A novel Zn4O-based triazolyl benzoate MOF: Synthesis, crystal structure, adsorption properties and solid state 13C NMR investigations

Article abstract of DOI:10.1039/c1dt11431j

The newly synthesized Zn₄O-based MOF ³ _∞[Zn₄(μ₄-O){(Metrz-pba) ₂mPh}₃]·8 DMF (1·8 DMF) of rare tungsten carbide (acs) topology exhibits a porosity of 43% and remarkably high thermal stability up to 430 °C. Single crystal X-ray structure analyses could be performed using as-synthesized as well as desolvated crystals. Besides the solvothermal synthesis of single crystals a scalable synthesis of microcrystalline material of the MOF is reported. Combined TG-MS and solid state NMR measurements reveal the presence of mobile DMF molecules in the pore system of the framework. Adsorption measurements confirm that the pore structure is fully accessible for nitrogen molecules at 77 K. The adsorptive pore volume of 0.41 cm³ g^-1 correlates well with the pore volume of 0.43 cm³ g^-1 estimated from the single crystal structure.

Full text of DOI:10.1039/c1dt11431j

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PAPER
A novel Zn4O-based triazolyl benzoate MOF: synthesis, crystal structure,
adsorption properties and solid state 13C NMR investigations†
Jo¨rg Lincke,a Daniel La¨ssig,a Karolin Stein,a Jens Moellmer,b Anusree Viswanath Kuttatheyil,c
Christian Reichenbach,c Andreas Moeller,b Reiner Staudt,d Grit Kalies,c Marko Bertmerc and
Harald Krautscheid*a
Received 28th July 2011, Accepted 14th September 2011
DOI: 10.1039/c1dt11431j
The newly synthesized Zn4O-based MOF 3•[Zn4(m4-O){(Metrz-pba)2mPh}3]·8 DMF (1·8 DMF) of rare
tungsten carbide (acs) topology exhibits a porosity of 43% and remarkably high thermal stability up to
430 ◦C. Single crystal X-ray structure analyses could be performed using as-synthesized as well as
desolvated crystals. Besides the solvothermal synthesis of single crystals a scalable synthesis of
microcrystalline material of the MOF is reported. Combined TG-MS and solid state NMR
measurements reveal the presence of mobile DMF molecules in the pore system of the framework.
Adsorption measurements confirm that the pore structure is fully accessible for nitrogen molecules at
77 K. The adsorptive pore volume of 0.41 cm3 g-1 correlates well with the pore volume of 0.43 cm3 g-1
estimated from the single crystal structure.
Introduction
In the last decades, metal–organic frameworks (MOFs) as highly
porous materials have gained increasing interest because of their
distinct adsorption properties.1 They exhibit a high potential for
applications in gas separation and storage,2 as sensors3 as well as in
heterogeneous catalysis.4 The potential of MOFs as porous solids
has been impressively demonstrated by the archetypical MOF-
55 and HKUST-1.6 While pure carboxylate ligands have been
extensively studied, less investigated nitrogen-containing hetero-
cycles such as pyrazoles, 1,2,4-triazoles, and tetrazoles were found
2-
Scheme 1 The {(Metrz-pba)2mPh} ligand.
to possess promising coordination chemistry for the synthesis of
ligand (cf. Scheme 1). The newly synthesized ligand can be
MOFs.7 In our work, we have developed a series of polyfunctional
regarded as a combination of two single (Me2trz-pba)- 8 molecules
organic linkers combining both, anionic carboxylates and neutral
with replacement of one methyl group each by a meta-substituted
1,2,4-triazole donors.8 On the basis of this series of ligands we have
phenylene spacer. In this way, an up to now unknown tetraden-
presented molecular building blocks for MOF synthesis,9 electron
tate linker with two 1,2,4-triazole and two carboxylate units is
paramagnetic resonance investigations on heteronuclear CoII/ZnII
generated.
and CoII/CdII coordination polymers10 as well as adsorption
In this work we present the novel three-dimensional mi-
studies on highly porous flexible copper based MOFs.11,12 In the
3
croporous framework •[Zn4(m4-O){(Metrz-pba)2mPh}3]·8 DMF.
present study, we focus on 4,4¢-(5,5¢-(1,3-phenylene)bis(3-methyl-
Besides the single crystal structure, PXRD as well as temperature
2-
4H-1,2,4-triazole-5,4-diyl))dibenzoate {(Metrz-pba)2mPh} as a
dependent PXRD and TG-MS characterization data, solid state
13C NMR spectra and adsorption properties of the desolvated
aUniversita¨t Leipzig, Fakulta¨t fu¨r Chemie und Mineralogie, Johannisallee
microporous material are discussed. It is shown that a combined
29, D-04103, Leipzig, Germany. E-mail: Krautscheid@rz.uni-leipzig.de;
application of all methods allows to gain deeper insights into the
real structure and properties of this MOF.
