Optimized synthesis of tetrafluoroterephthalic acid: A versatile linking ligand for the construction of new coordination polymers and metal-organic frameworks

Article abstract of DOI:10.1021/ic1009829

Pure 2,3,5,6-tetrafluoroterephthalic acid (H₂tfBDC) is obtained in high yields (95%) by reacting 1,2,4,5-tetrafluorobenzene with a surplus (>2 equiv) of n-butyllithium in tetrahydrofuran (THF) and subsequent carbonation with CO₂ without any extensive purification procedure. A single crystal X-ray structure analysis of H₂tfBDC (1) confirms former data obtained for a deuterated sample (P1, Z= 1). Recrystallization from water/acetone leads to single crystals of H₂tfBDC · 2H₂O (2, P2₁/c, Z= 2), where an extensive hydrogen bonding network is found. By reacting H₂tfBDC with an aqueous ammonia solution, single crystals of (NH₄)₂tfBDC (3, C2/m, Z= 2) are obtained. 3 is thermally stable up to 250 °C and shows an enhanced solubility in water compared to H₂tfBDC. Monosubstituted 2,3,5,6-tetrafluorobenzoic acid (H₂tfBC, 4) is obtained by reacting 1,2,4,5-tetrafluorobenzene with stoichiometric amounts (1 equiv) of n-butyllithium in THF. Its crystal structure (Fdd2, Z= 16) shows dimeric units as characteristic structural feature.

Full text of DOI:10.1021/ic1009829

9
350 Inorg. Chem. 2010, 49, 9350–9357
DOI: 10.1021/ic1009829
Optimized Synthesis of Tetrafluoroterephthalic Acid: A Versatile Linking Ligand for
the Construction of New Coordination Polymers and Metal-Organic Frameworks
†
‡
†
§
,†
,‡
Andreas Orthaber, Christiane Seidel, Ferdinand Belaj, J €o rg H. Albering, Rudolf Pietschnig,* and Uwe Ruschewitz*
†
Institute of Chemistry, Inorganic Chemistry, Karl Franzens University Graz, Schubertstrasse 1, A-8010 Graz, Austria,
‡
§
Department of Chemistry, University of Cologne, Greinstrasse 6, D-50939 Cologne, Germany, and Institute of
Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9, A-8010 Graz, Austria
Received May 18, 2010
Pure 2,3,5,6-tetrafluoroterephthalic acid (H tfBDC) is obtained in high yields (95%) by reacting 1,2,4,5-tetrafluoro-
2
benzene with a surplus (>2 equiv) of n-butyllithium in tetrahydrofuran (THF) and subsequent carbonation with CO2
without any extensive purification procedure. A single crystal X-ray structure analysis of H tfBDC (1) confirms former
2
data obtained for a deuterated sample (P1, Z = 1). Recrystallization from water/acetone leads to single crystals of
H tfBDC 2H O (2, P2 /c, Z = 2), where an extensive hydrogen bonding network is found. By reacting H tfBDC with an
aqueous ammonia solution, single crystals of (NH ) tfBDC (3, C2/m, Z = 2) are obtained. 3 is thermally stable up to
2
3
2
1
2
4
2
2
acid (H tfBC, 4) is obtained by reacting 1,2,4,5-tetrafluorobenzene with stoichiometric amounts (1 equiv) of
50 °C and shows an enhanced solubility in water compared to H tfBDC. Monosubstituted 2,3,5,6-tetrafluorobenzoic
2
2
n-butyllithium in THF. Its crystal structure (Fdd2, Z = 16) shows dimeric units as characteristic structural feature.
Introduction
The beneficial properties of fluorinated linkers are, how-
ever, supported by experimental results for a MOF based
Coordination polymers and especially their porous
congeners, which are frequently termed MOFs (Metal-
Organic Frameworks), are in the focus of many research
groups worldwide. The interest in this class of compounds
is mainly based on their easy synthetic accessibility and
potential applications.
on a triazolate with CF substituents, which shows excel-
3
8
1
lent gas storage capacities for O and H . To date only
2
2
few coordination polymers or MOFs employing perfluori-
2
-
nated linking terephthalates (tfBDC ) have been pub-
9
-21
2
-4
lished.
Most of them are non-porous.
One of the most frequently used
linker ligands is the dianion of terephthalic acid (H BDC),
2
(
8) Yang, C.; Wang, X.; Omary, M. A. J. Am. Chem. Soc. 2007, 129(50),
15454–15455.
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from which two of the most prominent members of
1
5
this class of compounds, MOF-5 and MIL-53, are con-
structed. For its perfluorinated counterpart, that is 2,3,
(
2
002, 566–567.
5
,6-tetrafluoroterephthalic acid (H tfBDC), theoretical
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2
Takata, M.; Kobayashi, T. C. Inorg. Chem. 2004, 43, 6522–6524.
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investigations predict superior H adsorbing properties
2
(
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of MOFs built with this linker ligand. By contrast, a differ-
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Online 2004, 60, m1504–m1506.
(
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between H and fluoroaromatic compounds may be even
2
7
(13) Chun, H.; Dybtsev, D. N.; Kim, H.; Kim, K. Chem.;Eur. J. 2005,
1, 3521–3529.
weaker compared with their non-fluorinated analogues.
1
(14) Chen, B.; Yang, Y.; Zapata, F.; Qian, G.; Luo, Y.; Zhang, J.;
*
To whom correspondence should be addressed. E-mail: rudolf.
pietschnig@uni-graz.at (R.P.), uwe.ruschewitz@uni-koeln.de (U.R.).
