Functional Versatility of a Series of Zr Metal-Organic Frameworks Probed by Solid-State Photoluminescence Spectroscopy

Article abstract of DOI:10.1021/jacs.7b02184

Many of the desirable properties of metal-organic frameworks (MOFs) can be tuned by chemical functionalization of the organic ligands that connect their metal clusters into multidimensional network solids. When these linker molecules are intrinsically fluorescent, they can pass on this property to the resultant MOF, potentially generating solid-state sensors, as analytes can be bound within their porous interiors. Herein, we report the synthesis of a series of 14 interpenetrated Zr and Hf MOFs linked by functionalized 4,4′-[1,4-phenylene-bis(ethyne-2,1-diyl)]-dibenzoate (peb^2-) ligands, and we analyze the effect of functional group incorporation on their structures and properties. Addition of methyl, fluoro, naphthyl, and benzothiadiazolyl units does not affect the underlying topology, but induces subtle structural changes, such as ligand rotation, and mediates host-guest interactions. Further, we demonstrate that solid-state photoluminescence spectroscopy can be used to probe these effects. For instance, introduction of naphthyl and benzothiadiazolyl units yields MOFs that can act as stable fluorescent water sensors, a dimethyl modified MOF exhibits a temperature dependent phase change controlled by steric clashes between interpenetrated nets, and a tetrafluorinated analogue is found to be superhydrophobic despite only partial fluorination of its organic backbone. These subtle changes in ligand structure coupled with the consistent framework topology give rise to a series of MOFs with a remarkable range of physical properties that are not observed with the ligands alone.

Full text of DOI:10.1021/jacs.7b02184

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Article
Functional Versatility of a Series of Zr MOFs Probed
by Solid-State Photoluminescence Spectroscopy
Ross J. Marshall, Yaroslav Kalinovskyy, Sarah L. Griffin, Claire Wilson, Barry A Blight, and Ross S. Forgan
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b02184 • Publication Date (Web): 07 Apr 2017
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Functional Versatility of a Series of Zr MOFs Probed by Solid-
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Ross J. Marshall,a Yaroslav Kalinovskyy,b Sarah L. Griffin,a Claire Wilson,a Barry A. Blightb,c* and
Ross S. Forgana*
aWestCHEM, School of Chemistry, University of Glasgow, University Avenue, Glasgow, G12 8QQ, UK.
bSchool of Physical Sciences, University of Kent, Ingram Building, Canterbury, CT2 7NH, UK.
cDepartment of Chemistry, University of New Brunswick, Toole Hall, Fredericton, NB, E3B 5A3, Canada.
ABSTRACT: Many of the desirable properties of metalꢀorganic frameworks (MOFs) can be tuned by chemical functionalization
of the organic ligands that connect their metal clusters into multidimensional network solids. When these linker molecules are inꢀ
trinsically fluorescent, they can pass on this property to the resultant MOF, potentially generating solidꢀstate sensors, as analytes
can be bound within their porous interiors. Herein, we report the synthesis of a series of 14 interpenetrated Zr and Hf MOFs linked
by functionalized 4,4ʹꢀ[1,4ꢀphenyleneꢀbis(ethyneꢀ2,1ꢀdiyl)]ꢀdibenzoate (peb2ꢀ) ligands, and analyse the effect of functional group
incorporation on their structures and properties. Addition of methyl, fluoro, naphthyl and benzothiadiazolyl units does not affect the
underlying topology, but induces subtle structural changes, such as ligand rotation, and mediates hostꢀguest interactions. Further,
we demonstrate that solidꢀstate photoluminescence spectroscopy can be used to probe these effects. For instance, introduction of
naphthyl and benzothiadiazolyl units yields MOFs that can act as stable fluorescent water sensors, a dimethyl modified MOF exhibꢀ
its a temperature dependent phase change controlled by steric clashes between interpenetrated nets, and a tetrafluorinated analogue
is found to be superhydrophobic despite only partial fluorination of its organic backbone. These subtle changes in ligand structure
coupled with the consistent framework topology give rise to a series of MOFs with a remarkable range of physical properties that
are not observed with the ligands alone.
Introduction
Metalꢀorganic frameworks (MOFs)1ꢀ7 are multidimensional
network materials containing both inorganic and organic conꢀ
stituents. The diverse choice of organic and inorganic units
that can be used to construct MOFs results in a wide variety of
structures.8ꢀ10 The high porosity of MOFs has prompted invesꢀ
tigations towards potential applications such as gas capture
and storage,11ꢀ16 catalysis,5,17ꢀ19 sensing20ꢀ22 and drug delivꢀ
ery.23ꢀ26 Lately, many synthetic efforts towards MOFs have
focused on those containing group IV transition metal ions,
especially zirconium and hafnium.27ꢀ32 Zr and Hf MOFs linked
by linear dicarboxylate ligands generally adopt the wellꢀ
documented UiOꢀ66 topology (UiO = University of Oslo)
which contains M6O4(OH)4 clusters (M = Zr or Hf) linked in
three dimensions by twelve bridging organic ligands.27 Alterꢀ
native topologies of Zr and Hf MOFs have been obtained,
usually with nonꢀlinear carboxylate ligands,33ꢀ37 whilst extendꢀ
Figure 1. a) Chemical structure of 4,4ʹꢀ[1,4ꢀphenyleneꢀ
bis(ethyneꢀ2,1ꢀdiyl)]ꢀdibenzoate, peb2ꢀ, termed L1 herein, alongꢀ
ed organic ligands have resulted in interpenetrated UiOꢀ66
side b) the solidꢀstate packing structure of the interpenetrated
analogues.38,39 Members of this series of Zr MOFs are conꢀ
MOF it forms with Zr, termed Zr-L1. c) Structural description
structed from substituted 4,4ʹꢀ[1,4ꢀphenyleneꢀbis(ethyneꢀ2,1ꢀ
and naming scheme of the functionalized peb2ꢀ ligands used
diyl)]ꢀdibenzoate (peb2ꢀ) ligands (Figure 1a) and exhibit a twoꢀ
throughout this study.
fold interpenetrated structure (Figure 1b).38
This family of Zr MOFs has been extended to include an anꢀ
thracene derivative40 and functionalized analogues designed
for postsynthetic modification (PSM), while they have been
investigated for catalytic applications40ꢀ42 and also CO2 separaꢀ
tion.43 We are particularly interested in Zr MOFs containing
integral alkyne moieties,44 having recently demonstrated their
successful postsynthetic halogenation for potential use as I2
sequestration materials,45 and for their ability to modulate the
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mechanical properties of Zr MOFs, which can be manipulated
all the MOFs are highly crystalline and structurally very simiꢀ
lar (Figure 2a), while the Hf MOFs display analogous strucꢀ
tures (see SI, Section S4).