Fax: (+49) 341 9736199; Tel: (+49) 341 9736172
bInstitut fu¨r Nichtklassische Chemie e.V., Permoserstraße 15, D-04318,
Leipzig, Germany
cUniversita¨t Leipzig, Fakulta¨t fu¨r Physik und Geowissenschaften,
Linne´straße 5, D-04103, Leipzig, Germany
X-ray single crystal structures
dHochschule Offenburg, Fakulta¨t fu¨r Maschinenbau und Verfahrenstechnik,
Badstraße 22, D-77624, Offenburg, Germany
3
Single crystals of •[Zn4(m4-O){(Metrz-pba)2mPh}3]·8 DMF
(1·8 DMF) were obtained under autogenous pressure from
an excess of Zn(NO3)2·6 H2O and the protonated ligand
† CCDC reference numbers 836622 and 836623. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1dt11431j
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Table 1 Selected bond lengths and angles of 1·8 DMF and 1
4,4¢-(5,5¢-(1,3-phenylene)bis(3-methyl-4H-1,2,4-triazole-5,4-
diyl))dibenzoic acid hydrate, H2{(Metrz-pba)2mPh}·H2O, in N,N-
dimethylformamide (DMF) at 140 ◦C. Larger amounts of mi-
crocrystalline material of 1·8 DMF were obtained by refluxing
Zn(NO3)2·6 H2O and H2{(Metrz-pba)2mPh}·H2O in 4 : 3 stoi-
chiometry in DMF for 36 h. Single crystals of 1·8 DMF were
desolvated by slow heating to 180 ◦C at ambient pressure within
24 h. The temperature was maintained for 4 h followed by
cooling to room temperature over a period of 12 h, yielding
the desolvated compound 1. During this process, a mass loss
of 24.5% was observed. While the single crystals remain intact,
only slight changes in the unit cell parameters are observed. Thus,
the crystallographic a axis becomes longer by 25 pm, while the
crystallographic c axis becomes shorter by 27 pm.
Bond length in pm
Angle in (◦)
Atoms
1·8 DMF 1
Atoms
1·8 DMF
1
O1–Zn1
O1–Zn2
O2–Zn1
O4–Zn2
191.3(6) 192.3(3) Zn1–O1–Zn2
197.8(2) 198.23(7) Zn2–O1–Zn2b 114.0(1) 114.31(6)
194.1(4) 195.0(2) O1–Zn1–O2
196.2(4) 197.0(2) O2–Zn1–O2b
104.4(2) 104.05(8)
113.2(2) 112.55(6)
105.5(2) 106.22(7)
135.3(2) 134.52(9)
Zn2–O3b 206.4(4) 205.4(2) O4–Zn2–N1a
Zn2–N1a 200.3(5) 202.5(2)
C1–O2
C1–O3
C11–O4
C11–O5
127.8(7) 127.4(4)
123.4(8) 125.4(4)
126.7(8) 127.8(4)
123.8(8) 123.7(4)
Both 1·8 DMF and 1 crystallize in the non-centrosymmetric
trigonal space group P 31c (no. 159) with two formula units
per unit cell. The [Zn4(m4-O)]6+ core as central structural motif
resides on the threefold axis, as shown in Fig. 1. The asymmetric
unit represents one third of the formula sum and contains two
crystallographically independent Zn2+ ions, an O2- anion and one
In MOF-5, the [Zn4(m4-O)]6+ core is surrounded by six biden-
tately binding carboxylate groups from the terephthalate ligands,
whereas in 1·8 DMF the monodentate carboxylate and triazole
groups lead to a unique SBU of lower symmetry that is up to
now unknown in the literature. Nevertheless, both SBUs resemble
each other in the bond lengths Zn1–O1 (MOF-5 193.5(2) pm;
1·8 DMF 191.3(6) pm; 1 192.3(3) pm) and Zn1–O2 (MOF-5
191.1(9) pm; 1·8 DMF 194.1(4) pm; 1 195.0(2) pm) as well as
in the bond angles O1–Zn1–O2 (MOF-5 112.4(3)◦; 1·8 DMF
104.4(2)◦; 1 112.55(6)◦) and O2–Zn1–O2 (MOF-5 106.4(4)◦; 1·8
DMF 105.5(2)◦; 1 106.22(7)◦). As in MOF-5, the SBU of 1·8 DMF
and 1 represents a six-connected nodal point, although there are
nine coordinating functional groups. This can be explained by the
2-
dianionic ligand {(Metrz-pba)2mPh} .
