Combination of covalent and hydrogen bonding in the formation of 3D uranyl-carboxylate networks

Article abstract of DOI:10.1016/j.ica.2010.06.043

Four compounds containing uranyl cation [UO₂]²⁺ have been synthesized hydrothermally by reacting uranyl acetate and uranyl nitrate with various N/O donor ligands. The structure of all compounds was elucidated by single crystal X-ray diffraction study. Compound [(UO₂)(6- methylnicotinato)₃](H₃O)·4H₂O (1) is a discrete complex (0D), that gives rise in the crystal to hydrophilic channels, while [(UO₂)(OH)(μ₂-3-pyridylpropionato)]_n (2) and [(UO₂)(H₂O)(μ₃-4,4′- oxybis(benzoato)]_n (3) show the formation of 1D coordination polymers. Moreover, oxalate anions, formed in situ by using 5-methylisophthalic or 2,3-pyrazinedicarboxylic acid as reactant ligands, gave rise to a 2D coordinating network [(UO₂)₂(μ₂-oxalate) (μ₂-OH)₂(H₂O)₂] _n·nH₂O (4). All the complexes expanded their dimensionality to 3D through hydrogen bonds.

Full text of DOI:10.1016/j.ica.2010.06.043

Inorganica Chimica Acta 363 (2010) 3407–3412
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Combination of covalent and hydrogen bonding in the formation
of 3D uranyl-carboxylate networks
a
a
a
b
Sudipta Dalai a, , Madhusudan Bera , Abhinandan Rana , Durga Sankar Chowdhuri , Ennio Zangrando
*
a Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721 102, WB, India
b Dipartimento di Scienze Chimiche, University of Trieste, 34127 Trieste, Italy
a r t i c l e i n f o
a b s t r a c t
Four compounds containing uranyl cation [UO2]2+ have been synthesized hydrothermally by reacting
uranyl acetate and uranyl nitrate with various N/O donor ligands. The structure of all compounds was
elucidated by single crystal X-ray diffraction study. Compound [(UO2)(6-methylnicotinato)3](H3O)ꢀ4H2O
Article history:
Received 23 February 2010
Received in revised form 1 June 2010
Accepted 21 June 2010
(1) is a discrete complex (0D), that gives rise in the crystal to hydrophilic channels, while [(UO2)(OH)(l2
-
Available online 30 June 2010
3-pyridylpropionato)]n (2) and [(UO2)(H2O)(
coordination polymers. Moreover, oxalate anions, formed in situ by using 5-methylisophthalic or 2,3-pyr-
azinedicarboxylic acid as reactant ligands, gave rise to a 2D coordinating network [(UO2)2( 2-oxalate)(l2
l
3-4,40-oxybis(benzoato)]n (3) show the formation of 1D
Keywords:
Uranyl cation
Hydrogen bond
5-Methylisophthalic acid
6-Methylnicotinic acid
Trans-3-(3-pyridyl)acrylic acid
4,40-Oxo-bis benzoic acid
l
-
OH)2(H2O)2]nꢀnH2O (4). All the complexes expanded their dimensionality to 3D through hydrogen bonds.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
duced either by the mixed metal uranium(IV) fluorides with differ-
ent Ni(H2O)6ꢁxFx octahedra [38] and by uranyl–lanthanide
The study of metal–organic solids continues to be a great inter-
est due to the variety in solid structures which can be applied to
shape selective catalysis [1–7], ion exchange [8], molecular sieving
[9], gas separation [10], gas storage [11–18], and host guest chem-
istry [19–21]. Although the design and synthesis of such materials
are influenced by many factors like the coordination trend of metal
centers, the nature of ligands used, the metal–ligand ratio, the
reaction conditions etc., the judicious selection of multifunctional
organic ligand is still an effective approach [22–27]. Literature sur-
vey revealed that transition metals, lanthanides and actinides are
competent of presenting fascinating networks [28–31].
