MnII-based MIL-53 analogues: Synthesis using neutral bridging μ2-ligands and application in liquid-phase adsorption and separation of C6-C8 aromatics

Article abstract of DOI:10.1021/ja910818a

"Chemical equation presented" Four MnII-based MIL-53 single crystals were prepared using four neutral pyridine N-oxides as bridging μ₂-ligands. In the case of 4,4!-bipridine-N,N!-dioxide (BPNO), the infinite manganese oxide chains were further

Full text of DOI:10.1021/ja910818a

Published on Web 03/02/2010
MnII-based MIL-53 Analogues: Synthesis Using Neutral Bridging µ2-Ligands and
Application in Liquid-Phase Adsorption and Separation of C6-C8 Aromatics
Guohai Xu, Xiaoguang Zhang, Peng Guo, Chengling Pan, Hongjie Zhang,* and Cheng Wang*
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin 130022, P.R. China
Received December 22, 2009; E-mail: cwang@ciac.jl.cn; hongjie@ciac.jl.cn
The C6-C8 aromatics, known as monoaromatic hydrocarbons
and mostly abbreviated as BTEX standing for benzene, toluene,
ethylbenzene, and the three xylene isomers, are major industrial
raw materials in plastic, synthetic rubber, and synthetic fiber
manufacture.1 On the other hand, BTEXs are ubiquitous in
numerous sites including areas used for fuel operations, refineries,
gasoline stations, gasification sites, and groundwater reservoirs and
display carcinogenic and neurotoxic potentials.2 Microporous
materials, such as zeolites and MOFs,3 are promising materials for
the recovery of these pollutants and the separation of BTEXs
targeted to individual chemicals with high purity.
well as guest-exchanged products of 4 is provided. The structure of 1
is illustrated in Figure 1 since 2 and 3 are isostructural to 1. The one-
dimensional (1D) channels in compounds 1-3 are blocked by pendant
PNOs as shown in Figure 1 and Figure S2 (SI). The structural
evolutions from 1 to 3 along with the increase of the substituent methyl
group in PNOs could be ascribed to π-π interactions, one of the
noncovalent interactions playing pivotal roles in many fields such as
chemistry, biology, and material science,10 between two adjacent
digonal pendant groups and explained using a simple electrostatic
model.11 Further explanation toward this is provided in SI.
As an important subsidiary group of metal-organic frameworks
(MOFs) and promising candidates for gas adsorption, the MIL-53
(MIII) systems developed by Fe´rey and co-workers have received
intensive attention owing to their remarkable framework flexibility.4
The framework flexibility is termed as “breathing effect”, and some
frameworks show abnormal expansions (contractions) toward
exhaling (inhaling) guest species.5 Similar to MOFs, both the
metallic sites and 1,4-benzenedicarboxylate (BDC) linkers in MIL-
53 systems have been the targets for modifications in order to impart
desired properties.6 However, much less attention has been paid to
modifying µ2-OH that bridged the metal cations along the chains.7
Besides µ2-OH, doubly bridging oxygen atoms (µ2-oxo) and neutral
ligands appeared in the structural analogues of MIL-53 such as
MIL-47(VIV),4b MOF-71,8 and MIL-53(FeII).9 The different charges
of the metal cations necessitate the variation of µ2 groups so that
their neutral frameworks could be maintained. In this work, we
report the synthesis of four MnII-based MIL-53 analogues [MIL-
53(MnII)] using pyridine N-oxide and its derivatives (PNOs) as
neutral µ2 ligands. The adsorption and separation of C6-C8
aromatics using one evacuated porous MIL-53(MnII) as an absorbent
were investigated via crystal to crystal transformations.
Compounds 1-4, formulated as Mn(BDC)Ln for 1-3 (L1 )
pyridine N-oxide (PNO), L2 ) 4-methyl-pyridine N-oxide, L3 )
3,5-dimethyl-pyridine N-oxide) and Mn2(BDC)2L4 ·(DMF)2 for 4
(L4 ) 4,4′-bipyridine-N,N′-dioxide (BPNO), DMF ) dimethyl
formamide) (Figure S1, Supporting Information), were prepared under
solvothermal conditions using Mn(NO3)2 aqueous solution, H2BDC,
and corresponding Ln as precursors in DMF at 120 °C. Details of
synthesis are provided in Supporting Information (SI). Despite the
hygroscopic nature of PNOs, compounds 1-4 are stable in atmospheric
conditions for at least six months. All four compounds are insoluble
in common organic solvents, but they do decompose in water. The
occluded DMF molecules in 4 can be exchanged by ethanol molecules
Figure 1. MnII-based MIL-53 frameworks with pendant PNO (1) and
BPNO incorporated into the skeleton (4). The occluded molecules in 4 are
DMF. Color code: green, Mn; red, O; blue, N; 50% gray, C.
