Triazolium-containing metal-organic frameworks: Control of catenation in 2D copper(ii) paddlewheel structures

Article abstract of DOI:10.1071/CH12462

One approach to exploit metal-organic frameworks (MOFs) as heterogeneous catalyst platforms requires the development of materials containing groups that can be utilised to anchor a catalytic moiety into the links within the structure. Here we report the synthesis of the first integrated triazolium-containing MOF linker and the first MOFs containing linkers of this type. 1,4-Bis(4-benzoic acid)-1-methyl-1H-1,2,3-triazolium chloride, H2L1Me, was synthesised in three steps by a 'click' reaction of methyl 4-ethynylbenzoate with methyl 4-azidobenzoate, methylation using methyl triflate, followed by ester hydrolysis in overall 74% yield. The equivalent neutral triazole precursor, 1,4-bis(4-benzoic acid)-1H-1,2,3-triazole hydrochloride, H2L1(HCl), was also prepared and a comparison of the chemistry with Zn(NO3)2·6H ₂O and Cu(NO3)2·3H₂O is presented. The results support the use of reaction conditions to control interpenetration and provide additional evidence that the charge on structurally similar ligands can drastically alter the types of structures that are accessible due to the requirements for charge balance in the final product.

Full text of DOI:10.1071/CH12462

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2013, 66, 409–418
Full Paper
http://dx.doi.org/10.1071/CH12462
Triazolium-Containing Metal Organic Frameworks:
]
Control of Catenation in 2D Copper(II)
Paddlewheel Structures
A
A
Alexandre Burgun, Christian J. Doonan,
A B
,
and Christopher J. Sumby
A
School of Chemistry and Physics, University of Adelaide, Adelaide, SA 5005, Australia.
Corresponding author. Email: christopher.sumby@adelaide.edu.au
B
One approach to exploit metal–organic frameworks (MOFs) as heterogeneous catalyst platforms requires the development
of materials containing groups that can be utilised to anchor a catalytic moiety into the links within the structure. Here we
report the synthesis of the first integrated triazolium-containing MOF linker and the first MOFs containing linkers of this
type. 1,4-Bis(4-benzoic acid)-1-methyl-1H-1,2,3-triazolium chloride, H2L1Me, was synthesised in three steps by a ‘click’
reaction of methyl 4-ethynylbenzoate with methyl 4-azidobenzoate, methylation using methyl triflate, followed by ester
hydrolysis in overall 74 % yield. The equivalent neutral triazole precursor, 1,4-bis(4-benzoic acid)-1H-1,2,3-triazole
hydrochloride, H2L1(HCl), was also prepared and a comparison of the chemistry with Zn(NO3)2ꢀ6H2O and
Cu(NO3)2ꢀ3H2O is presented. The results support the use of reaction conditions to control interpenetration and provide
additional evidence that the charge on structurally similar ligands can drastically alter the types of structures that are
accessible due to the requirements for charge balance in the final product.
Manuscript received: 8 October 2012.
Manuscript accepted: 6 November 2012.
Published online: 14 December 2012.
as diols.[8] In several cases, these require judicious choice of the
structural metal,[4a] post-synthetic modification,[4b] or protect-
ing groups,[8e] to prevent the secondary functional groups from
being used to form a non-desired framework. Azoliums, pre-
cursors to N-heterocyclic carbenes, have also been investigated
with a view to generating catalytically competent MOFs.[9–11]
Recent examples of azolium-containing ligands have all
been based on an imidazolium[9,10] or a benzimidazolium[11]
precursor to the N-heterocyclic carbene. The imidazolium-
containing ligands for MOF synthesis have come in two forms
(Fig. 1); the first where the azolium is integrated into the
backbone of the ligand,[9] and the second where the azolium
moiety is incorporated as a pendant to the link.[10] Examples of
the latter class were recently reported by Hupp and cow-
orkers[10] involving 4,40-biphenyldicarboxylates appended with
one or two azolium groups in the 2 and 20 positions of the
biphenyl (1a and 1b, respectively). These provided for the
synthesis of IRMOF-9 and IRMOF-10 analogues with
Zn(NO3)2ꢀ6H2O depending on whether the ligand contained
two or one azolium groups, respectively.[10] The first reports of
an imidazolium-containing linker concerned the use of a flexible
ligand, N,N0-diacetic acid imidazolium chloride (2).[9a–c] We,[9d]
Chun et al.,[9e,9f] and Hupp and coworkers[9g] have also reported
frameworks based on more rigid linkers where an imidazolium
is part of the link (3–6), which confers an unusual zeolite-like
geometry on the link component in these structures. Finally,
Yaghi and coworkers[11] reported a system partway between
these extremes by using a benzimidazolium core to generate a
linear dicarboxylate 7 whereby the azolium was integrated into
Introduction
Metal–organic frameworks (MOFs) or porous coordination
polymers (PCPs) are porous extended networks that can be
synthesised from a systematic combination of organic links and
metals or metal oxide clusters.[1] By judicious choice of both
precursor metal salt and organic ligand, materials with varying
topologies (pore sizes, shapes, and chemistry) and properties
can be synthesised.[2] Due to the exquisite control that can be
imparted during synthesis, their large pore volumes, and stable
structures, MOFs have been identified as materials with great
potential for size-selective heterogeneous catalysis.[3] By virtue
of these rational design principles, the desirable properties of
homogeneous catalysts can be transferred to a heterogeneous
MOF platform. One approach to exploit MOFs as heterogeneous
catalysts is to construct the organic backbone of the material
from links capable of anchoring a known homogeneous catalyst.