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pubs.acs.org/IC
Published on Web 09/16/2010
r 2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9351
In 1964 a synthesis of H tfBDC was described starting
continued, while the mixture was allowed to reach ambient tempera-
ture (1 h). To the recooled (0 °C) solution, aqueous HCl (1M) was
added and stirred overnight. The solvents were removed by distilla-
tion (the fraction boiling around 105° was collected, as it contains
2
from 1,2,4,5-tetrafluorobenzene, which was reacted with n-
22
butyllithium and carbonated with CO2. Although this route
yielded 67% of pure product, it suffers from incomplete
lithiation, and consequentlythe monosubstituted tetrafluoro-
benzene is always obtained as a byproduct. This disadvan-
tage makes an extensive and time-consuming purification
procedure necessary.
22
almost pure monocarboxylic acid, as described in literature ). The
residue of the distillation was washed with a small amount of pentane
yielding a crude product mixture of 1 and 4 in a ratio of about 7:3.
The above-described procedure, lithiation and subsequent carbona-
tion, employing the product mixture of 1 and 4, rather than tetra-
fluorobenzene was repeated two or three times giving highly pure 1in
a total yield of about 44% based on C F H (3.53 g, 14.8 mmol).
In the following we will present an optimized synthesis,
which allows the preparation of gram quantities of pure
6
4
2
19
H tfBDC by a comparatively simple procedure, also starting
Purity (> 97%) was determined by F-NMR spectroscopy.
2,3,5,6-Tetrafluoroterephthalic Acid Dihydrate (2). Single
crystals of a dihydrate of 1 were obtained by recrystallization
of 1 from a water/acetone mixture.
2
from 1,2,4,5-tetrafluorobenzene, which is available at a reaso-
nable price. Crystal structures of H tfBDC (1), H tfBDC 2H O
2
2
3
2
(
2), and (NH ) tfBDC (3) are presented, as well as the synthesis
4 2
Diammonium-2,3,5,6-tetrafluoroterephthalate (3). A 250.0 mg
portion of tetrafluoroterephthalic acid (1) (1.05 mmol) was sus-
pended in 25 mL of deionized water. Gaseous ammonia was bubbled
through the suspension, until it became clear. Water and excess
ammonia were removed by distillation, and 3was obtained as a white
powder in a total yield of 98% (280.2 mg, 1.03 mmol). After recrystal-
lization from water, colorless flaky crystals suitable for a single crystal
structure determination were obtained after 3 weeks. Elemental anal-
and crystal structure of the monosubstituted 2,3,5,6-
tetrafluorobenzoic acid (4), which can be obtained as a
byproduct using a slightly modified procedure.
Experimental Section
General Remarks. All sample handling was carried out in a
dry argon atmosphere using Schlenk techniques. 1,2,4,5-Tetra-
fluorobenzene was obtained from Molekula and Fluorochem,
n-butyllithium (1.6 M solution in hexane) and magnesium sulfate
from Acros Organics. They were used as purchased. Tetrahydro-
furan (THF) was dried using a MBRAUN MB SPS-800 solvent
purification system. All other solvents were used as purchased.
Synthesis. 2,3,5,6-Tetrafluoroterephthalic Acid (1). Synthe-
sis Protocol (a). In an argon atmosphere, 2.13 g of 1,2,4,5-
tetrafluorobenzene (14.2 mmol, 1.0 equiv) were dissolved in 250
mL of dry THF and cooled to approximately -75 °C. During
8 4 8 4 2
ysis for C O H F N (272.164): calcd N, 10.30%, C, 35.30%, H,
2.96%; found N, 10.24%, C, 35.87%, H, 2.94%. Purity was addition-
ally checked by XRPD. No additional reflections were found.
2,3,5,6-Tetrafluorobenzoic acid (4). 4 was obtained as a bypro-
duct of the synthesis of 1 using the synthesis protocol (b) as de-
scribed above. The fraction boiling between 100-108 °C was
collected and contains almost pure 2,3,5,6-tetrafluorobenzoic acid.
Single crystals were obtained by recrystallization of the crude reac-
tion mixture from acetone. An alternative synthesis of 4 was already
1
described in ref 23. H NMR (acetone-d6): [ppm] = 11.7 (s, 1H;
3
0 min 25 mL of n-BuLi (40.0 mmol, 2.8 equiv) were added
dropwise, while the reaction mixture was stirred. After 4 h of
stirring, CO obtained by sublimating dry ice was bubbled through
3
4
13
COOH) 7.74 (tt, JHF 10.2 Hz, JHF 7.4 Hz, C4-H). C NMR
1
acetone-d6) [ppm] = 160.5 (s; COOH); 146.96 (dm, JCF 243.5 Hz,
(
C3,5), 145.27 (dm, JCF 252.6 Hz, C2,6), 114.76 (t, JCF 18.7 Hz,
2
1
3
the solution, upon which the mixture became a white sludge. The
solvent was removed, and the white solid residue was hydrolyzed
with 100 mL of aqueous HCl (7.5%) and 100 mL of Et O. The aque-
2
3 19
C1), 109.76 (t, J 23.0 Hz, C4). F-NMR (acetone-d6) =
CF
-
139.82 (m, -F2,6), -142.03 (br.s, -F3,5).
X-ray Single Crystal Structure Analysis. Single crystals of
ous phase was additionally extracted two times with each 100 mL
of Et O. The collected ether phases were dried over magnesium
1-5 were isolated as described above and mounted in sealed glass
capillaries on a Stoe four-circle (STADI), Stoe IPDS II, or a Bruker
APEX-II single crystal diffractometer (MoKR radiation). For data
2
sulfate. After removing all volatiles the obtained white raw product
was recrystallized from ethylacetate by adding cyclohexane. The
total yield after recrystallization was 3.2 g (13.4 mmol, 95% based
on C F H ). Elemental analysis for C O H F (238.096): calcd C,
24
collection and reduction the Stoe program package was applied.