2-
fact that despite the two carboxylates per {(Metrz-pba)2mPh}
ligand that coordinate to the same [Zn4(m4-O)]6+ core, only one
out of two principally available triazoles coordinates. As a result,
2-
each {(Metrz-pba)2mPh} ligand topologically acts as a single
link between two [Zn4(m4-O)]6+ cores. As shown in Fig. 2, a three-
dimensional framework structure with rare tungsten carbide (acs)
topology is built up by the linkage of the six-connected nodal
Fig. 1 Structural motif of 1·8 DMF (50% ellipsoids). Symmetry codes:
a: 1 + x - y, 1 - y, -1, 5 + z; b: 1 - x + y, 1 - x, z; c: 1 - y, x - y, z.
The crystallographically independent Zn2+ ions Zn1 and Zn2 in
1·8 DMF and 1 are distorted tetrahedrally coordinated with ZnO4
and ZnO3N environments, respectively. The m4-O2- anion O1,
which resides together with Zn1 on the threefold axis, coordinates
to four zinc ions building up a Zn4 tetrahedron.
The distorted tetrahedral coordination sphere of Zn1 is accom-
plished by three bidentately binding carboxylate groups bridging
Zn1 and Zn2 (and the symmetry related atoms Zn2b/Zn2c). In
contrast, the Zn2+ ion Zn2 is coordinated by the m4-O2- anion O1,
by each one mono- and bidentately binding carboxylate as well as
by one triazole group. Bond lengths and angles are given in Table 1.
Although the ligand contains two triazole and two carboxylate
groups resulting in summary to four coordination sites, there is
only one triazole coordinating to Zn2. The observed SBU in 1·8
DMF is related to the one in the archetypical MOF-5.5
Fig. 2 Simplified representation of the acs topology of 1·8 DMF.
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Fig. 3 Presentation of a 3 ¥ 4 super cell of 1·8 DMF (view along c direction) with partial space filling projection of the channel structure.
points.13 In total, only 45 crystal structures of MOFs with acs
topology can be found in the TOPOS&RCSR database.14 Exam-
ples for MOFs with acs topology are {[Cu(mtz)]3(CuI)} (mtz:
3,5-dimethyl-1,2,4-triazole),15 a series of isomorphous formates
(NH4)[M(HCO2)3] (M = Mn, Co, Ni),16 MOF-235 and MOF-
236,17 the MIL-88 series18 and the recently reported DUT-7.19
According to the space filling presentation in Fig. 3, 1·8 DMF
possesses a one-dimensional pore system consisting of channels
of almost triangular shape with an edge length of 1000 pm
running along the crystallographic c axis. Using the program
PLATON,20 the porosity of 1 can be estimated to be 43% in total.
Although there are huge voids in the crystal structure of 1, no
solvent molecules, i.e. DMF, could be detected during the single
crystal structure refinement of1·8DMF. Nevertheless, as discussed
later, the coupled TG-MS measurement of the as-synthesized
microcrystalline material reveals the presence of 8 DMF molecules
per formula unit.
Fig. 4 13C MAS NMR spectra of the protonated ligand, the as-synthe-
sized and the desolvated MOF under different measurement conditions. *
denotes spinning sidebands, # signals from DMF, ‡ from adsorbed DMF
and ꢀ from a Teflon tape spacer used for the measurement.
Solid state NMR investigations
of the triazole and the carboxylate carbon atoms to lower field
due to metal coordination. However, additionally three narrow
signals at 31 ppm, 36 ppm and 163 ppm, characteristic of the
solvent DMF are present which are more pronounced in the direct
In order to gain insights into the MOF structure, solid state 13C
NMR spectra were recorded.