However, such an approach requires several challenges to be
overcome. First, MOFs with pores sufficiently large enough to
concurrently allow anchoring of the catalyst, diffusion of
chemical reactants through the pore structure, and to facilitate a
catalytic transition state are required. Second, reliable methods
for anchoring catalytic moieties to the framework need to be
established that do not result in unwanted side reactions during
MOF synthesis or hinder the formation of the desired network
topology. This second challenge is the focus of this contribution.
Several examples of MOFs containing non-structural func-
tional groups have been reported. These include the inclusion of
2,20-bipyridine and pyridyl imine motifs,[4] cyclometallating
moieties,[5] phosphines,[6] and other coordinating sites,[7] such
Journal compilation Ó CSIRO 2013
www.publish.csiro.au/journals/ajc

410
A. M. Burgun, C. J. Doonan, and C. J. Sumby
COOH
XϪ
condensation of two equivalents of a cyanoaniline with glyoxal,
cyclisation with paraformaldehyde to give the imidazolium, fol-
lowed by acid catalysed hydrolysis using hydrobromic acid to the
dicarboxylic acids.[9d] The synthesis of the triazolium equivalent
of 5 was proposed to proceed by a copper(I)-catalysed azide–
alkyne cycloaddition or click reaction (Scheme 1). Click chem-
istry has recently found application in a wide variety of areas[13]
and several groups[14] have extensively exploited stepwise
Huisgen cycloaddition reactions in triazole ligand synthesis. 1,4-
Bis(methyl 4-benzoate)-1H-1,2,3-triazole (9) was synthesised
using the general click reactionprocedure.[15] Equimolar amounts
of methyl 4-ethynylbenzoate and methyl 4-azidobenzoate were
reacted together in the presence of CuSO4ꢀ5H2O and sodium
ascorbate in EtOH/H2O (7: 3), and then heated under reflux for
16h (Scheme 1). After workup, 9 was isolated in 92% yield as a
pale beige powder. Of interest, when the reaction was carried out
at room temperature for one week, both starting materials, the
alkyne and the azide, were quantitatively recovered. This obser-
vation is consistent with the strong electron withdrawing effect of
the CO2Me group of the azide, which significantly slows down
the rate of the click reaction.[16] Surprisingly, 9 is insoluble in all
common solventsatroomtemperatureand can only besolubilised
when heated at 1508C in (D6)DMSO which enabled ‘quick’
1H NMR characterisation (no more than two transients) before
recrystallising out upon cooling to room temperature. Methy-
lation of 9 using trifluoromethane sulfonate in 1,1,2,2-
tetrachloroethane at 1508C afforded 10(OTf) in quantitative yield
(95 %).[17] Finally, both the biscarboxylic acid H2L1(HCl) and
H2L1Me as its chloride salt were obtained in excellent yield (82
and 85%, respectively) by conventional deprotection of the
methyl esters, refluxing 9 or 10(OTf) in a 1 : 4 KOH (2M)/
methanol mixture. Elemental analysis carried out on H2L1(HCl)
confirmed that H2L1 was isolated as its hydrochloride salt.
Compounds 9, 10(OTf), H2L1(HCl), and H2L1Me were
characterised by elemental analysis and the usual spectroscopic
methods when achievable. Indeed, the low solubility of 9 and
H2L1(HCl) did not enable 13C NMR and mass spectra to be
ϩ
N
N
N
HOOC
COOH
N
ϩ
R1
XϪ
2
XϪ
COOH
ϩ
R2
R2
N
N
R1 ϭ H
R1 ϭ
1a
1b
N
N
ϩ
XϪ
COOH
COOH
R2 ϭ
3
4
COOH
R2 ϭ
R2 ϭ
Nϩ
N
XϪ
COOH
COOH
5
6
R2 ϭ
COOH
COOH
7
2XϪ
ϩ
ϩ
COOH
HOOC
N
N
N
N
8
XϪ
COOH
HOOC
N
N
R3
N
H2L1Me
R3 ϭ Me
R3 ϭ nothing
X ϭ Cl
X ϭ nothing
H2L1
1
recorded for these compounds. In the H NMR spectra, the
Fig. 1. Reported examples of pendant (1a, 1b, and 7) and integrated (3–6,
8) imidazolium links for metal–organic frameworks.
characteristic protons of the triazole and triazolium units can be
found as singlets at ,9.6 and ,10.1 ppm for 9 or H2L1(HCl)
and 10(OTf) or H2L1Me, respectively. For 10(OTf) and
H2L1Me, the 1H and 13C NMR spectra confirmed that the
methylation had successfully occurred (NCH3: dH 4.49 for both
10(OTf) and H2L1Me, dC 39.57 for 10(OTf) and hidden in the
residual solvent peak for H2L1Me). 1H NMR spectroscopy also
confirmed the successful deprotection of the methyl esters by
the lack of the CH3 signals (found at d 3.92, 3.89 and d 3.94 in 9
and 10(OTf) respectively) and the appearance of a characteristic
the link backbone of a cubic MOF. More recently a linker with
two azolium groups in the backbone (8) was used to synthesise a
2D MOF network consisting of 80-membered macrocycle rings
of 8 bridging copper paddle-wheel subunits.[9h]
The focus of this current contribution is the first report of an
integrated triazolium-containing linker with carboxylate donors
and the first MOFs containing linkers of this type. The ability
to incorporate a triazolium precursor versus an imidazolium
link[9–11] offers an opportunity to tune the electronic and catalytic
properties of the resulting N-heterocyclic carbene.[12] Herein we
report the synthesis of a novel triazolium link (L1Me) by ‘click’
chemistry and a comparison of the coordination chemistry for
linkers containing a triazole (L1) or triazolium (L1Me) core. We
also investigate the control of interpenetration for a 2D copper(II)
broad singlet at d 13.14 and 13.54 in H2L1 and H2L1Me
,
respectively, due to the carboxylic acid protons. In the IR spectra
the C¼O stretch shifted from ,1720 cmꢁ1 for the diesters 9 and
10(OTf), to 1681 and 1711 cmꢁ1 for the dicarboxylic acids
H2L1 and H2L1Me, respectively. This was also accompanied by
the appearance of a characteristic large and broad O–H stretch at
,3000 cmꢁ1 for both dicarboxylic acids.
