding constants of different ligands with uranium in pyridine.
Table 2. Selected bond lengths [Å] of uranyl complex UO2([H4]-salen).
salen
[H4]-salen
2.3 ± 0.6
0.9998
[H2Me2]-salen
1.6 ± 0.6
K (/107 M-1)[a]
R2
1.3 ± 0.4
0.9994
Bond parameters
U1 N1
Cal.
Exp.
0.9994
2.678
2.696
1.782
2.626(6)
2.606(5)
1.783(4)
U1 N2
[a] Calculated based on the 1:1 complex.
U1 O1
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10.1002/ejic.201701401
European Journal of Inorganic Chemistry
FULL PAPER
reasonably consistent with the fact that the bimolecular
dimerization process proceeds to a lower extent at lowered
concentrations.
(a)
UO22+
0.6
0 eq
1.6 eq
0.4
0.2
0.0
2+
(a)
0.9
0.6
0.3
0.0
UO2
0 eq
1.6 eq
350 400 450 500 550 600 650
Wavelength (nm)
400
500
600
0.6
(b)
Wavelength (nm)
0.4
0.2
0.0
0.9
0.6
0.3
0.0
(b)
0.00 0.02 0.04 0.06 0.08
C(UO22+) (mM)
Figure 4. (a) Absorption spectra collected during titration of UO2(NO3)2·6H2O
to a solution of [H4]-salen (5.0 × 10-5 M) in pyridine (from 0 eq to 1.6 eq); (b)
the absorption change at 385 nm at varied UO2(NO3)2·6H2O concentration (the
red line represents the best fit to eq. 1 in SI).
0.00 0.02 0.04 0.06 0.08
C(UO22+) (mM)
Figure 5. (a) Absorption spectra collected during titration of UO2(NO3)2·6H2O
to a solution of [H2Me2]-salen (5.0 × 10-5 M) in pyridine (from 0 eq to 1.6 eq);
(b) the absorption change at 385 nm at varied UO2(NO3)2·6H2O concentration
(the red line represents the best fit to eq. 1 in SI).
Apparently, it was reasonable to suppose that [H2Me2]-
salen formed 1:1 complex with UO2 in solution, according
2+
to its crystal structure. However, since the dimer form was
observed in the crystalline state, extra care was necessarily
taken for [H4]-salen. Subsequently a two-step model was set
up and used to analyze the thermodynamic properties of a
2:2 binding process.[34] Basically, the model included a
dimerization step following the initial 1:1 complex formation.
As shown in Scheme 1, the equilibrium constant of 1:1
complexation between [H4]-salen and uranyl was defined to
be K1, and the dimerization constant of the subunit leading
to UO2([H4]-salen) was K2. According to this mechanistic
model, Eq. 8 was derived (see SI for details). By fitting the
experimental data to Eq. 1, K1 and K2 could be evaluated. As
the extent of dimerization was dependent on the concentration,
the titration experiment for [H4]-salen was also performed at a
higher concentration. Upon fitting the extinction data collected at
both low and high concentrations to Eq. 8, it was found that the
data collected at the lower concentration of 5.2 × 10-5 M were
better fitted to the 1:1 model than the 2:2 model (Figures 4b
and S3 in SI). However, the data recorded at the higher
concentration of 5 × 10-4 M were better fitted with the 2:2
complexation mechanism (Figure S4 in SI). These results were
By fitting the absorption change of [H4]-salen at 5.0 × 10-4
M to the dimer model (see the SI), the apparent binding constant
K1 was estimated to be ca. 1.1 × 107 M-1, which was reasonably
consistent with the apparent binding constant K of [H4]-salen
obtained at the lower concentration with the 1:1 binding model.
At the same time, a relatively small value of 1.1 M-1 was
obtained for the dimerization constant K2. Based on such K1 and
K2 values, it could be calculated that at 5 × 10-4 M, less than
0.03% of UO2([H4]-salen) existed as dimers at equilibrium (with
1.0 equivalent UO22+). In other words, at such a concentration
the dimerization of UO2([H4]-salen) was not particularly
significant. Imaginably, at an even lower concentration of 5.2 ×
10-5 M-1, the dimer content was negligible, and it was reasonable
to use the simple 1:1 model to describe the complexation (Table
3).
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Experimental Section
General Methods. Chemicals were purchased commercially
and used without further purification unless otherwise noted.
NMR spectra were recorded on Bruker ARX 400 (400 MHz)
using CDCl3 or DMSO-d6 as the solvent. Chemical shifts are
reported in parts per million (ppm) relative to TMS (0 ppm) or
DMSO-d6 (2.50 ppm) and to CDCl3 (77.23 ppm) or DMSO-d6
(39.52 ppm) for 1H and 13C NMR spectra, respectively.
Elemental analyses were performed using a German Vario EL III
elemental analyzer. Mass spectroscopy was performed on a
Bruker Solarix XR Fourier Transform Ion Cyclotron Resonance
Mass Spectrometer. Infrared spectra were recorded on a Bio-
Rad FTS-65A FT-IR spectrometer. UV-Vis absorption spectra
were recorded on a Hitachi U-4100 spectrophotometer using the
absorption mode in a 1-cm quartz cell or UV3600PLUS UV-VIS-
NIR spectrophotometer using the absorption mode in a 4-cm
quartz cell.
