Structural observations of heterometallic uranyl copper(ii) carboxylates and their solid-state topotactic transformation upon dehydration

Article abstract of DOI:10.1002/chem.201203748

The hydrothermal reactions of uranyl nitrate and metallic copper with aromatic polycarboxylic acids gave rise to the formation of five heterometallic UO₂²⁺-Cu²⁺ coordination polymers: (UO ₂)Cu(H₂O)₂(1,2-bdc)₂ (1; 1,2-bdc=phthalate), (UO₂)Cu(H₂O)₂(btec)×4 H₂O (2) and (UO₂)Cu(btec) (2′; btec=pyromellitate), (UO₂)₂Cu(H₂O)₄(mel) (3; mel=mellitate), and (UO₂)₂O(OH)₂Cu(H ₂O)₂(1,3-bdc)×H₂O (4; 1,3-bdc=isophthlalate). Single-crystal X-ray diffraction (XRD) analysis of compound 1 revealed 2D layers of chains of UO₈ and CuO ₄(H₂O)₂ units that were connected through the phthalate ligands. In compound 2, these sheets were connected to each other through the two additional carboxylate arms of the pyromellitate, thus resulting in a 3D open-framework with 1D channels that trapped water molecules. Upon heating, free and bonded water species (from Cu-OH₂) were evacuated from the structure. This thermal transition was followed by in situ XRD and IR spectroscopy. Heating induced a solid-state topotactic transformation with the formation of a new set of Cu-O interactions in the crystalline anhydrous structure (2′), in order to keep the square-planar environment around the copper centers. The structure of compound 3 was built up from trinuclear motifs, in which one copper center, CuO₄(OH₂)₂, was linked to two uranium units, UO₅(H₂O)₂. The assembly of this trimer, U₂Cu , with the mellitate generated a 3D network. Complex 4 contained a tetranuclear uranyl core of UO₅(OH)₂ and UO₆(OH) units that were linked to two copper centers, CuO(OH)₂(H₂O)₂, which were then connected to each other through isophthalate ligands and U=O-Cu interactions to create a 3D structure. The common structural feature of these different compounds is a bridging oxo group of U=O-Cu type, which is reflected by apical Cu-O distances in the range 2.350(3)-2.745(5) A. In the case of a shorter Cu-O distance, a slight lengthening of the uranyl bond (U=O) is observed (e.g., 1.805(3) A in complex 4). Copyright

Full text of DOI:10.1002/chem.201203748

DOI: 10.1002/chem.201203748
Structural Observations of Heterometallic Uranyl Copper(II) Carboxylates
and Their Solid-State Topotactic Transformation upon Dehydration
Jakub Olchowka, Clꢀment Falaise, Christophe Volkringer, Natacha Henry, and
Thierry Loiseau*[a]
Abstract: The hydrothermal reactions
of uranyl nitrate and metallic copper
with aromatic polycarboxylic acids
gave rise to the formation of five heter-
tate, thus resulting in a 3D open-frame-
work with 1D channels that trapped
water molecules. Upon heating, free
which one copper center, CuO
was linked to two uranium units, UO5-
(H2O)2. The assembly of this trimer,
“U2Cu”, with the mellitate generated a
3D network. Complex 4 contained a
tetranuclear uranyl core of UO5(OH)2
and UO6(OH) units that were linked
to two copper centers, CuO(OH)2-
4ACHTUNGTRENNUNG(OH2)2,
AHCTUNGTRENNUNG
À
and bonded water species (from Cu
2+
2+
À
ometallic UO2 Cu
polymers: (UO2)Cu
(1; 1,2-bdc=phthalate), (UO2)Cu-
(H2O)2A(btec)·4H2O (2) and (UO2)Cu-
(btec) (2’; btec=pyromellitate),
(UO2)2Cu(H2O) (mel) (3; mel=melli-
tate), and (UO2)2O(OH)2Cu(H2O)2-
(1,3-bdc)·H2O (4; 1,3-bdc=isophthla-
coordination
OH2) were evacuated from the struc-
ture. This thermal transition was fol-
lowed by in situ XRD and IR spectros-
G
CHTUNGTRENNUNG
E
T
ACHTUNGTRENNcUNG opy. Heating induced a solid-state top-
otactic transformation with the forma-
R
ACHTUGNTERN(NUGN H2O)2, which were then connected to
each other through isophthalate ligands
À
G
N
tion of a new set of Cu O interactions
À
G
in the crystalline anhydrous structure
(2’), in order to keep the square-planar
environment around the copper cen-
ters. The structure of compound 3 was
built up from trinuclear motifs, in
and U=O Cu interactions to create a
A
3D structure. The common structural
feature of these different compounds is
late). Single-crystal X-ray diffraction
(XRD) analysis of compound 1 re-
vealed 2D layers of chains of UO8 and
À
a bridging oxo group of U=O Cu type,
À
which is reflected by apical Cu O dis-
CuO
N
tances in the range 2.350(3)–
2.745(5) ꢀ. In the case of a shorter
through the phthalate ligands. In com-
pound 2, these sheets were connected
to each other through the two addition-
al carboxylate arms of the pyromelli-
Keywords: copper · hydrothermal
synthesis · topochemistry · uranium ·
X-ray diffraction
À
Cu O distance, a slight lengthening of
the uranyl bond (U=O) is observed
(e.g., 1.805(3) ꢀ in complex 4).
Introduction
lent uranium (UO22+), which represents its most stable oxi-
dation state under ambient conditions, a large number of co-
ordination polymers have been reported that show different
local environments around the cation (tetragonal, pentago-
nal, and hexagonal bipyramidal geometries), together with
different dimensionalities of the hybrid network. Following
the successful synthesis of metal–organic framework (MOF)
materials,[3] a wide variety of combinations of multi-topic
carboxylate-based organic ligands have been tested with
these uranyl species to create new atomic arrangements.[1c]
Besides the use of organic molecules with targeted function-
alities, an alternative strategy involves the formation of as-
semblies of 5f elements with distinct heterometallic ele-
ments, such as lanthanides or transition metals. An interest-
ing structural feature is observed in divalent copper, which
usually possesses a specific environment that is defined by
Over the last few decades, there has been growing interest
in the synthesis and structural characterization of actinide-
based compounds by associating metallic centers with O- or
N-donor organic ligands to generate multidimensional coor-
dination polymers.[1] Most of the contributions reported to
date have involved the elaboration of uranium-containing
solids, because this particular 5f element finds its main use
as a fuel in nuclear power plants. Present in many natural
minerals,[2] the chemical reactivity of uranium has been in-
tensively investigated in comparison with those of its neigh-
boring 5f metals in the periodic table (except for thorium),
which are characterized by highly radio-toxicity activity,
thus making their handling more difficult. By using hexava-
À
four short Cu O bonds in a square plane and two long axial
[a] J. Olchowka, C. Falaise, Dr. C. Volkringer, Dr. N. Henry,
Dr. T. Loiseau
À
Cu O bonds, thereby resulting in an elongated octahedral
Unitꢁ de Catalyse et Chimie du Solide (UCCS)
UMR CNRS 8181, Universitꢁ de Lille Nord de France
USTL-ENSCL, Bat C7, BP 90108, 59652 Villeneuve dꢂAscq (France)
Fax : (+33)3-20-43-48-95
geometry, owing to the Jahn–Teller effect. In the various re-
ported crystal structures (Inorganic Crystal Structure Data-
base, FIZ Karlsruhe, Germany) of mixed uranyl copper
oxides and their derived solids (phosphates, silicates, etc.),
E-mail: thierry.loiseau@ensc-lille.fr
À
the uranyl oxo group was often found to belong to the coor-
dination sphere of copper through a long apical bond. This
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203748.