Uranium offers interesting architectures due to its higher coordi-
nation number in comparison to main group/transition elements
and the structural diversity depends on the reaction condition as
well as choice of organic ligands [28]. It is perceptible; however, that
the tricky application of hydrogen bonding and other non-covalent
interactions during the synthesis of such materials are becoming
an area of interest and the possibility of generating unpredicted
dimensionality is opening up in connection to novel topologies [32].
Although a large number of 1D and 2D MOFs of uranium are re-
ported in the literature [33–36], examples of the 3D networks are
few in number [37]. In most of the cases the 3D topologies are pro-
heterometallic complexes [39]. Borkowshi and Cahill reported a
3D structure of uranium obtained by cross linking of adipic acid
[40]. However, the construction of 3D building networks of ura-
nium species through hydrogen bond are scarce.
With the aim to derive new network topologies, in this work we
have synthesized four uranyl complexes by using two heterocyclic
monocarboxylates (6-methylnicotinic acid, trans-3-(3-pyri-
dyl)acrylic acid) and three aromatic dicarboxylates (4,40-oxo-bis
benzoic acid, 5-methylisophthalic acid and 2,3-pyrazinedicarboxy-
lic acid) as organic linkers for their capability of participating in
hydrogen bonding and/or in metal coordination. Although some
complexes with 6-methylnicotinic acid [41], trans-3-(3-pyri-
dyl)acrylic acid [42–46], and 4,40-oxo-bis benzoic acid [47] with
different transition metals have been reported, the construction
of uranium coordination polymers using these ligands has never
been tried. Single crystal X-ray analysis shows that all the synthe-
sized complexes present a 3D network through hydrogen bonding.
2. Experimental
2.1. General consideration
Caution! Because uranium is a radioactive and chemically toxic
element, standard precautions for handling such materials should
* Corresponding author. Fax: +91 3222 275 329.
E-mail address: icsd2@yahoo.com (S. Dalai).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.06.043

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S. Dalai et al. / Inorganica Chimica Acta 363 (2010) 3407–3412
be followed. UO2(OAc)2ꢀ2H2O and UO2(NO3)2ꢀ6H2O were purchased
from Fluka, 6-methylnicotinic acid, trans-3-(3-pyridyl)acrylic acid
4,40-oxo-bis benzoic acid, 5-methylisophthalic acid and 2,3-pyraz-
inedicarboxylic acid from Sigma–Aldrich Inc. All were used without
further purification. Elemental analyses (C, H, N) were performed
using a Perkin–Elmer 240C elemental analyzer.
0.75 mmol) and demineralized water (10 ml) was taken in a sealed
25 ml Teflon-lined stainless steel vessel. Yellow crystals of complex
1 appeared within 3 days upon heating at 150 °C under autogenous
pressure. Yield: 50%. Elemental Anal. Calc. for C21H29N3O13U (1): C,
42.14; N, 5.46; H, 3.79. Found: C, 42.19; N, 5.32; H, 3.74%.
2.3. Preparation of [(UO2)(OH)(l2-3-pyridylpropionato)]n (2)
2.2. Preparation of [(UO2)(6-methylnicotinato)3](H3O)ꢀ4H2O (1)
A mixture of UO2(NO3)2ꢀ6H2O (0.251 g, 0.5 mmol), trans-3-(3-
pyridyl)acrylic acid (0.1491 g, 1 mmol), NaOH (0.04 g, 1 mmol)
and H2O (15 ml) was stirred at room temperature, then put into
A mixture of UO2(OAc)2ꢀ6H2O (0.106 g, 0.25 mmol), 5-methylni-
cotinic acid (0.1028 g, 0.75 mmol), Triethylamine (0.1 ml,
a
sealed 25 ml Teflon-lined stainless steel vessel, heated at
160 °C for 7 days, cooled to room temperature and then filtered.
Glossy yellow crystals were obtained from the filtrate after 7 days.
Yield: 60%. Elemental Anal. Calc. for C16H14N2O10U2 (2): C, 22.08; N,
3.21; H, 1.62. Found: C, 21.98; N, 3.15; H, 1.71%.
Table 1
Crystallographic data and details of structure refinements for complexes 1–3.