Scheme 1. Schematic representation of a two-step mechanism for the 2:2
complex formation of UO2([H4]-salen).
Uranyl Binding Study. The bind properties of new ligands to
U(VI) ions were investigated with the UV-Vis absorption
spectroscopy via the titration experiments carried out at
25 °C in pyridine solution. Prior to use, pyridine (HPLC grade)
was treated with molecular sieves to reduce the residual water
content. The titrations were performed by first making a stock
solution with the ligand (ca. 5.0 × 10-5 M) and UO2(NO3)2 (ca.
0.05 M) in pyridine. A given volume of the stock solution was
then added repeatedly to a pyridine solution with the same
ligand concentration, such that an exact 0.10 equivalent of the
salt was introduced per addition. The solution was shaken for
about 10 seconds after each addition before the absorption
spectrum was recorded. The titration was continued till 1.5 to 2
equivalent of UO2(NO3)2 was added, when no more evident
spectral change was observable. A baseline correction was
conducted by applying pyridine in the both the sample and
reference cells.
Conclusions
Here we report the design, syntheses and properties of two new
uranyl complexes, UO2([H4]-salen) and UO2 [H2Me2]-salen),
(
comprising tetradentate chelating ligands of [H4]salen
(tetrahydrosalen) and [H2Me2]-salen (N,N-dimethyltetrahydro-
salen), respectively. Instead of the unsaturated Schiff-base
structure (i.e., C=N bonds), these two ligands featured saturated
secondary or tertiary amine groups and hence possess higher
chemo-stability than the prototype salen ligand, particularly
under acidic conditions. In the crystal structure, complex
UO2([H2Me2]-salen) showed a distorted pentagonal bipyramidal
geometry by incorporating a water molecule besides [H2Me2]-
salen around UO22+. But interestingly, UO2([H4]-salen) was found
to assume a dimer form in the crystalline state. In the dimer, the
two subunits were held together by sharing one of the two
phenoxy oxygen atoms from each subunits as the fifth
coordinating site. UV-vis absorption titration experiments were
carried out to compare the binding properties of [H4]-salen and
[H2Me2]-salen to that of salen with UO22+ in solution. The results
showed that all three ligands displayed highly competent binding
to uranyl ion in the basic solvent of pyridine.[13b] Among the three
ligands, [H4]-salen with secondary amines exhibited slightly
higher binding affinity than the other two. We deem that both the
higher electron-donating ability of (secondary amine vs. imine)
and the smaller steric hindrance of the secondary amine
(compared to the N-methylated tertiary amine) have contributed
to the slightly enhanced binding affinity observed for [H4]-salen.
These results demonstrate that, compared to the prototype
salen, the tetrahydrosalen-type ligands, which boast both high
chemo-stability and competent binding affinity to uranyl ion are
promising functional chelating structures that may potentially be
useful for the future design of new recyclable adsorption
materials for uranium extraction.
X-ray Diffraction. Single crystal diffraction data of UO2
([H4]-
salen and UO2 [H2Me2]-salen) are presented in Table 4. The
(
data were collected using a Kappa single diffractometer with
graphite monochromator and Mo Kα radiation [λ (MoKα) =
0.71073 Å]. The structures were solved by Superflip[38] structure
solution program using Charge Flipping and refined with the
ShelXL[39] refinement package using Least Squares minimisation
or the XH[40] refinement package using CGLS minimization.
DFT Calculations. All calculations were carried out in the
Gaussian 09 program[41] using the DFT method[42,43] with the
B3LYP[44,45] hybrid functional. The quasi-relativistic effective core
potentials (RECP) replacing 60 core electrons for uranium and
the corresponding valence basis sets[46-48] were used. The 6-
311G (d, p) basis sets were adopted for hydrogen, carbon,
nitrogen, and oxygen atoms. Scalar relativistic calculations were
performed without considering spin−orbit coupling effects. The
geometry optimizations were carried out with no symmetry
restrictions. At the B3LYP/6-311G (d, p)/RECP level of theory,
vibrational frequency analyses were performed to verify the
minima character of the optimized structures.
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10.1002/ejic.201701401
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Table 4. Crystallographic parameters and structure-refinement statistics for UO2([H4]-salen) and UO2([H2Me2]-salen).