13C NMR spectra for the as-synthesized sample 1·8 DMF and
the desolvated sample 1 are shown in Fig. 4 together with that of
the protonated ligand for comparison. For the protonated ligand
(Fig. 4a), the two signals at 10.7 ppm and 11.3 ppm belong to the
methyl groups of the triazole units. A second region with signals
between 125–138 ppm represents the aromatic carbon atoms of
the phenyl rings. The signals at 151–154 ppm belong to the carbon
atoms of the aromatic triazole, the signal at 168 ppm can be
assigned to the carboxyl group. The cross-polarization (CPMAS)
spectrum of the as-synthesized MOF 1·8 DMF (Fig. 4b) mostly
resembles the ligand spectrum revealing a shift of the signals
excitation (DPMAS) spectrum (Fig. 4c) because of the shorter 13
C
T1 relaxation time. Because of the mobility of the DMF guest
molecules, the C–H dipolar interaction is weaker, hence a longer
contact time in the CPMAS was used. It can be concluded that
the DMF molecules possess a certain mobility within the pore
structure of the framework. This observation correlates well to
the refinement of the crystal structure, where no DMF molecules
could be localized.
All the carbon resonances are well resolved for the desol-
vated sample 1 (Fig. 4d). The linewidth is higher than for the
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as-synthesized sample and for the protonated ligand, presumably
due to an increased motion after the desolvation process. As
expected, no DMF signals were detected with direct excitation
(Fig. 4e).
The NMR observations correlate well to the observed mass loss
of the TG-MS (Fig. 7).
X-ray powder diffraction and thermal properties
Fig. 5 presents the X-ray powder patterns of the as-synthesized
microcrystalline material of 1·8 DMF, of 1 after the adsorption
experiments and the simulated pattern of 1 based on the crystal
structure. It can be seen from Fig. 5 that the reflection positions
of the powder pattern of 1·8 DMF are in good agreement with
the powder pattern simulated from the single crystal structure,
indicating phase purity. Nevertheless, in particular the intensity of
the observed (100) reflection at 2q = 5.3◦ is much smaller compared
to the simulation. This difference is due to the incorporated
solvent and can be explained by a more detailed analysis of the
temperature dependent X-ray powder diffraction (TD-PXRD).
Fig. 6 shows the TD-PXRD measurement of the microcrystalline
material of 1·8 DMF. Notably there is no phase transition in
the Guinier-Simon diagram up to 430 ◦C, the decomposition
temperature of the framework. Interestingly the intensity of ◦the
(100) reflection at 2q = 5.3◦ increases dramatically up to 330 C.
In this state, the observed reflection intensities fit much better to
the simulated powder pattern of 1. As has been previously shown
for 3•[Cu3(BTC)2(H2O)3],21 the reflection intensities in the powder
patterns of porous MOFs can change sensitively depending on
the degree of solvation. Furthermore, Fig. 5 contains the powder
pattern of the desolvated microcrystalline material 1 after the CO2
adsorption experiments (blue), in which a sample of 1·8 DMF was
heated up to 270 ◦C prior to the sorption analyses. The slight,
almost negligible shift in the position of the (100) reflection can be
explained by the slightly changed lattice constants of 1 compared
to 1·8 DMF as discussed earlier.
Fig. 6 3D presentation (top) and Guinier-Simon diagram (bottom) of
the temperature dependent PXRD pattern of 1·8 DMF.
Fig. 7 presents the TG-MS measurements of the as-synthesized
and desolvated samples of microcrystalline 1. It can be seen from
the TG curve of the as-synthesized 1·8 DMF, that there is a mass
loss of 25.3% up to 220 ◦C. As evidenced by mass spectrometry, the
reason is the loss of DMF (indicated by m/z = 73 and its fragment
[NMe2]+ with m/z = 44). There is a plateau and no further mass
loss observed until 430 ◦C, when decomposition of the framework
(indicated by [CO2]+ with m/z = 44 due to fragmentation of the
carboxylate from the benzoate and [CH3CN]+ with m/z = 41
by fragmentation of the triazole) begins. The mass loss can be
quantified to be 25.3% and corresponds to 8 DMF molecules.
Further tremendous mass losses of 1·8 DMF and 1 are observed
at temperatures higher than 470 ◦C.
