Synthesis and catalytic properties of MIL-100(Fe), an iron(III) carboxylate with large pores

Article abstract of DOI:10.1039/b704325b

The large-pore iron(iii) carboxylate MIL-100(Fe) with a zeotype architecture has been isolated under hydrothermal conditions, its structure solved from synchrotron X-ray powder diffraction data, while Friedel-Crafts benzylation catalytic tests indicate a

Full text of DOI:10.1039/b704325b

View Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Synthesis and catalytic properties of MIL-100(Fe), an iron(III)
carboxylate with large pores{
Patricia Horcajada,a Suzy Surble´,a Christian Serre,*a Do-Young Hong,b You-Kyong Seo,b Jong-San Chang,b
Jean-Marc Grene`che,c Irene Margiolakid and Ge´rard Fe´reya
Received (in Cambridge, UK) 21st March 2007, Accepted 1st May 2007
First published as an Advance Article on the web 15th May 2007
DOI: 10.1039/b704325b
deionised water (80 uC) for 3 h was applied to decrease the amount
of residual trimesic acid (typically, 1 g of MIL-100(Fe) in 350 ml of
water) followed by drying at room temperature.
The large-pore iron(III) carboxylate MIL-100(Fe) with a
zeotype architecture has been isolated under hydrothermal
conditions, its structure solved from synchrotron X-ray powder
diffraction data, while Friedel–Crafts benzylation catalytic tests
indicate a high activity and selectivity for MIL-100(Fe).
A laboratory powder X-ray diffraction pattern showed that
crystalline phase had been produced, isostructural with the
chromium carboxylate MIL-100(Cr).23 Elemental analysis
indicated that the contents of Fe, F, C and H (obs: 13.8% Fe,
1.3% F, 23.5% C) are in good agreement with the values based on
the structure formula, FeIII3O(H2O)2F?{C6H3(CO2)3}2?nH2O
(n y14.5) despite an excess of carbon content (calc.: 14% Fe,
1.8% F, 21.0% C). It has not been possible to prepare sizeable
crystals for single-crystal diffraction studies whatever the synthesis
conditions. Thermal analysis (TGA2050 TA apparatus, O2 flow,
heating rate 3 K min21) shows three weight losses between 298 and
873 K. The first (y40.1%) at 373 K is attributed to the departure
of the free water molecules inside the pores. The second at 473 K
(y4.5%) comes from the water molecules which interact with the
iron trimers. The final weight loss (y35.3%) at 573 K is related to
the combustion of the trimesic acid. These latter two losses are, on
the whole, in agreement with the theoretical values (calc: 4.6 and
35.2%). Note that the free water content deduced from the
structure determination (y29.5%) is slightly lower than the
experimental value (TGA). This is due to the variable water
content in MIL-100 solids which vary considerably depending on
the atmospheric conditions.
The recent interest in the synthesis of hybrid inorganic–organic
solids gives
a new dimension to the domain of porous
compounds.1–4 They offer significant new scientific and technolo-
gical opportunities5 by combining attractive features of both
inorganic and organic moieties and lead to many potential
applications in gas storage,6,7 catalysis,8,9 insertion,10,11 magnet-
ism,12,13 optical devices,14 etc. Most of them are prepared using
functionalized organic ligand (phosphonates, carboxylates, sulfo-
nates...) and many elements in the Periodic Table have been
incorporated in these new framework materials exhibiting novel
structures not seen in zeolite chemistry. The introduction of 3d
transition metals within the skeleton provides new electronic
properties. Among them, iron is an environmentally benign and
cheap component with non-toxicity and redox properties.
However, to the best of our knowledge, while some MOF
materials have been reported to date with iron(II) or iron(III),15–20
only two of them combine a permanent porosity and large
pores.21,22 We report here the successful synthesis and structure
determination of MIL-100(Fe) (MIL: Materials of Institut
Lavoisier), a new scarce example of an iron(III) carboxylate with
a large accessible and permanent porosity.
The structure of title solid was solved from high-resolution
synchrotron X-ray powder diffraction data using coordinates of
MIL-100(Cr) as the starting model (ESI{).{ The final Rietveld plot
is shown in Fig. 1. MIL-100(Fe) is an iron(III) carboxylate built up
from trimers of iron octahedra sharing a common vertex m3-O.