MOF based on dicopper(II) paddlewheels and L1Me
.
Crystal Structure of HL1MeꢀH2O
Further confirmation of the successful synthesis of H2L1Me
came from a single crystal X-ray crystal structure of L1Me as its
zwitterion. Crystals of HL1MeꢀH2O were obtained from a 1 : 1
solution of L1Me in DMF/H2O (1.6 mL) containing one drop
of concentrated nitric acid. H2L1Me crystallises in the mono-
clinic space group P21/c with one complete molecule in the
Results and Discussion
Ligand Synthesis
Our previous dicarboxylate azolium ligands, 1,3-bis(4-
carboxyphenyl)imidazolium bromide (5) and 1,3-bis(3-
carboxyphenyl)imidazolium bromide (6), were synthesised by

Triazolium-Containing MOFs
411
CuSO4⋅5H2O,
sodium ascorbate
EtOH/H2O (7:3),
MeO2C
C CH
MeO2C
CO2Me
ϩ
Reflux
N
N3
CO2Me
N
N
9 92 %
MeOTf
1,1,2,2-tetrachloroethane
MeO2C
CO2Me
150ЊC
(i ) MeOH, KOH
(2 M), reflux
(ii) HCl (2 M)
N
N
N
ϩ
OTfϪ
10 95 %
(i) MeOH, KOH(2 M), reflux
(ii) HCl (2 M)
HOOC
COOH
N
HOOC
COOH
N
N
N
H2L1(HCl) 82 %
N
N
ClϪ
ϩ
H2L1Me 85 %
Scheme 1. Preparation of the triazole and triazolium ligands H2L1 and H2L1Me
.
HL1Me (DOO ¼ 2.77, dOHꢀꢀꢀO ¼ 1.93 A, angle ¼ 167.08) and to
˚
the carbonyl oxygen of a carboxylic acid in a second molecule
˚
(DOO ¼ 2.85, dOHꢀꢀꢀO ¼ 2.03 A, angle ¼ 165.88). The third inter-
action is the acceptor interaction described above for the
triazolium core. The combined interactions result in a 3D
hydrogen bonded network.
MOF Synthesis
Due to the ease of access to a neutral analogue of H2L1Me
,
H2L1, which will provide a dianionic rather than monoanionic
ligand on deprotonation, we first examined the coordination
chemistry of H2L1 with zinc(II) and copper(II) metal salts.
Unfortunately, as noted above, H2L1 is remarkably insoluble.
However, after screening several conditions, H2L1(HCl), zinc
nitrate, and one drop of concentrated HNO3 were reacted at
858C for 2 days in a 1 : 1 DMF/ethanol solution. Washing the
resulting crystals gave [Zn(L1)2(H2O)2] (11) as a white crys-
talline powder in 39 % yield. The phase purity and composi-
tion of the material was confirmed by powder X-ray diffraction
(PXRD) (Figure S1 in the Supplementary Material), combus-
tion analysis, and IR spectroscopy.
Fig. 2. A view of a single molecule of HL1Me showing the angle subtended
by the two 4-carboxylate groups and the hydrogen bonded water molecule
(ball and stick representation). The dashed bond represents a hydrogen
˚
bond with the acidic triazolium CH (DCO ¼ 3.06, dCHꢀꢀꢀO ¼ 2.14 A,
angle ¼ 162.08).
asymmetric unit (Fig. 2). The compound adopts the expected
conformation with the phenyl rings twisted out of the plane of
the triazolium core by 15.3(1)8 and 20.5(1)8 and expected bond
lengths and angles for such a compound.[9,14] As was observed
for previously reported integrated azolium links,[9e–g] the angle
subtended by the two 4-carboxylate groups is 145.4(1)8 and is
consistent with the O–Si–O angle in zeolites. The structure
confirms that the methylation of L1 has taken place in the
3-position of the triazole to give H2L1Me. In the structure,
H2L1Me is found as a zwitterion with a water molecule hydrogen
Structure of [Zn(L1)2(H2O)2] 11
[Zn(L1)2(H2O)2] is a 2D MOF formed from infinite chains of
five-coordinate zinc centres that extend along the c-axis and
four-connecting molecules of L1 that are directed along the ac
diagonal (Fig. 3a). The compound crystallises in the monoclinic
space group P21/c with an asymmetric unit that contains a single
molecule of L1, a zinc atom, and a water molecule. Each zinc
centre is coordinated to four carboxylate oxygen atoms from
˚
bonded to the triazolium CH (DCO ¼ 3.06, dCHꢀꢀꢀO ¼ 2.14 A,
angle ¼ 162.08).