Adsorption studies
In order to verify the porosity of 43% estimated by PLATON20
from the crystal structure of 1, the adsorption isotherms of
nitrogen and carbon dioxide on 1 were measured at 77 K and
298 K, respectively (cf. Fig. 8 and 9).
According to Fig. 8, the nitrogen isotherm at 77 K corresponds
to type I of the IUPAC classification of physisorption isotherms.22
At a relative pressure of p/p0 ª 0.98, an adsorbed volume Vads
of 262 cm3 g-1 can be found providing a pore volume of 0.41
cm3 g-1 determined by the Gurvich rule.23 This value is in good
agreement with the pore volume of 0.43 cm3 g-1 calculated from
Fig. 5 PXRD patterns of the as-synthesized microcystalline 1·8 DMF
(black), the simulated powder pattern of 1 (blue) and the experimental
pattern of the desolvated microcrystalline sample 1 (green) after CO2
adsorption experiments.
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Fig. 7 TG-MS analyses of 1·8 DMF (blue) and 1 (black) with the mass channels m/z = 41, 44 and 73 (green).
9) at 298 K corresponds also to a type I isotherm.22 A nearly
constant adsorption amount in the pressure range of 3.0–3.5 MPa
clarifies that the adsorbent is saturated with carbon dioxide. The
maximum uptake of 6.30 mmol g-1 corresponds to 27.7 weight-%
of carbon dioxide. By the Gurvich rule, a pore volume of 0.35 cm3
g-1 is determined, which is lower than the calculated one from the
nitrogen adsorption isotherm. Note, that applying Gurvich’s rule
for an adsorptive near its critical point (as in the case for carbon
dioxide at 298 K, T/TC = 0.98) is more defective than in the case
for nitrogen at 77 K (T/TC = 0.61).24 At 3 MPa (298 K, p/p0 = 0.47)
1 adsorbs 6.3 mmol g-1 CO2, which is nearly in the same region
compared to M3[Co(CN)6]2 (M = Co, Zn),25 but lower than for
3
•[Cu(Me-4py-trz-ia)]12 and HKUST-1.26 A 13 X zeolite26 shows
slightly larger carbon dioxide uptake with 6.9 mmol g-1 at 3 MPa
(298 K), whereas a 5A molecular sieve with 5.2 mmol g-1 is much
lower than 1. If a pressure swing adsorption process is considered,
the CO2-working capacity for 1 of 5 mmol g-1 (22 weight-%)
between 0.1 MPa and 1.5 MPa at 298 K is higher compared to the
13 X zeolite and the 5A molecular sieve, but lower than HKUST-
1 (cf. Table 2). Nevertheless, the CO2-working capacity of 1 is in
the same order of magnitude as the activated carbon Norit RB2
and indicates that 1 could be a promising candidate for a pressure
swing adsorption process.
Fig. 8 N2 adsorption isotherm (77 K; p0 = 0.0972 MPa) on 1 after
activation at 200 ◦C.
Another important issue is the stability of the material at higher
temperatures, so that the CO2-working capacity is almost available
if the material is heated to 270 ◦C. This implies the possibility for
a temperature swing process, whereby the carbon dioxide can be
desorbed at high temperatures by a counter stream of nitrogen.
Conclusions
The novel microporous Zn4O-based MOF with the newly syn-
2-
Fig. 9 CO2 adsorption isotherms (298 K) on 1 after activation at 150 ◦C
thesized {(Metrz-pba)2mPh} ligand exhibits a porosity of 43%.
(black) and 270 ◦C (blue).
Besides the preparation of single crystals under autogenous
pressure, a scalable synthesis to produce larger amounts of the
microcrystalline MOF material is reported. TG-MS combined
with solid state 13C NMR measurements reveal the presence
of 8 mobile DMF molecules per formula unit, which can be
the single crystal structure. From the nitrogen isotherm, a BET
surface of 969 m2 g-1 (linear BET range p/p0 < 0.05) was
determined. The carbon dioxide adsorption isotherm (cf. Fig.
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Table 2 Comparison of CO2 loadings (3 MPa/298 K) and CO2-working capacities (0.1–1.5 MPa) of microporous materials
CO2 loading (3 MPa/298 K)
CO2-working capacity between
0.1–1.5 MPa/weight-%
Adsorbents
ns/mmol g-1
Reference
1
6.3
5.0
5.2
22.0
13.5
16.0
21.4
35.6
9.7
This study
Co3[Co(CN)6]2
Zn3[Co(CN)6]2
25
25
12
26
26
27
28
3
•[Cu(Me-4py-trz-ia)]
11.2
13.0
6.9
HKUST-1
13X zeolite
5A molecular sieve
Activated carbon Norit RB2
5.2a
9.5
4.4a
22.9
a At 303 K.
