Uranyl triazolate formation via an in situ Huisgen 1,3-dipolar cycloaddition reaction

Article abstract of DOI:10.1039/c0ce00231c

A two dimensional UO₂²⁺ coordination polymer, (UO₂)₃(C₁₀H₅N₃O ₄)₂(OH)₂(H₂O)₂, has been synthesized under solvothermal conditions. The triazolate ligand, 1-(4-carboxyphenyl)-1H-1,2,3-triazole-4-carboxylic acid (CPTAZ) has been generated via a 1,3-dipolar cycloaddition of 4-azidobenzoic acid and propiolic acid. Reactions of the UO₂²⁺ cation with both the in situ generated triazolate ligand and the presynthesized ligand have been explored. The structure, fluorescent and thermal behaviour of this material are presented, as is a discussion of the utility of in situ ligand formation versus direct assembly.

Full text of DOI:10.1039/c0ce00231c

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PAPER
Uranyl triazolate formation via an in situ Huisgen 1,3-dipolar cycloaddition
reaction†
*
Karah E. Knope and Christopher L. Cahill
Received 25th May 2010, Accepted 22nd July 2010
DOI: 10.1039/c0ce00231c
A two dimensional UO22+ coordination polymer, (UO2)3(C10H5N3O4)2(OH)2(H2O)2, has been
synthesized under solvothermal conditions. The triazolate ligand, 1-(4-carboxyphenyl)-1H-1,2,3-
triazole-4-carboxylic acid (CPTAZ) has been generated via a 1,3-dipolar cycloaddition of
4-azidobenzoic acid and propiolic acid. Reactions of the UO22+ cation with both the in situ generated
triazolate ligand and the presynthesized ligand have been explored. The structure, fluorescent and
thermal behaviour of this material are presented, as is a discussion of the utility of in situ ligand
formation versus direct assembly.
limited.4,6–9 Moreover, many examples of in situ ligand forma-
Introduction
tion are further complicated by convoluted speciation profiles
resulting from the oxidation or decomposition of the organic
ligand.10,11 The influence of these ‘‘spectator’’ species, generated
concurrently with the ligand (yet not observed in crystalline
products) on product formation is generally not considered
despite many instances where such species have been shown to
dramatically impact product formation.9,12–15
In situ ligand synthesis (ISLS) refers to a process wherein
organic species undergo oxidation, reduction, hydrolysis or
other reactions to yield a modified ligand that is subsequently
observed in crystalline reaction products. The notion of gener-
ating ligands in situ during the synthesis of coordination poly-
mers and as ‘‘a new approach to inorganic crystal engineering’’
was first proposed by Champness and Schroder et al. in 1997.1
Following their unexpected observation of the in situ cyclisation
of 1,2-trans-(4-pyridyl)ethene to form 1,2,3,4-tetrakis(4-pyr-
idyl)cyclobutane, a variety of hybrid materials were prepared in
this manner, many under hydro(solvo)thermal conditions.2
Others have sought to capitalize on this route since then by
pointing out possible advantages over traditional syntheses (i.e.
direct assembly wherein the organic ligands observed in the
product are the same as those introduced as reactants),
including simplified reaction schemes, one-pot syntheses, slow
ligand generation to promote single crystal growth and even
environmental friendliness. In situ ligand formation has even
been shown in some cases to provide a pathway to materials
that are not accessible through the direct reaction of the metal
center with the organic linker.2–5 Most reports of ISLS are
largely serendipitous, however, and little effort has been made
to carefully explore the usefulness of this approach through
controlled reactions. In other words, attempts to reproduce
compounds obtained via ISLS using direct assembly are fairly
One means of exploring in situ reactions without having to
consider such decomposition products is to construct the ligand
rather than generate it through a decomposition reaction.6,16,17
Click reactions are ideal candidates for this approach and have
become an increasingly popular way to create organic molecules
of diverse structure and function.18,19 In particular, the Huisgen
1,3-dipolar cycloaddition of alkynes to azides is well-suited to
assemble ligands in situ.20 Azides and alkynes are tolerant to
a range of reaction conditions and can be easily functionalized
without affecting reactivity. As such, they provide a relatively
simple system for exploring in situ ligand formation in materials
synthesis without the complication of decomposition products.