by the choice of organic ligand.46,47
1
2
In 2005, a report detailing the optical properties of the dimeꢀ
thyl ester of the πꢀconjugated peb2ꢀ ligand (L1-Me2), demonꢀ
strated that this ligand precursor exhibited strong absorption in
the UV region and was strongly fluorescent, with a quantum
yield of 0.91 (λabs = 335 nm) in dichloromethane.48 Since then,
the Zr MOF containing peb2ꢀ (Zr-L1; Figure 1b) has been
investigated for photocatalytic organic dye degradation; optiꢀ
cal measurements and DFT calculations confirmed that the
optical properties of the MOF are inherited from the πꢀ
conjugated organic ligand.41 A number of other fluorescent
zirconium MOFs have been reported and many of them have
been used for the detection and sensing of analytes such as
metals,49 explosives,50 harmful gases/vapours51ꢀ53 and antibiotꢀ
ics.54 Alternatively, the intrinsic fluorescence of Zr MOFs has
been demonstrated to be useful in pH sensing,55,56 while
changes in ligand conformation in tetraphenylethyleneꢀ57 and
porphyrinꢀlinked58 Zr MOFs has been shown to result in difꢀ
ferences in their steady state emission spectra, both in terms of
band positions and intensities.
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Inspired by the intrinsic fluorescence of L1-Me2, we herein
report the synthesis and structural/optical characterization of a
series of interpenetrated Zr and Hf MOFs containing substitutꢀ
ed peb2ꢀ ligands. We have varied the chemical substituents on
the central core of the extended ligand to include methyl, fluoꢀ
rine, naphthyl and benzothiadiazolyl moieties (Figure 1c). We
detail how linker functionalization modulates the structural
and optical properties of the resulting Zr and Hf MOFs, whose
unusual structural features and hostꢀguest behavior have been
probed via solidꢀstate emission techniques.
Results and Discussion
The dimethyl esters of each of the ligands shown in Figure
1c (see SI, Scheme S1) were synthesized by Pd/Cu catalysed
Sonogashira crossꢀcoupling reactions, followed by saponificaꢀ
tion to produce the free acids (see SI, Section S2). Solvotherꢀ
mal reactions containing the required ligand, ZrCl4 or HfCl4,
hydrochloric acid, and either benzoic acid59 or Lꢀproline60,61 as
modulators in DMF resulted in the isolation of a series of new
interpenetrated Zr and Hf MOFs (see SI, Section S3). Careful
choice of reaction parameters, such as concentration, temperaꢀ
ture and modulator choice/equivalency resulted in the isolation
of fourteen highly crystalline interpenetrated Zr and Hf MOFs.
We described the solidꢀstate structures of [M6O4(OH)4(L1)6]n
(M = Zr or Hf) recently45 (Figure 1b) and this repeating formuꢀ
la is common to all fourteen MOFs. The MOFs are herein
described as M-Ln, where M is either Zr or Hf and Ln is the
ligand used to construct the framework.
Figure 2. a) Comparison of the PXRD patterns of the Zr MOFs
synthesized during this study, with the inset highlighting the high
angle data. The analogous data for the Hf MOFs are provided in
the SI, Section S4. b) Portions of the solidꢀstate structures of Zr-
L4, which shows positional disorder of the fluorine atoms on the
ligand core; Zr-L6, highlighting the two disordered arrangements
of the naphthyl moieties which rotate out of the plane of conjugaꢀ
tion; and Zr-L7, showing disorder of the thiadiazolyl units over
both sides of the ligand.
Powder Xꢀray diffraction (PXRD) was used to first analyse
the bulk phase purity of the MOFs that were isolated from the
synthetic mixtures by centrifugation. Initial attempts at bulk
MOF syntheses were performed using our recently discovered
Lꢀproline modulation,60 which proved again to be very effiꢀ
cient. Lꢀproline effectively modulated twelve of the fourteen
MOFs, however it did not produce Zr or Hf MOFs containing
the tetrafluoro ligand (L5), which is unexpected considering
the diꢀfluorinated ligands (L3 and L4) were compatible with
these synthetic conditions. Instead, we turned to benzoic acid
modulation59 for Zr-L5 and Hf-L5 and bulk microcrystalline
samples were successfully obtained. Upon comparison of the
PXRD patterns of the Zr MOFs, it is immediately obvious that
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Figure 3. a) PXRD patterns of Zr-L2 before and after N2 adsorption measurements compared with predicted patterns of MOFs with orthoꢀ
rhombic and cubic symmetry. Peaks marked with an asterisk are lost on activation, indicating a phase change. b) Optical microscope image
of single crystals of Zr-L2. c) and d) represent the planar and twisted orientations of L2 observed within Zr-L2, respectively. e) A portion
of the solidꢀstate structure of Zr-L2 (protons and disordered methyl groups have been omitted for clarity) with dashed lines representing
the close proximity of the pendant methyl groups with the other framework.
Optimization of reaction conditions resulted in the isolation
of single crystals of thirteen of the MOFs, with Hf-L2 being
the only MOF that could not be prepared as diffraction quality
single crystals. The crystal structures of the Zr and Hf anaꢀ
logues of individual ligands are very similar, as expected
based on the close structural agreement between Zr-L1 and
Hf-L1.45 The pendant functionality of the ligands does not
disrupt formation of the MOFs with all materials displaying
twoꢀfold interpenetration. Crystal structures of the Zr and Hf
MOFs containing the diꢀfluorinated ligands L3 and L4 display
positional disorder of the fluorine atoms across all four sites of
the central phenylene ring and, on first inspection they, all
appear to be identical and resemble the MOFs containing L5.