Complex
UO2
(
[H4]-salen)
UO2([H2Me2]-salen)
Empirical formula
Formula weight (g/mol)
Temperature (K)
Crystal system
Space group
C34H39N5O8U2
C20H27N3O5U
627.47
1121.76
180.00(10)
100.00(10)
monoclinic
P21/c
orthorhombic
Pbca
a (Å)
19.5775(8)
11.3803(5)
12.4494(7)
15.6236(7)
90
b (Å)
15.0156(6)
c (Å)
25.1024(11)
α(°)
90
β(°)
90
91.828(4)
90
γ(°)
90
Volume (Å3)
7379.3(5)
2212.39(19)
4
Z
8
ρcalc (g/cm3)
μ(mm-1)
2.019
1.884
8.822
7.371
F(000)
4208.0
1200.0
Crystal size (mm3)
Radiation (λ, Å)
2Θ range for data collection (°)
Index ranges
0.2 × 0.1 × 0.1
0.15 × 0.1 × 0.1
0.71073
7.21 to 52.04
0.71073
7.03 to 52.044
-24 ≤ h ≤ 23, -18 ≤ k ≤ 18, -30 ≤ l ≤ 30
72949
-14 ≤ h ≤ 14, -15 ≤ k ≤ 14, -19 ≤ l ≤ 19
11254
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes[I>=2σ (I)]
Final R indexes [all data]
Largest diff. peak and hole (e Å-3)
7250 [R(int) = 0.1047, R(sigma) = 0.0438]
7250/6/443
4226 [R(int) = 0.0919, R(sigma) = 0.0857]
4226/42/266
1.080
1.019
R1 = 0.0405, wR2 = 0.0799
R1 = 0.0541, wR2 = 0.0842
2.46/ -1.19
R1 = 0.0744, wR2 = 0.1965
R1 = 0.0865, wR2 = 0.2067
4.69/-5.39
Synthesis of UO2([H4]-salen). A solution of uranyl nitrate
hexahydrate (15.1 mg, 0.03 mmol) in methanol (5 mL) was
added dropwise to a methanol solution (5 mL) of [H4]-salen (9.00
mg, 0.03 mmol) with constant stirring. The resulting reaction
mixture was stirred overnight at room temperature and the
colour was turned to orange. The precipitate was filtrated and
11.7 Hz, 4H), 3.78 (d, J = 4.8 Hz, 4H), 3.35 (m, 4H). 13C NMR
(100 MHz, DMSO-d6): δ 169.1, 129.7, 129.2, 128.8, 127.9, 118.8,
56.0, 52.1. HR-MS (ESI, M=C32H36N4O8U2, dimer form): Anal.
Calcd. for C32H37N4O8U2 [(M+H)+]: 1081.3645, Found:
1081.3621; Elemental analysis (%) calcd. for C32H37N4O8U2: C,
35.56; H, 3.36; N, 5.18; Found: C, 35.62; H, 3.35; N, 5.07.
washed with
a
small amount of cold methanol and
Synthesis of UO2([H2Me2]-salen). A solution of uranyl
dichloromethane. It was then recrystallized from acetonitrile to
afford a red crystalline solid (29.2 mg, yield: 90%). 1H NMR (400
MHz, DMSO-d6): δ 7.28-7.26 (m, 8H), 6.82-6.79 (m, 4H), 6.52-
6.47 (m, 4H), 5.73 (m, 4H), 4.72 (t, J = 11.6 Hz, 4H), 4.30 (d, J =
nitrate hexahydrate (25.11 mg, 0.05 mmol) in 5 mL
methanol was added dropwise to a solution of [H2Me2]-salen
(16.6 mg 0.05 mmol) in MeOH (5 mL) with constant stirring.
The resulting reaction mixture was stirred overnight at room
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10.1002/ejic.201701401
European Journal of Inorganic Chemistry
FULL PAPER
[10] G. Benay, G. Wipff, J. Phys. Chem. B 2013, 117, 7399-7415.
temperature. The color was turned from yellow to orange.
The orange crystalline precipitate was filtrated and collected
as the product (23 mg, yield: 80%). H NMR (400 MHz, DMSO-
d6): δ 7.35-7.30 (m, 2H), 7.24-7.22 (m, 2H), 6.82-6.80 (m, 2H),
6.55 (td, J = 7.3, 0.9 Hz, 2H), 4.92 (d, J = 13.4 Hz, 2H), 4.08 (d,
J = 13.5 Hz, 2H), 3.98 (d, J = 10.9 Hz, 2H), 3.34 (d, J = 10.7 Hz,
2H), 2.92 (s, 6H). 13C NMR (100 MHz, DMSO-d6): δ 168.1, 130.1,
129.9, 126.6, 119.2, 116.6, 66.9, 58.2, 44.6. HR-MS (ESI,
M=C18H24N2O5U): Anal. Calcd. for C18H23N2O4U [(M-H2O+H)+]:
569.2147; Found: 569.2160.
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Scheme 2. Syntheses of uranyl complexes UO2([H4]-salen) and UO2([H2Me2]-
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Keywords: Tetrahydrosalen • Uranyl(VI) complex • Crystal
structure • Coordinative ligand
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Entry for the Table of Contents (Please choose one layout)
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A pair of uranyl(VI) complexes
Key Topic* Uranyl(VI) Complexes
composed of tetrahydrosalen-derived
tetradentate ligands are synthesized,
with the crystal structures obtained
and high binding affinity to uranyl in
solution proven for both ligands.
Xiao Zhao, Di Zhang, Yu Ren, Shusen
Chen, Dahui Zhao*
Page No. – Page No.
Tetrahydrosalen Uranyl(VI)
Complexes: Crystal Structures and
Solution Binding Study
*one or two words that highlight the emphasis of the paper or the field of the study
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