Syntheses and structures of a series of uranyl phosphonates and sulfonates: An insight into their correlations and discrepancies

Article abstract of DOI:10.1021/ic302847g

Six uranyl phosphonates and sulfonates have been hydrothermally synthesized, namely, (H₂tib)[(UO₂)₃(PO ₃C₆H₅)₄]·2H₂O (UPhP-1), Zn(pi)₂(UO₂)(PO₃C₆H ₅)₂ (UPhP-2), Zn(dib)(UO₂)(PO₃C ₆H₅)₂·2H₂O (UPhP-3), (HTEA)[(UO₂)(5-SP)] (USP-1), (Hdib)₂[(UO₂) ₂(OH)(O)(5-SP)] (USP-2), and Zn(phen)₃(UO ₂)₂(3-SP)₂ (USP-3) (tib = 1,3,5-tri(1H- imidazol-1-yl)benzene, pi = 1-phenyl-1H-imidazole, dib = 1,4-di(1H-imidazol-1- yl)benzene, TEA = triethylamine, phen = 1,10-phenanthroline, 5-SP = 5-sulfoisophthalic acid, and 3-SP = 3-sulfoisophthalic acid). UPhP-1 has been determined to be a layered structure constructed by UO₇ pentagonal bipyramids, UO₆ octahedra, and phenylphosphonates. Protonated tib plays a role in balancing the negative charge and holding its structure together. UPhP-2 is made up of UO₆ octahedra, ZnO₂N ₂ tetrahedra and PO₃C tetrahedra in phenylphosphonates, forming a 1D assembly, which is stabilized by chelate phen ligand. Further connection of such chainlike structure via dib yields a 2D layered architecture of UPhP-3. Although sulfonate group possesses similar tetrahedral structure as the phosphonate group, a unidentated coordination mode is only found in this work. UO₇ pentagonal bipyramids are linked by 5-SP to form the layered assembly of USP-1. USP-2 also consists of the same sulfonate ligand, but features tetranulear uranyl clusters. Similarly, protonated TEA and dib molecules enable stabilization of their structures, respectively. Formed by dinuclear uranyl cluster and 3-SP ligand, USP-3 appears as a 1D arrangement, in which Zn(phen)₃ acts as the counterion to compensate the negative charge. All of these compounds have been characterized by IR and photoluminescent spectroscopy. Their characteristic emissions have been attributed as transition properties of uranyl cations.

Full text of DOI:10.1021/ic302847g

Article
pubs.acs.org/IC
Syntheses and Structures of a Series of Uranyl Phosphonates and
Sulfonates: An Insight into Their Correlations and Discrepancies
Weiting Yang,‡,† Tao Tian,‡,† Hong-Yue Wu,‡ Qing-Jiang Pan,*,§ Song Dang,‡ and Zhong-Ming Sun*,‡
‡State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
5625 Renmin Street, Changchun, Jilin 130022, China
§Key Laboratory of Functional Inorganic Material Chemistry of Education Ministry, School of Chemistry and Materials Science,
Heilongjiang University, Harbin 150080, China
S
* Supporting Information
ABSTRACT: Six uranyl phosphonates and sulfonates have been
h yd r ot he r ma l ly s y nth es i z ed , name ly , (H 2 t ib ) -
[(UO2)3(PO3C6H5)4]·2H2O (UPhP-1), Zn(pi)2(UO2)-
(PO3C6H5)2 (UPhP-2), Zn(dib)(UO2)(PO3C6H5)2·2H2O
( U P h P - 3 ) , ( H T E A ) [ ( U O 2 ) ( 5 - S P ) ] ( U S P - 1 ) ,
(Hdib)2[(UO2)2(OH)(O)(5-SP)] (USP-2), and Zn-
(phen)3(UO2)2(3-SP)2 (USP-3) (tib = 1,3,5-tri(1H-imidazol-1-
yl)benzene, pi = 1-phenyl-1H-imidazole, dib = 1,4-di(1H-
imidazol-1-yl)benzene, TEA = triethylamine, phen = 1,10-phenanthroline, 5-SP = 5-sulfoisophthalic acid, and 3-SP = 3-
sulfoisophthalic acid). UPhP-1 has been determined to be a layered structure constructed by UO7 pentagonal bipyramids, UO6
octahedra, and phenylphosphonates. Protonated tib plays a role in balancing the negative charge and holding its structure
together. UPhP-2 is made up of UO6 octahedra, ZnO2N2 tetrahedra and PO3C tetrahedra in phenylphosphonates, forming a 1D
assembly, which is stabilized by chelate phen ligand. Further connection of such chainlike structure via dib yields a 2D layered
architecture of UPhP-3. Although sulfonate group possesses similar tetrahedral structure as the phosphonate group, a
unidentated coordination mode is only found in this work. UO7 pentagonal bipyramids are linked by 5-SP to form the layered
assembly of USP-1. USP-2 also consists of the same sulfonate ligand, but features tetranulear uranyl clusters. Similarly,
protonated TEA and dib molecules enable stabilization of their structures, respectively. Formed by dinuclear uranyl cluster and 3-
SP ligand, USP-3 appears as a 1D arrangement, in which Zn(phen)3 acts as the counterion to compensate the negative charge.