The positional disorder, however, is accounted for by adjustꢀ
ing chemical occupancies (Figure 2b). Similarly, the benzothiꢀ
adiazolyl unit of L7 is disordered across two orientations in
Zr-L7 and Hf-L7, maintaining the cubic symmetry despite the
lower symmetry of the ligand. Interestingly, we observe difꢀ
ferences in the solidꢀstate structures of Hf-L6 and Zr-L6,
which contain naphthyl units. In Hf-L6 there is similar posiꢀ
tional disorder of the naphthyl unit across both sides of the
ligand, while in Zr-L6 the same disorder is observed, however
in this case the naphthyl core twists out of the plane of conjuꢀ
gation of the ligand by approximately 23°, presumably to minꢀ
imise steric interactions with other linkers in the interpenetratꢀ
ed structure. The reason for the different behaviour in the Zr
and Hf analogues has not been established.
the twelve ligands connected to each Zr6 cluster, four ligands
in an equatorial plane are planar with disordered methyl units
(Figure 3c) while the other eight ligands adopt a conformation
where the central dimethylphenylene unit is twisted by apꢀ
proximately 40° out of the plane of conjugation, and the meꢀ
thyl groups are fully ordered (Figure 3d). Twisting of the ligꢀ
ands in Zr-L2 is believed to be the result of steric interactions
between the bulky methyl groups and adjacent phenyl units of
the other interpenetrated net, which are in close proximity
(Figure 3e).
It is interesting to note that L4, which contains fluorine atꢀ
oms in same positions that L2 contains methyl groups, can be
incorporated into Zr and Hf MOFs with the expected cubic
symmetry, as the steric interactions imposed by the fluorine
atoms are insufficient to drive the structural perturbation obꢀ
served in Zr-L2. In the crystal structure of Zr-L2 the ligands
of one net bow away from the Zr6 cluster of the second net,
while in Zr-L4 and the rest of the MOFs the ligands bow in
towards the cluster, and this structural difference is likely to be
due to the differing extent of steric interactions (see SI, Secꢀ
tion S5).
The PXRD pattern of Zr-L2 changed significantly over the
course of N2 adsorption experiments (Figure 3a). Comparing
the experimental PXRD pattern of chloroform exchanged Zr-
L2 (Zr-L2 expt) with the predicted pattern from the orthoꢀ
rhombic single crystal structure (Zr-L2 pred), it is clear that
some of the peaks match well, while some of them are split,
indicating the presence of multiple phases.
All the functionalized MOFs discussed thus far adopt the
typical cubic structure and crystallise with the Fd-3m symꢀ
metry of the parent MOFs, however, close inspection of the
PXRD patterns reveals slight differences observed for MOFs
containing L2 (Figure 3a), with additional peaks observed.
Single crystals of Zr-L2 (Figure 3b) have both lozengeꢀshaped
and rounded morphologies, unlike the typical wellꢀdefined
octahedral crystals of the other members of the series.
Both of these forms of Zr-L2 crystallize in the lower symꢀ
metry orthorhombic Imma space group, but have the same
connectivity and composition of the other MOFs, and this is
attributed to the presence of different ligand orientations. Of
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Figure 4. a) N2 adsorption and desorption isotherms collected at 77 K for the Zr MOFs. b) Corresponding pore size distributions (QSDFT)
for the MOF series. Analogous data for the Hf MOFs are given in the SI, Section S7. c) CO2 adsorption isotherms (273 K) of the Zr MOFs.
d) Calculated BET surface areas for all fourteen Zr and Hf MOFs.
The PXRD pattern of cubic Zr-L1 was also predicted (Zr-
L1 pred), revealing that the experimental pattern of chloroꢀ
form exchanged Zr-L2 resembles both the orthorhombic and
cubic predicted patterns to some extent, again suggesting a
mixture of two phases. The presence of mixed phases of Zr-
L2 suggests that the material is dynamic and that it may be
able to transition from the orthorhombic (Imma) to the cubic
(Fd-3m) phase by rotation of the central dimethylphenylene
units. This is indeed confirmed by PXRD analysis of Zr-L2
after N2 adsorption experiments (Zr-L2 postꢀBET) with the
pattern now in excellent agreement with the predicted pattern
for cubic Zr-L1. Prior to N2 uptake experiments the material
was activated by heating at 120 °C for 20 hours and we beꢀ
lieve that, upon heating, the ligands rotate to adopt the linear
geometry found in the cubic MOFs. We further investigated
this phenomenon by performing variable temperature PXRD
and the same trend is observed, confirming that heating results
in a structural modification and crystallographic phase change
(see SI, Section S5).
similar to that of the MOFs containing pendant diꢀ
methyl/fluorine moieties, whilst Zr-L6 displays a slightly
lower uptake. The reason for the lower than expected BET
surface area of Zr-L5 (1420 m2gꢀ1) is not immediately obviꢀ
ous, however, low values were consistently observed for mulꢀ
tiple batches. It should be noted that the uptake of Hf-L5 (675
m2gꢀ1) is also lower than expected, and therefore it may be
plausible that the activation conditions were ineffective for
MOFs containing L5 or that during activation the MOFs were
partially collapsing. The calculated poreꢀsize distributions
(QSDFT) are consistent with the functional groups occupying
the pore space of the MOFs, with an observed reduction of the
main pore diameter from 14.2 Å in Zr-L1 to 13.0 Å in Zr-L7
(Figure 4b). Similar trends were observed for the Hf MOFs.
CO2 uptake isotherms of the Zr MOFs were collected at 0 °C
(see SI, Section S7) to examine the potential for MOFꢀguest
interactions and reveal that while ligand functionalization does
not significantly improve the CO2 uptake capacities under the
pressure range investigated (Figure 4c), the similar uptakes
obtained for Zr-L1, Zr-L6 and Zr-L7 (they are superimposed
in Figure 4c) suggest that naphthyl and benzothiadiazolyl units
do enhance CO2 uptake to some extent. This enhancement
comes in spite of the incorporation of bulky aromatꢀ
ics/heterocycles, presumably through favourable interactions
between CO2 and either the πꢀsystem of Zr-L6 or the electron
rich heterocycle of Zr-L7, which has been observed previousꢀ
ly in a related CuꢀMOF.62
With the series of interpenetrated Zr and Hf MOFs in hand,
we decided to analyse and compare the effect of substitution
on their physical properties. From the thermogravimetric analꢀ
ysis (TGA) profiles (see SI, Section S6) it is clear that the
thermal stabilities of the materials are relatively unaffected by
the presence of either Zr6 or Hf6 clusters with degradation
occurring at approximately the same temperature. TGA experꢀ
iments were performed under an air atmosphere, resulting in
decomposition of the MOFs to either ZrO2 or HfO2, and the
increased mass of Hf relative to Zr accounts for the smaller
percentage mass losses that are observed for the Hf MOFs.