The packing of HL1Me in the crystal is mediated by the
˚
four separate molecules of L1 (Zn1–O19 1.957(6) A, Zn1–O18
˚
˚
formation of a strong hydrogen bond (DOO ¼ 2.47, dOHꢀꢀꢀO
¼
2.129(8) A) and a water molecule (Zn1–O20 1.912(12) A). The
zinc(II) cations are best described as having a distorted five-
coordinate geometry part way between trigonal bipyramidal and
square planar with the water in the trigonal plane directed along
the b-axis. In turn each ligand coordinates four separate zinc
centres through monodentate coordination. Notably, the triazole
nitrogens are not involved in coordination of the zinc atom.
˚
1.56 A, angle ¼ 172.78) between the protonated and the
deprotonated carboxylates to form a 1D tape of HL1Me. The
water solvate molecule acts as a three connecting centre to form
three hydrogen bonding interactions with three different mole-
cules of HL1Me. The water molecule acts as a hydrogen bond
donor to the deprotonated carboxylate of one molecule of

412
A. M. Burgun, C. J. Doonan, and C. J. Sumby
(a)
(b)
Fig. 3. (a) A perspective view of the 2D metal–organic framework structure in [Zn(L1)2(H2O)2] 11 showing the
infinite zinc-bridging carboxylate chains running along the c-axis. (b) The close-packed 3D structure of 11. Multiple
inter-sheet hydrogen bonds involving the carboxylate oxygens, the triazole moieties, and the coordinated water
ligands that stabilise the packing.
This may be due to a combination of factors, including sterics,
the reaction stoichiometry, and a favourable hydrogen bonding
interaction in the repeating structure as described below.
The 2D sheets adopt a zig-zag conformation in the solid-state
and within the crystal are close-packed to give a dense, non-
porous 3D hydrogen bonded network (Fig. 3b). The crystal
packing is mediated by inter-sheet hydrogen bonding interac-
tions involving the triazole rings of adjacent 2D MOFs which
crystals that correspond to a mixture of catenation isomers of
[Cu2(L1Me)2(DMF)2](NO3)2; specifically a near close-packed
three-fold interpenetrated isomer, a-[Cu2(L1Me)2(DMF)2]
(NO3)2 (12), and a more open two-fold interpenetrated structure,
b-[Cu2(L1Me)2(DMF)2](NO3)2 (13). The formation of 12 (blue
blocks) as the sole product was achieved by undertaking the
reaction in DMF, containing one drop of concentrated HNO3, at
858C for 2 days. This was confirmed by PXRD (Fig. 4) that
showed an extremely good match between the calculated pattern
for 12 and the experimental patterns for samples obtained from
reactions undertaken in the presence of nitric acid. The forma-
tion of 12 was supported by elemental analysis (as a hydrate,
[Cu2(L1Me)2(H2O)2](NO3)2ꢀ1½H2O, after washing and drying
under high vacuum). Formation of the open structure as the sole
product was more difficult. Indeed, when the reaction is carried out
at higher temperature the percentage of 13 in the mixture of 12 and
13 increases, which was confirmed by the PXRD studies. How-
ever, it was difficult to isolate isomer 13 as a pure compound; the
best conditions to obtain 13 as the major product was to undertake
the reaction at 1208C for 1 day (Fig. 4), although on certain
attempts pure 13 (blue rods) was obtained as the sole product.
˚
form hydrogen bonded tapes (DCN ¼ 3.71, dCHꢀꢀꢀN ¼ 2.78 A,
˚
angle ¼ 168.98; DCN ¼ 3.71, dCHꢀꢀꢀN ¼ 2.86 A, angle ¼ 163.68),
as is commonly observed for triazoles[14,18] that are orthogonal
to the 2D MOF. Within the 2D MOF the triazole ligands
alternate orientation so the tapes run in both directions in the
crystal. The inter-sheet bonding is supported by further strong
hydrogen bonds involving the water ligands as hydrogen bond
donors and the carboxylate oxygen atoms of adjacent chains
˚
as acceptors (DOO ¼ 2.62, dOHꢀꢀꢀO ¼ 1.76 A, angle ¼ 157.98;
˚
DOO ¼ 2.61, dOHꢀꢀꢀO ¼ 1.77 A, angle ¼ 162.98).
With poor solubility severely limiting the ability to form
MOFs with H2L1, we moved onto investigations involving
H2L1Me. The triazolium compound is noticeably more soluble
than H2L1, and the methylation of the triazole ring prevents the
formation of triazole C–HꢀꢀꢀNtriazole hydrogen bonding as a
structure directing interaction. Thus, reaction with zinc(II)
nitrate with H2L1Me, as reported above for H2L1, does not lead
to the formation of a structure isomorphous with 11. However,
reaction of H2L1Me with copper(II) nitrate in DMF did yield,
after one night at 858C, smaller and larger blue block-shaped
Structures of a- and b-[Cu (L1Me)2(DMF)2](NO3)2 (12 and 13)
Both 12 and 13 have very similar four-connected 2D network
structures based around dicopper(II) paddlewheel secondary
building units (SBUs), however, there are noticeable differences
in the conformation of the 2D MOF and in the solid-state

Triazolium-Containing MOFs
413
this pore volume is not available to do chemistry as two further
2D networks, which are packed perpendicular to the first net-
work, are accommodated in the pore to give a three-fold inter-
penetrated structure. This results in a 3D mechanically
interlocked structure (Fig. 6c, d).
12 (expt)
12 (sim.)