removed leaving the single crystals intact. Combined temperature
dependent PXRD and TG-MS studies confirm the stability of the
framework up to 430 ◦C. Adsorption measurements show that the
pore system of the rigid MOF material is fully accessible towards
nitrogen (77 K) with a pore volume of 0.41 cm3 g-1.
s, 1477 s, 1440 s, 1425 s, 1387 m, 1360 m, 1326 m, 1278w, 1256 m,
1228vs, 1166w, 1093w, 1077 s, 1038 m, 998w, 975 s, 956 s, 904 m,
808 s, 775 s, 711vs, 681 s, 521w, 461w, 439w. LR-MS (EI): m/z =
242.0 [M]+.
4,4¢-(5,5¢-(1,3-Phenylene)bis(3-methyl-4H -1,2,4-triazole-5,4-
diyl))dibenzoic acid hydrate, H2{(Metrz-pba)2mPh}·H2O. Under
nitrogen atmosphere a suspension of 1.21 g (5.0 mmol) of 1,3-
bis(5-methyl-1,3,4-oxadiazol-2-yl)benzene, 1.71 g (12.5 mmol, 2.5
eq) of 4-aminobenzoic acid and 0.24 g (1.26 mmol, 0.25 eq) p-
toluene sulphonic acid hydrate in 25 ml absolute xylene was heated
under reflux for 48 h. Afterwards the solvent was decanted and
the residue was washed with hot DMF/ethanol (1 : 4, v/v), filtered
and dried in air.
Experimental section
All chemicals were commercially available and used as received
without further purification. 1H and 13C solution-state NMR
spectra of the ligand were recorded in DMSO-d6 solution using a
BRUKER Avance DRX 400 spectrometer (400 MHz). The TG-
MS analysis was carried out on a Netzsch F1 Jupiter device
connected to an Aeolos mass spectrometer. The sample was
heated at a rate of 10 K min-1. The melting points (uncorrected)
were determined on an Electrothermal 9200 (Barnstead). The
IR spectrum was obtained using an IR-spectrometer TENSOR
27 (Bruker) and OPUS 6.0 (Bruker). EI mass spectra were
recorded on a VG ZAB HSQ (WATERS), ESI mass spectra were
recorded on an ESQUIRE (BRUKER). Solvothermal syntheses
were carried out in steel autoclaves with appropriate Teflon
vessels (PARR). The temperature programmes were applied in an
oven ULE400 (MEMMERT) using the software CELSIUS 2007
(Version 9.2).
Yield: 0.94 g (1.89 mmol, 38% of theory). 1H-NMR (400 MHz,
DMSO-d6): d = 2.22 ppm (s, 6 H, CH3); 7.19 (m, 2 H, aromat.
CH); 7.27 (m, 1 H, aromat. CH); 7.48 (d, 4 H, 3J = 8.1 Hz, aromat.
CH); 7.60 (s, 1 H, aromat. CH); 8.06 (d, 4 H, 3J = 8.1 Hz, aromat.
1
CH); 13.3 (br, 2 H, CO2H). 13C{ H}-NMR (100 MHz, DMSO-d6):
d = 10.9 ppm (s, 2 C, CH3); 127.5 (s, 2 C, aromat. Cq); 127.8 (s, 4
C, aromat. CH); 127.9 (s, 1 C, aromat. CH); 128.8 (s, 2 C, aromat.
CH); 128.9 (s, 1 C, aromat. CH); 130.9 (s, 4 C, aromat. CH); 131.8
(s, 2 C, aromat. Cq); 138.0 (s, 2 C, aromat. Cq); 152.2 (s, 2 C,
N
Cq); 152.3 (s, 2 C, N Cq); 166.4 (s, 2 C, CqO2H). EA: found:
C: 62.66 H: 4.58 N: 16.60; anal. calc. for C26H22N6O5: C: 62.64
H: 4.45 N: 16.86. Tm: 380 ◦C (decomp.). IR (KBr): n [cm-1] 3447
m, 3071w, 2999w, 2925w, 2779w, 2601w, 2480w, 2361w, 1923w,
1705 s, 1608 m, 1511 m, 1471 m, 1399 m, 1307 m, 1268 s, 1169
m, 1120 m, 1101w, 1061 m, 983w, 866w, 805 m, 783w, 728w, 700
m, 668w, 521w. LR-MS (ESI): m/z = 479.1 [M–H2O–H]-, 959.2
[M2–2 H2O–H]-.