2012
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Chem. Eur. J. 2013, 19, 2012 – 2022

FULL PAPER
group would correspond to a type of heterometallic bridging
oxo group that is known as a cation–cation interaction
(CCI)[4] and defines a bonding of the “yl” oxygen atom with
À
neighboring metallic cations (usually U=O U in uranyl).
À
Indeed, the occurrence of contrasting Cu O distances
À
(equatorial/apical) seems to favor such U=O Cu linkage,
owing to the long bond of the apical group that is attached
to the copper atom. The heterometallic bridging oxo group
À
was only found in very few of the various reported uranyl
copper hybrid complexes,[5] which implied the use of mixed
N/O-donor ligands.[1b,6]
Following our investigation into the preparation of mixed
[7]
À
À
uranyl lanthanide carboxylate-based compounds, we con-
À
tinued our studies in the examination of the uranyl copper
chemical system under mild hydrothermal conditions. The
origin of this work was the use of metallic copper as a start-
ing reactant to analyze the redox behavior towards uranyl
cations in aqueous solution under mild hydrothermal condi-
tions. In fact, the hydrothermal oxidation of metallic copper
into its divalent state was observed and gave rise to the for-
Figure 1. Top: view of the coordination environments around the uranyl
(dark gray) and copper cations (light gray) in (UO2)Cu
(1). Bottom: infinite ribbon with strict alternation of UO8 and CuO4-
(H2O)2 polyhedra (as indicated). A similar chain-like motif is observed in
ACHUTGTNERN(NUG H2O)2ACHTUNGTRENNUNG(1,2-bdc)2
AHCTUNGTRENNUNG
compound 2.
À
mation of mixed uranyl copper(II) coordination polymers.
Herein, four distinct phases have been isolated in the pres-
ence of aromatic polycarboxylate linkers, such as phthalic
acid: ((UO2)Cu
((UO2)Cu(H2O)2A(btec)·4H2O (2)), mellitic acid ((UO2)2Cu-
(H2O)4A(mel) (3)), and isophthalic acid ((UO2)2O(OH)2Cu-
(H2O)2A(1,3-bdc)·H2O (4)). Their synthesis and their single-
crystal structures have been established. The thermal behav-
ior of compounds 1 and 2 has also been studied and special
(H2O)
E
O distances from 2.380(3) to 2.504(4) ꢀ. Four of the carboxy
oxygen atoms correspond to two chelating carboxylate arms
from two distinct phthalate ligands and are located in a
trans geometry. The second type of carboxylate arms adopts
a bidentate bridging mode between the uranyl cation and
the copper cation. The latter atom is coordinated to two car-
E
CHTUNGTRENNUNG
G
CHTUNGTRENNUNG
E
CHTUNGTRENNUNG
À
À
À
attention has been paid to U Cu pyromellitate compound
2, which exhibits a potentially porous tunnel-based frame-
work with encapsulated water. Indeed, upon heating, water
molecules are removed, thereby leading to the formation of
boxy oxygen atoms (Cu O 1.923(3) ꢀ) and two terminal
À
aquo species (Cu O1W 1.973(3) ꢀ), which occupy the cor-
ners of a square plane (bond-valence calculations[8] give a
value of 0.452, which is in agreement with the assignment of
a terminal water molecule). Two additional oxo groups com-
plete the coordination environment of the copper atom,
an anhydrous crystalline phase, (UO2)CuACTHNUTRGNEUNG(btec) (2’). Its crys-
tal structure and the topotactic phase transitions were char-
acterized by both in-situ X-ray thermodiffraction and IR
spectroscopy.
À
À
with
a
quite-long axial Cu O distance (Cu O11U
2.517(3) ꢀ), thereby resulting in an elongated octahedral ge-
ometry. This distorted octahedral polyhedron is quite
common for divalent copper species (Jahn–Teller effect).
The oxo species that results from significant axial lengthen-
Results and Discussion
À
ing of two of the copper oxygen bonds is shared with the
Structure description: Compounds 1–4 were synthesized hy-
drothermally from a mixture of uranyl nitrate hexahydrate
and metallic copper in aqueous medium with different aro-
matic poly-carboxylate molecules. Single-crystal X-ray dif-
fraction analysis revealed that copper(II) cations were incor-
uranyl O=U=O entity, thus forming a m2 connection mode.
À
The uranyl oxo species is known to be quite chemically
inert and rarely engages in bonding with other uranyl or
other heterometallic cations. However, some rare cases of
purely inorganic compounds or coordination complexes
À
À
À
porated into the final uranyl organic networks, thus indicat-
ing the occurrence of an oxidization reaction during the hy-
drothermal treatment.
have reported such a U=O U or U=O M (M=metal) link-
age, which is known as a cation–cation interaction[4] and has
been encountered in some uranyl carboxylates.[9] With
copper, this situation is not new and has been described in a
few uranyl copper carboxylates.[1b,6] The occurrence of such
m2-oxo bridges leads to the formation of infinite heterome-
tallic chains (Figure 2) with a strict alternation of hexagonal
ACHTUNGTRENNUNG(UO2)CuACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(1,2-bdc)2 (1): The structure of compound 1
is composed of an asymmetric unit (Figure 1) that contains
one uranyl cation and one copper(II) cation at special posi-
tions 1g and 1f (Wyckhoff position), respectively. The
uranyl center is eightfold-coordinated with two short U=O
double bonds (1.783(3) ꢀ) in apical positions and six car-
UO8 bipyramids and distorted CuO4ACTHNUTRGNE(UNG H2O)2 octahedra along
the [110] direction. These ribbons are then connected to
each other through the carboxylate groups of the phthalate
À
À
À
boxy oxygen atoms in a hexagonal equatorial plane with U
ligands, thereby creating mixed organic uranyl copper
Chem. Eur. J. 2013, 19, 2012 – 2022
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2013

T. Loiseau et al.
Figure 3. Top: view of the coordination environments around the uranyl
(dark gray) and copper cations (light gray) in (UO2)Cu
(btec)·4H2O (2), which represents a fragment of the infinite chains of al-
ternating uranyl and copper centers, as in compound 1. Bottom: structur-
al relationship between (UO2)Cu(H2O)2A(1,2-bdc)2 (1) and (UO2)Cu-
(H2O)2A(btec)·4H2O (2), which shows a crystallographic shift of a/2 of the
layers of compound 1 with respect to the 3D framework of compound 2,
along with the elimination of phthalate groups, which are replaced by
two additional carboxylates groups from the pyromellitate linker.
