An illustration of the limit of the metal organic framework's isoreticular principle using a semirigid tritopic linker obtained by "click" chemistry

Article abstract of DOI:10.1021/ja0744091

A new nitrogen-rich tricarboxylate linker was prepared by "click" chemistry and used for the preparation of a lanthanum-based open metal organic framework. This latter is built of inorganic 1-D rods connected through the tritopic linkers and illustrates o

Full text of DOI:10.1021/ja0744091

Published on Web 10/03/2007
An Illustration of the Limit of the Metal Organic Framework’s Isoreticular
Principle Using a Semirigid Tritopic Linker Obtained by “Click” Chemistry
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Thomas Devic,* Olivier David,* Marion Valls, Jerome Marrot, Franc¸ois Couty, and Gerard Ferey*
Institut LaVoisier, CNRS UMR 8180, UniVersite´ de Versailles, Saint-Quentin-en-YVelines, 45 aVenue des Etats-Unis,
78035 Versailles cedex, France
Received June 18, 2007; E-mail: devic@chimie.uvsq.fr
The search for very large pores1 in metal organic frameworks
(MOFs) is currently topical,2 due to the unprecedented properties
they generate in adsorption and now in drug delivery.3 The
isoreticular principle4 is one way to tune the size of the pores by
acting on the length of the rigid linker, keeping constant the
inorganic part. It was applied on a few series based either on
molecular4-7 or 1-D8,9 inorganic parts. We recently prepared a
porous MOF (denoted MIL-103, MIL ) Materials Institut Lavoisi-
er) based on an extended tritopic linker (1,3,5-benzenetrisbenzoate)
and lanthanide chains.10 In order to see the effect of the addition
of nitrogen lone pairs and small flexible endings at the periphery
of the rigid core on the sorption properties of this structure type,11
we prepared a new trigonal nitrogen-rich linker12 including 1,2,3-
triazole rings, which was obtained by a triple Huisgen 1,3-dipolar
cycloaddition. This reaction was described as a case example of
“click” chemistry13 and is currently widely used in various fields
Figure 1. View of MIL-112 along the c-axis, showing the two types of
channels, both containing free water molecules. On the left side, successive
layers of linkers are colored in green and orange.
Scheme 1. Synthesis of LH3
of chemistry,14 ranging from bio-related applications to material
science or coordination chemistry. The key features of this reaction
(high yield, reasonably easy scale-up, etc.) prompted us to use it
for the synthesis of new nitrogen-rich linkers on the multigram scale,
a prerequisite to further potential applications of the related MOFs.
This paper describes the synthesis of a new nitrogen-rich tricar-
boxylate linker obtained by “click” chemistry, the preparation, and
characterization of an open metal organic framework (hereafter
The parallel rods act as scaffolds for both 3-D structures.18 In
terms of projected 2-D net, the highly porous MIL-103 is hexagonal
63 with a perfect AAA stacking of the layers, the linker having a
strict C3-symmetry; MIL-112 corresponds to a 44 net despite the
tritopic character of the linkers. Both the pentagonal triazole rings
and the flexibility of the methylene groups are responsible of the
difference. The linkers are T-shaped, with different orientations,
and the ABA staggered stacking defines in each layer four- (square)
and eight-membered (rectangle) rings, thus preventing the formation
of large pores (Figure 2).
This example illustrates that, in rod-based MOFs,9 even if the
core of the ligand remains rigid, the introduction of some flexibility
on the shell drastically changes the structure. Therefore, the
isoreticular principle here no longer applies and remains valid only
for strictly rigid ligands which impose strong geometric constraints
to the structure, as already pointed out by Chae et al. in the case of
trigonal linkers and molecular inorganic SBUs.19 The free rotation
of the carboxylate function around the methylene group does not
force a strict C3-symmetry and allows other configurations,
governed by lattice energy minima, to happen.
denoted MIL-112) using this linker.
{4-[3,5-Bis-(1-carbonylmethyl-1H-[1,2,3]triazol-4-yl)-phenyl]-
[1,2,3]triazol-1-yl}acetic acid (later denoted LH3) was obtained in
two steps starting from 1,3,5-triethynylbenzene15 and azidoglycine
ethylester16 on the 10 g scale, using the standard “click” conditions13b
(Scheme 1 and Supporting Information for details).
Using reaction conditions identical to those of MIL-103,10
a
crystalline phase appeared with light lanthanides (Ln ) La-Nd).
Optimized conditions led to pure powders and to single crystals
suitable for X-ray diffraction (see Supporting Information).
MIL-112 is formulated La(L)(H2O)2‚6H2O from X-ray17 and
chemical analyses. The 10-folded LaIII ions (eight carboxylate
oxygen atoms and two terminal H2O) connect to each other through
bridging µ2-oxygen atom to define rods of edge-sharing [LaO10]
polyhedra running along the c-axis. Each tritopic linker L3- is
bonded to three inorganic chains, defining two types of small
channels developing along the c direction, both filled with free water
molecules (Figure 1).
MIL-103 and -112 have close formulations Ln(L)(H2O)x‚(solv)y
(x ) 1, solv ) H2O (MIL-103) and x ) 2, solv ) C6H11OH (MIL-
112)), and both structures are built up from chains of edge-sharing
[LnO9/10] polyhedra, owing to similar experimental conditions. The
only difference concerns the coordination modes of the carboxylate
groups (two chelating bridging and one bridging groups in MIL-
103 and two chelating bridging and one chelating carboxylate
groups in MIL-112).
By heating under dioxygen, MIL-112 shows two weight losses
at low temperature (15 and 20% (experimental as calculated) at 50
and 160 °C, respectively; see Figure 3). They correspond to the
evacuation of the water molecules of the tunnels and further to the
formation of the fully dehydrated Ln(L). The structure collapses
at 300 °C to finally yield La2O3 at higher temperature.
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J. AM. CHEM. SOC. 2007, 129, 12614-12615
10.1021/ja0744091 CCC: $37.00 © 2007 American Chemical Society