In compound 4, the manganese oxide chains are further intercon-
nected by BPNO units besides BDC (Figure 1). Its structure can
be also viewed as evolved from 1 by connecting two closest µ2-
PNO molecules of adjacent manganese oxide chains in 1 to form
a BPNO molecule. This extra connection exerts forces to the
manganese oxide chains and results in the corrugation of the linear
-Mn-Mn-Mn- chains in 1-3 accompanied with an even more
severe COO distortion (Figure S3, SI). The advantage of this
connection is that the blocking of the channels by pendant µ2 ligands
in 1-3 could be avoided. The delimited channel sizes change from
9.32 to 13.24 Å and 19.51 to 17.71 Å, respectively, as shown in
Figure 1. The open 1D channels in 4 are occupied by DMF
molecules. Despite being incorporated into the framework skeleton,
the adjacent bi-µ2 BPNO ligands still interact with each other via
π-π interactions, which spread throughout the whole crystal, with
a closest 4.606 Å centroid-centroid distance and a severe offset
(Figure S2, SI). It is worthy of noting that BPNO has a µ4-η2η2
connection mode toward Mn2+ in 4. Such mode is unusual for
BPNO in constructing coordinative framework polymers.12
Thermal gravimetric analysis and X-ray thermodiffractogram of
sample 4 indicate that these compounds show high thermal stability
yielding 4eth or completely removed giving 4vac
.
Single-crystal X-ray diffraction analysis revealed that compounds
1-4 are built up from infinite chains of corner-sharing MnO6 octahedra
interconnected by organic moieties, which is similar to those of MIL-
53 systems, and the net of them is sra.8 In Table S1 (SI), a summary
of crystallographic data of these four compounds along with 4vac as
9
3656 J. AM. CHEM. SOC. 2010, 132, 3656–3657
10.1021/ja910818a  2010 American Chemical Society

C O M M U N I C A T I O N S
(Figured S4 and S5, SI). Standard N2 sorption measurements
revealed that no appreciable pore could be detected for 1-3 as
expected from the single X-ray diffraction analysis. The low
hydrogen adsorption isotherm of 4 shows a reversible hydrogen
sorption, and the adsorbed amount of hydrogen corresponds to ∼1.0
wt % at 1 bar and 77 K (Figure S6, SI), suggesting a favorable
interaction of H2 with the host framework.6a
Although the occluded DMF molecules could be exchanged by a
small molecule, e.g. ethanol, or removed by evacuation processes (see
SI and Figure 2), they could not be exchanged by big molecules such
as benzene or toluene directly. Therefore 4vac was chosen for studying
its adsorption and separation of C6-C8 aromatics. Upon immersing
of 4vac is likely to be the packing efficiency. Increasing the number of
electron-donating substituent groups also leads to an increase of
intermolecular repulsions of their dimers that might make the
dimensional sizes of these dimers too large to be accommodated by
the 1D channels in 4vac
.
In summary, we succeeded in preparing MIL-53(MnII) single
crystals using PNOs as µ2-ligands. A porous crystal 4 could be
formed using BPNO as a bi-µ2-ligand. Its evacuated form 4vac
showed selective adsorptions toward C6-C8 aromatics due to the
different degrees of guest-linker interactions.
Acknowledgment. This work is supported by the National Basic
Research Program of China (2007CB925101), NSFC (20671087),
and the NSFC Fund for Creative Research Groups (20921002). We
thank Prof. Zhijian Wu and Ms. Lin Cheng for helpful discussions.