Ligand functionalization results in slightly altered thermal
properties, however there is no obvious negative impact on the
MOFs’ thermal stabilities, with all fourteen materials decomꢀ
posing at ~450–500 °C.
Given that L1-Me2 and its derivatives exhibit interesting abꢀ
sorption properties, and with the incorporation of known
chromophores such as naphthyl63,64 and benzothiadiazolyl65,66
units into the MOFs, solidꢀstate UVꢀVis (SSꢀUVꢀVis) spectra
of all the Zr-Ln MOFs were collected (Figure 5a) and comꢀ
pared with those of the dimethyl esters (the diesters are a betꢀ
ter model for the Zr MOFs as hydrogen bonding between carꢀ
boxylates is nullified) and free acids of the ligands (see SI,
Section S8). The comparisons revealed that in most cases the
spectroscopic properties of the MOFs are generally inherited
from the respective ligand.
Comparing the N2 uptakes of the Zr MOFs (see SI, Section
S7 and Figure 4a) it is evident that ligand functionalization
results in a reduction in gravimetric N2 uptake compared with
Zr-L1, as would be expected. The N2 uptakes of Zr-L2, Zr-
L3 and Zr-L4 are similar, which is reassuring as all three
MOFs contain two pendant moieties of similar mass: either
methyl groups or fluorine atoms. The porosity of Zr-L7 is
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Figure 5. a) Comparison of the solidꢀstate UVꢀVis spectra of the
Zr MOFs. Photographs of b) Zr-L1 and c) Zr-L5 highlight the
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unexpected intense yellow colour of Zr-L5.
Figure 6. Normalized solidꢀstate photoluminescence emission
profiles of a) Zr-L1 and b) Zr-L5, under dry and wet conditions.
Contact angles were measured for c) Zr-L1 and d) Zr-L5.
In particular, it is clear that the benzothiadiazolyl containing
MOF (Zr-L7; a deep yellow solid) absorbs furthest into the
visible region (~600 nm), with its strongest absorbance occurꢀ
ring at λmax = 391 nm. Zr-L6, a pale yellow solid comprised of
naphthyl chromophores, also absorbs well into the visible reꢀ
gion (λmax = 333 nm), aligning well with the absorption propꢀ
erties of L6-Me2. Similarly, Zr-L5 absorbs in the visible reꢀ
gion and is yellow (Figure 5c), correlating well with the SSꢀ
UVꢀVis spectra, despite L5ꢀH2 and L5-Me2 being white. The
redꢀshifted absorption of Zr-L5 relative to that of L5-Me2 can
be ascribed to an LMCT transition that appears as a shoulder
at approximately 460 nm.67 These transitions have been well
described for both ZrIV and TiIV based UiOꢀ66 systems,68 and
here are further redshifted due to the high degree of conjugaꢀ
tion within these peb2ꢀ ligand systems. More generally, the
transitions would be more appropriately described as ligandꢀ
toꢀcluster charge transfer (LCCT) since any participation in
the CT comes from a cumulative clusterꢀcentred energy
state.69
We see no such effects with Zr-L5, where the central arylꢀ
moiety of L5 is decorated with four fluorine atoms. The emisꢀ
sion profiles are almost identical under both dry and wet conꢀ
ditions with little impact upon ΦF (Figure 6b). Having pores
lined with fluorine atoms, we posit that the fluorescence emisꢀ
sion of Zr-L5 does not change under hydrating conditions due
to the increased hydrophobicity of the material, preventing
water from penetrating into and interacting with the frameꢀ
work. Contact angles of packed powdered samples of Zr-L1
and Zr-L5 were measured to understand whether differences
in hydrophobicity are responsible for the different emission
behaviors (Figure 6c, 6d, and SI Section 10). Zr-L1 has a conꢀ
tact angle of ~73.8° indicative of a hydrophilic material, while
Zr-L5 has a contact angle of ~164.8° which is typical of suꢀ
perhydrophobic materials.70
These measurements show that small changes to the bridgꢀ
ing organic ligand can considerably alter the MOFs hydrophoꢀ
bicity.71 Recently, during a report by Maji et al., a selfꢀ
cleaning Zn MOF containing alkoxyoctadecyl (C18) substitutꢀ
ed peb2ꢀ ligands displayed superhydrophobic behaviour,72
while MOFs containing fluorineꢀabundant ligands have been
shown to be hydrophobic.73,74 In contrast, we have shown that,
by substitution of only one third of the aromatic protons for
fluorine atoms in the organic ligand, one can generate a superꢀ
hydrophobic surface comparable to the remarkable examples
detailed above.70ꢀ74 Zr-L5 is an example of a stable, carboxꢀ
ylateꢀbased fluorinated MOF, and we anticipate that other
functionalized peb2ꢀ ligands could be synthesized and incorpoꢀ
rated into interpenetrated Zr MOFs to control hydrophobicity.
The SSꢀUVꢀVis absorption features of the MOFs and the
conjugated nature of their bridging ligands prompted us to
examine their respective emission behavior (see SI, Section
S9) by solidꢀstate photoluminescence spectroscopy in the
presence of different small molecule analytes to determine
their potential for sensing. Emission spectra were collected for
dry and wetted ligands, diesters andMOFs, as well as MOF
samples in the presence of gaseous N2, CO2 and H2S. Small
shifts in emission maxima were observed when the MOFs
were exposed to various gases, although the most significant
changes occurred upon wetting (see SI, Figure S27), which
was not evident for the diesters (see SI, Figure S26). For exꢀ
ample, Zr-L1 shows a demonstrable redꢀshift upon exposure
to a hydrated environment, with λem = 407 nm drifting to 423
nm, and ΦF decreasing from 0.17 to 0.12 (Figure 6a).
Of all the MOFs examined, Zr-L6 and Zr-L7 exhibited the
most significant changes in the presence of the different anaꢀ
lytes likely as a consequence of the intrinsic fluorescence of
their functional units. The solidꢀstate fluorescence emission of
evacuated Zr-L7 (λem = 500 nm; λex = 468 nm, Figure 7) is
noticeably different to the corresponding diester L7-Me2 (λem
= 525 nm; λex = 450 nm), with a hypsochromic shift in the
major emission band due to separation of ligands in the MOF
removing any interligand CT, as well as the influence of the
more accessible LCCT noted above. More specifically, Zr-L7
exhibits two clear transitions centered at 500 nm and 525 nm.