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
21H29N3O13
U
C16H14N2O10U2 C14H10O8U
2.4. Preparation of [(UO2)(H2O)(l
3-4,40-oxybis(benzoato)]n (3)
769.50
trigonal
P 31c
870.35
orthorhombic
P bca
544.25
monoclinic
P 21/c
Compound 3 was synthesized by the similar procedure as de-
scribed for complex 2. The ligand 4,40-oxo-bis benzoic acid
(0.1291 g, 0.5 mmol) is used instead of trans-3-(3-pyridyl)acrylic
acid. Needle shaped yellow crystals of 3 were obtained from solu-
tion after 15 days. Yield: 60%. Elemental Anal. Calc. for C14H10O8U
(3): C, 30.89; H, 1.85. Found: C, 30.86; H, 1.87%.
16.271(3)
23.933(4)
18.704(3)
8.494(1)
16.018(3)
8.884(2)
10.200(2)
95.71(2)
1444.3(5)
4
b (Å)
c (Å)
6.822(2)
b (°)
V (Å3)
1564.1(6)
2
1.634
5.248
744
24.15
17 378
1318
3802.3(10)
8
Z
Dcalc (g cmꢁ3
)
3.041
17.075
3104
2.503
11.279
1000
l
(mmꢁ1
)
F(0 0 0)
hmax (°)
Reflections collected
Unique reflections
Independent reflections
2.5. Preparation of [(UO2)2(
l
2-oxalate)(
l
2-OH)2(H2O)2]nꢀnH2O (4)
26.42
54 496
3869
29.65
16 791
4045
A mixture of UO2(NO3)2ꢀ6H2O (0.251 g, 0.5 mmol), 5-methyli-
sophthalic acid (0.09 g, 0.5 mmol), NaOH (0.04 g, 1 mmol) and
demineralized water (10 ml) was sealed in a 25 ml Teflon-lined
stainless steel vessel. Yellow crystals of complex 4 appeared within
0.0640
0.0790
0.0600
(Rint
)
Observed I > 2
r
(I)
681
114
2247
271
2917
214
Parameters
Goodness-of-fit (GOF) on
0.774
0.906
0.935
F2
Table 2
R1/wR2a
0.0447/
0.0904
0.0957/
0.0976
0.0562/0.1316
0.0934/0.1466
0.0436/
0.1037
0.0619/
0.1097
1.068,
Selected bond lengths (Å) and angles (°) of 1.
(I > 2
R1/wR2a
(all data)
(e/Å3)
r (I))
U(1)–O(1)
U(1)–O(2)
1.76(2)
1.74(3)
U(1)–O(3)
U(1)–O(4)
2.457(12)
2.507(16)
D
q
0.849, ꢁ0.460 2.625, ꢁ1.921
O(2)–U(1)–O(3)
O(1)–U(1)–O(3)
O(2)–U(1)–O(4)
90.5(3)
89.5(3)
90.3(6)
O(1)–U(1)–O(4)
O(3)–U(1)–O(4)
89.7(6)
54.2(4)
ꢁ1.897
h
i
1=2
P
P
P
P
2
2
wðF2o ꢁ Fc2Þ = wðFo2Þ
a
R1 =
kFoj ꢁ jFck= jFoj; wR2 ¼
Fig. 1. The [UO2(6-methylnicotinato)3]ꢁ complex anion of 1 with labelling scheme of the independent atoms. The H-bond between the methylnicotinato nitrogen and a H3O+/
H2O oxygen is indicated.

S. Dalai et al. / Inorganica Chimica Acta 363 (2010) 3407–3412
3409
Fig. 2. (a) View of the crystal packing of 1 showing the channels built by [(UO2)(6-methylnicotinato)3] fragments and (b) disordered H2O/H3O+ species (big spheres) bound to
the framework through H-bonds.
6 days upon heating at 160 °C under autogenous pressure. Yield:
65%. Elemental Anal. Calc. for C2H8O13U2 (4): C, 3.35; H, 1.12.