Click reactions have been used successfully to prepare a variety
of transition metal containing complexes yet direct assembly was
not explored in these systems.15,21–25
In this work, we explored in situ ligand formation as a means
2+ 2+
of generating UO2 containing hybrid materials. As the UO2
cation is a relatively hard Lewis acid that tends to bind harder
functional groups, carboxylate functionalized azides and alkynes
were used as starting materials in this study. The in situ formation
of the triazolate ligand 1-(4-carboxyphenyl)-1H-1,2,3-triazole-4-
carboxylic acid (CPTAZ) is depicted in Scheme 1. The products
obtained via the ISLS and direct assembly synthetic pathways
have been compared in the context of assessing the utility of
generating ligands in situ. The thermal and fluorescent properties
of the resulting UO22+ triazolate have also been explored.
Department of Chemistry, The George Washington University, 725 21st,
Street, NW, Washington, DC, USA. E-mail: cahill@gwu.edu; Fax: +1
(202) 994-5873; Tel: +1 (202) 994-6959
† Electronic supplementary information (ESI) available: Spectrum,
fluorescence spectrum, TGA plot and PXRD data. CCDC reference
numbers 778238. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0ce00231c
This journal is ª The Royal Society of Chemistry 2011
CrystEngComm, 2011, 13, 153–157 | 153

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0.61 mmol) and 4 mL of a 50/50 ACN : H2O (v/v) solution were
placed into a 23 mL Teflon-lined Parr bomb; the initial pH of the
solution was 2.3. The reaction vessel was then sealed and heated
ꢂ
statically at 90 C. After 5 days the reaction was removed from
the oven and cooled to room temperature over 4 hours. Upon
cooling to room temperature, a cloudy yellow liquid (pH 2.7) was
decanted and yellow needles and a yellow powder were obtained.
The product was washed with distilled water, ethanol and THF
and then allowed to air dry at room temperature. Yield: 45%
(based on uranium). Elemental analysis (Galbraith Laboratories,
Knoxville, TN), observed (calculated): C 17.83% (17.89%); N
Scheme 1 In situ triazole formation from 4-azidobenzoic acid and
propiolic acid.
6.14% (6.26%);
(KBr/cmꢁ1): 3604, 3498, 3406, 3168, 2368 (w), 2130 (w), 1576,
H 1.04% (1.20%). Main IR frequencies
Experimental
Synthesis
1512, 1434, 1320, 1272, 1064, 928, 858, 780, 726.
Caution: whereas the uranium oxyacetate (UO2)(CH3-
CO2)2$2H2O used in this investigation contains depleted U,
standard precautions for handling radioactive substances should
be followed. Compound 1, (UO2)3(OH)2(H2O)2(C10H5N3O4)2,
was prepared through both direct assembly and in situ ligand
formation as described below.
X-Ray structure determination
A yellow plate-like crystal of 1 (0.10 mm ꢃ 0.04 mm ꢃ
0.04 mm) was isolated from the product obtained via ISLS and
mounted on
a MiTeGen micromount. Reflections were
collected at 100 K on a Bruker SMART diffractometer
equipped with an APEX II CCD detector using Mo Ka radi-
ation (l ¼ 0.71073) and a combination of 0.5ꢂ u and 4 scans.
The data were integrated and corrected for absorption using
the APEX2 suite of crystallographic software.26 The compound
was solved using direct methods and refined using SHELXL-
9727 within the WinGX software suite.28 All non-hydrogen
atoms were located using difference Fourier maps and were
ultimately refined anisotropically. Hydrogen atoms residing on
the carbon atoms of the –C6H4 and –C2HN3 rings of the
CPTAZ ligand were placed in calculated positions and bond
Synthesis of CPTAZ ligand
The triazolate ligand, 1-(4-carboxyphenyl)-1H-1,2,3-triazole-4-
carboxylic acid, was prepared from the reaction of 4-azido-
benzoic acid (1.174 g, 7.2 mmol) and propiolic acid (0.372 mL,
6.0 mmol) in 40 mL of a 50 : 50 H2O/THF (v/v) solution. The
solution was stirred under refluxing conditions for 24 hours, after
which the reaction was placed on ice. The precipitate was isolated
by filtration to give CPTAZ as a white powder. The IR spectrum
of the product (KBr) showed nearly complete disappearance of
the azide peak at ꢀ2100 cmꢁ1 and appearance of peaks at ca.