For both MOFs, the most sensitive fluorescence emission
change is observed upon hydration, with the pronounced
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changes in Zr-L7 suggesting application as a water vapor less pronounced solvatochromism, with no distinct trends reꢀ
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sensor (Figure 7).
lating to solvent dipole moment, dielectric, or polarity indices.
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Figure 8. Normalized solidꢀstate photoluminescence emission
spectra of Zr-L2 after exposure to various solvents (λex = 396
nm). Inset: Correlation of change in λmax with solvent dipole moꢀ
ment; water and toluene have been excluded from correlation as
they demonstrate direct interaction.
Figure 7. Normalized solidꢀstate photoluminescence spectra of
Zr-L7 upon exposure to differing relative humidity (λex = 468
nm). Inset: Chromaticity diagram demonstrating dramatic redꢀ
shift at 97% humidity.
As Zr-L7 is exposed to hydrated environments, the 500 nm
emission band begins to quench while the emission at 525 nm
redshifts to 586 nm (both at 97% relative humidity (Hrel) and
when wetted, λex = 468 nm); a significant λmax color shift of 86
nm (see chromaticity in Figure 7 inset). Zr-L7 also exhibits
the largest response factor (RF = (λmax/λ0)ꢀ1 where λ0 is the
emission of dried Zr-L7) for Hrel = 97% for a ZrꢀMOF at
0.17.75 Particularly noteworthy is the emission shift at Hrel
levels as low as 11% (RF = 0.05) demonstrating the high senꢀ
sitivity of this material towards water vapor. Of the other
MOFs, Zr-L6 shows the most significant changes in emission
as humidity increases with a bathochromic shift of λem from
487 nm to 521 nm (see SI, Figure S36), while gaseous CO2, N2
and H2S cause slight alterations to the fluorescence emission
of both Zr-L6 and Zr-L7 (see SI, Figure S34).
We believe that hydration of the nodes,76 coupled with the
degree of conjugation for Zr-L7 (and Zr-L6) results in the
raising of the HOMO levels for the noted LCCT, causing a
slight bathochromic shift in the solidꢀstate absorption specꢀ
trum (see SI, Figure S38) and dramatic redꢀshift in the emisꢀ
sion. For Zr-L7 this is further shifted by cooperative hydrogen
bonding effects with L7 (as seen with other protic solvents),
compared with Zr-L6 where hydrogen bonding to the naphꢀ
thyl units is not possible. Few studies have reported intrinsic
fluorescence sensing of water by MOFs.75,77ꢀ79 This is noteworꢀ
thy since ZrꢀMOFs are ideal platforms for water sorption32 and
sensing applications due to their wellꢀknown aqueous stabilꢀ
ity,45,80,81 and inherent vacancies made available upon activaꢀ
tion from indiscriminately defective Zrꢀclusters within the
networks.28,82,83 Indeed, PXRD analysis shows Zr-L7 was
unchanged after the humidity profile was collected (see SI,
Figure S39).
It is worth noting that L2-Me2 and L7-Me2 show no distincꢀ
tive solvent dependent emission shifts in the solidꢀstate (see
SI, Figure S43), in contrast to their respective Zr MOFs. This
confirms the requirement of the framework topology for the
solvent and hydration dependent emission behavior.
Interestingly, Zr-L2 exhibits two radiative transitions in its
emission profile (Figure 9), which appear to be inherited from
the ligand (see SI, Section 9). We hypothesize that the two
radiative transitions are related to differing ligand conforꢀ
mations derived from twisting of the central dimeꢀ
thylphenylene units, as seen in its solidꢀstate structure; twistꢀ
ing of the bridging dimethyphenylene moiety is also present in
the crystal structure of L2-Me2 (see SI, Figure S3). In comparꢀ
ison with the emission spectrum of dried Zr-L2, the intensity
of the transition at 465 nm decreases upon wetting. This deꢀ
crease in intensity suggests that water is causing a structural
perturbation of the MOF, presumably by altering the degree of
ligand twisting. Furthermore, the decrease in intensity at λem
465 nm is accompanied with an increase in ΦF, indicative of a
higher population of decay centered on the transition at λem
=
=
486 nm. It is worth noting that this observation is purely with
material that has been exposed to liquid water; exposure to a
range of increasing Hrel values perturbs the system only miniꢀ
mally. Coupled with the observed crystallographic transforꢀ
mation from the orthorhombic (twisted/planar ligands) to cuꢀ
bic structure (planar ligands) under heating noted above, these
emission data lead us to believe that wetting may result in an
increased population of the planar ligand conformation.
In parallel to the emission studies noted above, we examꢀ
ined the photoluminescence spectra of the MOFs in the presꢀ
ence of liquid analytes, with a range of different behaviors
observed across the series (see SI, Figure S40). Zr-L2 exhibits
the most pronounced solvatochromism of the series, with a
modest trend relating to solvent dipole moment (Figure 8;
where interacting water (node coordination) and toluene (πꢀ
stacking) behave as outliers). In contrast, Zr-L7 demonstrates
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the potential of the series for simple introduction of versatile
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functionality into MOFs to enhance their physical properties,
but also the potential for using photoluminescence spectroscoꢀ
py as a facile technique to probe these subtle changes in MOF
structure, physical properties and hostꢀguest interactions. We
also expect the dynamic behavior of these interpenetrated Zr
and Hf MOFs to modulate their mechanical properties, while
studies investigating modulation of their physical and optical
properties by synthesizing new functionalized analogues are
underway.
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ASSOCIATED CONTENT
Supporting Information. Synthesis of all ligands and MOFs,
PXRD, TGA, gas adsorption analysis, solidꢀstate UVꢀVis and
photoluminescence spectroscopy. This material is available free
of charge via the Internet at http://pubs.acs.org. The data which
underpin
this
work
are
available
at
http://dx.doi.org/10.5525/gla.researchdata.398. CCDC 1516193ꢀ
1516211 contain the supplementary crystallographic data for this
paper.
Figure 9. Normalized solidꢀstate photoluminescence emission of
Zr-L2 under dry and wet conditions alongside a schematic repreꢀ
sentation of the observed twisting of the ligands (λex = 396 nm).
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AUTHOR INFORMATION
From these results, it is clear that solidꢀstate photoluminesꢀ
cence spectroscopy is a versatile tool to not only probe hostꢀ
guest interactions in MOFs (with potential for sensing) but
also physical properties such as hydrophobicity, and subtle
structural features such as the ligand rotation phenomenon
observed in Zr-L2.