Found: C, 3.41; H, 1.19%.
formed using programs DENZO and SCALEPACK [48]. All the structures
were solved by direct methods and subsequent Fourier analyses
[49] and refined by the full-matrix least-squares method based
on F2 with all observed reflections [49]. In complex 1 the residuals
were interpreted as a disorder water molecule (O1w, O2w with
occupancies 0.56(8)/0.44(8)) and an oxygen atom (O3w) to which
was assigned an occupancy of 0.6666, based on peak height. The
short H-bond distance between N1and O3w (2.79(3) Å) could indi-
cate a H3O+ cation for the latter in order to guarantees the charge
neutrality of the UO2 complex. However diffraction data did not al-
low fixing the H atoms of these species, being likely disordered.
The hydrogen atoms of compounds 2 and 3 were fixed at geomet-
The same compound is formed by a different reaction when a
mixture of UO2(NO3)2ꢀ6H2O (0.251 g, 0.5 mmol), 2,3-pyrazinedi-
carboxylic acid (0.084 g, 0.5 mmol), KOH (0.056 g, 1 mmol) and
demineralized water (10 ml) was sealed in a 25 ml Teflon-lined
stainless steel vessel. Yellow crystals of complex 4 appeared within
3 days upon heating at 160 °C under autogenous pressure. Yield:
50%. Elemental Anal. Calc. for C2H8O13U2 (4): C, 3.35; H, 1.12.
Found: C, 3.4; H, 1.17%.
rical positions or derived from the
DF map (constrained O–H dis-
3. X-ray crystallography
tances at 0.85 Å) and their contribution was included in the final
cycles of refinement. All the calculations were performed using
the WINGX System, Ver 1.80.05 [50].
Crystal data and details of data collections and refinements for
the structures reported are summarized in Table 1. Data collections
were carried at room temperature on a Nonius DIP-1030H system
4. Results and discussion
(Mo Ka radiation, k = 0.71073 Å, graphite monochromatized). Cell
refinement, indexing and scaling of all the data sets were per-
Four complexes containing a central uranyl cation [UO2]2+
moiety with monocarboxylate anions (6-methylnicotinate and
trans-3-(3-pyridyl)acrylate) and with aromatic dicarboxylate
(4,40-oxo-bis-benzoate, 5-methylisophthalate and 2,3-pyrazinedi-
carboxylate), have been synthesized, namely [(UO2)(6-methylni-
cotinato)3](H3O)ꢀ4H2O (1), [(UO2)(OH)(
l
2-3-pyridylpropionato)]n
(2), [(UO2)(H2O)(
l
3-4,40-oxybis(benzoato)]n (3), and [(UO2)2(l2
-
Table 3
Selected bond (Å) and angles (°) of 2.
U(1)–O(1)
U(1)–O(1)#1
U(1)–O(2)
U(1)–O(3)
U(1)–O(4)
U(1)–O(7)
U(1)–O(8)#1
2.395(8)
2.356(8)
2.490(9)
1.752(10)
1.729(11)
2.372(11)
2.465(10)
U(2)–O(1)
U(2)–O(2)
U(2)–O(2)#2
U(2)–O(5)
U(2)–O(6)
U(2)–O(9)
U(2)–O(10)#1
2.442(9)
2.447(8)
2.415(9)
1.766(11)
1.786(10)
2.349(10)
2.455(9)
O(4)–U(1)–O(3)
O(1)–U(1)–O(2)
O(1)#1–U(1)–O(2)
O(1)#1–U(1)–O(8)#1
O(7)–U(1)–O(8)#1
O(7)–U(1)–O(1)
177.8(4)
68.6(3)
70.4(3)
75.0(3)
72.2(3)
75.4(3)
O(5)–U(2)–O(6)
O(1)–U(2)–O(2)
O(2)–U(2)–O(10)#1
O(9)–U(2)–O(10)#1
O(9)–U(2)–O(2)#2
O(2)#2–U(2)–O(1)
176.5(4)
68.5(3)
75.6(3)
72.8(3)
78.9(3)
70.3(3)
Fig. 3. 1D ribbon of compound 2 running along axis c showing the labelling scheme
of oxygen donors.