1518 and 1448 cmꢁ1 suggestive of triazole formation. Elemental
analysis (Galbraith Laboratories, Knoxville, TN) suggested that
the product contained 75% CPTAZ and 25% unreacted 4-azi-
dobenzoic acid, observed (calculated): C 51.21% (51.51%); N
19.60% (19.48%); H 3.00% (3.04%). The crude product was then
used without further purification.
ꢀ
distances were fixed at 0.93 A. Hydrogen atoms of the bound
water molecule (O8) in 1 were located and refined with distance
ꢀ
restraints of 0.82 A. The hydrogen atom bound to O4 was also
located in the difference Fourier map and refined with an O–H
ꢀ
distance restraint of 0.80 A.
Crystal data for compound 1. Mw ¼ 1342.48, monoclinic, P21/
ꢀ
ꢀ
n, a ¼ 12.9037(11) A, b ¼ 6.1373(5) A, c ¼ 18.3478(16), b ¼
98.450(2) , V ¼ 1437.3(2) A , Z ¼ 2, Dcalc ¼ 3.102 Mg mꢁ3, m ¼
16.955 mmꢁ1, 26 513 reflections collected, 4090 independent
[R(int) ¼ 0.0456], Final R indices [I > 2s(I)] R1 ¼ 0.0215, wR2 ¼
0.0438, GooF ¼ 1.029, largest diff. peak and hole 1.245 and
ꢂ
3
ꢀ
Synthesis of 1 via direct assembly
Uranium oxyacetate dihydrate (0.148 g, 0.35 mmol), crude
CPTAZ (0.080g, 0.35 mmol) and 4 mL of a 50/50 ACN : H2O
(v/v) solution were placed into a 23 mL Teflon-lined Parr bomb;
the initial pH of the solution was 2.5. The reaction vessel was
then sealed and heated statically at 90 ꢂC. After 5 days the
reaction was removed from the oven and cooled to room
temperature over 4 hours. Upon cooling to room temperature,
a cloudy yellow liquid (pH 3.0) was decanted and yellow plate-
like crystals were obtained. The product was washed with
distilled water, ethanol and THF and then allowed to air dry at
room temperature. Yield: 80% (based on uranium).
ꢁ
ꢁ1.196 e Aꢁ3.†
ꢀ
Powder X-ray diffraction data were collected for the products
obtained via both direct assembly and ISLS using a Rigaku
Miniflex diffractometer (Cu Ka, 3–60ꢂ) and manipulated using
the JADE software package.29 Agreement between the calculated
and observed patterns (Fig. 1) suggests that the single crystal
used for structure determination was representative of the bulk
sample. Moreover the products synthesized by both direct
assembly and in situ ligand formation reactions are the same.
Characterization
Synthesis of 1 via in situ ligand formation
The emission spectrum for 1 was collected on a Shimadzu RF-
5301 PC Spectrofluorophotometer (uranium excitation wave-
length 365 nm; emission wavelength: 450–600 nm; slit width:
1.5 nm (excitation) and 1.5 nm (emission); sensitivity: high with
Compound 1, (UO2)3(OH)2(H2O)2(C10H5N3O4)2, was also
prepared via the in situ formation of the triazolate ligand.
Uranium oxyacetate dihydrate (0.149 g, 0.35 mmol), 4-azido-
benzoic acid (0.119 g, 0.73 mmol), propiolic acid (0.038 mL,
a
UV-35 filter). Thermogravimetric analysis (TGA) was
154 | CrystEngComm, 2011, 13, 153–157
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Fig. 1 Powder X-ray diffraction spectra (shown from 5–32ꢂ 2q, Cu Ka)
for 1 synthesized via direct assembly (green) and in situ ligand formation
(red). The calculated pattern is shown in black.
performed on a Perkin Elmer Pyris 1 at a rate of 10 ꢂC minꢁ1 over
ꢂ
a temperature range of 30–800 C under flowing nitrogen gas.
PXRD data, the fluorescence spectrum and the TGA plot can be
found in the ESI†.
Results
Structure description
Compound 1 is built from two unique U(VI) metal centers and
one unique CPTAZ ligand as shown in Fig. 1. U1 is bound to two
ꢀ
axial oxygen atoms, O1 and O2, at an average distance of 1.780A
2+
2+
Fig. 3 Polyhedral representation of 1 viewed down the (a) [1 0 ꢁ1]
direction showing the topology of the 2-dimensional sheets and (b) [010]
illustrating the stacking of the layers. Yellow polyhedra are U(VI) atoms
in pentagonal and hexagonal bipyramidal geometry. Black, blue and red
spheres represent the carbon, nitrogen, and oxygen atoms, respectively.