4vac into liquids including benzene, toluene, xylenes, ethylbenzene, and
chlorobenzene, only C6-C7 molecules could be intercalated, and
crystals of 4ben, 4tol, and 4chl were obtained (Table S1, SI). Single-
crystal structural analysis shows that the intercalated molecules have
definite positions in the channels and fill the channels pairwise. Along
each channel, there are two symmetrically equivalent positions
available for the pairs. Furthermore, when 4vac was immersed into a
mixture of benzene and toluene with 1:1 volume ratio, only benzene
could be selectively adsorbed. These results clearly demonstrate that
Supporting Information Available: Experimental details and data,
CIF files, thermal ellipsoid of crystal structures of 1-4, TGA and
powder X-ray diffractions for 1-4, X-ray thermodiffractogram and the
H2 sorption isotherms for 4, and the views of the noncovalent
interactions. This material is available free of charge via the Internet
at http://pubs.acs.org.
4
vac could be a potential absorbent for the separation of C6, C7, and
References
C8 aromatics in liquid phase.3b,13 A higher chlorobenzene selectivity
of 4vac over benzene (Figure 2) was also observed in a process similar
to that using benzene and toluene.
(1) (a) Wang, Z. D.; Fingas, M.; Landriault, M.; Sigouin, L.; Xu, N. N. Anal.
Chem. 1995, 67, 3491–3500. (b) Arce, A.; Earle, M. J.; Rodriguez, H.;
Seddon, K. R.; Soto, A. Green Chem. 2008, 10, 1294–1300.
(2) (a) Huttenloch, P.; Roehl, K. E.; Czurda, K. EnViron. Sci. Technol. 2001,
35, 4260–4264. (b) Sarafraz-Yazdi, A.; Amiri, A. H.; Es’haghi, Z. Talanta
2009, 78, 936–941.
(3) (a) Ranck, J. M.; Bowman, R. S.; Weeber, J. L.; Katz, L. E.; Sullivan,
E. J. J. EnViron. Eng. ASCE 2005, 131, 434–442. (b) Wang, X. Q.; Liu,
L. M.; Jacobson, A. J. Angew. Chem., Int. Ed. 2006, 45, 6499–6503.
(4) (a) Fe´rey, G.; Serre, C. Chem. Soc. ReV. 2009, 38, 1380–1399. (b) Barthelet,
K.; Marrot, J.; Riou, D.; Fe´rey, G. Angew. Chem., Int. Ed. 2002, 41, 281–
284. (c) Serre, C.; Millange, F.; Thouvenot, C.; Nogues, M.; Marsolier,
G.; Louer, D.; Fe´rey, G. J. Am. Chem. Soc. 2002, 124, 13519–13526. (d)
Loiseau, T.; Serre, C.; Huguenard, C.; Fink, G.; Taulelle, F.; Henry, M.;
Bataille, T.; Fe´rey, G. Chem.sEur. J. 2004, 10, 1373–1382.
(5) (a) Millange, F.; Guillou, N.; Walton, R. I.; Greneche, J. M.; Margiolaki,
I.; Fe´rey, G. Chem. Commun. 2008, 4732–4734. (b) Coudert, F. X.; Mellot-
Draznieks, C.; Fuchs, A. H.; Boutin, A. J. Am. Chem. Soc. 2009, 131,
11329–11331. (c) Meilikhov, M.; Yusenko, K.; Fischer, R. A. Dalton Trans.
2009, 600–602. (d) Horcajada, P.; Serre, C.; Maurin, G.; Ramsahye, N. A.;
Balas, F.; Vallet-Regi, M.; Sebban, M.; Taulelle, F.; Fe´rey, G. J. Am. Chem.
Soc. 2008, 130, 6774–6780.
(6) (a) Fe´rey, G.; Millange, F.; Morcrette, M.; Serre, C.; Doublet, M. L.;
Greneche, J. M.; Tarascon, J. M. Angew. Chem., Int. Ed. 2007, 46, 3259–
3263. (b) Couck, S.; Denayer, J. F. M.; Baron, G. V.; Remy, T.; Gascon,
J.; Kapteijn, F. J. Am. Chem. Soc. 2009, 131, 6326–6327. (c) Ahnfeldt, T.;
Gunzelmann, D.; Loiseau, T.; Hirsemann, D.; Senker, J.; Fe´rey, G.; Stock,
N. Inorg. Chem. 2009, 48, 3057–3064. (d) Himsl, D.; Wallacher, D.;
Hartmann, M. Angew. Chem., Int. Ed. 2009, 48, 4639–4642.