ACHTUNGTRENNUNG(H2O)2-
AHCTUNGTRENNUNG
U
CHTUNGTRENNUNG
A
CHTUNGTRENNUNG
Figure 2. Views of the layered structure in (UO2)CuACHTNUGTRNENUG(H2O)2CAHTUNGTRENN(NGU 1,2-bdc)2 (1)
along the ac plane (top) and the ab plane (bottom).
layers in the ab plane (Figure 2). The benzene rings of the
phthalate molecules point up or down the plane of the sheet
and are oriented along the c axis. The cohesion of the struc-
ture is ensured by p–p interactions between the aromatic
rings, which are stacked along the a axis (C···C distances of
about 3.7 ꢀ). Thermogravimetric analysis (see the Support-
ing Information, S3a) indicated one weight loss from 1808C,
which was assigned to the decomposition of compound 1.
The observed weight loss was 52.8%, which agreed very
well with a theoretical value (52.6%) based on the chemical
formula UCuO4. Evolution of the powder XRD patterns
(see the Supporting Information, S4) showed the collapse of
the structure from 1808C and the crystallization of CuU3O10
(PDF number: 44-0979) between 420 and 6008C, followed
by the formation of the final product CuUO4 (PDF number:
24-038).
which is in agreement with the assignment of a terminal
water molecule. The arrangement of the carboxylates arms
at the 1,2 or 4,5 positions of the pyromellitate linker is iden-
tical to that of the two adjacent carboxylates groups in the
phthalate groups in compound 1. For each pair, one group
chelates to the uranyl center, whereas the other is a biden-
tate bridge between the uranyl and copper cations. This ar-
rangement results in the generation of infinite heterometal-
lic ribbons along the [110] direction, which are connected to
each other through one pair of carboxylate groups to form
À
À
uranyl copper carboxylate layers in the ab plane. The tetra-
dentate character of the pyromellitate ligands induces the
shift of the layer of compound 1 along the a axis (a/2 trans-
lation, Figure 3) to generate a 3D framework with the for-
mation of channels that run along the a axis (Figure 4). In
fact, the 3D network of compound 2 corresponds to a modi-
fied structure of compound 1, in which two carboxylate
functions have been symmetrically added to the benzene
ACHTUNGTRENNUNG(UO2)CuACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(btec)·4H2O (2): The structure of coordina-
tion polymer 2 is closely related to that of compound 1. In
fact, the asymmetric units are identical (Figure 3), with one
eightfold-coordinated uranyl center and one octahedrally
coordinated copper center. The uranyl bond is 1.776(1) ꢀ
À
À
ring to connect the hybrid uranyl copper organic layers to
each other. In this operation, one phthalate group has been
replaced by the two additional carboxylate functions. Free
water molecules are encapsulated within the channels, which
offer a free aperture window of 3.7ꢄ3.8 ꢀ2. These molecules
can be easily removed upon heating and thermogravimetric
analysis (see the Supporting Information, Figure S3b) indi-
cated that two water molecules per UO2 unit were evacuat-
ed between 50 and 1208C. We also observed that the water
species that were coordinated to copper atoms were also re-
À
long and the U O distances from the hexagonal equatorial
plane range from 2.386(1) to 2.525(1) ꢀ. The copper cation
À
is surrounded by two carboxy oxygen atoms (Cu O
À
1.969(1) ꢀ), two terminal aquo species (Cu OW1
1.937(1) ꢀ), and two uranyl m2-oxo groups, which corre-
À
spond to the elongated Cu O distances (2.437(1) ꢀ). Bond-
valence calculations[8] give a value of 0.498 (for OW1),
2014
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Heterometallic Uranyl Copper(II) Carboxylates
FULL PAPER
Figure 5. Top: representation of the coordination environment of the
uranyl (dark gray) and copper cations (light gray) in a trinuclear building
unit in (UO2)2Cu
ACHUTNGTREN(NUG H2O)4ACHTUNGTRENN(UNG mel) (3). Bottom: scheme of the m8-connection
mode of the mellitate ligand in compound 3.
À
are located in a square plane, as well as two axial uranyl
oxo groups (2.561(2) ꢀ), thus resulting in an elongated octa-
À
hedral geometry. The Cu Ouranyl bond is slightly longer than
those in previous phases 1 or 2 (Table 1). The uranyl cation
(general position 4e) is sevenfold-coordinated to two axial
oxo groups, with the expected short U=O bonds (U=O
Figure 4. Views of the 3D structure of (UO2)Cu
along the bc plane (top) and the ac plane (bottom).
ACHUTGTNRNE(NUG H2O)2ACHUTNGTREN(NUGN btec)·4H2O (2)
À
1.769(2) and 1.772(2) ꢀ), four carboxy oxygen atoms (U O
À
2.308(2)–07(2) ꢀ), and one terminal water species (U OW1
moved during the dehydration process, with a corresponding
weight loss of 15.2%, which was in good agreement with the
theoretical value (15.6%): 4H2O (calcd: 10.4%)+2H2O
(from copper, calcd: 5.2%). The organic part decomposed
from 3208C up to 3808C and the remaining final weight loss
was 53.6%, which was in good agreement with the expected
value (53.0%) based on CuUO4. Powder XRD pattern of
the residue at 8008C indicated a major CuUO4 phase (PDF
number: 24-038) and some weak Bragg peaks that were as-
signed to CuU3O10 (PDF number: 44-0979).
2.465(3) ꢀ). Bond-valence calculations[10] (0.450) agree well
with the attribution of water to this oxygen atom. The con-
nection of one copper cation to two uranium centers
À
through the uranyl oxo groups generates a discrete trinu-
clear unit with a U/Cu ratio of 2:1 (Figure 5). Only one
2+
À
uranyl oxo ligand (OU1) is shared between the UO2 and
Cu2+ cations, whereas the second ligand (OU2) is terminal;
this latter configuration is commonly observed in most
À
uranyl-based compounds. The remaining non-bonded oxo
ACHTUNGTRENNUNG(UO2)2CuACHTUNGTRENNUNG(H2O)4ACHTUNGTRENNUNG(mel) (3): The crystal structure of
À
Table 1. U=O and Cu O distances in different uranyl copper carboxylates that exhibit
À
compound 3 also shown heterometallic bridging
oxo groups between the uranyl and copper centers.