Ligand synthesis
1,3-Bis(5-methyl-1,3,4-oxadiazol-2-yl)benzene. According to
a modified method29 17.1 g (80.0 mmol) 1,3-di(2H-tetrazol-5-
yl)benzene30 were refluxed in 94 ml (102 g, 1.0 mol, 12.5 eq) acetic
anhydride for 24 h. After cooling to room temperature the excess
of acetic anhydride was evaporated under reduced pressure. After
washing the residue with 100 ml of distilled water and filtration
the product was obtained as a colourless solid.
Preparation of single crystals of 1·8 DMF
Yield: 18.60 g (76.8 mmol; 96% of theory). 1H-NMR (400 MHz,
DMSO-d6): d = 2.61 ppm (s, 6 H, CH3); 7.78 (t, 1 H, 3J = 7.8 Hz,
A steel autoclave with a Teflon vessel (PARR) was loaded with
297.5 mg (1.0 mmol) Zn(NO3)2·6 H2O, 24.9 mg (0.05 mmol)
H2{(Metrz-pba)2mPh}·H2O and 5.0 ml DMF, sealed and the
3
4
arom. CH); 8.15 (dd, 2 H, J = 7.8 Hz, J = 1.5 Hz, arom. CH);
8.40 (m, 1 H, arom. CH). 13C{ H}-NMR (100 MHz, DMSO-d6):
1
◦
d = 10.5 ppm (s, 2 C, CH3); 123.5 (s, 1 C, arom. CH); 124.5 (s, 2
C, arom. Cq); 129.0 (s, 2 C, arom. CH); 130.6 (s, 1 C, arom. CH);
162.9 (s, 2 C, Cq N); 164.3 (s, 2 C, Cq N). EA: found: C: 59.40
H: 4.22 N: 22.85; anal. calc. for C12H10N4O2: C: 59.50 H: 4.16 N:
23.13. Tm: 166–167 ◦C IR (KBr): n [cm-1] 3068w, 3008 m, 2979w,
2933w, 1977w, 1848w, 1803w, 1708w, 1620 m, 1583vs, 1558 s, 1548
reaction mixture was heated within one hour up to 140 C. The
temperature was kept constant for five hours, then the autoclave
was cooled slowly to room temperature during a period of 60 h.
Afterwards the product was washed with fresh DMF, filtered off
and dried, yielding colourless prismatic crystals of 1·8 DMF.
Yield: 17.8 mg (7.7 mmol, 46% of theory)
822 | Dalton Trans., 2012, 41, 817–824
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Table 3 Crystal data of 1·8 DMF and 1
(outer diameter 0.5 mm). The TD-PXRD measurements were
carried out in steps of 5 ◦C from room temperature to 500 ◦C.
Compound reference
Chemical formula
1·8 DMF
1
Solid state NMR
∑
C78H54N18O13Zn4 C78H54N18O13Zn4
8(C3H7NO)
Solid state NMR measurements were performed on a Bruker
Avance 400 spectrometer operating at a field of 9.4 T. All the
experiments were performed at room temperature using a 4 mm
MAS probe. 13C MAS spectra were measured both using cross
polarisation (CPMAS)34 and direct excitation (DPMAS) at a
spinning rate of 10 kHz (6 kHz for the CPMAS of the as-
synthesized sample).
CPMAS experiments were carried out under Hartmann–Hahn
conditions with 1 ms contact time and 2 to 3.5 s recycle delay.
For the as-synthesized sample a contact time of 5 ms was
chosen. Typically 6200–12300 scans were collected. For the direct
excitation 3000 scans were taken with a recycle delay of 3 s which
favors fast relaxing components (e.g., solvent molecules). The
relative intensities are therefore not quantitative. All the spectra
were referenced to TMS by using adamantane as a secondary
reference (leftmost resonance at 38.56 ppm).