Compound 13 also crystallises in an orthorhombic space
group, but in Pbcn rather than Pbca, with a single copper(II)
atom, a molecule of L1Me, and a DMF ligand in the asymmetric
unit. The unit cell volume of 13 is considerably larger at
mixture (expt)
3
3
˚
˚
6101(2) A compared with 12 (4235.4(4) A ). While the nitrate
anion could be observed in some data collections on the
structure, in the final refinement it could not be sensibly
modelled and the SQUEEZE routine of PLATON[21] was applied
to the collected data. A perspective view of the 2D MOF
structure in 13 is shown in Fig. 5b. The dicopper(II) paddlewheel
SBUs are typical[20] and the triazolium link maintains a geome-
try similar to that observed in the solid-state structure seen for
HL1MeꢀH2O and 12 with an angle between the two carboxylate
groups of 147.28 (compared with 145.4(1) 8 in HL1MeꢀH2O and
151.48 in 12). The distance bridged by the link (between the
13 (sim.)
13 (expt)
5
10
15
20
25
30
35
40
2θ [degrees]
Fig. 4. Experimental powder X-ray diffraction (PXRD) patterns for
a-[Cu2(L1Me)2(DMF)2](NO3)2 (12, pink) and a-[Cu2(L1Me)2(DMF)2](NO3)2
(13, aqua), and calculated PXRD patterns for 12 (red) and 13 (blue). The
initial experimental PXRD of the mixture of 12 and 13 is shown in green.
˚
centroids of the paddlewheels) is 17.9(1) A, although the win-
˚
dows are not regular with width 12.9(1) A and length 23.1(1) A.
˚
2
˚
This provides windows of roughly ,9.5 ꢂ 19.7 A taking into
account the van der Waals radii. Thus the windows in the 2D
grid are more pinched widthways and slightly elongated length-
ways compared with the windows in 12.
packing. Contrary to previous observations,[19] compound 12,
which is produced at lower temperatures or in the presence of
acid that slows down the rate of reaction, is three-fold inter-
penetrated, while the material grown more rapidly at higher
temperatures (13) is only two-fold interpenetrated. Previously
the groups of Zaworotko,[19a] and more recently Matzger,[19b]
showed that the lower temperature phase was non-
interpenetrated. Zaworotko and coworkers rationalised this
observation on the basis that the formation of the more thermo-
dynamically stable product, i.e. a denser interpenetrated struc-
ture, is favoured at higher temperatures. Given our current
experimental observations we believe the synthesis of 12 and 13
is under kinetic control, thus higher temperatures and a shorter
reaction time (1 day versus 3 days) lead to the formation of
two-fold interpenetrated 13 as the preferred product.
In structure 13, adjacent 2D networks, which are packed
parallel to the original network (parallel to the ab diagonal), are
slightly offset to accommodate the packing. In 13 the 2D MOFs
are planar and not undulating as observed in the structure of 12.
By comparison with 12 this creates large rectangular channels
that are viewed along the b-axis (Fig. 7a). In 13 only one 2D
network is accommodated in each window to give a two-fold
interpenetrated 3D mechanically interlocked structure (Fig. 7b).
In this instance the networks are packed such that small
˚
triangular shaped channels with ,9.5(1) A sides percolate down
the b-axis.
Conclusion
This work describes the synthesis and structures of a series of
MOFs made from novel triazole and triazolium-based links.
Due to exploitation of the well-developed click reaction
methodology, triazolium links bearing appropriate donor
groups can be synthesised in high yield by short synthetic
pathways. Careful manipulation of the conditions was required
to facilitate both the click reaction in the presence of electron
withdrawing substituents on the azide and the methylation step
to overcome the poor solubility of the triazole diester 9. We
further demonstrate that subtle differences in the structure of
the link, the choice of metal salt, and the conditions used for
synthesis (e.g. temperature and additives) can have a dramatic
effect on the net topology and degree of catenation. Current
work in our laboratory is focussed on using this knowledge to
design new azolium links that will give rise to architectures
with larger pore volumes that will facilitate the binding of
known homogeneous catalytic moieties.
Compound 12 crystallises in the orthorhombic space group
Pbca with a single copper(II) atom, a molecule of L1Me and a
DMF ligand in the asymmetric unit and a unit cell volume of
3
˚
4235.4(4) A . A perspective view of the 2D MOF structure in 12
is shown in Fig. 5a. The dicopper(II) paddlewheel SBUs are
typical[20] and the triazolium link maintains a geometry similar
to that observed in the solid-state structure seen for HL1MeꢀH2O
with an angle between the two carboxylate groups of 151.48
(compared with 145.4(1)8 in HL1MeꢀH2O). The distance bridged
by the link (between the centroids of the paddlewheels) is
˚
18.1(1) A, although the angle subtended by the ligand and the
twist relative to the plane of the 2D MOF means the windows are
˚
not regular with width 15.1(1) A and length 21.7(1) A. This
˚
2
˚
provides windows of roughly ,11.7 ꢂ 18.3 A taking into
account the van der Waals radii. A similar topology was
observed with the diazolium linker 8 and dicopper(II) paddle-
wheel SBUs[9h] and in the imidazolium structure reported by
Son and coworkers.[9e]
Experimental
Adjacent 2D networks that are packed parallel to the original
˚
network (parallel to the acdiagonal) are offset by 9.4(1)A and the
General Experimental
Melting points were measured on a Gallenkamp melting point
apparatus and are uncorrected. Elemental analyses were per-
formed by the Campbell Microanalytical Laboratory at the
DMF ligands on the dicopper(II) paddlewheels are interdigitated
into the windows (Fig. 6a). This creates small rectangular
channels that are viewed along the a-axis (Fig. 6b). Unfortunately

414
A. M. Burgun, C. J. Doonan, and C. J. Sumby
(a)
(b)
Fig. 5. The 2D metal–organic frameworks in the structures of (a) 12 and (b) 13.