Corresponding Author
*Ross.Forgan@glasgow.ac.uk; *B.Blight@unb.ca
Author Contributions
All authors have given approval to the final version of the manuꢀ
script.
Conclusions
ACKNOWLEDGMENT
We have prepared a series of interpenetrated Zr and Hf
MOFs comprised of functionalized 4,4′ꢀ[1,4ꢀphenyleneꢀ
bis(ethyneꢀ2,1ꢀdiyl)]ꢀdibenzoate ligands, and shown that while
functionalization does not affect overall topology, it does inꢀ
duce subtle changes in linker orientation and netꢀnet interacꢀ
tions in the solidꢀstate. In particular, the pendant methyl
groups of Zr-L2 induce a change in crystal habit and symꢀ
metry, through steric clashes and resultant twisting of dimeꢀ
thylphenylene units to form an orthorhombic structure, which
can subsequently be converted to the parent cubic form by
heating, with the twisted dimethylphenylene units returning to
planarity. The MOFs have excellent porosity, with the introꢀ
duction of aromatic units and nucleophilic heterocycles enꢀ
hancing CO2 uptake. Access to this related series of MOFs
with intrinsically fluorescent linkers has allowed us to probe
their structures and properties using solidꢀstate photoluminesꢀ
cence spectroscopy, demonstrating the versatility and potential
power of the technique. The subtle structural changes deꢀ
scribed for Zr-L2 can be observed in the relative intensities of
different emission maxima when spectra are collected under
different conditions. Incorporation of naphthyl and benzothiꢀ
adiazolyl fluorophores, into Zr-L6 and Zr-L7 respectively,
generates MOFs that can detect guest molecules, with highly
sensitive emission changes upon wetting and structural stabilꢀ
ity suggesting possible use of Zr-L7 as a water sensor. Addiꢀ
tionally, the superhydrophobicity of the partially fluorinated
Zr-L5 can be seen by the close correlation between its spectra
collected when wet and dry, in contrast to the large shifts seen
for the hydrophilic Zr-L1, and these results have been conꢀ
firmed by contact angle measurements.
RSF thanks the Royal Society for receipt of a University Research
Fellowship and the University of Glasgow for funding. The reꢀ
search was supported by EPSRC (EP/L004461/1). BAB thanks
the University of Kent for funding and Edinburgh Instruments
(Livingston, UK) for inꢀkind support. YK is a DSTLꢀfunded postꢀ
graduate researcher. We thank Mauro Davide Cappelluti and Prof
Duncan Gregory for access to solidꢀstate UVꢀVis facilities,
Rigaku OD for single crystal data collection of Zr-L2 and the
EPSRC UK National Crystallographic Service for single crystal
data collection.84
REFERENCES
(1)
1546.
(2)
Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112,
Kondo, M.; Yoshitomi, T.; Matsuzaka, H.; Kitagawa, S.;
Seki, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 1725.
(3) Chui, S. S.ꢀY.; Lo, S. M.ꢀF.; Charmant, J. P. H.; Orpen, A.
G.; Williams, I. D. Science 1999, 283, 1148.
(4) Li, H.; Eddaoudi, M.; O'Keeffe, M.; Yaghi, O. M. Nature
1999, 402, 276.
(5)
Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y.
J.; Kim, K. Nature 2000, 404, 982.
(6)
(7)
Long, J. R.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1213.
Zhou, H.ꢀC.; Long, J. R.; Yaghi, O. M. Chem. Rev. 2012,
112, 673.
(8)
Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. K.;
Eddaoudi, M.; Kim, J. Nature 2003, 423, 705.
(9) Kitagawa, S.; Kitaura, R.; Noro, S.ꢀi. Angew. Chem. Int.
Ed. 2004, 43, 2334.
(10) Lu, W.; Wei, Z.; Gu, Z.ꢀY.; Liu, T.ꢀF.; Park, J.; Park, J.;
Tian, J.; Zhang, M.; Zhang, Q.; Gentle Iii, T.; Bosch, M.; Zhou, H.ꢀC.
Chem. Soc. Rev. 2014, 43, 5561.
(11) He, Y.; Zhou, W.; Qian, G.; Chen, B. Chem. Soc. Rev.
2014, 43, 5657.
The fact that functionalization of the peb2ꢀ scaffold induces
such structural and physical variety in the resulting MOFs,
coupled with the fact that many of the properties are not preꢀ
sent in the free ligands, has allowed us to demonstrate not only
(12) Murray, L. J.; Dinca, M.; Long, J. R. Chem. Soc. Rev.
2009, 38, 1294.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 20
(13) Tranchemontagne, D. J.; Park, K. S.; Furukawa, H.; Eckert,
(43) Babarao, R.; RubioꢀMartinez, M.; Hill, M. R.; Thornton, A.
J.; Knobler, C. B.; Yaghi, O. M. J. Phys. Chem. C. 2012, 116, 13143.
(14) Li, J.ꢀR.; Kuppler, R. J.; Zhou, H.ꢀC. Chem. Soc. Rev.
2009, 38, 1477.
(15) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T.
M.; Bloch, E. D.; Herm, Z. R.; Bae, T.ꢀH.; Long, J. R. Chem. Rev.
2012, 112, 724.
(16) Zhang, Z.; Zhao, Y.; Gong, Q.; Li, Z.; Li, J. Chem. Com-
mun. 2013, 49, 653.
(17) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen,
S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450.
(18) Yoon, M.; Srirambalaji, R.; Kim, K. Chem. Rev. 2012, 112,
1196.
W. J. Phys. Chem. C. 2016, 120, 13013.
(44) Marshall, R. J.; Griffin, S. L.; Wilson, C.; Forgan, R. S. J.
Am. Chem. Soc. 2015, 137, 9527.
(45) Marshall, R. J.; Griffin, S. L.; Wilson, C.; Forgan, R. S.
Chem. Eur. J. 2016, 22, 4870.
(46) Hobday, C. L.; Marshall, R. J.; Murphie, C. F.; Sotelo, J.;
Richards, T.; Allan, D. R.; Düren, T.; Coudert, F.ꢀX.; Forgan, R. S.;
Morrison, C. A.; Moggach, S. A.; Bennett, T. D. Angew. Chem. Int.
Ed. 2016, 55, 2401.
1
2
3
4
5
6
7
8
(47) Marshall, R. J.; Richards, T.; Hobday, C. L.; Murphie, C.