Formula mass
Diffractometer
Crystal system
2297.64
IPDS-I
Trigonal
18.9863(11)
18.9863(11)
18.0965(10)
90.00
90.00
120.00
5649.4(6)
213(2)
P31c
2
0.916
14932
5986
0.0467
1712.87
IPDS-2T
Trigonal
19.2401(8)
19.2401(8)
17.8208(9)
90.00
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
90.00
120.00
5713.1(4)
180(2)
P31c
2
0.880
24961
7490
0.0553
0.0345
0.0876
0.0372
0.0889
1.079
3
˚
Unit cell volume/A
T/K
Space group
No. of formula units per unit cell, Z
Absorption coefficient, m/mm-1
No. of reflections measured
No. of independent reflections
Rint
Final R1 values (I > 2s(I))
Final wR(F2) values (I > 2s(I))
Final R1 values (all data)
Final wR(F2) values (all data)
Goodness of fit on F2
0.0457/0.0333a
0.1282/0.0858a
0.0575/0.0414a
0.1352/0.0889a
1.036
Adsorption studies
Flack-x parameter
0.004(18)
-0.006(9)
The nitrogen adsorption isotherm at 77 K on 1 was obtained
by using the commercially available volumetric sorption analyzer
ASAP 2000 (Micromeritics) equipped with a high resolution
pressure sensor.
a Residual R values before/after application of the PLATON/SQUEEZE
routine20 to 1·8 DMF. SQUEEZE was applied due to the fact that the
DMF molecules could not be localized.
The high pressure adsorption isotherms of carbon dioxide
at 298 K were measured using a magnetic suspension balance
(Rubotherm, Germany) that can be operated at up to 15 MPa.
Various pressure transducers (Newport Omega, US) were used
in a range from vacuum up to 5 MPa with an accuracy of
0.05%. Taking into account the buoyancy correction with helium
measurement, the excess adsorbed amount nExcess of carbon dioxide
was calculated by applying the procedure reported by Staudt
et al.35
Synthesis of microcrystalline material of 1·8 DMF
A mixture of 148.7 mg (0.50 mmol) Zn(NO3)2·6 H2O and 186.9 mg
(0.375 mmol) H2{(Metrz-pba)2mPh}·H2O in 30 ml DMF was
heated under reflux for 36 h. After cooling to room temperature
the obtained solid was filtered off, washed with 30 ml N,N-
dimethylformamide and dried in air.
Yield: 261.0 mg (113.6 mmol, 91% of theory)
IR (KBr): n [cm-1] 3068w, 3006w, 2931w, 1653 s, 1615 s, 1573
m, 1510, 1487, 1413sh, 1376 s, 1293w, 1254w, 1173w, 1140w, 1100
m, 1062w, 1015 m, 988w, 896w, 877 m, 847 m, 802w, 779w, 707 m,
661w, 633w, 586 m, 511w.
Gases were obtained from Air Products (US) with purity of
more than 99.995% (more specific: CO2 99.995%, N2 99.995% and
He 99.9992%).
X-ray crystallography
Acknowledgements
Crystallographic measurements were performed at 213 K and 180
K using Stoe Imaging Plate Detector Systems (IPDS-I and IPDS-
2T) with Mo-Ka radiation (l = 71.073 pm). The data reduction
was performed using the STOE X-AREA software package.31
The structures were solved by direct methods using the program
SHELXS-97 and refined using SHELXL-97.32 All non-H atoms
were refined anistropically and CH hydrogen atoms were added
geometrically using a riding model. In the case of 1·8 DMF,
additionally the PLATON/SQUEEZE routine20 was applied as
the DMF molecules could not be localized. The improved residual
R values obtained by SQUEEZE are given in Table 3. Graphical
visualization of the structure was performed using the program
Diamond 3.2e,33 the topological analysis was performed using
TOPOS 4.0.14 The PXRD and TD-PXRD measurements were
carried out on a STOE STADI-P diffractometer in the Debye-
Scherrer mode using Cu-Ka1 radiation (l = 154.060 pm). The
samples for these measurements were prepared in glass capillaries
We thank M.Sc. F. Kettner for assistance with TG-MS analyses.
Prof. D. Proserpio (University of Milan, Italy) is gratefully ac-
knowledged for help with interpretation of the topology. Financial
support by Deutsche Forschungsgemeinschaft (DFG SPP 1362 -
Poro¨se metallorganische Geru¨stverbindungen, STA 428/17-1, KR
1675/7-1, BE 2434/4-1, and KA 1560/3-2, 4-2), the University of
Leipzig (PbF-1) and the graduate school BuildMoNa (fellowship
for A. V. K.) is gratefully acknowledged. DL acknowledges the
fellowship of the Fonds der Chemischen Industrie. JL thanks for
a ESF fellowship. Funded by the European Union and the Free
State of Saxony.
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