The trimers are then linked by the benzene-1,3,5-tricarboxylate
moieties in such a way that this leads to the formation of hybrid
supertetrahedra which further assemble into a zeolitic architecture
of the MTN type (Fig. 2). This delimits two types of mesoporous
This solid was isolated as a polycrystalline powder from a
reaction mixture of composition 1.0 Fe0 : 0.66 1,3,5-BTC : 2.0 HF
: 1.2 HNO3 : 280 H2O (1,3,5-BTC = benzene tricarboxylic or
trimesic acid) that was held at 150 uC in a Teflon-lined autoclave
for 6 days with a initial heating ramp of 12 h and a final cooling
ramp of 24 h. The pH remains acidic (,1) throughout the
synthesis. The light-orange solid product was recovered by
filtration and washed with deionized water. A treatment in hot
˚
cages of free apertures of ca. 25 and 29 A, accessible through
˚
microporous windows of ca. 5.5 and 8.6 A. Bond valence
aInstitut Lavoisier, UMR CNRS 8180, Universite´ de Versailles Saint-
Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035, Versailles
Ce´dex, France. E-mail: serre@chimie.uvsq.fr; Fax: 00 33 1 39 25 43 58;
Tel: 00 33 1 39 25 43 05 ;
calculations indicate a trivalent state of iron.
As is illustrated in Fig. 3, the transmission Mo¨ssbauer spectra
recorded at 300 and 77 K consist of asymmetrical quadrupolar
doublets with broadened and overlapped lines, in agreement with
the large number of different environments of Fe atoms.24
Whatever the fitting model, the isomer shift values (0.54 and
0.42 mm s21 at 300 K and 77 K, respectively) remain consistent
with the presence of high spin state of Fe3+ ions located in
octahedral units. Taking into account the crystallographic
structure, one might describe the spectra by means of seven
bCatalysis Centre for Molecular Engineering, Korea Research Institute
of Chemical Technology (KRICT), Jang-dong 100, Yuseong-Gu, 305-
600, Daejon, South Korea
cLaboratoire de Physique de L’Etat Condense´, UMR CNRS 6087,
Universite´ du Maine, 72085, Le Mans Cedex 9, France
dESRF, rue J. Horowitz, 38043, Grenoble Cedex, France
{ Electronic supplementary information (ESI) available: Crystallographic
details, TGA, adsorption, Mo¨ssbauer and catalysis data. See DOI:
10.1039/b704325b
2820 | Chem. Commun., 2007, 2820–2822
This journal is ß The Royal Society of Chemistry 2007

View Online
Fig. 3 Transmission Mo¨ssbauer spectra of MIL-100(Fe) recorded at 300
and 77 K.
Fig. 1 Final Rietveld refinement plot for FeIII3O(H2O)2F?
¯
{C6H3(CO2)3}2?nH2O (MIL-100(Fe)) in the space group Fd3m.
fluorine atoms bound to chromium atoms from the trimers, was at
the origin of the three types of environments for the metal sites as
evidenced by CO adsorption experiments.25 Thus, as MIL-100(Fe)
possesses the same fluorine composition as MIL-100(Cr), i.e. one
fluorine atom per trimer, a similar environment is expected.
The different values of isomer shift confirm this hypothesis with
some Fe ions mainly surrounded by O while the environment of
others (with higher isomer shift) also contain F ions. The values of
quadrupolar splitting (0.30, 0.52 and 0.90 mm s21) are consistent
with different degrees of distortions and the highest distorted
octahedral unit contains F anions. Finally, the significant increase
of the absorption spectral area when decreasing the temperature
should be noted. This is due to a large increase of the Debye–
Waller factor, resulting from the strengthening of the structure,
particularly due to its hybrid character which is temperature
sensitive.
Observed, calculated and difference profiles are plotted on the same scale.
Inset is an expanded region of a small part of the data.