All of these compounds have been characterized by IR and photoluminescent spectroscopy. Their characteristic emissions have
been attributed as transition properties of uranyl cations.
and/or η3 coordination modes. Compared with metal
phosphonates, studies of sulfonate coordination polymers are
INTRODUCTION
■
In recent years, the class of uranyl phosphonates has been
considerably less, not to mention the actinide sulfonates. To
developed into an important member of uranium organic
increase the coordination ability of sulfonate ligands in
coordination polymer family due to their fantastic structural
construction of new uranyl hybrid materials, a synergistic
diversities and excellent physicochemical properties. Uranyl
functional group such as hydroxyl or carboxylate group is
phosphonates have shown potential applications in ion-
usually attached to the ligand.28−35 For example, Thuer
́
y
exchange,1,2 proton conductivity,3 chiral materials,4 and
biomaterials.5,6 The UO2 species, as the dominating state of
synthesized a family of uranyl and heterometallic complexes
using 2-, 3-, and 4-sulfobenzoic, and 4,5-dihydroxy-1,3-
benzenedisulfonic acids.33−35 Accordingly, 3- and 5-sulfoisoph-
thalic acids with two carboxylate groups, that would construct
more possible structures and further extend the structural
diversities of uranyl sulfonates, arise our interest. In addition,
apart from the important roles played by cooperative functional
groups, structural directing agents or templates also play a key
role in construction of uranyl compounds. In our recent work,
imidazole-based complexes were utilized either as templates or
coligands to guide the formation of a series of uranyl
diphosphonates, with chains, layers, as well as framework
2+
uranium, is equatorially coordinated by 4−6 ligands, in the
most cases, to form tetragonal, pentagonal, and hexagonal
bipyramidal geometries.7−11 It is precisely because of the
generally inert nature of the two yl oxo atoms, 1D and 2D
uranyl coordination assemblies are favored. However, by
modulation and modification of the organic residues of
phosphonate ligands, various uranyl phosphonate structures
including 1D chains, ribbons4,12−14 or tubules,3,15−17 2D
layers,18−22 and even 3D frameworks22−26 have been isolated.
In contrast with phosphonate, sulfonate group displays a similar
geometry but with lower charge and weaker coordination
ability, therefore usually adopts η1 and η2 coordination
modes.27 Such character is different from phosphonates
functionalizing in uranyl networks, which generally adopt η2
Received: December 27, 2012
Published: February 21, 2013
© 2013 American Chemical Society
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Article
structures.21,22 Those results exhibit the outstanding directing
ability of imidazole-based species, and encourage us to further
investigate the syntheses of uranyl hybrids by expanding the
sorts of imidazole-based template complexes and modulating
the organic ligands.
In this article, six uranyl phosphonates and sulfonates,
(H2tib)[(UO2)3(PO3C6H5)4]·2H2O (UPhP-1), Zn-
(pi)2(UO2)(PO3C6H5)2, (UPhP-2) Zn(dib)(UO2)-
(PO3C6H5)2·2H2O (UPhP-3), (HTEA)[(UO2)(5-SP)]
(USP-1), (Hdib)2[(UO2)2(OH)(O)(5-SP)] (USP-2), and
Zn(phen)3(UO2)2(3-SP)2 (USP-3) (tib =1,3,5-tri(1H-imida-
zol-1-yl)benzene, pi =1-phenyl-1H-imidazole, dib =1,4-di(1H-
imidazol-1-yl)benzene, TEA = triethylamine, phen =1,10-
phenanthroline, 5-SP = 5-sulfoisophthalic acid, 3-SP = 3-
sulfoisophthalic acid) have been prepared based on phenyl-
phosphonate, and sulfoisophthalate ligands. Their crystal
structures, correlations, discrepancies, as well as infrared
spectroscopy and photoluminescence are studied.