F.; Wilson, C.; Moggach, S. A.; Bennett, T. D.; Forgan, R. S. Dalton
Trans. 2016, 45, 4132.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(19) Liu, J.; Chen, L.; Cui, H.; Zhang, J.; Zhang, L.; Su, C.ꢀY.
Chem. Soc. Rev. 2014, 43, 6011.
(20) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Chem. Rev. 2012, 112,
1126.
(21) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van
Duyne, R. P.; Hupp, J. T. Chem. Rev. 2012, 112, 1105.
(22) Hu, Z.; Deibert, B. J.; Li, J. Chem. Soc. Rev. 2014, 43,
5815.
(23) Horcajada, P.; Serre, C.; ValletꢀRegí, M.; Sebban, M.;
Taulelle, F.; Férey, G. Angew. Chem. Int. Ed. 2006, 45, 5974.
(24) McKinlay, A. C.; Morris, R. E.; Horcajada, P.; Férey, G.;
Gref, R.; Couvreur, P.; Serre, C. Angew. Chem. Int. Ed. 2010, 49,
6260.
(25) Della Rocca, J.; Liu, D.; Lin, W. Acc. Chem. Res. 2011, 44,
957.
(26) OrellanaꢀTavra, C.; Baxter, E. F.; Tian, T.; Bennett, T. D.;
Slater, N. K. H.; Cheetham, A. K.; FairenꢀJimenez, D. Chem. Com-
mun. 2015, 51, 13878.
(27) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamꢀ
berti, C.; Bordiga, S.; Lillerud, K. P. J. Am. Chem. Soc. 2008, 130,
13850.
(28) Cliffe, M. J.; Wan, W.; Zou, X.; Chater, P. A.; Kleppe, A.
K.; Tucker, M. G.; Wilhelm, H.; Funnell, N. P.; Coudert, F.ꢀX.;
Goodwin, A. L. Nat Commun 2014, 5.
(29) Feng, D.; Jiang, H.ꢀL.; Chen, Y.ꢀP.; Gu, Z.ꢀY.; Wei, Z.;
Zhou, H.ꢀC. Inorg. Chem. 2013, 52, 12661.
(30) Valenzano, L.; Civalleri, B.; Chavan, S.; Bordiga, S.; Nilꢀ
sen, M. H.; Jakobsen, S.; Lillerud, K. P.; Lamberti, C. Chem. Mater.
2011, 23, 1700.
(31) Bai, Y.; Dou, Y.; Xie, L.ꢀH.; Rutledge, W.; Li, J.ꢀR.; Zhou,
H.ꢀC. Chem. Soc. Rev. 2016, 45, 2327.
(32) Furukawa, H.; Gándara, F.; Zhang, Y.ꢀB.; Jiang, J.; Queen,
W. L.; Hudson, M. R.; Yaghi, O. M. J. Am. Chem. Soc. 2014, 136,
4369.
(33) Ma, J.; WongꢀFoy, A. G.; Matzger, A. J. Inorg. Chem.
2015, 54, 4591.
(34) Wang, R.; Wang, Z.; Xu, Y.; Dai, F.; Zhang, L.; Sun, D.
Inorg. Chem. 2014, 53, 7086.
(35) Feng, D.; Gu, Z.ꢀY.; Li, J.ꢀR.; Jiang, H.ꢀL.; Wei, Z.; Zhou,
H.ꢀC. Angew. Chem. Int. Ed. 2012, 51, 10307.
(36) Morris, W.; Volosskiy, B.; Demir, S.; Gándara, F.;
McGrier, P. L.; Furukawa, H.; Cascio, D.; Stoddart, J. F.; Yaghi, O.
M. Inorg. Chem. 2012, 51, 6443.
(48) Fasina, T. M.; Collings, J. C.; Burke, J. M.; Batsanov, A.
S.; Ward, R. M.; AlbesaꢀJove, D.; Porres, L.; Beeby, A.; Howard, J.
A. K.; Scott, A. J.; Clegg, W.; Watt, S. W.; Viney, C.; Marder, T. B.
J. Mater. Chem. 2005, 15, 690.
(49) Carboni, M.; Lin, Z.; Abney, C. W.; Zhang, T.; Lin, W.
Chem. Eur. J. 2014, 20, 14965.
(50) Nagarkar, S. S.; Desai, A. V.; Ghosh, S. K. Chem. Com-
mun. 2014, 50, 8915.
(51) Nagarkar, S. S.; Desai, A. V.; Ghosh, S. K. Chem. Eur. J.
2015, 21, 9994.
(52) Desai, A. V.; Samanta, P.; Manna, B.; Ghosh, S. K. Chem.
Commun. 2015, 51, 6111.
(53) Drache, F.; Bon, V.; Senkovska, I.; Adam, M.; Eychmüller,
A.; Kaskel, S. Eur. J. Inorg. Chem. 2016, 4483.
(54) Wang, B.; Lv, X.ꢀL.; Feng, D.; Xie, L.ꢀH.; Zhang, J.; Li,
M.; Xie, Y.; Li, J.ꢀR.; Zhou, H.ꢀC. J. Am. Chem. Soc. 2016, 138,
6204.
(55) Jiang, H.ꢀL.; Feng, D.; Wang, K.; Gu, Z.ꢀY.; Wei, Z.;
Chen, Y.ꢀP.; Zhou, H.ꢀC. J. Am. Chem. Soc. 2013, 135, 13934.
(56) AguileraꢀSigalat, J.; Bradshaw, D. Chem. Commun. 2014,
50, 4711.
(57) Wei, Z.; Gu, Z.ꢀY.; Arvapally, R. K.; Chen, Y.ꢀP.; McDouꢀ
gald, R. N.; Ivy, J. F.; Yakovenko, A. A.; Feng, D.; Omary, M. A.;
Zhou, H.ꢀC. J. Am. Chem. Soc. 2014, 136, 8269.
(58) Deria, P.; Yu, J.; Balaraman, R. P.; Mashni, J.; White, S.
Chem. Commun. 2016, 52, 13031.
(59) Roy, P.; Schaate, A.; Behrens, P.; Godt, A. Chem. Eur. J.
2012, 18, 6979.
(60) Marshall, R. J.; Hobday, C. L.; Murphie, C. F.; Griffin, S.
L.; Morrison, C. A.; Moggach, S. A.; Forgan, R. S. J. Mater. Chem. A
2016, 4, 6955.
(61) Gutov, O. V.; Molina, S.; EscuderoꢀAdán, E. C.; Shafir, A.