It consists of two independent crystallographic met-
allic centers, which are defined by a trinuclear
motif in which one central copper-centered octahe-
dron is linked to two peripheral uranyl-centered
heterometallic cation–cation Cu O=U interactions.
À
Compound
U=O [ꢀ]
Cu O [ꢀ]
Bond valence
for O(CuÀO)
A
(3,5-pdc)2·2H2O[a,1b]
1.780(9)
1.771(3)
1.783(3)
1.776(1)
1.754(2)
1.772(2)
1.805(3)
1.783(3)
2.593(11)
2.504(2)
2.517(3)
2.437(1)
2.745(5)
2.561(2)
2.350(3)
2.692(4)
0.085
0.108
0.104
0.129
0.056
0.092
0.163
0.065
[b,6]
R
G
CHTUNGTRENNUNG
E
E
N
R
À
pentagonal bipyramids through a U=O Cu bridge
U
ACHTUNGTRENNUNG
(Figure 5). The copper cations lie at a special posi-
R
G
CHTUNGTRENNUNG
tion (2a) and are sixfold-coordinated to two car-
A
N
CHTUNGTRENNUNG
À
boxy oxygen atoms (Cu O 1.918(2) ꢀ) and two ter-
À
minal water species (Cu OW2 1.972(3) ꢀ), which [a] 3,5-pdc=3,5-Pyrazoledicarboxylate; [b] nic=nicotinate.
Chem. Eur. J. 2013, 19, 2012 – 2022
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T. Loiseau et al.
uranyl group (OU2) prevents further condensation with ad-
ditional copper cations to form infinite chains, as was ob-
served in compounds 1 and 2. The “U2Cu” blocks are then
linked to each other through the mellitate molecules, which
exhibit a quite-complex multidentate connection mode with
the different cations. Indeed, two of the carboxylate arms
(positions 1,4) act as a bidentate linkage in bridging two
uranyl centers from two distinct trimers. Two other carboxy-
late arms (positions 2,5) also adopt a bidentate connection
fashion, but bridge one uranyl center and one copper
center. The last two carboxylate arms (positions 3,6) are
monodentate with respect to the uranyl centers and there
ACHTGNUERTN(NUGN UO2)2O(OH)2CuACHTUNREGTGNN(UN H2O)2ACHTGUNTREN(NUGN 1,3-bdc)·H2O (4): The structure of
compound 4 exhibits a distinct type of connection mode of
the uranyl groups with the copper cations. The asymmetric
building unit consists of two inequivalent crystallographic
uranyl centers (U1 and U2), in a tetranuclear motif, that are
linked to two copper atoms (Figure 7). The uranium atoms
À
remains one terminal C=O bond (C6 O6B 1.224(4) ꢀ).
Therefore, the mellitate is an octadentate linker toward the
2+
UO2 and Cu2+ cations, which generates a rather dense 3D
network, without any voids (Figure 6).
Figure 7. Representation of the building unit in (UO2)2O(OH)2Cu
ACHTUNGTRENNUNG(H2O)2-
AHCTUNGTRENNUNG
enfold-coordinated uranyl centers with two divalent copper cations.
are sevenfold-coordinated and describe a classical pentago-
nal bipyramidal geometry, with uranyl distances (U=O) in
the range 1.764(4)–1.805(3) ꢀ. For U1, the five oxygen
atoms in the pentagonal plane correspond to one carboxy
À
À
oxygen atom (U1 O5B 2.398(3) ꢀ), two oxo groups (U1
À
O2 2.244(3)–2.284(3) ꢀ), and two hydroxo groups (U1 O
2.448(3)–2.571(3) ꢀ). For U2, the five oxygen atoms are
À
comprised of three carboxy oxygen atoms (U2 O 2.358(3)–
À
2.525(3) ꢀ), one oxo group (U2 O2 2.225(3) ꢀ), and one
À
hydroxo group (U2 O1 2.363(3) ꢀ). The uranyl cations are
exclusively connected to each other through an edge-sharing
mode, thereby generating a tetrameric motif, which has pre-
viously been encountered many times in several types of
uranyl carboxylates.[11] Copper cations are also linked
through edge-sharing with the uranyl groups to two hydroxo
À
À
groups (Cu O1 1.977(3) ꢀ and Cu O3 1.912(3) ꢀ). Two
other oxygen atoms are located in a square plane and corre-
À
spond to terminal aquo species (Cu1 O4 2.002(3) ꢀ and
À
Cu O5 1.990(3) ꢀ). As expected for divalent copper cation,
À
two long Cu O bonds are observed for the apical oxo
groups; however, in compound 4, they are found in an asym-
Figure 6. Views of the structure of (UO2)2CuACHTNUGRTENNUG(H2O)4ACHTUNTGRNE(NUGN mel) (3), which show
the arrangement of the trinuclear building blocks in the bc plane (top)
and the ab plane (bottom).
metric manner. One of these bonds is rather short, with a
2016
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Chem. Eur. J. 2013, 19, 2012 – 2022

Heterometallic Uranyl Copper(II) Carboxylates
FULL PAPER
À
Cu OU1B distance of 2.350(3) ꢀ, whereas the second bond
À
(Cu OU2A) is quite long (2.692(4) ꢀ). This particular con-
À
trast in Cu O distances results in either a square-pyramidal
geometry for the copper center or in a distorted octahedral
À
geometry if the long Cu O distance is considered. As previ-
À
ously observed in other mixed uranyl copper phases (1–3),
the apical oxygen atoms belong to the uranyl bonds (U=O).