(7) Meilikhov, M.; Yusenko, K.; Fischer, R. A. J. Am. Chem. Soc. 2009, 131,
9644–9645.
Figure 2. Guest exchange of 4 with EtOH and selective absorptions of
C6-C8 aromatics by single crystals of 4vac
.
For selective adsorption and separation of C6-C8 aromatic using
4vac as absorbents, the π-π interactions including the guest-guest
and guest-linker interactions are considered to play key roles for the
(8) Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B. L.; O’Keeffe, M.; Yaghi,
O. M. J. Am. Chem. Soc. 2005, 127, 1504–1518.
crystal to crystal transformations. The three occluded aromatics in 4ben
,
(9) Whitfield, T. R.; Wang, X. Q.; Liu, L. M.; Jacobson, A. J. Solid State Sci.
2005, 7, 1096–1103.
4tol, and 4chl tend to form antiparallel dimers to facilitate the
dipole-dipole interactions.14 Besides intermolecular parallel displaced
(PD) π-π interactions, they can also interact with BDC rings with
nearly isoenergetic T-shaped configurations.14,15 There is only one
T-shaped π-π interaction between each toluene molecule and the
phenyl ring of BDC linker, while there are two T-shaped π-π
interactions for benzene and chlorobenzene (Figure S7). In addition,
one C-H· · ·Cl hydrogen bonding between each chlorobenzene and
the BPNO can be formed (Figure S7, SI). These two interactions might
be responsible for the selectivity trend (chlorobenzene > benzene >
toluene) of 4vac. As we already noticed, all three aromatics present as
dimers in order to have high packing densities within the 1D
channels.3b The dimeric C8 aromatics are unlikely favored within the
channels as the number of guest-host T-shaped π-π interactions
might be reduced when more electron-donating substituent groups were
attached to the benzene rings, a case having already occurred in 4tol.
Another dominant factor for filling guest molecules in the 1D channel
(10) Janiak, C. Dalton Trans. 2000, 3885–3896.
(11) Cozzi, F.; Cinquini, M.; Annunziata, R.; Dwyer, T.; Siegel, J. S. J. Am.
Chem. Soc. 1992, 114, 5729–5733.
(12) (a) Hill, R. J.; Long, D. L.; Champness, N. R.; Hubberstey, P.; Schroder,
M. Acc. Chem. Res. 2005, 38, 335–348. (b) Ma, S. L.; Qi, C. M.; Guo,
Q. L.; Zhao, M. X. J. Mol. Struct. 2005, 738, 99–104.
(13) (a) Alaerts, L.; Kirschhock, C. E. A.; Maes, M.; van der Veen, M. A.;
Finsy, V.; Depla, A.; Martens, J. A.; Baron, G. V.; Jacobs, P. A.; Denayer,
J. E. M.; De Vos, D. E. Angew. Chem., Int. Ed. 2007, 46, 4293–4297. (b)
Finsy, V.; Verelst, H.; Alaerts, L.; De Vos, D.; Jacobs, P. A.; Baron, G. V.;
Denayer, J. F. M. J. Am. Chem. Soc. 2008, 130, 7110–7118. (c) Alaerts,
L.; Maes, M.; Giebeler, L.; Jacobs, P. A.; Martens, J. A.; Denayer, J. F. M.;
Kirschhock, C. E. A.; De Vos, D. E. J. Am. Chem. Soc. 2008, 130, 14170–
14178. (d) Liu, Q. K.; Ma, J. P.; Dong, Y. B. Chem.sEur. J. 2009, 15,
10364–10368.
(14) Tsuzuki, S.; Honda, K.; Uchimaru, T.; Mikami, M.; Tanabe, K. J. Am.
Chem. Soc. 2002, 124, 104–112.
(15) (a) Wheeler, S. E.; Houk, K. N. J. Am. Chem. Soc. 2008, 130, 10854–
10855. (b) Sherrill, C. D.; Takatani, T.; Hohenstein, E. G. J. Phys. Chem.
A 2009, 113, 10146–10159. (c) Park, Y. C.; Lee, J. S. J. Phys. Chem. A
2006, 110, 5091–5095.
JA910818A
9
J. AM. CHEM. SOC. VOL. 132, NO. 11, 2010 3657