(a)
(c)
(b)
(d)
b
a
c
Fig. 6. (a) A view of the packing of 12 showing the offset arrangement of the 2D metal–organic frameworks and the canting of the
dicopper(II) paddlewheels. (b) A view down the a-axis and (c) the interpenetration of the 2D grids (red) by two perpendicular layers (green
and blue) to give a close-packed structure (hydrogen atoms omitted for clarity). (d) A simplified schematic of the interpenetrated
structure.
University of Otago. Infrared spectra were collected on a Perkin
Elmer 100S Infrared spectrometer in Universal ATR mode.
NMR spectra were recorded on a Varian Gemini 300 MHz or
600 MHz NMR spectrometer at 238C using a 5 mm probe.
1H (13C) NMR spectra recorded in (D6)DMSO were referenced
to the solvent peak: 2.5 (39.5) ppm. Electrospray (ES) mass
spectra were recorded using a Finnigan LCQ mass spectrometer.
Unless otherwise stated, all chemicals were obtained
from commercial sources and used as received. Methyl
4-ethynylbenzoate[22] and methyl 4-azidobenzoate[23] were
prepared according to the methods described in the literature.
Synthesis
Synthesis of 1,4-Bis(methyl 4-benzoate)-
1H-1,2,3-triazole, 9
To a stirred solution of methyl 4-ethynylbenzoate (351 mg,
2.19 mmol) and methyl 4-azidobenzoate (388 mg, 2.19 mmol)
in EtOH/H2O (25 mL, 7 : 3) was added CuSO4 5H2O (109 mg,
0.44 mmol) and sodium ascorbate (174 mg, 0.88 mmol). The
solution was then heated to reflux under a nitrogen atmo-
sphere for 16 h. After the reaction mixture was cooled to room
temperature, ammonia (75 mL, 14 %) was added. The result-
ing precipitate was filtered off and washed well with H2O,

Triazolium-Containing MOFs
415
(a)
(b)
c
a
b
c
a
b
Fig. 7. Views down (a) the b-axis and (b) the c-axis showing the two-fold interpenetration (hydrogen atoms omitted for
clarity). The approximately triangular channels that percolate along the b-axis are shown in (a).
and then with dichloromethane (3 ꢂ 20 mL) to afford 9 as an
insoluble pale beige powder (681 mg, 92 %). Mp 2988C. Anal.
Calc. for C18H15N3O4: C 64.09, H 4.48, N 12.46. Found:
C 63.99, H 4.41, N 12.44 %. nmax (powder)/cmꢁ1 n(CO2Me)
1723s, n(C¼C) 1608m. dH ((D6)DMSO, 300 MHz) 9.55 (s,
1H, Htriazole), 8.22–8.10 (m, 8H, Haromatic), 3.92 (s, 3H, CH3),
3.89 (s, 3H, CH3).
126.67, 121.65, 52.72 (CO2CH3), 52.63 (CO2CH3), 39.57
(NCH3). m/z (ESI, positive ion mode, MeOH) 352.3 [Mþ].
Synthesis of 1,4-Bis(4-benzoic acid)-1-methyl-1H-1,2,3-
triazolium Chloride, H2L1Me
Potassium hydroxide solution (15 mL, 2 M) was added to a
stirred solution of 10(OTf) (978 mg, 1.95 mmol) in methanol
(60 mL). The reaction mixture was then heated to reflux for 16 h.
After the reaction mixture cooled to room temperature and was
filtered, HCl solution (2 M) was added dropwise until pH 1–2
was reached. The resulting precipitate was filtered off, washed
well with H2O, and dried under high vacuum to afford H2L1Me
as a white powder (597 mg, 85 %). nmax (powder)/cmꢁ1 n(O–H)
2889s, n(CO2H) 1711s. dH ((D6)DMSO, 300 MHz) 13.54 (s, 2H,
CO2H), 10.13 (s, 1H, Htriazolium), 8.32–8.22 (m, 6H, Haromatic),
7.99 (d, 3JH–H 8.0, 2H, Haromatic), 4.49 (s, 3H, NCH3). dC ((D6)
DMSO, 75 MHz) 166.40 (CO2H), 165.91 (CO2H), 142.45,
137.44, 133.66, 133.50, 131.44, 130.11, 129.71, 128.19,
126.30, 121.51. m/z (ESI, positive ion mode, MeOH) 324.2
[Mþ]. X-Ray quality crystals of HL1MeꢀH2O were obtained by
heating a 1 : 1 DMF/H2O solution (3 mL, containing one drop of
concentrated HNO3) of H2L1Me (5 mg) at 858C overnight. Anal.
Calc. for C17H13N3O4 H2O: C 59.82, H 4.43, N 12.31. Found: C
59.86, H 4.23, N 12.26 %.
Synthesis of 1,4-Bis(4-benzoic acid)-1H-1,2,3-triazole
Hydrochloride, H2L1(HCl)
Potassium hydroxide solution (4 mL, 2 M) was added to a
stirred solution of 9 (250 mg, 0.74 mmol) in methanol (16 mL).