À
However, in compound 4, the quite-short Cu O distance
(2.350(3) ꢀ) induces a slight lengthening of the U=O bond,
with a U1=OU1B distance of 1.805(3) ꢀ. In comparison, the
neighboring U=O bond length is 1.783(3) ꢀ for U1 and the
U=O bond lengths are 1.764(4) and 1.786(3) ꢀ for U2. Con-
sidering the average distance of 1.778 ꢀ for the U=O bonds,
À
which is not affected by the U=O Cu bond, the shift in dis-
tance for the second U=O bond is +0.027 ꢀ. Within the
“U4Cu2” brick, two of the oxygen atoms, which bridge the
uranyl atom, are oxo groups (bond valence for O2: 2.042[10]
)
and are shared between three uranium atoms (m3). Two
other groups, which bridge two uranium atoms and one
copper atom (m3), are hydroxo groups (bond valence for O1:
1.362[8,10]). The last two oxygen atoms, which bridge one ura-
nium atom and copper atom (m2), are also hydroxo groups
(bond valence for O1: 0.998[8,10]). For the terminal oxygen
atoms that are bonded to copper atoms, bond-valence calcu-
lations[8] gave values of 0.431 for O5 and 0.418 for O4. The
“U4Cu2” building units are linked to each other through the
isophthalate ligands, with one chelating connection type for
one carboxylate arm and a bidentate bridging connection
type for the second carboxylate arm, with only uranyl cen-
ters. This type of connection generates infinite ribbons
Figure 8. Top: view of the connection mode of the heterometallic
“U4Cu2” building blocks through the isophthalate moiety, thereby gener-
ating infinite ribbons in (UO2)2O(OH)2Cu
ACHUTGTNRNE(NUG H2O)2ACHTUNGTREN(NUGN 1,3-bdc)·H2O (4).
Middle: connection of the [U4Cu2-1,3-bdc] ribbons with copper cations
À
À
À
through uranyl oxo bonds (U=O Cu, with C O=2.350(3) ꢀ). Bottom:
À
3D cohesion of the structures that are connected through long U=O Cu
linkages (2.692(4) ꢀ).
À
À
(Figure 8), which are then linked through uranyl oxo
À
copper bonds (U1=O Cu), which involve the short apical
À
Cu O bonds to create layers (Figure 8). The 3D character
of the structure is ensured by the connection of the remain-
ing free second apical oxo group (OU2A) to a copper
center, which has weak interactions with the uranyl U2 cat-
ACHTUNGTRENNUNGions (Figure 8). Free water molecules are intercalated be-
tween the layers and show preferential hydrogen-bonding
interactions with the m2-hydroxo group (OW1···O3
2.941(9) ꢀ) and carboxy oxygen atoms (OW1···O1B
2.817(8) ꢀ).
In situ thermal studies of the dehydration of (UO2)Cu-
ACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(btec)·4H2O (2): The dehydration of hydrated com-
pound 2 was characterized by in situ X-ray diffraction (up
to 8008C) and by IR spectroscopy (up to 2108C) as a func-
tion of temperature. We focused our attention on character-
izing the thermal behavior of this specific phase because its
structure possesses an open-framework with 1D channels
that encapsulate free water molecules.
The thermodiffractogram of phase 2 (Figure 9) indicated
the rapid disappearance of its Bragg peaks when heated to
1008C. These peaks showed a progressive thermal transfor-
mation into a new set of Bragg peaks, which were visible up
to 3608C. Then, phase 2 transformed into an amorphous
phase and a recrystallization process was observed from
5008C, with the formation of CuU3O10 (PDF number: 44-
Figure 9. X-ray thermodiffractograms of (UO2)Cu
in air (CuKa radiation).
ACHUTGTNRNE(NUG H2O)2ACHUTNGTREN(NUGN btec)·4H2O (2)
0979), followed by the formation of CuUO4 (PDF number:
24-038) from 6208C. The powder XRD pattern of the solid
that crystallized between 100 and 3608C can be indexed in a
triclinic cell (a=5.0092, b=6.9847, c=8.5309 ꢀ; a=97.286,
b=106.280, g=92.0418; V=283.40 ꢀ3), with a good figure
of merit M20 =51 (by using the DICVOL06[12] program).
These cell parameters were drastically different to those of
the as-synthesized solid 2 (Table 2). From the TGA observa-
Chem. Eur. J. 2013, 19, 2012 – 2022
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T. Loiseau et al.
Table 2. Crystal data and structure refinement for mixed uranyl copper carboxylates.
1
2
2’
3
4
formula
formula weight
T [K]
C16H8CuO12U
693.8
296(2)
C10H14CuO16U
691.78
293(2)
C10H2CuO10U
583.7
293(2)
C12H8CuO20U2
1011.8
293(2)
C8H12CuO14U2
871.78
293(2)
crystal type
crystal size [mm]
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
a [8]
b [8]
green block
0.53ꢄ0.51ꢄ0.40
triclinic
green block
0.07ꢄ0.05ꢄ0.03
triclinic
blue–green block
0.05ꢄ0.02ꢄ0.02
triclinic
green needle
0.31ꢄ0.14ꢄ0.13
monoclinic
P21/c
7.9835(2)
11.5456(2)
10.9719(2)
90
105.350(1)
90
975.25(3)
2, 3.445
green block
0.21ꢄ0.07ꢄ0.05
triclinic
¯
¯
¯
¯
P1
P1
P1
P1
6.9898(5)
7.0913(5)
10.0712(11)
100.537(4)
96.433(4)
114.224(3)
437.71(6)
1, 2.658
7.1070(2)
7.2234(2)
9.2050(2)
95.377(1)
91.256(1)
114.893(1)
425.78(2)
1, 2.698
4.9959(3)
6.9710(4)
8.5143(5)
97.310(3)
106.420(3)
91.960(4)
281.35(3)
1, 3.439
8.5643(1)
8.7504(1)
12.4227(2)
84.916(1)
77.175(1)
61.926(1)
800.80(2)
2, 3.590
g [8]
V [ꢀ3]
Z, 1calcd [gcmÀ3
]
m [mmÀ1
q range [8]
]
10.526
10.833
16.322
17.754
21.56
2.10-29.99
À9ꢀhꢀ9
À9ꢀkꢀ9
À14ꢀlꢀ14
11275
2.23-36.67
À11ꢀhꢀ11
À12ꢀkꢀ12
À16ꢀlꢀ16
19546
2.95-36.36
À8ꢀhꢀ8
À11ꢀkꢀ11
À13ꢀlꢀ14
10041
2.65–30.56
À11ꢀhꢀ11
À16ꢀkꢀ16
À15ꢀlꢀ15
23419
1.68–36.41
À14ꢀhꢀ14
À14ꢀkꢀ14
À20ꢀlꢀ20
37605
limiting indices
total reflns
unique reflns
parameters
2547 [R
139
1.136
(int)=0.0435]
4209 [R
125
1.0176
(int)=0.0215]
2734 [R
103
0.956
E
2988 [R
160
1.110
(int)=0.0340]
7809 [R
221
1.186
ACHTUNGTREN(NUNG int)=0.0462]
GOF on F2
final R indices [I>2s(I)]
R1=0.0278
wR2=0.0713
R1=0.0289
wR2=0.0789
2.467/À4.931
R1=0.0176
wR2=0.0421
R1=0.0176
wR2=0.0422
1.745/À0.950
R1=0.0267
wR2=0.0497
R1=0.0278
wR2=0.0502
1.606/À2.648
R1=0.0185
wR2=0.0491
R1=0.0193
wR2=0.0495
1.837/À1.907
R1=0.0239
wR2=0.0571
R1=0.0325
wR2=0.0718
3.136/À3.695
R indices (all data)
largest diff. peak/hole [eꢀÀ3
]
tions, this new crystallized phase (denoted 2’) could be as-
signed to the dehydrated form of phase 2, with the chemical
formula (UO2)CuACHTUNGTRENNUNG(btec). To obtain single crystals of the de-
hydrated phase 2’, we attempted to synthesize it at higher
temperatures from the mixture of reactants that was used
for the formation of compound 2. After hydrothermal treat-
ment at 2008C, a new compound was successfully isolated
with single crystals that were suitable for XRD structure de-
termination. Indeed, the cell parameters of the sample that
was prepared hydrothermally at 2008C were similar to those
that were obtained by the dehydration of phase 2.