The structural models were solved using SIR-92 (3) or SHELXS (1,
2, 4, 5) and completed using difference Fourier maps calculated
with SHELXL-97, which was also used for final refinements.
6
4
2
8
4
2 4
4
0.35%, H, 0.85%; found C, 40.44, H, 0.85%. mp: 275 °C (dec.).
25,26
The melting point is somewhat lower than that given in the literature
(
22
283-284 °C), but agrees well with the melting point of the raw
For the structure of 3 and 5 all programs were run under the
WinGX system. All non-hydrogen atoms were refined anisotro-
22
27
material before recrystallization (261-276 °C) and the commer-
cially available product (275-277 °C, Sigma-Aldrich). We assume
pically. The treatment of hydrogen atoms is described in the
following chapter for each compound. More details of the struc-
22
that recrystallization from water leads to the dihydrate (2), which
shows a slightly higher melting point. Actually, 1 does not melt,
instead it decomposes. A proof based on DTA/TG investigations
2
8
tural analysis are given in Table 1. Selected interatomic distances
and angles are listed in Table 2.
1
will be given below. H NMR (acetone-d6): [ppm] = 11.2 (s, 2H;
COOH). C NMR (acetone-d6) [ppm] = 160.1 (s; COOH); 145.9
13
(23) Tamborski, C.; Soloski, E. J. J. Org. Chem. 1966, 31, 743–745.
1 19
dm; J = 253.1 Hz, C2,3,5,6), 116.4 (m, C1,4). F-NMR
acetone-d6) = -140.75 (s; F2,3,5,6). The purity was checked by
NMR and X-ray Powder Diffraction (XRPD). As no additional
(
(
CF
(24) Stoe, IPDS manual; X-Red 1.22, Stoe Data Reduction Program; Stoe
& Cie GmbH: Darmstadt, Germany, 2001.
(25) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Gualardi, A. J. Appl.
Crystallogr. 1993, 26, 343–350.
1
13 19
signals or reflections were visible in the NMR spectra ( H, C, F)
and XRPD patterns the purity can be estimated to be >98%.
Synthesis Protocol (b). A 5.00 g portion of 1,2,4,5-tetrafluoro-
benzene, (33.3 mmol, 1.0 equiv), dissolved in THF (200 mL),
was cooled to approximately -75 °C, and 42.7 mL of n-BuLi (68.3
mmol, 2.05 equiv) were added over a period of 30 min. The sus-
pension was allowed to stir for 30 min at this temperature never rising
(
26) Sheldrick, G. M. SHELXL-97: A program for crystal structure
refinement, release 97-2; University of G €o ttingen: G €o ttingen, Germany, 1997.
27) WinGX, An Integrated System of Windows Programs for the Solution,
(
Refinement and Analysis of Single Crystal X-Ray Diffraction Data, Version
1.64.04; Department of Chemistry, University of Glasgow: Glasgow, U.K.,
1997-2002; Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(28) Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-770475 (H tfBDC, 1),
CCDC-770476 (H tfBDC 2H O, 2), CCDC-770477 ((NH tfBDC, 3), and
CCDC-770478 (H tfBC, 4). Copies of the data can be obtained free of charge on
over -60 °C. Dried CO
2 4
(passed through a P O10 column) was
bubbled through the solution, 10 min at about -70 °C, and then
2
2
3
2
4 2
)
2
(
22) Harper, R. J.; Soloski, E. J.; Tamborski, C. J. Org. Chem. 1964, 29,
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. [fax.:
2
385–2389.
(internat.) þ 44 1223/336-033; e-mail: deposit@ccdc.cam.ac.uk].

9
352 Inorganic Chemistry, Vol. 49, No. 20, 2010
Orthaber et al.
Table 1. Details of X-ray Single Crystal Structure Determination of Compounds 1-5
tfBDC (1) tfBDC 2H O (2)
H
2
H
2
2
(NH
4
)
2
tfBDC (3)
H
2
tfBC (4)
2 4
H tfBC NH HtfBC (5)
3
3
formula
C
238.10
8
H
2
F
4
O
4
C
274.13
8
H
6
F
4
O
6
C
272.16
8
H
8
F
4
O
4
N
2
C
7
H
2
F
4
O
2
14 7 8 4
C H F O
formula weight
crystal description
crystal size
194.09
block, colorless
0.24 ꢀ 0.18
405.21
needles, colorless
0.44 ꢀ 0.06
block, colorless
0.36 ꢀ 0.22
block, colorless
0.40 ꢀ 0.36
platelet, colorless
0.2 ꢀ 0.1
ꢀ
0.18 mm
P1 (No. 2), 1
ꢀ 0.36 mm
ꢀ 0.1 mm
ꢀ 0.12 mm
ꢀ 0.04 mm
space group; Z
P2 /c (No. 14), 2
1
C2/m (No. 12), 2
Fdd2 (No. 43), 16
Flack x = -0.5(10)
1 1 1
P2 2 2 (No. 19), 4
Flack x = 0.2 (7)
unit cell
˚
a, A
4.565(2)
5.832(2)
7.452(2)
87.32(3)
78.41(3)
74.11(3)
186.92(10)
2.115
8.5206(15)
7.9910(8)
7.2845(14)
90
99.739(15)
90
488.84(14)
1.862
none
6.632(2)
19.771(6)
3.7145(11)
90
92.38(3)
90
10.1937(15)
12.890(3)
20.425(4)
90
90
90
2683.8(9)
1.921
none
Stoe four-circle
(STADI), MoKR
-178(2)
52.00
6.5616(3)
7.2376(4)
30.442(2)
90
90
90
1445.71(13)
1.862
none
Bruker APEX-II
CCD, MoKR