The permanent porosity of the new solid was measured by N2
adsorption experiments performed in liquid nitrogen. MIL-
100(Fe) revealed an adsorption isotherm characteristic of micro-
porous solids (Fig. 4). However, due to the presence of two types
of microporous windows and mesoporous cages with different
sizes, two secondary uptakes at ca. P/P0 = 0.06 and 0.12 can be
distinguished from the isotherm, in agreement with our previous
results with MIL-100(Cr).23 The corresponding Langmuir surface
area is estimated to be .2800(100) m2 g21. This value is, on the
whole, in agreement with that of the isostructural solid MIL-
100(Cr) (S = 3100 m2 g21). The thermal stability of MIL-100(Fe)
Fig. 2 Structure of MIL-100(Fe). (A) A trimer of iron octahedra and
trimesic acid. (B) Schematic view of one unit cell of MIL-100(Fe). (C) the
two types of cages in polyhedral mode. (D) Pentagonal and hexagonal
windows in balls and sticks (Fe: grey; O: red; C: black).
different quadrupolar components: different solutions can be
found without any clear and sound interpretation. On the
contrary, assuming that three main types of Fe octahedral units
can be distinguished according to their nearest chemical environ-
ments, this gives rise to a reasonable fitting model involving three
quadrupolar components, as shown in Fig. 3. This could be
explained by the presence of different fluorine environments for
the iron atoms within the structure. It has been proved previously
with the isostructural solid MIL-100(Cr) that the distribution of
Fig. 4 N2 adsorption isotherm of MIL-100(Fe) at 77 K (P0 = 1 atm).
Chem. Commun., 2007, 2820–2822 | 2821
This journal is ß The Royal Society of Chemistry 2007

View Online
Korea Ministry of Commerce, Industry and Energy through the
Research Center for Nanocatalysis (TS066-26) and the
Institutional Research Program (KK-0703-E0). The KRICT s
authors thank Dr S. H. Jhung and Dr Y. K. Hwang for helpful
discussion. We thank ESRF for provision of synchrotron beam
time.
Notes and references
{ Coordinates of MIL-100(Fe) have been deposited with the CCDC data
bank, deposition number CCDC 640536. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/b704325b
1 G. Fe´rey, C. Mellot-Draznieks, C. Serre and F. Millange, Acc. Chem.
Res, 2005, 38, 217.
Fig. 5 Benzyl chloride conversion in the Friedel–Crafts benzylation of
benzene over different catalysts. Reaction conditions: 70 uC, 7.8 ml
benzene, benzene/benzyl chloride = 10 (molar ratio), 0.1 g catalyst.
2 H. Li, M. Eddaoudi, M. O’Keeffe and O. M. Yaghi, Nature, 1999, 402,
276.
3 S. Kitagawa and K. Uemura, Chem. Soc. Rev., 2005, 34, 109.
4 Y. Liu, V. C. Kravtsov, R. Larsena and M. Eddaoudi, Chem. Commun.,
2006, 1488.
has been studied by X-ray thermodiffractometry and reveals that
this solid is stable up to 270 uC.
5 U. Mueller, M. Schubert, F. Teich, H. Puetter, K. Schierle-Arndt and
J. Pastre, J. Mater. Chem., 2006, 16, 626.
6 G. Fe´rey, M. Latroche, C. Serre, T. Loiseau, F. Millange and
A. Percheron-Guegan, Chem. Commun., 2003, 2276.
7 A. G. Wong-Foy, A. J. Matzger and O. M. Yaghi, J. Am. Chem. Soc.,
2006, 128, 3494.
8 J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon and K. Kim,
Nature, 2000, 404, 982.
9 R.-Q. Zou, H. Sakurai and Q. Xu, Angew. Chem., Int. Ed., 2006, 45,
2542.
10 G. Fe´rey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour,
S. Surble´ and I. Margiolaki, Science, 2005, 309, 2040.
11 S. Hermes, M. K. Schro¨ter, R. Schmid, L. Khodeir, M. Muhler,
A. Tissler, R. W. Fischer and R. A. Fischer, Angew. Chem., Int. Ed.,
2005, 44, 6237.
12 S. Konar, P. S. Mukherjee, E. Zangrando, F. Lloret and
N. R. Chaudhuri, Angew. Chem., Int. Ed., 2002, 41, 1561.
13 G. Guillou, C. Livage, M. Drillon and G. Fe´rey, Angew. Chem., Int. Ed.,
2003, 115, 5472.
14 F. Pelle´, S. Surble´, C. Serre, F. Millange and G. Fe´rey, J. Lumin., 2007,
122–123, 492.
15 M. Sanselme, J. M. Grene`che, M. Riou-Cavellec and G. Fe´rey, Chem.
Commun., 2002, 2172.
16 C. Serre, F. Millange, S. Surble´ and G. Fe´rey, Angew. Chem., Int. Ed.,
2004, 43, 6286.
17 W. Schmitt, J. P. Hill, M. P. Juanico, A. Caneschi, F. Costantino,
C. E. Anson and A. K. Powell, Angew. Chem., Int. Ed., 2005, 44,
4187.