Symmetry codes: #1 x, ꢁy + 1/2, z + ½; #2 x, ꢁy + 1/2, z ꢁ 1/2.

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S. Dalai et al. / Inorganica Chimica Acta 363 (2010) 3407–3412
Fig. 4. Crystal packing of 2 viewed down axis c showing the H-bond interactions between the aqua ligands and pyridine N atoms.
Table 4
Hydrogen bonds (Å, °).
D–H
d(D–H)
d(Hꢀ ꢀ ꢀA)
<DHA
d(Dꢀ ꢀ ꢀA)
A
Complex 2
O(1)–H(1)
O(2)–H(2A)
0.98
0.98
1.82
1.82
173
169
2.794(15)
2.793(16)
N(1)
N(2)
ꢁx + 3/2, y + 1/2, z
ꢁx + 2, ꢁy + 1, ꢁz + 2
Complex 3
O(1w)–H(1)
O(1w)–H(2)
0.85(6)
0.86(6)
1.98(7)
2.36(8)
167(9)
141(7)
2.808(8)
3.078(8)
O(2)
O(5)
x, ꢁy + 3/2, z + 1/2
ꢁx + 1, y + 1/2, ꢁz + 3/2
oxalate)(
l
2-OH)2(H2O)2]nꢀnH2O (4). The oxalate anion of the latter
4.2. Structure description of [(UO2)(OH)(
l
2-3-pyridylpropionato)]n (2)
resulted by using the 5-methylisophthalic or 2,3-pyrazinedicarb-
oxylic acid as reactant ligand. All the complexes have been deter-
mined by X-ray single crystal analysis, but the crystal structural
determination of (4), showing a 2D layered network, has been al-
ready reported [57] and it will be not described.
The X-ray structural characterization of 2 shows a 1D ladder-
like coordination polymer running parallel to axis c and formed
by (UO2)2+ units connected by
l3-OH groups (Fig. 3). Thus the pen-
tagonal metal polyhedra are connected each other sharing two
edges. The two crystallographic independent uranium atoms U1
and U2 constitute the side rails of the ladder and are alternatively
separated by 3.881(1) and 3.934(1) Å, with an intermetallic angle
of 65.95(2)°. In addition the ribbon is flanked by the 3-pyridylpro-
pionato ligands bridging adjacent metals (Fig. 3). Both the indepen-
4.1. Structure description of [(UO2)(6-methylnicotinato)3](H3O).4H2O
(1)
The structure consists of discrete [(UO2)(6-methylnicotinato)3]ꢁ
complex anions located on crystallographic three-fold axes coun-
terbalanced by H3O+ cations. An ORTEP drawing of the complex
is shown in Fig. 1 and a selection of bond lengths and angles is re-
ported in Table 2. The UO22þ unit is chelated by carboxylate groups
of three 6-methylnicotinato ligands with U–O bond lengths of
2.457(12) and 2.507(16) Å, and a chelating angle of 54.2(4)°. These
values, although at low accuracy, agree with those reported for
analogous derivatives with benzoate [51–53], salicylato [54], p-
aminosalicylato [55] and 2-aminobenzenecarboxylato [56]. The
residuals in the
DF map were interpreted as disordered lattice
water oxygens. In order to guarantee the electroneutrality we be-
lieve (see Section 2) that the partially occupied species O3w could
be a H3O+ cation, being at a short H-bond distance from the nico-
tinate nitrogen atom (N1ꢀ ꢀ ꢀO3w = 2.79(3) Å). Beside this interac-
tion, the crystal packing shows an H-bonding scheme occurring
between the disordered water molecule O1w/O2w with carboxyl-
ate O4 (Oꢀ ꢀ ꢀO 2.89 Å). Finally the packing evidences the presence of
hydrophilic channels having diameter of ca. 9.7 Å and extending
parallel to axis c filled by the disordered water molecules (Fig. 2).
The same framework was also found in the salicylato [54] and p-
aminosalicylato derivatives [55], where the tubular arrangement
is occupied by water molecules and sodium ions, respectively.
Fig. 5. The 1D coordination polymer of 3.