mmol for UPhP-3), and deionized water (1.0 mL) was loaded into a
20 mL Teflon-lined stainless steel autoclave (pH 2.0 and 2.5,
respectively). The mixture was heated at 160 °C for 2 days, and then
cooled to room temperature. Yellow rodlike crystals were isolated,
yield 17 mg and 14 mg, respectively (46% and 40% based on
uranium). Anal. Calcd (wt %) for C30H26N4O8P2UZn (UPhP-2): C,
38.47; H, 2.78; N, 5.98. Found: C, 39.03; H, 2.81; N, 6.11. For
C24H20N4O10P2UZn (UPhP-3): C, 32.37; H, 2.25; N, 6.29. Found: C,
33.24; H, 2.36; N, 6.15.
Synthesis of USP-1. A mixture of (UO2)(OAc)2·2H2O (40 mg,
0.1 mmol), sodium 3,5-dicarboxybenzenesulfonate (54 mg, 0.2 mmol),
TEA (20 μL, 0.14 mmol) and deionized water (3.0 mL) was loaded
into a 20 mL Teflon-lined stainless steel autoclave (pH 3.5). The
autoclave was sealed and heated at 160 °C for 2 days, and then cooled
to room temperature. Yellow rhombic plate crystals were isolated,
yield 20 mg (32% based on uranium). Anal. Calcd (wt %) for
C14H19NO19SU: C, 27.30; H, 3.09; N, 2.27; S, 5.20. Found: C, 27.78;
H, 3.15; N, 2.14; S, 5.12.
Synthesis of USP-2. A mixture of Zn(UO2)(OAc)4·7H2O (40 mg,
0.04 mmol), sodium 3,5-dicarboxybenzenesulfonate (27 mg, 0.1
mmol), dib (20 mg, 0.1 mmol) and deionized water (1.0 mL) was
loaded into a 20 mL Teflon-lined stainless steel autoclave (pH 3.5).
The autoclave was sealed and heated at 160 °C for 2 days, and then
cooled to room temperature. Yellow rodlike crystals were isolated,
yield 11 mg (45% based on uranium). Anal. Calcd (wt %) for
C32H28N8O14SU2: C, 30.55; H, 2.23; N, 8.92; S, 2.55. Found: C, 31.26;
H, 2.31; N, 8.79; S, 2.46.
Synthesis of USP-3. A mixture of Zn(UO2)(OAc)4·7H2O (40 mg,
0.04 mmol), 3-SP (100 μL, 0.2 mmol), phen (20 mg, 0.11 mmol) and
deionized water (3.0 mL) was loaded into a 20-mL Teflon-lined
stainless steel autoclave (pH 1.5). The autoclave was sealed and heated
at 160 °C for 2 days, and then cooled to room temperature. Yellow
rodlike crystals were isolated, yield 12 mg (39% based on uranium).
Anal. Calcd (wt %) for C52H32N6O19S2U2Zn: C, 37.81; H, 1.94; N,
5.09; S, 3.88. Found: C, 38.05; H, 2.03; N, 5.14; S, 3.64.
EXPERIMENTAL SECTION
Caution! Standard procedures for handling radioactive material should
be followed, although the uranyl compounds used in the lab contained
depleted uranium.
■
Materials and Syntheses. All chemicals were purchased
commercially and used without further purification. Template tib
was synthesized according to the documented procedures.36 The
phenylphosphonate and sulfonate ligands, as well as the corresponding
templates are listed in Scheme 1. Elemental analyses of C, H, N, and S
Scheme 1. Schematic Representation of the Ligands
X-ray Crystal Structure Determination. Suitable single crystals
for title compounds were selected for single-crystal X-ray diffraction
analyses. Crystallographic data were collected at 293 K on a Bruker
Apex II CCD diffractometer with graphite monochromated Mo−Kα
radiation (λ = 0.71073 Å). Data processing was accomplished with the
SAINT program.37 The structures were solved by direct methods and
refined on F2 by full-matrix least-squares using SHELXTL-97.38 Non-
hydrogen atoms were refined with anisotropic displacement
parameters during the final cycles. All hydrogen atoms were placed
by geometrical considerations and were added to the structure factor
calculation. A summary of the crystallographic data for these title
complexes is listed in Table 1. Selected bond distances and angles are
given in Table S1 of the Supporting Information.