-183(2)
52.00
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
volume, A
calc. density, g cm
3
˚
486.6(3)
1.857
-3
3
absorption correction
diffractometer, radiation
none
Stoe four-circle
numerical
Stoe IPDS II,
MoKR
20(2)
59.00
-9 e h e 9
-27 e k e 27
-5 e l e 4
2857/701
Stoe four-circle
(STADI), MoKR
-178(2)
(
STADI), MoKR
temperature, °C
-178(2)
60.00
2
index ranges
θmax, deg
60.00
-6 e h e 6
-9 e h e 11
-11 e k e 11
-10 e l e 10
2758/1426
0 e h e 12
-1 e k e 15
-1 e l e 25
898/683
-8 e h e 8
-8 e k e 7
-37 e l e 37
25193/2825
-
8 e k e 8
9 e l e 10
-
1376/1086
reflections
collected/independent
significant reflections,
with I > 2σ(I)
R(int)
data/parameters/
restraints
951
1314
479
652
2285
0.030
1086/76/0
0.026
1426/94/3
0.054
701/52/2
0.016
683/127/1
0.048
2825/257/4
GoF = Sall
1.08
0.034
0.091
0.38/-0.24
1.07
0.035
0.091
0.38/-0.26
1.00
0.041
0.103
0.26/-0.20
1.07
0.025
0.063
0.18/-0.24
1.04
0.031
0.081
0.23/-0.21
2
2
R [F >2σ(F I)]
wR(F )
2
-3
˚
ΔFmax/ΔFmin, e A
3
2
2
XRPD. XRPD data were collected on a Huber G670 with a
radiation at room
temperature, with exposure times of approximately 2 h. Samples
literature and was confirmed by us (see protocol (b)). So the
synthesis described in protocol (a), which exclusively leads to
germanium monochromator and Cu KR
1
H tfBDC, presents a convenient route to gram quantities of
2
were sealed in capillaries (Ø 0.3-0.5 mm). Within the WinXPow
pure 1.
2
9
software suite the recorded patterns were compared with theore-
tical patterns calculated from the obtained crystal structure data.
Thermoanalytical Investigations. A differential thermal anal-
ysis (DTA) and thermogravimetry (TG) investigation was per-
formed on diammonium-2,3,5,6-tetrafluoroterephthalate (3)
Crystal Structure of 2,3,5,6-Tetrafluoroterephthalic
Acid (1). Compound 1 crystallizes in the triclinic space
group P1 as colorless blocks from acetone. The unit cell
constants are quite similar to those previously reported in
X-ray and neutron diffraction studies of the deuterated deri-
(
sample mass: 19.1 mg) in the temperature range 24-400 °C
30
using a Netzsch STA 409C housed in a glovebox (M. Braun,
Garching/Germany), heating rate 10 °C/min.
NMR. NMR spectra have been recorded on a Bruker Avance
vative, which have been performed at room temperature.
The molecular structure of 1 (Figure 1) is almost identical to
the reported structures from these studies, although slight
deviations occur. For instance, the plane of the carboxylate
group is twisted by 19.3(1)° around the bond C1-C7 out of
the least-squares plane of the aryl ring, which is slightly
smaller than reported for the structure of the perdeuterated
acid (19.8(1)°). But in both structures a disordered proton
H1 is found. This disorder is also reflected in similar C7-O1
and C7-O2 distances (Table 2).
Compound 1 shows an infinite one-dimensional chain
structure (Figure 2) connected by hydrogen bonds between
neighboring carboxylate units. As mentioned the H atoms of
the OH groups are disordered over two sites. They were re-
fined with site occupation factors of 0.5, tetrahedral C-O-
H angles, enabling rotation around the C-O bond, O-Hdis-
1
13
19
3
00 spectrometer ( H, 300.13 MHz, C, 75.47 MHz, F, 282.35
MHz), with H decoupling for F and C. Chemical shifts are
1
19
13
1 13
specified relative to the residual solvent signal ( H, C) and
1
9
3
CCl F as internal standard ( F).
Results and Discussion
Pure 2,3,5,6-tetrafluoroterephthalic acid (H tfBDC, 1) is
2
obtained in high yields (95%) by reacting 1,2,4,5-tetrafluoro-
benzene with a surplus (>2 equiv) of n-BuLi in THF and sub-
sequent carbonation with CO without any extensive purifica-
2
tion procedure. The underlying reactions are summarized in
Scheme 1. It was found that a larger surplus (approximately
2.8 equiv) of n-BuLi is needed to avoid the formation of the
monosubstituted product 2,3,5,6-tetrafluorobenzoic acid (4).
A mixture of the mono- and disubstituted products makes an
extensive purification procedure necessary, as was shown in the
˚
tances of 0.84 A, and with individual isotropic displacement
parameters. Relevant distances and angles of the hydrogen
bonds are given in Table 3.
(
29) Win XPOW, Version 1.04; Stoe & Cie GmbH: Darmstadt, Germany,
(30) Schajor, W.; Post, H.; Grosescu, R.; Haeberlen, U.; Blockus, G.
1
999.