The reaction mixture was then heated to reflux for 16 h. After the
reaction mixture cooled to room temperature, HCl solution
(2 M) was added dropwise until pH 1–2 was reached. The
resulting precipitate was filtered off, washed well with H2O,
and dried under high vacuum to afford H2L1(HCl) as a white
powder (211 mg, 82 %). Anal. Calc. for C16H11N3O4 HCl:
C 55.58, H 3.50, N 12.15. Found: C 56.79, H 3.22, N 12.29 %.
nmax (powder)/cmꢁ1 n(O–H) 2990s, n(CO2H) 1681s, n(C¼C)
1608m. dH ((D6)DMSO, 600 MHz) 13.14 (s, 2H, CO2H), 9.57 (s,
1H, Htriazole), 8.18–8.08 (m, 8H, Haromatic). dC ((D6)DMSO,
150 MHz) 166.90 (CO2H), 166.33 (CO2H), 146.62, 139.39,
134.07, 131.17–130.13 (m br), 125.34, 120.85, 119.79.
[Zn(L1)2(H2O)2] (11)
Synthesis of 1,4-Bis(methyl 4-benzoate)-1-methyl-1H-
1,2,3-triazolium Triflate, 10(OTf)
H2L1(HCl) (4mg, 0.013mmol) and zinc(II) nitrate (3.8 mg,
0.013 mmol) were sealed in a 20mL glass vial with a Teflon-
lined screw cap along with a 1 : 1 DMF/ethanol solution (4mL)
and one drop of conc. HNO3. The mixture was heated at 858C for
2 days, and then allowed to cool to room temperature. The
resulting crystals were washed with fresh DMF, dichloro-
methane, and then dried under vacuum to afford 11 as a white
crystalline powder (2mg, 39%). Anal. Calc. for C16H11N3O5Zn:
C, 49.19; H, 2.84; N, 10.76. Found: C 49.26, H 2.73, N 10.84 %.
To a stirred solution of 9 (800 mg, 2.37 mmol) in well
degassed 1,1,2,2-tetrachloroethane (40 mL) was added drop-
wise methyl triflate (0.54 mL, 4.74 mmol). The solution was
then heated at 1508C for 16 h. After the reaction mixture cooled
to room temperature, the solution was filtered and then diethyl
ether (150 mL) was added to the mixture. The resulting precipi-
tate was filtered off and washed with diethyl ether (3 ꢂ 50 mL)
to afford 10(OTf) as a white powder (1.13 g, 95 %). Anal. Calc.
for C20H18F3N3O7S1: C 47.91, H 3.62, N 8.38. Found: C 47.97,
H 3.46, N 8.35 %. nmax (powder)/cmꢁ1 n(CO2Me) 1724s. dH
((D6)DMSO, 600 MHz) 10.05 (s, 1H, Htriazolium), 8.35 (d, 3JH–H
n
max (powder)/cmꢁ1 3106s, 1603m, 1518m, 1398s.
a-[Cu2(DMF)2(L1Me)2](NO3)2 (12) and
b-[Cu2(DMF)2(L1Me)2](NO3)2 (13)
Compound 12: H2L1Me (5 mg, 0.014 mmol) and copper
3
8.7, 2H, Haromatic), 8.26 (m, 4H, Haromatic), 8.01 (d, JH–H 8.3,
2H, Haromatic), 4.49 (s, 3H, NCH3), 3.94 (s, 6H, CO2CH3). dC
((D6)DMSO, 150 MHz) 165.38 (CO2CH3), 164.90 (CO2CH3),
142.33, 137.69, 132.38, 132.25, 131.39, 130.02, 129.83, 128.24,
nitrate (3.2 mg, 0.014 mmol) were sealed in a 20 mL glass vial
with a Teflon-lined screw cap along with a DMF solution

416
A. M. Burgun, C. J. Doonan, and C. J. Sumby
(1.5 mL) and one drop of conc. HNO3. The mixture was heated
at 858C for 3 days, and then allowed to cool to room temperature.
The resulting crystals were washed with fresh DMF, dichlor-
omethane, and then dried under vacuum to afford 12 as blue
crystals (3 mg, 43 % based on the hydrate). Anal. Calc. for
C17H14N4O8Cu 1½H2O): C 41.43, H 3.48, N 11.37. Found:
C 41.39, H 3.30, N 11.19 %. nmax (powder)/cmꢁ1 3077s, 1605m,
1552m, 1379s.
903866–903869 contain the supplementary crystallographic
data for these structures. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre by
www.ccdc.cam.ac.uk/data_request/cif.
Specific Details of the Structure Refinements
Compound HL1MeꢀH2O
The hydrogen atoms on the water solvate molecule and the
carboxylic acid were located in the difference map. Due to the
Compound 13: H2L1Me (5 mg, 0.014 mmol) and copper
nitrate (3.2 mg, 0.014 mmol) were sealed in a 20 mL glass vial
with a Teflon-lined screw cap along with a DMF solution
(1.5 mL). The mixture was heated at 1208C for 1 day, and then
allowed to cool to room temperature. The resulting crystals were
washed with fresh DMF and then dried under vacuum to
afford predominantly 13 as blue needle-shaped crystals.
˚
very short OꢀꢀꢀO distance (2.465 A) between the carboxylic
acid hydrogen bonded to its own parent carboxylate, the hydro-
gen atom was allowed to freely refine. The position of the
hydrogen atom following refinement is very close to the centre
˚
point between the two oxygen atoms (O–H distance of 1.106 A).