RESULT AND DISCUSSION
■
in the solid samples were performed with a VarioEL analyzer. All IR
measurements were obtained using a Bruker TENSOR 27 Fourier
Transform Infrared Spectrometer. Samples were diluted with
spectroscopic KBr and pressed into a pellet. Scans were run over
the range 400−4000 cm−1. The fluorescence spectra were performed
on a Horiba Jobin Yvon Fluorolog-3 fluorescence spectrophotometer,
equipped with a 450 W Xe-lamp as the excitation source and a
monochromator iHR320 equipped with a liquid-nitrogen-cooled
R5509−72 PMT as detector.
Synthesis of UPhP-1. A mixture of (UO2)(OAc)2·2H2O (40 mg,
0.1 mmol), phenylphosphonic acid (20 mg, 0.13 mmol), tib (20 mg,
0.07 mmol), and deionized water (1.0 mL) was loaded into a 20 mL
Teflon-lined stainless steel autoclave (pH 3.0). The autoclave was
sealed and heated at 160 °C for 2 days, and then cooled to room
temperature. Yellow rodlike crystals were isolated, yield 15 mg (26%
based on uranium). Anal. Calcd (wt %) for C39H32N6O20P4U3: C,
26.86; H, 1.84; N, 4.82. Found: C, 27.08; H, 1.98; N, 4.58.
Structure of UPhP-1. UPhP-1 comprises a 2D layered
structure. There are three crystallographically distinct uranium
atoms and four distinct phenylphosphonate groups in the
asymmetric unit (Figure 1a). U(1) is in the octahedral
environment defined by four bridging oxygen (μ-O) atoms
(O(7), O(16), O(17), and O(18)) from four unique
phenylphosphonate groups in the equatorial plane (U−O:
2.221(12)−2.287(12) Å), and two yl oxo atoms (UO:
1.758(12) and 1.775(12) Å). U(2) and U(3) are five-
coordinated by three μ-O atoms and two tribridging oxygen
(μ3-O) atoms from four distinct phenylphosphonates in the
equatorial plane (U−O: 2.254(12) − 2.559(12) Å), leaving two
axial atoms (UO: 1.745(13) − 1.765(12) Å), resulting in
pentagonal bipyramidal geometry. Such U(2)- and U(3)-
centered pentagonal bipyramids connect each other into a
dimer via edge-sharing. The calculated bond-valence sum for
the uranium atoms indicates 6.13 for U(1), 6.14 for U(2) and
Syntheses of UPhP-2 and UPhP-3. A mixture of Zn(UO2)-
(OAc)4·7H2O (40 mg, 0.04 mmol), phenylphosphonic acid (20 mg,
0.13 mmol), pi (20 mg, 0.17 mmol for UPhP-2), or dib (20 mg, 0.1
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Table 1. Crystal Data and Structure Refinement for Synthesized Uranyl Phosphonates and Sulfonates
compound
CCDC
UPhP-1
916 425
UPhP-2
916 426
UPhP-3
916 427
USP-1
916 428
USP-2
916 429
USP-3
916 430
empirical formula
C39H32N6O20P4U3
1742.68
C30H26N4O8P2UZn
935.89
C24H20N4O10P2UZn
889.78
C14H19NO9SU
1230.78
C32H28N8O14SU2
1256.74
C52H32N6O19S2U2Zn
1650.39
Fw
cryst syst
triclinic
triclinic
monoclinic
P21/n
triclinic
monoclinic
P21/n
triclinic
space group
P1
P1
P1
P1
̅
̅
̅
̅
a/Å
9.7096(12)
10.6095(14)
14.018(3)
101.815(3)
93.434(3)
117.157(2)
1238.0(3)
1
10.4332(6)
16.2774(10)
20.1860(12)
71.3210(10)
82.4270(10)
79.9300(10)
3186.9(3)
4
13.1880(11)
10.4948(9)
21.5361(18)
90
9.2047(7)
13.1351(9)
16.0557(11)
84.2900(10)
83.1800(10)
86.8280(10)
1916.0(2)
4
13.6408(9)
20.8488(13)
13.9140(8)
90
12.8625(12)
13.1683(13)
17.2155(17)
72.216(2)
71.658(2)
71.0660(10)
2550.0(4)
2
b/Å
c/Å
α/°
β/°
γ/°
V/Å3
95.9990(10)
90
115.9900(10)
90
2964.4(4)
4
3556.9(4)
4
Z
T/K
293(2)
293(2)
293(2)
293(2)
293(2)
293(2)
λ (Mo Kα), Å
0.71073
0.71073
0.71073
0.71073
0.71073
0.71073
F(000)
804
1800
1696
1160
2352
1568
ρcalcd (Mg/m3)
μ (Mo Kα), mm−1
R1/wR2 (I > 2σ(I))a
R1/wR2 (all data)
2.337
1.951
1.994
2.133
2.347
2.149
9.998
5.984
6.433
8.625
9.236
6.971
0.0418/0.0980
0.0445/0.1000
0.0444/0.0998
0.0662/0.1154
0.0308/0.0681
0.0468/0.0752
0.0496/0.1092
0.0759/0.1227
0.0400/0.0637
0.0744/0.0738
0.0311/0.0622
0.0456/0.0685
U(3). These values are consistent with the formal valence of
U(VI).39 All of the four phenylphosphonate groups are bridged