J. Magn. Reson. 1983, 53, 213–228.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9353
˚
Table 2. Selected Interatomic Distances [A] and Angles [deg] for Compounds 1-4
H
2
tfBDC (1)
1.395(2)
H
2
tfBDC 2H
3
2
O (2)
(NH
4
)
2
tfBDC (3)
2
H tfBC (4)
C1-C3
C1-C2
C2-C3
C1-C7
C1-C2
1.391(2)
1.394(2)
1.384(2)
1.502(2)
C1-C3
C3-C3
C1-C2
1.389(2)
1.380(3)
1.524(3)
C11-C12
C12-C13
C13-C14
C11-C15
C21-C22
C22-C23
C23-C24
C21-C25
1.399(3)
1.376(4)
1.379(3)
1.499(5)
1.392(3)
1.383(3)
1.375(3)
1.488(5)
1.397(2)
1.383(2)
1.500(2)
C1-C3
C2-C3
C1-C4
C2-F2
C3-F3
1.3310(13)
1.3379(13)
C2-F2
C3-F3
1.3406(12)
1.3411(13)
F1-C3
C2-O1
1.343(2)
1.244(2)
C12-F12
C13-F13
C22-F22
C23-F23
1.343(3)
1.347(3)
1.339(3)
1.343(3)
C7-O1
C7-O2
1.257(2)
1.2638(14)
C4-O1
C4-O2
1.2194(14)
1.3042(14)
C15-O15
C25-O25
C14-H14
C24-H24
1.266(2)
1.270(2)
0.95
0.95
C3-C1-C2
C3-C2-C1
C2-C3-C1
C3-C1-C7
C2-C1-C7
115.81(10)
121.85(10)
122.34(10)
121.94(10)
122.23(10)
C2-C1-C3
C3-C2-C1
C2-C3-C1
C2-C1-C4
C3-C1-C4
116.72(10)
122.01(10)
121.26(10)
120.43(10)
122.82(10)
C3-C1-C3
C3-C3-C1
C3-C1-C2
115.9(2)
122.05(9)
122.05(9)
C12-C11-C12
C13-C12-C11
C12-C13-C14
C13-C14-C13
C12-C11-C15
C22-C21-C22
C23-C22-C21
C24-C23-C22
C23-C24-C23
C22-C21-C25
116.5(3)
121.3(3)
121.7(3)
117.5(3)
121.73(14)
117.5(3)
121.0(2)
120.8(2)
118.9(3)
121.3(2)
F2-C2-C3
F2-C2-C1
F3-C3-C2
F3-C3-C1
116.65(10)
121.49(10)
116.46(10)
121.18(10)
F2-C2-C3
F2-C2-C1
F3-C3-C2
F3-C3-C1
117.77(10)
120.17(10)
118.01(10)
120.70(10)
F1-C3-C3
F1-C3-C1
117.93(7)
120.00(13)
F12-C12-C13
F12-C12-C11
F13-C13-C12
F13-C13-C14
F22-C22-C23
F22-C22-C21
F23-C23-C24
F23-C23-C22
117.8(2)
120.9(2)
118.3(2)
120.0(2)
118.2(2)
120.6(2)
120.8(2)
118.5(2)
O1-C7-O2
125.42(11)
O1-C4-O2
125.21(10)
O1-C2-O1
O1-C2-C1
125.7(2)
O15-C15-O15
O25-C25-O25
124.5(3)
124.2(3)
O1-C7-C1
O2-C7-C1
117.69(10)
116.89(10)
O1-C4-C1
O2-C4-C1
121.13(10)
113.66(10)
117.13(10)
O15-C15-C11
O25-C25-C21
117.7(2)
117.9(2)
C7-O1-H1
C7-O2-H2
109.5
109.5
C4-O2-H2
109.8
104.6
C15-O15-H15
C25-O25-H25
C13-C14-H14
C23-C24-H24
109.5
109.5
121.2
120.5
H31-O3-H32
H1-N1-H2
109(2)
Scheme 1. Reactions of 1,2,4,5-Tetrafluorobenzene with Different Amounts of n-BuLi and Subsequent Carbonation with CO
2
The packing of the structures of 1 and its deuterated
translation along the crystallographic a-axis showing a
0
30
˚
congener reveal, however, significant differences. In dif-
ferent layers the infinite chains are arranged in a way that
the carboxylate groups are above and below the aryl rings
of the neighboring layers for 1, while in the deuterated
variety the aryl rings are stacked above each other. In 1 the
planes of the aryl rings of different layers are related by
distance C3-C3 of 3.294(2) A, which is significantly shor-
ter than in its perdeuterated analogue (3.377 A). Con-
˚
comitantly, the centroids of the aryl rings are closer in 1
˚
˚
(4.565(2) A) than in the deuterated variety (4.617(2) A).
This arrangement results in a short intramolecular contact
˚
between the layers (O1-O2: 3.033(2) A). Furthermore,

9
354 Inorganic Chemistry, Vol. 49, No. 20, 2010
Orthaber et al.
Figure 1. ORTEP diagram of H
thermal ellipsoids and the atom-numbering scheme. Hydrogen atoms
H1, H2) are disordered over two sites with occupancy of 0.5.
2
tfBDC (1) showing 50% probability
(
Figure 3. ORTEP diagram of H
ability thermal ellipsoids and the atom-numbering scheme.
2
tfBDC 2H O (2) showing 50% prob-
2
3
˚
Table 3. Hydrogen Bonds (A, deg) in Compounds 1-5
D-H
3 3 A
D-H
H
3 3 3 A
D
3 3 3 A
D-H 3 3 3 A
3
H
2
tfBDC (1)
O1-H1 O2
0.84
0.84
1.84
1.83
2.655(2)
2.655(2)
162
168
3
3 3
O2-H2 O1
3
3 3
H
2
tfBDC 2H
3
2
O (2)
O2-H2
3 3 O3
0.95
0.95
0.95
1.59
1.95
1.89
2.540(1)
2.859(1)
2.817(1)
174
160
164
3
O3-H31 O1
3
3 3
O3-H32 O1
3
3 3
(
NH
4
)
2
tfBDC (3)
N1-H1 O1
0.97(2)
0.98(2)
1.93(2)
1.98(2)
2.821(2)
2.908(2)
151(2)
158(2)
3
3 3
N1-H2 O1
3
3 3
H
2
tfBC (4)
O15-H15 O25
0.95
0.95
1.72
1.76
2.644(2)
2.644(2)
163
154
3
3 3
O25-H25 O15
3
3 3
2
Figure 2. Packing diagram of H tfBDC (1) (C: white, O: red, F: green).