Figure 10. Representation of the asymmetric unit in (UO2)CuACHTUNGTRENNUNG(btec) (2’).
The copper environment is indicated by a square plane and the uranyl
environment us indicated by a hexagonal bipyramid.
The crystal structure of (UO2)CuACTHUNTGRNEUNG(btec) (2’) reveals a new
type of connection mode between the uranyl and copper
cations, which reflects a structural transition that involved
À À
water elimination, together with the formation of Cu O U
through a second carboxylate arm, thereby adopting a bi-
dentate bridging mode. This mode results in the formation
of infinite chains of alternating uranyl and copper cations
along the [110] direction. These chains are then connected
to each other through the carboxylate arms of the pyromel-
litate ligands to form a 3D network (Figure 11).
In fact, the structure of phase 2’ is closely related to that
of its hydrated form (2) and only differs in the water-mole-
cule content. In the hydrated phase (2), water species are
present within 1D tunnels, as well as coordinated ligands
that are attached to the copper atoms. Upon heating, the
water molecules are removed, which modifies the local coor-
dination environment around the copper cations. A new
bonds, during the dehydration of compound 2. The structure
is composed of an asymmetric unit that contains one eight-
fold-coordinated uranyl center and one copper cation with a
À
surrounding square plane (Figure 10). The uranium oxygen
distances are 1.754(2) ꢀ for the two uranyl bonds and range
from 2.360(2) to 2.622(2) ꢀ for the other bonds in the hex-
agonal plane of the uranyl-centered polyhedron. The copper
atom is coordinated to four oxygen atoms in a square plane,
À
with two sets of Cu O distances of 1.922(2) (O1B) and
1.969(2) ꢀ (O4A). Apical oxygen atoms that lead to an
elongated octahedral geometry could be considered around
the divalent cation, but are located quite far (2.745(5) ꢀ)
from the copper centers. The uranyl atom is linked to the
copper center through one carboxy oxygen atom (O4A) and
À
type of copper oxygen bond is formed to satisfy the square-
planar coordination around the copper atom and a possible
2018
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Heterometallic Uranyl Copper(II) Carboxylates
FULL PAPER
Figure 12. Top: detailed view of the structural relationship that reflects
the possible transition pathway from
a
hydrated ribbon fragment,
[(UO2)Cu (btec)], in compound 2 into the dehydrated ribbon,
[(UO2)CuCAHTUNGTENR(NUNG btec)], in compound 2’. Black arrows indicate the formation of
ACHUTGTNREN(NUG H2O)2ACHTNUGTRENNNUG
m3-oxo bonds, in which the carboxy oxygen atoms are linked to the
uranyl cations, owing to the elimination of coordinated water molecules
upon heating. Bottom: representation of the structural transition that is
involved in the dehydration of phase 2 into anhydrous phase 2’ and the
irreversible shrinkage of the framework.
phase 2 was confirmed by IR spectroscopy, which showed a
very broad absorption band within the range 3650–
2500 cmÀ1, which corresponded to the stretching vibrations
of water (see the Supporting Information, S7). We observed
the asymmetric stretch (nasym(OH)) at 3530 cmÀ1, as well as
the symmetric stretch (nsym(OH)) at 3386 cmÀ1; the broad
band that was centered at 2500 cmÀ1 is typical of intermolec-
ular hydrogen-bonding interactions. Furthermore, the peak
at 1651 cmÀ1 was attributed to the deformation d
ACTHNUTRGNEUGN(H2O). The
IR spectrum of the parent structure of compound 1, which
only possessed terminal bonded water molecules, did not
show any sharp band at around 3500 cmÀ1 (only a broad
signal was visible in the range 3000–3500 cmÀ1, for bonded
water). Therefore, the resonance at 3530 cmÀ1 for compound
2 can be easily assigned to free water species that are trap-
ped within the structure channels. The sharpness of this
band confirms the relative confinement of these molecules.
Between 1600 and 1140 cmÀ1, the IR spectrum displayed
very intense bands, owing to the carboxylate groups and
phenyl-ring deformations, which could not be precisely de-
termined. Among the numerous bands that characterize
metal–oxygen vibrations at lower wavenumbers, we assigned
Figure 11. Views of the structure of (UO2)Cu
planes.
ACHTUNGERTN(NUNG btec) (2’) in the ac and bc
transition pathway can be proposed regarding the relation-
ship between the two structures (2 and 2’). This pathway in-
volves the shift of some carboxy oxygen atoms in equatorial
À
U O bonds toward the copper centers (Figure 12), which in-
duces a rotation of 458 of the equatorial plane of the uranyl-
centered bipyramids with respect to the plane of the ben-
zene rings of the tetracarboxylate molecules. Thus, a new
square-planar environment is obtained at the copper center
À
from this topotactic transition and longer Cu Oapical distan-
ces are observed (2.745(5) ꢀ in phase 2’ instead of
2.437(1) ꢀ in 2). This result implies the irreversible shrink-
age of the network channels, without any modification of
the uranyl environment. The cell volume is reduced to 34%
compared to that of phase 2 and this structural transforma-
tion prevents any re-adsorption of water molecules from, for
instance, the ambient atmosphere. Such a thermal solid-state
transition has only scarcely been reported in other metal–or-
ganic-framework-type metal carboxylates, which showed
network flexibility upon dehydration.[13]
the peaks at 904 cmÀ1 and 874 cmÀ1 to nasym
nsym(U=O), respectively. Indeed, the calculated uranyl bond
length, from asymmetric vibration by using the empirical re-
lationship defined by Bartlett and Cooney,[14] (d
calcdA(U=O)
1.781 ꢀ) is in good agreement with that found in the XRD
data (dobsA(U=O) 1.776(1) ꢀ).