to three unique uranyl cations. Two of the phenylphosphonate
groups link the uranyl dimer through edge-sharing. The
connection between the dimer pentagonal bipyramids and
phenylphosphonates produces a chain, which is joined by U(1)-
centered octahedra to form the layered structure of UPhP-1
(Figure 1b). Such layers are stacked directly on top of each
other (AA stacking) to give rise to a 3D supramolecular
architecture (Figure 1c). Protonated tib molecules lie between
the layers to hold the structure and compensate the negative
charge.
the uranium site is 5.96, in agreement with the formal valence
of U(VI).39 A same chain as in UPhP-2 is formed by UO6,
ZnO2N2, and PO3C polyhedra (Figure 3b). Such chains are
linked by dib via sharing N atoms together with Zn-centered
tetrahedra to create a layered structure of UPhP-3. The layers
stagger each other to make the supramolecular structure
(Figure 3c).
Structure of USP-1. The layered structure of USP-1
comprises two crystallographically distinct uranyl centers in
form of pentagonal bipyramids, which is defined by two yl oxo
atoms and five equatorial μ-O atoms from three carboxylates in
three 5-SP and one sulfonate in the fourth 5-SP (Figure 4a).
The UO distances are from 1.747(8) to 1.752(7) Å, and the
OUO angles are 178.3(3) and 179.1(3)o. The valence of
uranium atoms is 6.15 for U(1) and 6.19 for U(2) based on
calculated bond-valence sum. The carboxylates and sulfonates
in the 5-SP ligand possess different coordination modes. One
carboxylate is bidentately coordinated to two distinct uranyl
centers with U−O distances from 2.337(6) to 2.374(6) Å. The
other carboxylate is also bidentate, but links to one uranyl
center. The sulfonate is unidentately bridged to a uranyl group
through corner sharing (average U−O: 2.454(7) Å). The UO7
pentagonal bipyramids are connected by bridging 5-SP to form
the 2D layered structure of USP-1 (Figure 4b). Such layers
stack parallel to (101) plane with protonated TEA cations
locating between them to compensate the molecular charge and
stabilize the supramolecule (Figure 4c).
Structure of USP-2. USP-2 also represents a layered
structure, which features a well-known tetranuclear uranyl
structural building cluster. All of the uranyl centers are in the
pentagonal bipyramidal geometry (Figure 5a). The average
uranyl UO bonds is 1.776(5) Å, while the distances for the
equatorial U−O bonds are in the range of 2.194(4) to 2.525(5)
Å. The valences of uranium atoms are 6.07 for U(1) and 6.08
for U(2) based on calculated bond-valence sum. The uranium-
centered bipyramids condense into clusters through sharing
three common edges. In addition, two μ3-oxygen donors and
two hydroxy groups serve as common corners for each cluster.
The connection mode of 5-SP is similar to that in USP-1. One
Structure of UPhP-2. Single crystal X-ray diffraction study
reveals that UPhP-2 crystallizes in the triclinic space group P1.
̅
The asymmetric unit consists of two zinc atoms, four
phenylphosphonate groups and four pi molecules (Figure
2a). Both of the uranium atoms are octahedrally coordinated by
two yl oxo atoms and four equatorial μ-O atoms from four
distinct phenylphosphonates. The valence of uranium atoms is
5.94 for U(1) and 5.98 for U(2) based on calculated bond-
valence sum. This is in agreement with the formal valence of
U(VI).39 Two zinc atoms are in tetrahedral coordination
defined by two μ-O atoms and two N atoms, which are from
two phenylphosphonates and two pi molecules, respectively. All
of the phenylphosphonate groups coordinate to two uranyl
centers and one zinc atoms through sharing oxygens. As shown
in Figure 2b, the connection of UO6 octahedra, ZnO2N2, and
PO3C tetrehedra leads to 1D chainlike structure, in which pi
molecules coordinate to zinc atoms to stabilize the whole
structure (Figure 2c).