C O M M U N I C A T I O N S
helpful comments, and P. Llewellyn and S. Bourrelly for the CO2
sorption experiments. This work was granted by the EU through
the FP6-STREP “DeSANNS” (SES6-020133).
Supporting Information Available: Full synthetic method, char-
acterizations, and the cif file for (La(L)(H2O)2‚6H2O) are available.
This material is available free of charge via the Internet at http://
pubs.acs.org.
References
Figure 2. Comparison of the network topologies in MIL-103 (left) and
MIL-112 (right). In black: lanthanide chains. Three successive layers of
linkers (in blue, red, and green, respectively) are pictured. Square and
rectangle rings in MIL-112 are highlighted in yellow and light blue,
respectively.
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Figure 3. Thermal behavior of MIL-112. Thermodiffractogram performed
under air between 20 and 400 °C. In black: La(L)(H2O)2‚6H2O; red: La-
(L)(H2O)2; blue: La(L); green: amorphous. Inset: Thermogravimetric
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(17) Single crystal data for La[C18H12N9O6][H2O]2‚6(H2O): monoclinic, space
group P21/c (No. 14), a ) 12.401(3) Å, b ) 24.897(5) Å, c ) 8.779(2)
Å, â ) 92.27(3)°, V ) 2708.5(9) A3, Z ) 4, Dcalcd ) 1.799 g‚cm-3, T )
250 K, R1 ) 0.0815, wR2 ) 0.1284 for all data; R1 ) 0.0442, wR2 )
0.1006 for 5327 observed data (I > 2σ(I)) with 0 restraints and 379
parameters. Powder data for La[C18H12N9O6][H2O]2: monoclinic, space
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Å, â ) 97.987(4)°, V ) 2267.0 A3.
As shown by X-ray thermodiffractometry (Figure 3), the title
solid Ln(L)(H2O)2‚6H2O phase is stable up to 50 °C. Above, Ln-
(L)(H2O)2 appears. Its X-ray pattern is new and almost invariant
until 170 °C. Its indexation proves that its cell parameters are close
to those of MIL-11217 except for the b-axis which contracts by
15%.
The N2 adsorption isotherms were performed at 77 K on MIL-
112 for La(L)(H2O)2 and La(L) after vacuum activation at 25 and
150 °C. Whatever the conditions, almost no microporosity relative
to nitrogen was observed (BET surfaces are 20 and 28 m2‚g-1).
This might relate to the contraction, induced by the linker intrinsic
flexibility, which prevents the achievement of any permanent
porosity. Rehydration is slowly reversible (see Supporting Informa-
tion), but attempts to re-open the network upon gas pressure (CO2,
P ) 11 bar) were unsuccessful.
To conclude, MIL-112, which contains a new tritopic “click”
carboxylate linker, illustrates the limits of the isoreticular principle
when some flexibility is introduced, even when infinite 1-D
inorganic SBUs are used. This flexibility prevents the formation
of a network isotypic with the porous MIL-103.
(18) O’Keeffe, M.; Andersson, S. Acta Crystallogr. 1977, A33, 914-923.
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Acknowledgment. T.D. thanks B.X. Colasson for seminal
discussions on “click” chemistry, C. Serre and N. Guillou for their
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