ACHTUNGTRENN(UNG U=O) and
AHCTUNGTRENNUNG
CHTUNGTRENNUNG
CTHUNGTRENNUNG
Upon heating, we analyzed the evolution of the vibration
bands that were related to the water molecules and to the
uranyl bonds because they appeared to be the most relevant
for examining the thermal dehydration of compound 2 and
its in situ transformation into compound 2’ (Figure 13). Up
This structural transition was also followed by in situ IR
spectroscopy. At room temperature, the hydration state of
Chem. Eur. J. 2013, 19, 2012 – 2022
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T. Loiseau et al.
was observed between them, that is, the occurrence of heter-
ometallic bridging oxo groups between the uranyl and
copper atoms. The copper cations are typically surrounded
À
by four oxo groups that are located in a square plane (Cu
O=1.90–2.00 ꢀ) whilst the two remaining oxo groups occupy
À
the apical positions, with quite long Cu Oapical distances,
thus resulting in an elongated octahedral polyhedron. For
compounds 1–4, the apical oxygen atoms also bridge the
uranium centers through short U=O bonds, which corre-
À
À
spond to a U=O Cu-type linkage. The relatively long Cu
Oapical distances, which range from 2.350(3) to 2.745(5) ꢀ
(Table 1), are in agreement with those previously found in
other mixed uranyl copper carboxylates and do not strongly
À
affect the U O distances. The uranyl bond lengths were
within the expected range but we did observe that a short-
À
ening of the Cu Oapical distance (2.350(3) ꢀ in compound 4)
induced
a
slight lengthening of the U=O distance
À
(1.805(3) ꢀ). In contrast, the longer Cu Oapical bond in the
anhydrous form (2’) is quite long (2.745(5) ꢀ) and the corre-
sponding U=O bond is rather short (1.754(2) ꢀ). These dif-
ferent examples illustrate the amplitude of the elongated
À
Figure 13. Evolution of the in situ IR spectra as a function of tempera-
ture, which represents the structural transition of compound 2 into com-
pound 2’, between 22–2108C in the range 3600–3200 cmÀ1 (top) and 960–
830 cmÀ1 (bottom), with an interval of 4.58C between two consecutive
spectra. Absorbance is represented in arbitrary units on the right-hand
side.
apical Cu O bond (about 0.4 ꢀ), thus reflecting a relative
À
structural flexibility of this U=O Cu interaction, which is
À
À
adopted in the different uranyl copper organic assemblies.
The uranyl bond length is not affected so much by the
neighboring copper cation, except in the case of shorter
À
Cu Oapical distances.
The second aspect of this study concerned the possibility
of designing different structural arrangements from a given
building motif and their solid-state structural transforma-
tions upon heating. In our study, 3D open-framework 2 is
formed from a 2D network (1) by increasing the number of
carboxylate connectors on going from phthalate groups (1,2-
benzenedicarboxylate) to pyromellitate groups (1,2,4,5-ben-
zenetetracarboxylate). The topological arrangement of the
to 1008C, we observed a significant decrease in intensity
and the disappearance of the bands that were assigned to
water. Unfortunately, this process did not show any differen-
tiation between the water molecules that were linked to the
copper centers and those that were trapped within the tun-
nels. This phenomenon is in perfect agreement with the
TGA results, which did not show any specific weight-loss
events owing to the successive evacuation of free and
bonded water molecules. By analogy with the departure of
water, the rearrangement of the uranium environment is
À
À
structural “uranyl copper carboxylate” entity is identical
for compounds 1 and 2, but, in one case, a layered com-
pound is obtained (1) whereas, in the second case, it is a 3D
framework (2). This potentially porous structure encapsu-
lates the water species within its channels, which could be
removed upon heating. In situ thermodiffraction and IR
spectroscopy showed that the water molecules that were co-
ordinated to copper centers followed the same process and
no distinct step of evacuation of such bonded water species
was visible. Heating resulted in a topotactic transformation
into a new crystalline anhydrous structure (2’), in which the
eightfold-coordinated uranyl environment was identical, but
the equatorial hexagonal plane was shifted to satisfy the
square-planar coordination of copper, with the formation of
highlighted by the continuous shift of the nasym
ACHTUNGTRENN(UNG U=O) and
nsym
ACHTUNGTRENNUNG
respectively, thus indicating a shortening of the uranyl bond
during the topotactic transition (U=O 1.754(2) ꢀ).
Conclusion
This study showed the association of uranyl cations with di-
valent copper cations in combination with aromatic polycar-
boxylate linkers. After a hydrothermal reaction in aqueous
solvent, five distinct heterometallic coordination compounds
were isolated with phthalate (1), pyromellitate (2, 2’), melli-
tate (3), and isophthalate ligands (4). A diverse range of in-
organic building blocks have been structurally identified as
discrete trinuclear units, “UCu2”, hexanuclear units,
“U4Cu2”, or infinite chains of alternating uranyl and copper
centers. Despite the observed structural diversity in this
series of organic–inorganic assemblies, a common feature
À À
a new set of U O Cu linkages from a m3-oxo bridge (be-
longing to a carboxylate arm). The dehydration transition
implied the irreversible shrinkage of the structure and pre-
vented any rehydration process. This thermal transformation
gave another illustration of the flexibility of the weak
À
À
Cu Oapical bond that was involved in U=O Cu bonding,
which seemed to favor such structural transitions.
2020
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Heterometallic Uranyl Copper(II) Carboxylates
FULL PAPER
were collected on a Bruker X8-APEX2 CCD area-detector diffractome-
ter by using MoKa radiation (l=0.71073 ꢀ) with optical fiber as a colli-
mator. Several sets of narrow data frames (20 s per frame) were collected
at different values of q for two initial values of f and w, respectively, by
using 0.38 increments of f or w. Data reduction was accomplished by
using SAINT V7.53a.[15] The substantial redundancy in data allowed a
semi-empirical absorption correction (SADABS V2.10)[16] to be applied,
on the basis of multiple measurements of equivalent reflections. The
structures were solved by using direct methods, which were developed by
successive difference Fourier syntheses, and were refined by full-matrix
least-squares on all F2 data by using the SHELX[17] program suite with
the WINGX[18] interface. Hydrogen atoms on the benzene rings were in-
cluded at calculated positions and were allowed to ride on their parent
atoms. However, the hydrogen atoms on the aquo or hydroxo groups
were not located and not included in the calculations. The final refine-
ments included anisotropic thermal parameters of all non-hydrogen
atoms. The crystal data are given in Table 2. CCDC-906140 (1), CCDC-
906141 (2), CCDC-906142 (2’), CCDC-906143 (3), CCDC-906144 (4)
contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallograph-
ic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Experimental Section
Synthesis: Caution! Uranyl nitrate UO2ACHTNUTRGEN(UNG NO3)2·6H2O is a radioactive and
chemically toxic reactant and precautions, with suitable care and protec-
tion for handling such substances, should be followed.