Structure of UPhP-3. UPhP-3 crystallizes in the
monoclinic space group P21/n and contains one crystallo-
graphically unique uranium atom, one crystallographically
unique zinc atoms, two crystallographically unique phenyl-
phosphonate groups and one dib ligand (Figure 3a). Similar to
UPhP-2, the uranium atom is in octahedral environment and
chelated by four P-centered tetrahedra of the phenyl-
phosphonates, and the phenylphosphonate joins two UO6
octahedra and one ZnO2N2 tetrahedron. Bond-valence sum at
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Figure 2. (a) ORTEP representation of the coordination environment
in UPhP-2. Thermal ellipsoids are drawn at the 50% probability level.
pi molecules were deleted for clarity. Symmetry code: A, 1 + x, y, z; B,
−1 + x, y, z. (b) 1D structure of UPhP-2. (c) View of whole
supramolecule of UPhP-2 along the [100] direction showing one
single chain in highlight.
forming the 3D supramolecular structure (Figure 5c).
Protonated dib molecules fill in the interlayers to compensate
the negative charge of the structure and hold it.
Figure 1. (a) ORTEP representation of the coordination environment
in UPhP-1. Thermal ellipsoids are drawn at the 50% probability level.
Symmetry code: A, x, −1 + y, z; B, −1 + x, −1 + y, z; C, −1 + x, y, z;
D, 1 + x, y, z; E, 1 + x, 1 + y, z; F, x, 1 + y, z. (b) The layer of UPhP-1
contains the chain in highlight. (c) The layers stack along the [100]
direction.
Structure of USP-3. The structure of USP-3 comprises a
1D chainlike architecture. There are two crystallographically
distinct uranyl centers, two 3-SP and one Zn(phen)3 in its
asymmetric unit (Figure 6a). Both of the uranium atoms are in
the pentagonal bipyramidal environment. Two UO7 pentagonal
bipyramids polymerize into a dinuclear cluster by edge-sharing.
The valences of uranium atoms are 6.12 for U(1) and 6.13 for
U(2) based on calculated bond-valence sum. The sulfonate of
3-SP is unidentate, and shares a common corner with a uranyl
center (U−O(sulfonate): 2.361(4) and 2.383(4) Å). One
unidentate carboxylate of 3-SP is joined to a dimer via μ3-
oxygen. The other carboxylate of 3-SP is bidentate, and links
two dimers, leading to a chainlike structure of USP-3 (Figure
bidentate carboxylate coordinates to two pentagonal bipyr-
amids of one tetranuclear cluster, and the other bidentate
carboxylate is linked to another cluster via one uranyl center.
The unidentate sulfonate also is connected to one uranyl group
of a cluster through corner-sharing. Thus, one 5-SP is linked to
three clusters, and one cluster is connected by six 5-SP ligands.
Such connection produces the 2D arrangement of USP-2
(Figure 5b). The layers of USP-2 stack parallel (011) plane
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Figure 4. (a) ORTEP representation of the coordination environment
in USP-1. Thermal ellipsoids are drawn at the 50% probability level.
Symmetry code: A, −x, 1 − y, 1 − z; B, −x, −y, 1 − z; C, 1 − x, −y,
−z; D, 1 − x, 1 − y, −z. (b) Layer of USP-1. (c) TEA cations exit
between the layers.
deprotonated phosphonates and imidazole-based complexes
play key roles in construction of structures. In UPhP-1,
protonated tib, serves as template to stabilize the structure, as
well as the charge compensator. For UPhP-2 and UPhP-3,
which contain second metal Zn inside, the same chain can be
clearly separated from their structures (Figure 2b and Figure
3b). This chain is constructed by UO6 octahedra, PO3C, and
ZnO2N2 tetrahedra. In UPhP-2, only one N donor of pi
molecule can be utilized to connect Zn atom. Thus, 1D chain is
finally produced. Whereas in UPhP-3, every dib is linked to two
such chains leading to a 2D structure. For most known organo-
templated uranyl phosphonates, amines, pyridines, piperazines,
and encapsulated cations serve as structure-directing agent-
s.1,18a,20,23 Until recently, our group used imidazole-based
complexes to successfully generate a series of uranyl
diphosphonates.21 On the basis of these structural features of
our previous and present work, some conclusions can be drawn.