Disordered hydrogen atoms have been omitted for clarity. Hydrogen
bonds between oxygen atoms are drawn as red broken lines.
H
2
tfBC NH
3
4
HtfBC (5)
O1-H1B O4
0.84
0.84(2)
1.71
2.09(2)
2.541(2)
2.868(2)
171
153(2)
3
3 3
N1-H3 O3
3
3 3
˚
˚
short F-Caryl (2.979(2) A-3.109(2) A) contacts contribute
to the packing of this structure.
˚
to a bond length of 0.95 A, but no further constraints were
applied to the hydrogen atoms. Structural parameters for
the perfluoro aryl moiety are almost identical to the
parameters of 1 (Table 2). The carboxylate group shows
two distinctive CO distances of 1.219(1) A and 1.304(1) A,
which is in the typical range for CdO and C-O bonds,
respectively. The planes spanned by the aryl moiety and
the carboxylate group enclose an angle of 39.9(1)°, which
is significantly larger than in 1. The acids are bridged
According to a preliminary DTA/TG investigation a
mass loss of 1 accompanied by an exothermal signal
started at approximately 220 °C. This process is finished
at approximately 290 °C with no mass remaining. To
prove whether this effect is due to decomposition or
sublimation of 1, in an additional experiment performed
in an argon atmosphere some of the gases evolved upon
heating were condensed at the wall of a glass tube. XRPD
data revealed that the colorless solid is solely 2,3,5,6-
tetrafluorobenzoic acid (4). Thus, 1 decomposes to give 4
by releasing CO2:
˚
˚
by H O molecules (Figure 4). The O-H O distances
2
3 3 3
˚
˚
˚
are 1.59(2) A, 1.89(2) A, and 1.95(2) A (Table 3). Via these
hydrogen bonds the acids are connected to a complex
three-dimensional (3D) structure.
2
20 - 290 °C
Crystal Structure of Diammonium-2,3,5,6-tetrafluoro-
terephthalate (3). Compound 3 crystallizes in the mono-
clinic spacegroup C2/m as colorless platelets. Hydrogen
atoms were located in difference Fourier maps and re-
p-HOOC-C6F4-COOH ð1Þ
f
H-C6F4-COOH ð4Þ þ CO2 ð4Þ
Crystal Structure of 2,3,5,6-Tetrafluoroterephthalic
Acid Dihydrate (2). In the presence of water, 1 forms a
˚
1
:2 adduct with this solvent (Figure 3). Compound 2
crystallizes in the monoclinic space group P2 /c. The
fined with fixed N-H distances (1.00(2) A) (Figure 5).
The resulting N-H bond lengths and H-N-H bond
angles (Tables 2 and 3) agree well with those expected for
a perfect tetrahedral NH4 cation. Structural parameters
1
hydrogen atoms were refined with individual isotropic
displacement parameters. All O-H distances were fixed
þ

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9355
2 2
Figure 4. Packing diagram of H tfBDC 2H O (2) (C, white; O, red;
3
F, green; H, white, small spheres). Hydrogen bonds are drawn as red
broken lines.
Figure 6. Packing diagram of (NH
001] (C, white; O, red; F, green; N, blue; H, white, small spheres). Hydro-
gen bonds are drawn as red broken lines.
4 2
) tfBDC (3) in a projection along
[
4 2
Figure 5. ORTEP diagram of (NH ) tfBDC (3) showing 50% prob-
ability thermal ellipsoids and the atom-numbering scheme.
for the perfluoro aryl moiety are almost identical to the
parameters obtained for 1 and 2 (Table 2). The perfluoro
aryl moieties are aligned parallel to each other along
[
010]. The carboxylate groups of one tfBDC anion are
parallel to each other and enclose an angle of 44.5(2)° with
the plane of the aryl ring. This twist is much larger than in 1,
slightly larger than in 2 and also larger than in the non-
31
fluorinated congener (18(1)° and 29(2)°). But as the latter
was solved and refined from powder diffraction data the
reliability of these angles is somewhat lower. Thus, a further
comparison between the fluorinated and the non-fluorinated
compound shall be omitted here. The tfBDC anions are
bridged via oxygen atoms of the carboxylate groups and
4 2
Figure 7. (NH ) tfBDC (3): DTA (blue) and TG (black) curves.
3
2
CO , and C H gives an exothermic signal. To check
2
2
2
whether 3decomposes or sublimes, some of the gases evolved
upon heating were condensed at the wall of a glass tube in an
argon atmosphere. XRPD data revealed that the collected
colorless solid is neither 3 (sublimation) nor 1 or 4 (decom-
position). By recrystallization from dry acetone single crys-
tals have been obtained. According to the structure solution,
the composition of this new compound (5) can be described
as a 1:1 adduct of 2,3,5,6-tetrafluorobenzoic acid (4) with its
ammonium salt (Figure 8). Elemental analysis of the white
residue gave N, 5.98%, C, 40.90%, H, 2.28%. The calculated
values for 5 are C O H F N (405.201): N, 3.46%, C,
41.50%, H, 1.74%. The large deviation between these values
proves that the collected white residue does not contain
,3,5,6-tetrafluorobenzoic acid and ammonium 2,3,5,6-tetra-
fluorobenzoate in a 1:1 ratio. The high value for nitrogen
indicates a higher fraction of ammonium 2,3,5,6-tetrafluoro-
benzoate.