This is consistent with the situation for a very strong hydrogen
n
max (powder)/cmꢁ1 3068s, 1653m, 1621m, 1384s.
bond (DpKa ,0).[30]
X-Ray Crystallography
Compound 11
Crystals were mounted under oil on nylon loops. X-Ray dif-
fraction data were collected at 150(2) K with (i) MoKa radiation
The triazole ring of L1 is disordered over two positions and
both sites (N1 and C4) refined with 50 % occupancy by carbon
and 50 % occupancy by nitrogen. EXYZ and EADP commands
were employed.
˚
(l 0.71073 A) using an Oxford Diffraction X-calibur single
crystal X-ray diffractometer (HL1MeꢀH2O) or (ii) at the MX1
beamline of the Australian Synchrotron[24] (l 0.71073 A; com-
˚
pounds 11, 12, and 13). Datasets were corrected for absorption
using a multi-scan method, and structures were solved by direct
methods using SHELXS-97[25] and refined by full-matrix least-
squares on F2 by SHELXL-97,[26] interfaced through the pro-
gram X-Seed.[27] In general, all non-hydrogen atoms were
refined anisotropically and hydrogen atoms were included as
invariants at geometrically estimated positions, unless specified
otherwise below. Figures were produced using the program
POV-Ray,[28] interfaced through X-Seed. Publication materials
were prepared using CIFTAB.[29] Details of data collections and
structure refinements are given below and in Table 1. CCDC
Compound 12
A total of six DFIX restraints were used to maintain chemi-
cally sensible bond lengths and angles for the coordinated DMF
molecule in the structure.
Compound 13
The nitrate anion could not be located properly in the
difference map. Four DFIX restraints were used to maintain
chemically sensible bond lengths and angles for the coordinated
DMF molecule in the structure. The structure also contains
Table 1. Crystal data and X-ray experimental data for HL1Me H2O, 11, 12, and 13
.
Compound
HL1MeꢀH2O
11
12
13
Empirical formula
Formula weight
Crystal system
Space group
C17H15N3O5
341.32
Monoclinic
P21/c
C16H11N3O5Zn
390.65
C20H19CuN5O8
520.94
C20H19CuN5O8
520.94
Orthorhombic
Pbcn
Monoclinic
P21/c
Orthorhombic
Pbca
˚
a [A]
˚
b [A]
˚
c [A]
6.0690(5)
34.215(4)
7.1683(5)
90
16.432(3)
11.630(2)
7.6510(15)
90
17.632(3)
9.4690(19)
25.544(5)
90
25.182(5)
10.411(2)
23.273(5)
90
a [deg.]
b [deg.]
g [deg.]
93.316(7)
90
94.39(3)
90
90
90
90
90
3
˚
Volume [A ]
1468.0(2)
4
1457.9(5)
4
4264.8(14)
8
6101(2)
8
Z
Density (calculated) [Mg mꢁ3
]
1.526
1.780
1.623
1.134
Absorption coefficient [mmꢁ1
]
0.115
1.721
1.084
0.758
F(000)
712
792
2136
2136
Crystal size [mm3]
Theta range [deg.]
Reflections collected
Independent reflections
0.47 ꢂ 0.22 ꢂ 0.07
2.91–29.17
13 276
0.13 ꢂ 0.09 ꢂ 0.02
2.15–27.10
21 972
0.08 ꢂ 0.07 ꢂ 0.07
1.97–27.12
63 628
0.18 ꢂ 0.11 ꢂ 0.04
2.29–26.84
88 763
3555
3161
4671
6460
Observed reflections [I . 2s(I)]
Goodness-of-fit on F2
R1 [I . 2s(I)]
2646
3019
3998
5102
1.061
1.057
1.655
1.292
0.0563
0.1324
0.0342
0.0986
0.0888
0.3052
wR2 (all data)
0.0903
0.3505

Triazolium-Containing MOFs
417
disordered solvent molecules in the large channels that run along
the b-axis. The SQUEEZE routine of PLATON[21] was applied
to the collected data, which resulted in significant reductions in
R1 and wR2 and an improvement in the goodness of fit (GOF).
R1, wR2, and GOF before the SQUEEZE routine: 14.3 %,
46.1 %, and 2.06; after the SQUEEZE routine: 8.9 %, 30.5 %,
and 1.29. The contents of the solvent region calculated from
the result of the SQUEEZE routine (one nitrate anion per
asymmetric unit) are represented in the unit cell contents of
the crystal data.
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Supplementary Material
Powder X-ray diffraction data for compound 11 are available on
the Journal’s website.
(d) K. S. Jeong, Y. B. Go, S. M. Shin, S. J. Lee, J. Kim, O. M. Yaghi,
N. Jeong, Chem. Sci. 2011, 2, 877. doi:10.1039/C0SC00582G
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Acknowledgements
The Australian Research Council (ARC) is acknowledged for a Future
Fellowships to C.J.S (FT0991910), C.J.D (FT100100400), and for funding
this research through DP110103741. The ARC is also acknowledged for
funding the Bragg Crystallography Facility (LE0989336 and
LE120100012). The Australian Synchrotron is thanked for funding travel
and access to the MX1 beam line through the Australian Synchrotron Access
Program (AS123/MX1/5435). The views expressed herein are those of
the authors and are not necessarily those of the owner or operator of the
Australian Synchrotron.
(b) Z. Fei, T. D. Geldbach, D. Zhao, R. Scopelliti, P. J. Dyson, Inorg.
Chem. 2006, 45, 6331. doi:10.1021/IC060297N
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(e) J. Chun, I. G. Jung, H. J. Kim, M. Park, M. S. Lah, S. U. Son, Inorg.
Chem. 2009, 48, 6353. doi:10.1021/IC900846S
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