First, the imidazole-based complexes are good templates for the
syntheses of uranyl phosphonates; meanwhile, they could be
easily protonated to compensate the negative charge of the
structures. Second, imidazole-based complexes are hard to
coordinate with uranyl center. At last, the zinc atom is
important in construction of novel heterobimetallic uranyl
Figure 3. (a) ORTEP representation of the coordination environment
in UPhP-3. Thermal ellipsoids are drawn at the 50% probability level.
Symmetry code: A, 1.5 − x, −0.5 + y, 0.5 − z; B, 0.5 + x, 0.5 − y, 0.5 +
z. (b) Chains (in highlight) are connected by dib to form the layered
structure of UPhP-3. (c) View along the [010] direction showing the
stacking of layers, purple, light, and dark blue represent different dib in
different layers.
6b). Among these chains, airscrew-like Zn(phen)3 fills in and
balances the charge.
Structure Discussion. As far as we known, only 1D linear
or tubular structures of uranyl phenylphosphonates have been
isolates.15−17 The syntheses of UPhP-1, -2, and -3 enrich the
structural diversities of uranyl phosphonates. Insight into these
synthesized uranyl phenylphosphonate compounds, fully
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Figure 6. (a) ORTEP representation of the coordination environment
in USP-3. Thermal ellipsoids are drawn at the 50% probability level.
Symmetry code: A, −x, 2 − y, 1 − z; B, 1 − x, 2 − y, −z. (b) Chainlike
structures of USP-3 stack with Zn(phen)3 locating in the void space.
The single chain is in highlight.
Scheme 2. Summary of Coordination Modes of
Phenylphosphonate and Arylsulfonates in Uranyl Complexes
Figure 5. (a) ORTEP representation of the coordination environment
in USP-2. Thermal ellipsoids are drawn at the 50% probability level.
Symmetry code: A, 2 − x, −y, −z; B, 2 − x, −y, 1 − z; C, 1 − x, −y,
−z. (b) Layer of USP-2 comprises the tetranuclear cluster. (c) View of
the 2D assembly along the [100] direction.
architectures, where they can link phosphonate groups,
uranium-centered polyhedra and N-donor organic complexes
resulting in rich structural diversities.
As for the synthesized sulfonates, a common feature is the
unidentate sulfonate group (η1 bonding mode) of the ligand.
The S, in distorted tetrahedral coordination defined by one C
and three O atoms, is connected to UO7 pentagonal bipyramid
through corner sharing. The S−O distances range from
1.418(8) to 1.493(4) Å, slightly shorter than that of P−O
bond lengths. This coordination mode is common for
sulfonates, and different from that in phenylphosphonates,
which are usually bidentate or tridentate in coordination with
uranyl center (Scheme 2). The pKa value of phenylsulfonic acid
is 0.7, much lower than that of phenylphosphonic acid (1.86
and 7.51). This means that the phenylphosphonate ligand is
more likely to be partially protonated in synthesized structures.
The low pH values are curial for crystallization of title
compounds (2.0−3.0 for uranyl phosphonates, and 1.5−3.5 for
uranyl sulfonates). We summarize the coordination modes of
phenylphosphonate and arylsulfonate ligands-based uranyl
complexes including this work (Scheme 2). It is noteworthy
that for known uranyl or mixed uranyl−transition metal
arylsulfonates,33−35 the bidentate (η2) coordination of sulfonate
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groups are less happened compared to unidentate one, and the
tridentate (η3) mode never occurs. Moreover, additional
functional groups especially carboxylate extend the coordina-
tion sites and manners leading to more diverse architectures.
Interestingly, although the carboxylate groups of 5-SP possess
same coordination manner, mononuclear and tetranuclear
uranyl units take place in USP-1 and USP-2, respectively,
resulting in totally different layered arrangement. Whereas in
USP-3, binuclear uranyl units are connected by 3-SP ligand. It
seems that the position of sulfonate and carboxylate groups of
3-SP prefers to form a 1D assembly. In our work, an additional
carboxylate group is introduced into the sulfonate ligand
compared to previously reported examples,33−35 and new
structures are produced.