Crystal Structure of Ammonium 2,3,5,6-Tetrafluoro-
benzoate 2,3,5,6-Tetrafluorobenzoic Acid Adduct (5). Com-
pound 5 crystallizes in the orthorhombic chiral space group
protons of the ammonium cations to form a 3D structure
(Figure 6). As each oxygen atom is connected to two NH4
cations the tfBDC anion acts as an 8-connector. Consistently,
þ
þ
each NH4 cation connects to four different tfBDC anions.
The resulting H O distances of these hydrogen bonds are
3
3 3
˚ ˚
.93(2) A and 1.98(2) A. We found that 3 shows an enhanced
1
solubility in water compared to 1. This makes 3 an attractive
candidate for the synthesis of new coordination polymers
14
4
7 8
2-
with tfBDC as bridging ligand in aqueous solutions.
To explore the thermal stability of 3 we performed basic
thermoanalytical measurements. In Figure 7 results of the
DTA/TG investigation on 3 are shown. Starting at approxi-
mately 225 °C a complete mass loss is observed, which is
accompanied by a strong endothermic signal. This effect is
finished at about 300 °C. For comparison decomposition
2
2-
of (NH ) ADC (ADC =acetylenedicarboxylate) to NH ,
4
2
3
(
31) Kaduk, J. A. Acta Crystallogr., Sect. B: Struct. Sci. 2000, 56, 474–
4
85.
(32) Stein, I.; N €a ther, C.; Ruschewitz, U. Solid State Sci. 2006, 8, 353–358.

9
356 Inorganic Chemistry, Vol. 49, No. 20, 2010
Orthaber et al.
Figure 9. ORTEP diagram of H tfBC (4) showing 50% probability
2
thermal ellipsoids and the atom-numbering scheme. Hydrogen atoms
(H15, H25) are disordered over two sites with occupancy of 0.5.
2 4
Figure 8. ORTEP diagram of H tfBC (NH )HtfBC (5) showing 50%
3
probability thermal ellipsoids and the atom-numbering scheme. The H
atom of carboxylic acid was refined isotropically with tetrahedral
C-O-H angles.
3
3
P2 2 2 as colorless needles (Table 1). All non-hydrogen
1
1 1
atoms were refined with anisotropic displacement para-
meters without any constraints. The H atoms H5 and H12
were put at the external bisector of the C-C-C angle at a
˚
C-H distance of 0.95 A, but the individual isotropic
displacement parameters are free to refine. H atoms of the
ammonium ion are located in the difference Fourier map
and refined isotropically. The H atom of carboxylic acid was
refined isotropically with a tetrahedral C-O-H angle.
Owing to the lack of heavier atoms, determination of the
absolute structure was not possible. In 5 tetrafluorobenzoic
34
2
Figure 10. PackingdiagramofH tfBC(4) (C, white, O, red, F, green, H,
acid forms a quite strong hydrogen bond to tetrafluoro-
benzoate via the carboxylic OH group (donor-acceptor
white, small spheres). Disordered hydrogen atoms (H15, H25) have been
omitted for clarity. Hydrogen bonds between oxygen atoms are drawn as
red broken lines.
˚
D/A] distance 2.541(2) A), which is significantly shorter
[
than in 1 and 4. A second hydrogen bond between the ion
bonds between the phenyl rings and the carboxylate groups
(
pairs of the tetrafluorobenzoate and the ammonium ion
˚
φ= 22.8(1)° and φ= 40.9(1)° for C11-C15 and C21-C25,
(D/A distance 2.833(2) A) is formed, resulting in a 2-dimen-
respectively) resulting in a torsional angle between the two
aryl groups of 60.9(1)°. Structural parameters of the phenyl
ring and the carboxylic moiety in 4 are almost identical to its
disubstituted congener 1 (Table 2). The F22 H24 and
sional network built up by the ammonium ion acting as a
-connector. The carboxylic groups are twisted out of the
4
least-squares planes of the aryl rings by 40.2(1)° and 50.1(1)°
for the tetrafluorobenzoic acid and the tetrafluoro-
benzoate, respectively, which is for the latter even larger
than in 3. In essence, the composition of 5 proves that the
thermal decomposition of 3 involves the release of both CO2
and NH3.
3
3 3
˚
˚
F12 H14 distances are 2.418(2) A and 2.771(2) A, whichis
3
3 3
for the former significantly shorter than the sum of their van
˚
der Waals radii (2.67 A). The axis along the dimers is
perpendicular to the (001) plane (Figure 10). This is in sharp
contrast to crystal structures of benzoic acid, which also
forms dimers in the solid state, but in the packing two
Crystal Structure of 2,3,5,6-Tetrafluorobenzoic Acid
4). Compound 4 crystallizes in the acentric orthorhombic
(
35,36
distinctive orientations of the dimers are found.