Chem. Eur. J. 2016, 22, 13582.
(62) Song, C.; He, Y.; Li, B.; Ling, Y.; Wang, H.; Feng, Y.;
Krishna, R.; Chen, B. Chem. Commun. 2014, 50, 12105.
(63) Gutierrez Tovar, M.; Cohen, B.; Sanchez, F.; Douhal, A.
Phys. Chem. Chem. Phys. 2016, 18, 27761.
(64) Mallick, A.; Garai, B.; Addicoat, M. A.; Petkov, P. S.; Heiꢀ
ne, T.; Banerjee, R. Chem. Sci. 2015, 6, 1420.
(65) Parker, T. C.; Patel, D. G.; Moudgil, K.; Barlow, S.; Risko,
C.; Bredas, J.ꢀL.; Reynolds, J. R.; Marder, S. R. Mater. Horiz. 2015,
2, 22.
(66) Neto, B. A. D.; Carvalho, P. H. P. R.; Correa, J. R. Acc.
Chem. Res. 2015, 48, 1560.
(67) Pritchard, V. E.; ThorpꢀGreenwood, F. L.; Balasingham, R.
G. Williams, C. F.; Kariuki, B. M.; Platts, J. A.; Hallet, A. J.; Coogan,
M. P. Organometallics, 2013, 32, 3566.
(68) Fu, Y.; Sun, D.; Chen, Y.;Huang, R.; Ding, Z.; Fu, X.; Li,
Z. Angew. Chem. Int. Ed. 2012, 51, 3364.
(69) Horiuchi, Y.; Toyao, T.; Saito, M.; Mochizuki, K.; Iwata,
M.; Higashimura, H.; Anpo, M.; Matsuoku, M. J. Phys. Chem. C.
2012, 116, 20848.
(70) Law, K.ꢀY. J. Phys. Chem. Lett. 2014, 5, 686.
(71) Nguyen, J. G.; Cohen, S. M. J. Am. Chem. Soc. 2010, 132,
4560.
(72) Roy, S.; Suresh, V. M.; Maji, T. K. Chem. Sci. 2016, 7,
2251.
(37) Mondloch, J. E.; Bury, W.; FairenꢀJimenez, D.; Kwon, S.;
DeMarco, E. J.; Weston, M. H.; Sarjeant, A. A.; Nguyen, S. T.; Stair,
P. C.; Snurr, R. Q.; Farha, O. K.; Hupp, J. T. J. Am. Chem. Soc. 2013,
135, 10294.
(38) Schaate, A.; Roy, P.; Preuße, T.; Lohmeier, S. J.; Godt, A.;
Behrens, P. Chem. Eur. J. 2011, 17, 9320.
(39) Lippke, J.; Brosent, B.; von Zons, T.; Virmani, E.; Lilienꢀ
thal, S.; Preuße, T.; Hülsmann, M.; Schneider, A. M.; Wuttke, S.;
Behrens, P.; Godt, A. Inorg. Chem., 2017, 56, 748.
(40) Chen, D.; Xing, H.; Wang, C.; Su, Z. J. Mater. Chem. A
2016, 4, 2657.
(41) Doan, T. L. H.; Nguyen, H. L.; Pham, H. Q.; PhamꢀTran,
N.ꢀN.; Le, T. N.; Cordova, K. E. Chem. Asian J. 2015, 10, 2660.
(42) Doan, T. L. H.; Dao, T. Q.; Tran, H. N.; Tran, P. H.; Le, T.
N. Dalton Trans. 2016, 45, 7875.
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Page 9 of 20
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(73) Chen, T.ꢀH.; Popov, I.; Zenasni, O.; Daugulis, O.; Miljanic,
O. S. Chem. Commun. 2013, 49, 6846.
1
(74) Chen, T.ꢀH.; Popov, I.; Kaveevivitchai, W.; Chuang, Y.ꢀC.;
Chen, Y.ꢀS.; Jacobson, A. J.; Miljanić, O. Š. Angew. Chem. Int. Ed.
2015, 54, 13902.
2
3
4
5
6
7
8
9
(75) Drache, F.; Bon, V.; Senkovska, I.; Adam, M.; Eychmüller,
A.; Kaskel, S. Eur. J. Inorg. Chem. 2016, 2016, 4483.
(76) The hydrogen bonding of water to μ3ꢀOH units of
Zr6O4(OH)4 clusters in related Zr MOFs has been observed crystalloꢀ
graphically. See: Ko, N.; Hong, J.; Sung, S.; Cordova, K. E.; Park, H.
J.; Yang, J. K.; Kim, J. Dalton Trans., 2015, 44, 2047.
(77) Yu, Y.; Zhang, X.ꢀM.; Ma, J.ꢀP.; Liu, Q.ꢀK.; Wang, P.;
Dong, Y.ꢀB. Chem. Commun. 2014, 50, 1444.
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(78) Douvali, A.; Tsipis, A. C.; Eliseeva, S. V.; Petoud, S.; Paꢀ
paefstathiou, G. S.; Malliakas, C. D.; Papadas, I.; Armatas, G. S.;
Margiolaki, I.; Kanatzidis, M. G.; Lazarides, T.; Manos, M. J. Angew.
Chem. Int. Ed. 2015, 54, 1651.
(79) Fard, Z. H.; Kalinovskyy, Y.; Spasyuk, D. M.; Blight, B.
A.; Shimizu, G. K. H. Chem. Commun. 2016, 52, 12865.
(80) Liu, X.; Demir, N. K.; Wu, Z.; Li, K. J. Am. Chem. Soc.
2015, 137, 6999.
(81) Mondloch, J. E.; Katz, M. J.; Planas, N.; Semrouni, D.;
Gagliardi, L.; Hupp, J. T.; Farha, O. K. Chem. Commun. 2014, 50,
8944.
(82) Katz, M. J.; Brown, Z. J.; Colon, Y. J.; Siu, P. W.; Scheidt,
K. A.; Snurr, R. Q.; Hupp, J. T.; Farha, O. K. Chem. Commun. 2013,
49, 9449.
(83) Shearer, G. C.; Chavan, S.; Ethiraj, J.; Vitillo, J. G.; Svelle,
S.; Olsbye, U.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. Chem. Ma-
ter. 2014, 26, 4068.
(84) Coles, S. J.; Gale, P. A. Chem. Sci. 2012, 3, 683.
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Figure 1 - single column
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TOC image
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