IR Spectroscopy. The IR spectra of these synthesized
uranyl phosphonates and sulfonates are shown in Figure S1 of
the Supporting Information. The asymmetric and symmetric
stretching modes of UO are observed from about 840 to 925
cm−1.15 The bands between 1400−1650 cm−1 are attributed to
the skeletal vibrations of the aromatic rings. The bands in the
low wavenumber region from 680 to 760 cm−1 are dominated
by the out-of-plane vibrations of the phenyl rings. The
stretching vibrations of H2O and OH are determined at
around 3450 cm−1. For phosphonates, UPhP-1 to UPhP-3, the
group of peaks around 1000−1150 cm−1 is assigned to the
vibrations of PO3 group. For sulfonates, USP-1 to USP-3, the
adsorption in the region of 1000 − 1260 cm−1 is related to
sulfonate groups. The intensive peak at 624 cm−1 is attributed
to the S−O stretching vibrations.27c
Photoluminescent Properties. All of the photolumines-
cent spectra of the title compounds are illustrated in Figure 7.
They all exhibit characterized emission from uranyl cations,
which usually consists of several emission peaks. This charge-
transfer based emission centered near 520 nm is always related
to the symmetric and antisymmetric vibrational modes of the
uranyl cation. Five peaks are observed in the spectra for UPhP-
1 (472, 504, 525, 549, and 575 nm), UPhP-2 (469, 506, 526,
555, and 579 nm), UPhP-3 (470, 508, 530, 553, and 577 nm),
USP-1 (475, 491, 512, 535, and 562 nm), and USP-3 (486,
502, 524, 548, and 574 nm) that correspond to the electronic
and vibronic transitions S11−S00 and S10−S0v (v = 0−4).
Compared to the benchmark compound UO2(NO3)2·6H2O,22
these compounds are red-shifted by a value of 15 nm (UPhP-
1), 16 nm (UPhP-2), 20 nm (UPhP-3), 2 nm (USP-1), and 14
nm (USP-3). The spectral shift may originate from the
influence of equatorial phenylphosphonate and sulfonate
groups. Although no fine-structured spectrum is obtained for
USP-2, the main broad peak centered at 524 nm is
unambiguously attributed to the charge transfer of uranyl
cations.40 In principle, not all uranyl complexes can exhibit
fluorescence. Their luminescence and specially fine−structure
ones are related to many factors, such as size and quality of the
crystal, disorder within the equatorial plane of the uranyl group,
and so on.24
Figure 7. Emission spectra of UPhP-1 (λex = 420 nm), UPhP-2 (λex
274 nm), UPhP-3 (λex = 277 nm), USP-1 (λex = 280 nm), USP-2 (λex
= 362 nm), and USP-3 (λex = 350 nm).
=
follows. First of all, the addition of imidazole-based species
remarkably enriches the structural diversities of uranyl
phenylphosphonates. Among these synthesized compounds,
UPhP-1 comprises 2D layered assemblies with tib as the
template. UPhP-2 is a chain-like structure composed of U-, Zn-,
and P-centered polyhedra. Such chains are further connected by
dib to form the layered UPhP-3. Second, although the
sulfonate group possesses the similar geometry to phosphonate
with potential unidentate, bidentate and tridentate coordination
sites, only unidentate sulfonates are observed in this study. For
previously reported uranyl arylsulfonates, such coordination
manner of sulfonte group is very common; however, bidentate
mode are less happened, and tridentate fashion never occurs.
Third, additional carboxylate groups play a key role in
constructing new uranyl sulfonates. Despite the 5-SP ligands
display the same coordination manner, USP-1 and USP-2
CONCLUSIONS
■
In this work, by combining with N-based structure directing
agents, ligands of phenylphosphonic acid, and two arylsulfonic
acid have been chosen to construct novel uranyl hybrids. Their
correlations and discrepancies have also been investigated.
Three uranyl phosphonates and three uranyl sulfonates have
been successfully synthesized and structurally characterized.
Some important phenomena and conclusions are yielded as
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ASSOCIATED CONTENT
* Supporting Information
■
S
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4669−4675.
X-ray crystallographic cif files, selected bond lengths and angles,
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the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: szm@ciac.jl.cn (Z.-M.S.), panqj@yahoo.com.cn (Q.-
J.P.).
■
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Author Contributions
†These authors contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the support of this work by National Nature Science
Foundation of China (No. 21171662, 21101148, and
21273063), Jilin Province Youth Foundation (201201005),
SRF for ROCS (State Education Ministry), and Program for
New Century Excellent Talents in University (NECT-11-
0958).
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