Hydrogen atoms have been omitted for clarity.
to form the UO2 moiety. Further, the UO2 cation is equa-
torially coordinated to 4 oxygen atoms (O3, O4, O4iv, and O5)
and one nitrogen atom (N1) to form an overall pentagonal
bipyramidal coordination geometry. U2 alternatively adopts an
overall hexagonal bipyramidal geometry with the uranyl oxygen
ii
ꢀ
atoms (O9 and O9 ) at an average distance of 1.779 A. U2 is
equatorially coordinated to six oxygen atoms, four (O6, O7 and
their symmetry equivalents) from two bidentate CPTAZ units
and two (O8 and its symmetry equivalent) from bound water
molecules. Two U1 sites coordinate to hydroxyl oxygen atoms
O4 and O4iv to form the edge-shared dimers (Fig. 2a) which are
subsequently linked along [010] via the triazolate ligand. Addi-
tional coordination of the CPTAZ units to U2 results in 2D
sheets (Fig. 3a). The sheets stack as shown in Fig. 3b. Selected
bond lengths and angles are listed in Table 1.
Powder X-ray diffraction
The powder patterns of the reaction products obtained via direct
assembly and in situ ligand reactions are shown in Fig. 1.
Comparison of the observed patterns reveals that the products
assembled through the two synthetic routes are the same.
Fluorescence studies
The emission spectrum for 1 showed weak uranyl fluorescence
2+
and exhibited characteristic vibronic structure of the UO2
a
ꢂ
ꢀ
Table 1 Selected bond distances (A) and angles ( ) for 1
U1–O1
U1–O2
U1–O3
U1–O4
U1–O5
U1–N1
U2–O9
1.775(3)
1.786(3)
2.415(3)
2.299(3)
2.373(3)
2.605(3)
1.779(3)
U2–O7
U2–O8
U2–O6
2.436
2.493
2.467
Fig. 2 ORTEP illustration of 1. Ellipsoids are shown at 50% probability
level. Hydrogen atoms have been omitted for clarity. Superscript denotes
symmetry transformations i ¼ ꢁx + 5/2, y ꢁ 1/2, ꢁz + 1/2; ii ¼ x, y ꢁ 1, z;
iii ¼ ꢁx + 1, ꢁy, ꢁz; iv ¼ ꢁx + 1, ꢁy + 1, ꢁz; v ¼ x, y + 1, z; vi ¼ ꢁx + 3,
ꢁy + 1, ꢁz + 1.
Bond angles
O1–U1–O2
O9–U2–O9ii
174.37(12)
180.00(11)
a
Superscript denotes symmetry transformations ii ¼ x, y ꢁ 1, ꢁz.
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cation with peaks ranging from 475 to 600 nm. The emission
over the course of the reaction. In other words, the building
blocks needed for assembly and those that are ultimately
observed in the final product are not present at the start of the
reaction. The carboxylate functional groups are immediately
spectrum for 1 is available in the ESI† as Fig. S3.
Thermogravimetric analysis
2+
available for coordination to the UO2 cation in the click
The TGA curve for 1 exhibits four weight loss steps. The first step
took place between 200 and 300 ꢂC with an initial weight loss of
ꢀ4%, consistent with the loss of the two bound water molecules
and an additional molecule of H2O presumably from one of the
–OH units. Decomposition of the triazolate ligand occurred in
three steps beginning around ꢀ300 ꢂC and complete by ꢀ800 ꢂC.
Loss of the triazolate ligand from the structure resulted in an
additional weight loss of approximately 26%. The TGA curve for
1 is consistent with decomposition of the materials to multiple
uranyl oxide phases that likely include UO3, UO2 and U3O7.
Powder X-ray diffraction data of the resulting products support
this finding. The TGA plot and powder diffraction data are
available in the ESI† (Fig. S4 and S5).
system, however, in systems wherein the ligand is generated
through decomposition or degradation of the organic species, the
starting organic often has no sites available for direct metal–
ligand coordination. In these cases, the in situ generated ligands
are ‘‘gently introduced’’ over the course of the reaction. Metal–
ligand coordination is thus dependent on the rate of oxidation or
hydrolysis and hence the availability of metal coordination sites.