space group Fdd2 as colorless blocks. Non-hydrogen atoms
were refined with anisotropic displacement parameters with-
out any constraints. The H atoms H14 and H24 were put at
the external bisector of the C-C-C angleat a C-H distance
Conclusion
By a simple modification of the synthesis known from the
22
˚
literature we developed a convenient synthesis for pure
2,3,5,6-tetrafluoroterephthalic acid (H tfBDC). Just by add-
of 0.95 A, but the individual isotropic displacement para-
meters are free to refine. The disordered H atoms H15 and
H25 of the COOH groups were refined with site occupation
factors of 0.5, tetrahedral C-O-H angles, enabling rotation
2
ing a surplus of n-BuLi the formation of the byproduct
2,3,5,6-tetrafluorobenzoic acid is suppressed so that an
extensive purification procedure no longer is necessary. This
allows the synthesis of gram quantities of this acid with
˚
around the C-O bond, O-H distances of 0.95 A, and with
individual isotropic displacement parameters. The molecules
are lying on 2-fold axes parallel to the c-axis forming dimers
held together by two hydrogen bonds (Figure 9). Whereas
the two carboxylate groups are almost coplanar (angle
between the root mean square (rms) planes φ = 2.7(1)°),
there are considerable torsions around the C-C single
2-
comparatively low efforts. As tfBDC is expected to be an
important ligand in the synthesis of coordination polymers
and MOFs we think that this synthesis might boost the
research with this ligand. Several compounds have already
9-21
been synthesized with this ligand,
but only few of them
show permanent porosity. To the best of our knowledge an
“all-F-MOF” is still unknown, although such a compound
(
33) Crystallographic data (excluding structure factors) for the structure
of 5 have been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication no. CCDC-790323. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road, Cambridge
Cc c Bd 2c . c1 aE mZ . ,a cU . uK k] [. fax.: (internat.) þ 44 1223/336-033; e-mail: deposit@
(35) Bruno, G.; Randaccio, L. Acta Crystallogr., Sect. B: Struct. Sci.
1980, 36, 1711–1712.
(36) Wilson, C. C.; Shankland, N.; Florence, A. J. J. Chem. Soc., Faraday
Trans. 1996, 92, 5051–5057.
(
34) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48–76.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9357
should show interesting hydrogen storage properties and
would be a perfect model compound for the investigation
In contrast, for the fluorinated compounds the carboxylate
groups are tilted with respect to the plane of the aryl rings
(1: 19.35(7)°; 4: 22.8(1)° and 40.9(1)°, respectively), whereas in
the non-fluorinated compounds they are almost coplanar.
of H bonding sites in such a MOF, as no deuteration of the
2
ligand for neutron diffraction experiments is necessary. But it
was stated that “a second, non-fluorinated ligand is usually
necessary to facilitate the incorporation of perfluorinated
The crystal structure of the non-fluorinated congener (Pbc2 ,
1
3
1
Z=4) of 3 (C2/m, Z=2) was solved and refined from
synchrotron powder diffraction data. Here angles between
the planes of the carboxylate groups and the aryl ring of
29.0(8)° and 31(1)° are found, which are also significantly
smaller than in 3 (44.54(7)°). Thus, the presence of the F
atoms reduces the electron density in the aryl rings and
therefore conjugation between the aryl π-system and the
carboxyl group, which in turn allows stronger deviations
from the coplanarity. Furthermore, deviation from copla-
narity may be a consequence of electrostatic repulsion
21
dicarboxylates into hybrid structures”. With gram quanti-
ties of H tfBDC at hand at comparatively low costs, it might
2
be worthwhile to prove whether this assumption is correct.
Next to H tfBDC (1) the dihydrate H tfBDC 2H O (2),
2
2
3
2
the ammonium salt (NH ) tfBDC (3), and the monosubsti-
4
2
tuted acid H tfBC (4) were synthesized and characterized by
2
an X-ray single crystal structure analysis. 1 and 4 exhibit
hydrogen bonding via the carboxylate groups, which leads to
a dimer in 4 (Figure 9) and a chain-like polymer in 1
38,39
(Figure 2). In both compounds the proton is disordered. In
between O and the o-fluorine atoms.
Both effects work
2
3
additionally water molecules are included so that a complex
D hydrogen bonding network is formed (Figure 4), where,
synergistically and illustrate nicely that structural properties
of non-fluorinated compounds cannot be transferred one to
one to their fluorinated counterparts. This different structural
behavior might be among the reasons why perfluorinated
analogues of MIL-53 or MOF-5 are currently still unknown.
with respect to the distances, the strongest hydrogen bond is
˚
found (O2-H2 O3; D A 2.540(1) A, Table 3), which
3 3 3 3 3
3
are comparable to those found for 5 (O1-H1B O4;
3 3
3
þ
˚
A 2.541(2) A, Table 3) . In 3 the cations (NH ) and
4
D
3
3 3
2-
anions (tfBDC ) are connected by hydrogen bonds again
arranged in a 3D network (Figure 6).
For 1, 3, and 4 non-fluorinated congeners are known,
but all of them exhibit crystal structures with distinct differ-
ences compared to the fluorinated counterparts, although
the general structural arrangements of 1 (P1, Z=1) and its
Acknowledgment. The authors R.P. and A.O. would
like to thank the Austrian Science Fund (FWF) for
financial support (Projects P20575 N19 and P18591-
B03). The authors U.R. and C.S. would like to thank
I. Pantenburg and I. M u€ ller for collecting X-ray single
crystal diffraction data and P. Kliesen for the DTA/TG
investigations. Special thanks shall be expressed to
B. Hoge for many fruitful discussions.
37
non-fluorinated congener (P1, Z = 1) , both form infinite
chains of H tfBDC and H BDC molecules linked by double
2
2
hydrogen bonds, and 4 (Fdd2, Z=16) and its non-fluorinated
3
6
congener (P2 /c, Z = 4) , both form dimers with disordered
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
H atoms participating in the hydrogen bonds, are very similar.
(
(
37) Bailey, M.; Brown, C. J. Acta Crystallogr. 1967, 22, 387–391.
38) Wang, Z.; Kravtsov, V. C.; Walsh, R. B.; Zaworotko, M. J. Cryst.
(39) Hulvey, Z.; Furman, J. D.; Turner, S. A.; Tang, M.; Cheetham, A. K.
Growth Des. 2007, 7, 1154–1162.
Cryst. Growth Des. 2010, 10, 2041–2043.