S. Dalai et al. / Inorganica Chimica Acta 363 (2010) 3407–3412
3411
Fig. 6. Detail of the polymeric arrangement 3 showing the centrosymmetric eight-membered ring with labeling scheme of independent atoms.
dent U atoms are in a distorted pentagonal bipyramidal geometry
being connected in the equatorial plane by three hydroxyl anions
and two oxygens from different carboxylate groups. The U@O bond
length values reported in Table 3 show comparable values for the
two independent uranium atoms (range from 1.729(11) to
1.786(10) Å), following a trend as observed in all the compounds
here presented. The U–O(hydroxo) and U–O(carboxylate) bond dis-
tances fall in between 2.356(8) and 2.447(8) Å and 2.349(10)–
2.465(10) Å, respectively. Fig. 4 depicts the crystal packing that
evidences strong H-bonds occurring between OH groups with py
nitrogens of adjacent chains (OHꢀ ꢀ ꢀN of 2.79 Å, Table 4) that give
rise to a 3D supramolecular structure.
ylate (U–O3 and U–O4 of 2.401(5) and 2.435(5) Å, respectively),
and the U–O1w is even slightly longer (2.468(5) Å). The angle at
oxygen of the oxybis(benzoate) connector presents an angle of
120.8(5)° and the phenyl rings form an a dihedral angle of
59.5(3)°. The aqua ligands act as H donors towards symmetry re-
lated oxygen atoms O2 and O5 of adjacent chains leading to a 3D
structure, but the packing does not show
phenyls.
p–p interactions between
5. Conclusion
In this paper we describe the crystal structure of three uranium
organic frameworks (UOFs) having uranyl cation [UO2]2+ as central
species. The use of 6-methylnicotinato, 3-pyridylpropionato, and
4,40-oxybis(benzoato) lead to a discrete complex and to two 1D
uranium polymers, which expand their dimensionality to 3D
supramolecular network through an extensive hydrogen bonding
scheme.
4.3. Structure description of [(UO2)(H2O)(l
3-4,40-oxybis(benzoato)]n
(3)
The crystal structure comprises of 1D coordination polymers
built by [UO2(H2O)2+ units connected by a pair of 4,40-oxy-
]
2
bis(benzoate) anions in a head-to-tail arrangement as shown in
Fig. 5. In each organic moiety one carboxylate group acts as bridg-
ing, the other as chelating ligand towards the metals. This lead to
8- and 28-membered rings that alternate along the chain: in the
former arrangement the metals are separated by 5.274 Å while
the intermetallic distance spanned by the oxybis(benzoate) anion
is 16.018(3) Å. The uranyl units are equatorially coordinated by
five oxygen atoms, resulting in a pentagonal bipyramidal environ-
ment (Fig. 6). The almost linear UO22+ unit presents U@O distances
of 1.758(5) and 1.770(5) Å (Table 5). The U–O bond distances of
bridging carboxylate group are shorter (U–O5 = 2.322(5), U–
O6 = 2.332(5) Å) in comparison with those of the chelating carbox-
Acknowledgements
Financial support from DST, New Delhi, India (Fast track Pro-
posal: SR/FTP/CS-26/2007) is gratefully acknowledged. M.B is
thankful to CSIR for providing research fellowship.
Appendix A. Supplementary material
CCDC 758155–758157 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.06.043.
Table 5
Selected bond lengths (Å) and angles (°) of 3.
U–O(1)
U–O(2)
U–O(5)
U–O(6)#1
1.758(5)
1.770(5)
2.322(5)
2.332(5)
U–O(3)
U–O(4)
U–O(1w)
2.401(5)
2.435(5)
2.468(5)
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O(5)–U–O(3)
O(1)–U–O(2)
O(3)–U–O(4)
O(4)–U–O(1w)
O(6)#1–U–O(1w)
O(5)–U–O(6)#1
77.20(18)
178.7(3)
54.21(17)
71.59(18)
74.53(19)
82.58(19)
O(5)–U–O(3)
C(1)–O(3)–U
C(1)–O(4)–U
C(14)–O(5)–U
C(14)–O(6)–U#1
77.20(18)
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