18 T. R. Whitfield, X. Wang, L. Liu and A. J. Jacobson, Solid State Sci.,
2005, 7, 1096.
19 S. Surble´, C. Serre, C. Mellot-Draznieks, F. Millange and G. Fe´rey,
Chem. Commun., 2006, 284.
20 C. Serre, F. Millange, S. Surble´, J. M. Grene`che and G. Fe´rey, Chem.
Mater., 2004, 16, 2706.
21 A. C. Sudik, A. P. Coˆte´, A. G. Wong-Foy, M. O’Keefe and O. M. Yaghi,
Angew. Chem., Int. Ed., 2005, 118, 2590.
22 J. Jia, X. Lin, C. Wilson, A. J. Blake, N. R. Champness, P. Hubberstey,
G. Walker, E. J. Cussena and M. Schro¨der, Chem. Commun., 2007, 840.
23 G. Fe´rey, C. Serre, C. Mellot-Draznieks, F. Millange, S. Surble´,
J. Dutour and I. Margiolaki, Angew. Chem., Int. Ed., 2004, 43, 6296.
24 J. Teillet and F. Varret, in ‘MOSFIT program’.
25 A. Vimont, J.-M. Goupil, J.-C. Lavalley, M. Daturi, S. Surble´, C. Serre,
F. Millange, G. Fe´rey and N. Audebrand, J. Am. Chem. Soc., 2006, 128,
3218.
The use of heterogeneous catalysts in the liquid phase is highly
desirable for Friedel–Crafts type reactions27 because the use of
conventional homogeneous catalysts for these reactions leads to
several problems, such as difficulty in separation and recovery,
disposal of spent catalyst and corrosion. In the light of the
importance of heterogenous catalysis, we have performed Friedel–
Crafts benzylation to confirm the suitability of iron-containing
MIL-100 as a new porous catalyst (see ESI{). Fig. 5 shows the
conversion of benzyl chloride in the liquid phase benzylation of
benzene by benzyl chloride (BZC) to diphenylmethane (DPM) at
70 uC over MIL-100(Fe), MIL-100(Cr) and zeolite catalysts for
comparison. We find that MIL-100(Fe) gives high activity and
selectivity, showing 100% BZC conversion [X(BZC)] with nearly
100% DPM selectivity [S(DPM)] being quickly attained after a
short induction period (5 min). By contrast, MIL-100(Cr) was
poorly active for the reaction, i.e., 42% X(BZC) after 30 h. Solid
acid catalysts such as HBEA and HY zeolites were not so active
under the same reaction conditions: 43.4% X(BZC) with 97.6%
S(DPM) for HBEA and 54.0% X(BZC) with 95.8% S(DPM) for
HY after 5 h. These results clearly indicate that iron species in
MIL-100(Fe) play a role as catalytically active sites in Friedel–
Crafts alkylation. The observed high benzylation activity of MIL-
100(Fe) might be attributed to the redox property of trivalent iron
species (Fe3+ + e2 « Fe2+) to play a significant role in activating
both the reactants, consistent with results observed in iron-
containing solid catalysts.26–28 The origin of the induction period
in the benzylation is generally ascribed to the inhibition effect by
moisture present in the catalyst and/or in the reaction mixture26 or
the diffusion limitation of reactant molecules into the active site in
the pore.
In summary, we report the synthesis and characterisation of a
new example of a large-pore iron(III) carboxylate under hydro-
thermal conditions. First catalytic experiments suggest that
iron(III) species metal sites are particularly interesting in catalysis
and might lead to new applications. We are currently surveying
phases produced from other iron(III) carboxylate systems.
This work was supported by CNRS, the EU funding via FP6-
Specific Targeted Research Project DeSANNS (SES6-020133), the
26 V. R. Choudhary and S. K. Jana, Appl. Catal., A, 2004, 224, 51.
27 T. Cseri, S. Bekassy, S. Rizner and F. Figueras, J. Mol. Catal. A: Chem.,
1995, 98, 101.
28 M. S. Hamdy, G. Mul, J. C. Jansen, A. Ebaid, Z. Shan, A. R. Overweg
and T. Maschmeyer, Catal. Today, 2005, 100, 255.
2822 | Chem. Commun., 2007, 2820–2822
This journal is ß The Royal Society of Chemistry 2007