The compounds described herein were synthesized hydrothermally under
autogenous pressure by using Teflon-lined Parr-type autoclaves from a
mixture of uranyl nitrate hexahydrate (UO2ACHTNUTRGNEU(NG NO3)2·6H2O, Merck, 99%),
powdered copper metal (Aldrich, ꢁ99.5%), phthalic acid (1,2-benzenedi-
carboxylic acid or 1,2-H2bdc, Acros Organics, 99%), pyromellitic acid
(1,2,4,5-benzenetetracarboxylic acid or H4btec, Aldrich, 96%), mellitic
acid (1,2,3,4,5,6-benzenehexacarboxylic acid or H6mel, Aldrich, 99%),
isophthalic acid (1,3-benzenedicarboxylic acid or 1,3-H2bdc, Aldrich,
99%) ,and deionized water. The starting chemical reactants were com-
mercially available and were used without any further purification.
ACHTUNGTRENNUNG(UO2)CuACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(1,2-bdc)2 (1): A mixture of UO2ACTHNGUTREN(UNNG NO3)2·6H2O (250 mg,
0.5 mmol), copper metal (31 mg, 0.5 mmol), phthalic acid (100 mg,
0.6 mmol), and water (5 mL, 277 mmol) was placed in a Parr bomb and
then heated statically at 1508C for 24 h. The pH value of the solution
was 1 at the end of the reaction. The resulting green product was then fil-
tered off, washed with water, and dried at RT. Compound 1 was analyzed
by SEM (Hitachi S-3400N) and showed typical large truncated parallele-
piped-like crystals of size 100–800 mm (see the Supporting Information,
S1).
Thermogravimetric analysis: The thermogravimetric experiments were
carried out on a TGA 92 SETARAM thermoanalyzer in air with a heat-
ing rate of 58CminÀ1 from RT up to 8008C. X-ray thermodiffractometry
was performed under a flow of air (rate: 5 LhÀ1) in an Anton Paar
À
HTK1200N of a D8 Advance Bruker diffractometer (q q mode, CuKa ra-
(UO2)Cu
(H2O)
E
A
mixture of UO2ACHTGUNTERNNU(G NO3)2·6H2O
diation) that was equipped with a Vantec1 linear position-sensitive detec-
tor (PSD). Each powder pattern was recorded in the range 2q=5–608 (at
intervals of 208C up to 8008C) with a 0.5 s/step scan, which corresponded
to an approximate duration of 30 min. The temperature ramp rate be-
tween the two patterns were 0.088CsÀ1 up to 8008C.
(250 mg, 0.5 mmol), copper metal (31 mg, 0.5 mmol), pyromellitic acid
(150 mg, 0.59 mmol), and water (5 mL, 277 mmol) was placed in a Parr
bomb and then heated statically at 1508C for 24 h. The pH value of the
solution was 1 at the end of the reaction. The resulting green product
was then filtered off, washed with water, and dried at RT. Compound 2
was analyzed by SEM and showed typical elongated crystals of size 20–
50 mm (see the Supporting Information, S1).
Infrared spectroscopy: IR spectra of compounds 1 and 2 were measured
on a Perkin–Elmer Spectrum Two spectrometer that was equipped with a
diamond attenuated total reflectance (ATR) accessory between 4000 and
400 cmÀ1 (see the Supporting Information). Dehydration of compound 2
was characterized by in situ IR spectroscopy in air with a heating rate of
108CminÀ1 from RT up to 2108C. During this period, 195 spectra were
recorded in the range 4000–400 cmÀ1, with a resolution of 4 cmÀ1, on a
Perkin–Elmer Spectrum Two spectrometer that was equipped with a Pike
Special-IR GladiATR accessory.
R
CTHUNGTRENNUNG
(250 mg, 0.5 mmol), copper metal (31 mg, 0.5 mmol), pyromellitic acid
(150 mg, 0.59 mmol), and water (5 mL, 277 mmol), which was placed in a
Parr bomb and then heated statically at 2008C for 24 h. The pH value of
the solution was 1 at the end of the reaction. The resulting blue–green
product was then filtered off, washed with water, and dried at RT. Com-
pound 2’ was analyzed by SEM and showed typical elongated crystals of
size 20–50 mm (see the Supporting Information, S1).
ACHTUNGTRENNUNG(UO2)2CuACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(mel) (3): A mixture of UO2ACHUTNTGREGN(NNU NO3)2·6H2O (180 mg,
0.36 mmol), copper metal (20 mg, 0.3 mmol), mellitic acid (80 mg,
0.23 mmol), and water (5 mL, 277 mmol) was placed in a Parr bomb and
then heated statically at 1508C for 24 h. The resulting green product was
then filtered off, washed with water, and dried at RT. However, optical
microscopy clearly showed the presence of different colored phases
(yellow and green). Green crystals, which corresponded to phase 3, were
selected for X-ray diffraction analysis. Different attempts (by changing
the concentrations of the starting reactants, reaction time, or tempera-
ture) were made to isolate and obtain the pure phase (3), but were un-
successful.
Acknowledgements
The authors thank the GNR MATINEX of PACEN interdisciplinary pro-
gram for financial support. We also thank Prof. Francis Abraham for his
helpful discussions and Mrs. Nora Djelal and Laurence Burylo for their
assistance with the SEM images, powder XRD patterns, and TG meas-
urements (UCCS). The Fonds Europꢁen de Dꢁveloppement Rꢁgional
(FEDER), the CNRS, the Rꢁgion Nord Pas-de-Calais, and the Ministꢅre
de l’Education Nationale de l’Enseignement Supꢁrieur et de la Recher-
che are acknowledged for funding the X-ray diffractometers. C.F. ac-
knowledges Universitꢁ Lille 1 and Rꢁgion Nord Pas-de-Calais for a PhD
grant.
A
N
(1,3-bdc)·H2O (4):
A
mixture of UO2-
ACHTUNGTRENNUNG
phthalic acid (100 mg, 0.6 mmol), and water (5 mL, 277 mmol) was
placed in a Parr bomb and then heated statically at 1708C for 24 h. The
resulting product was then filtered off, washed with water, and dried at
RT. However, optical microscopy clearly showed the presence of differ-
ent colored phases (yellow, green, or unreacted copper powder). Green
crystals, which corresponded to phase 4, were selected for X-ray diffrac-
tion analysis. Different attempts (by changing the concentrations of the
starting reactants, reaction time, or temperature) were made to isolate
and obtain the pure phase (4), but were unsuccessful.
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Received: October 19, 2012
Published online: December 23, 2012
2022
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Chem. Eur. J. 2013, 19, 2012 – 2022