This would not necessarily be the case in click reactions where
functional groups that are candidates for metal coordination are
immediately available.
The primary benefit of generating the click product in situ, in
this case, is that it provides an easy one-pot synthesis. Generating
the triazolate in situ removes the need to presynthesize the ligand
and also provides a facile route to a ligand that is not commer-
cially available. More generally, click reactions also offer the
ability to explore in situ ligand synthesis via controlled reactions.
Admittedly this is not a tremendous advantage in this case but
this observation highlights a significant difference between
‘‘construction’’ versus ‘‘destruction’’ reactions. That is, we must
be cognizant of organic species present and evolving over the
course of the reaction in order to fully understand factors that
are contributing to phase formation and mechanisms of product
formation. Further, these efforts are in fact control experiments
that, with the exception of a few examples,5,9,10 have not been
explored elsewhere.
Discussion
Although ISLS has been a largely serendipitous process, there
are many reported benefits of this synthetic route. For example,
some products have been synthesized by ISLS that are not
accessible via direct assembly.2,3 In some cases, this was attri-
buted to the slow release of the ligand in situ, thereby promoting
the formation of unique products. Alternatively, in situ ester
hydrolysis has been explored in metal–phosphonate systems
wherein the stability of metal–phosphate complexes has often
made it difficult to obtain single crystals suitable for structure
determination.4,12,13,30–32
Most reports of in situ ligand formation including the ester
hydrolysis mentioned above, however, have focused on hydro-
lysis, oxidation or decomposition reactions;2,3 systems in which
the number of organic species in solution likely increases over
time. To give another example, we previously reported the
oxidation of DABCO as a means of preparing a UO22+–oxalate–
glycolate.10 In this system, in situ oxalate formation occurs via
a complex reaction mechanism wherein decomposition or
degradation of the organic species yields a potentially compli-
cated organic speciation profile. Though efforts were made to
elucidate the mechanism of product formation, we were unable to
account for all of the species generated in situ. This was somewhat
problematic considering the numerous examples wherein spec-
tator species, charge balancing counter cations and templates
have been found to influence product formation.9,12,14,33,34
In the click system, by contrast, the organic speciation profile
is relatively simple. Click reactions and products assembled via
these reactions rely on bond formation and as such the number of
organic species in solution likely decreases over the course of the
reaction. Thus, the number of ‘‘spectator’’ species is limited to the
starting materials and the assembled click product. The fact that
both in situ ligand formation and direct assembly synthetic routes
yield the same product can perhaps be attributed to the absence
of other, unaccounted for, organic species.
Conclusion
2+
–
In summary, we have prepared a novel 2-dimensional UO2
triazolate wherein the CPTAZ unit was prepared via a 1,3-
dipolar cycloaddition. The utility of in situ ligand synthesis as an
alternative route for synthesizing hybrid materials has been
examined through a controlled set of reactions. The product
assembled via in situ ligand formation has been compared to the
product synthesized by direct assembly and it was found that
both synthetic approaches resulted in the same UO22+–triazolate
product. Here the benefit of generating the triazolate product in
situ is that it removes the need to presynthesize the organic
ligand. We also note that this work provides only one data point
and that inquiries into in situ click reactions are ripe for future
exploration. Variables such as alkane chain length, rigidity,
functionality and metal ion coordination modes can be surveyed
within the click system by choosing appropriately functionalized
azides and alkynes. Efforts in these areas are currently under
investigation.
Acknowledgements
This work was supported by (1) The Materials Science of Acti-
nides, an Energy Frontier Research Center funded by the US
Department of Energy, Office of Science, Office of Basic Energy
Science under grant DE-SC0001089 and (2) The Chemical
Sciences, Geosciences and Biosciences Division, Office of
Science, Heavy Elements Program, US Department of Energy,
Differences between in situ oxidation/hydrolysis/degradation
reactions and click reactions may also be attributed to the
availability of metal–ligand coordination sites. As mentioned
previously, in situ ligand formation ‘‘slowly releases’’ the ligand
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16 R. Murugavel, K. Baheti and G. Anantharaman, Inorg. Chem., 2001,
40, 6870–6878.
17 F. Li, L. Xu, B. Bi, X. Liu and L. Fan, CrystEngComm, 2008, 10,
693–698.
under grant DE-FG02-05ER15736 at GWU. The X-ray
diffraction instrumentation was purchased with the support from
The National Science Foundation under grant DMR-0419754.
18 H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int. Ed.,
2001, 40, 2004–2021.
19 W. H. Binder and R. Sachsenhofer, Macromol. Rapid Commun., 2007,
28, 15–54.
References
20 J. E. Hein, J. C. Tripp, L. B. Krasnova, K. B. Sharpless and
V. V. Fokin, Angew. Chem., Int. Ed., 2009, 48, 8018–8021.
21 J.-P. Zhang, Y.-Y. Lin, X.-C. Huang and X.-M. Chen, J. Am. Chem.
Soc., 2005, 127, 5495–5506.
22 L. Cheng, W.-X. Zhang, B.-H. Ye, J.-B. Lin and X.-M. Chen, Inorg.
Chem., 2007, 46, 1135–1143.
1 A. J. Blake, N. R. Champness, S. S. M. Chung, W.-S. Li and
M. Schroder, Chem. Commun., 1997, 1675.
2 X.-M. Zhang, Coord. Chem. Rev., 2005, 249, 1201–1219.
3 X.-M. Chen and M.-L. Tong, Acc. Chem. Res., 2006, 40, 162–170.
4 K. E. Knope and C. L. Cahill, Eur. J. Inorg. Chem., 2010, 8,
1177–1185.
23 D.-W. Fu, W. Zhang and R.-G. Xiong, Cryst. Growth Des., 2008, 8,
3461–3464.
5 Y.-T. Wang, H.-H. Fan, H.-Z. Wang and X.-M. Chen, Inorg. Chem.,
2005, 44, 4148–4150.
24 X.-S. Wang, Y.-Z. Tang, X.-F. Huang, Z.-R. Qu, C.-M. Che,
P. W. H. Chan and R.-G. Xiong, Inorg. Chem., 2005, 44, 5278–5285.
25 L. Hsiu-Mei and C. Tsung-Yuan, Cryst. Growth Des., 2009, 9,
2988–2990.
6 C. E. Rowland, N. Belai, K. E. Knope and C. L. Cahill, Cryst. Growth
Des., 2010, 10, 1390–1398.
7 K. L. Ziegelgruber, K. E. Knope, M. Frisch and C. L. Cahill, J. Solid
State Chem., 2008, 181, 373–381.
26 Apex2, Bruker-AXS, Madison, WI, 2008.
27 G. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008, 64,
112–122.
28 L. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
29 JADE, V6.1, Materials Data Inc., Livermore, CA, 2001.
30 G. B. Hix, B. M. Kariuki, S. Kitchin and M. Tremayne, Inorg. Chem.,
2001, 40, 1477–1481.
8 J. Y. Lu, J. Macias, J. Lu and J. E. Cmaidalka, Cryst. Growth Des.,
2002, 2, 485–487.
9 B. Li, W. Gu, L.-Z. Zhang, J. Qu, Z.-P. Ma, X. Liu and D.-Z. Liao,
Inorg. Chem., 2006, 45, 10425–10427.
10 K. E. Knope and C. L. Cahill, Inorg. Chem., 2007, 46, 6607–6612.
11 X. Li, R. Cao, D. Sun, Q. Shi, W. Bi and M. Hong, Inorg. Chem.
Commun., 2003, 6, 815–818.
ꢁ
31 P.-A. Jaffres, D. Villemin and V. Caignaert, Chem. Commun., 1999,
1997.
32 X.-M. Zhang, Eur. J. Inorg. Chem., 2004, 544–548.
33 C. S. Cundy and P. A. Cox, Microporous Mesoporous Mater., 2005,
82, 1–78.
12 K. E. Knope and C. L. Cahill, Inorg. Chem., 2008, 47, 7660–7672.
13 J.-J. Hou and X.-M. Zhang, Cryst. Growth Des., 2006, 6, 1445–1452.
14 A.-G. D. Nelson, T. H. Bray, W. Zhan, R. G. Haire, T. S. Sayler and
T. E. Albrecht-Schmitt, Inorg. Chem., 2008, 47, 4945–4951.
15 J.-P. Zhang, Y.-Y. Lin, X.-C. Huang and X.-M. Chen, Dalton Trans.,
2005, 3681–3685.
ꢂ
34 G. Ferey, Chem. Mater., 2001, 13, 3084–3098.
This journal is ª The Royal Society of Chemistry 2011
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