Tritopic Triazatruxene Ligands for Multicomponent Metal-Organic Frameworks

Article abstract of DOI:10.1002/asia.201801546

Multicomponent metal-organic frameworks (MOFs) are built up from multiple ligands that are geometrically distinct. These ligands occupy specific positions in the MOF lattice. Installing different functionalities at precise locations in the framework is an important step in making MOFs for specific applications. This can be achieved by designing functionalized ligands for multicomponent MOFs. Here, we report a simple synthetic procedure for a new tritopic triazatruxene based tricarboxylic acid, H₃tat. We show that this ligand can be symmetrically derivatized with various substituents on its nitrogen centres. We report a new isoreticular series of well-ordered quaternary MOFs based on these new triazatruxene ligands together with two linear carboxylate ligands and Zn₄O clusters. These MOFs are isostructural to the previously reported MUF-77 series and show similar high surface areas and large pore volumes. Furthermore, H-bonding between the NH sites of the incorporated triazatruxene ligands and guest molecules is employed to modify their fluorescence behavior.

Full text of DOI:10.1002/asia.201801546

DOI: 10.1002/asia.201801546
Full Paper
Supramolecular Chemistry
Tritopic Triazatruxene Ligands for Multicomponent Metal-Organic
Frameworks
Adil Alkas¸, Joel Cornelio, and Shane G. Telfer*[a]
Abstract: Multicomponent metal-organic frameworks
(MOFs) are built up from multiple ligands that are geometri-
cally distinct. These ligands occupy specific positions in the
MOF lattice. Installing different functionalities at precise loca-
tions in the framework is an important step in making MOFs
for specific applications. This can be achieved by designing
functionalized ligands for multicomponent MOFs. Here, we
report a simple synthetic procedure for a new tritopic triaza-
truxene based tricarboxylic acid, H3tat. We show that this
ligand can be symmetrically derivatized with various sub-
stituents on its nitrogen centres. We report a new isoreticu-
lar series of well-ordered quaternary MOFs based on these
new triazatruxene ligands together with two linear carboxyl-
ate ligands and Zn4O clusters. These MOFs are isostructural
to the previously reported MUF-77 series and show similar
high surface areas and large pore volumes. Furthermore, H-
bonding between the NH sites of the incorporated triaza-
truxene ligands and guest molecules is employed to modify
their fluorescence behavior.
grow within each other and reduce the overall porosity.[6] The
prototype for tritopic linkers is 1,3,5-benzenetricarboxylic acid
(H3btc). By the addition of phenylene spacers it can be extend-
ed to 1,3,5-benzenetribenzoate (H3btb), which forms MOF-177
with octahedral Zn4O clusters.[7] H3btb can be extended further
to obtain 4,4’,4“-(benzene-1,3,5-tryl-tris(ethyne-2,1diyl))triben-
zoate (H3bte), and 4,4’,4”-(benzene-1,3,5-tryl-tris(benzene-4,1-
diyl))tribenzoate (H3bbc). Using H3bte and H3bbc ligands, Yaghi
and co-workers prepared MOF-180 and MOF-200, which have
the same topology as MOF-177.[8] A drawback of this type of
elongation by phenylene rings is a lack of planarity due to
ligand curvature and the repulsion of the ortho-hydrogen
atoms on adjacent phenyl subunits.[9] On the other hand, in tri-
topic linkers based on truxene[10] the phenyl subunits are con-
nected by a bridge to rigidify the structure and keep the four
phenyl rings coplanar (Figure 1). Furthermore, these ligands
can be derivatized with various functionalities at the methyl-
ene moieties.[11]
Introduction
The geometry, symmetry and number of binding sites of or-
ganic ligands play a central role in the architecture of metal-or-
ganic frameworks (MOFs).[1] Typical organic linkers used in
MOF chemistry are: linear ditopic, triangular tritopic, square
tetratopic and tetrahedral tetratopic linkers.[1,2] These ligands
can be functionalized with appropriate substituents to tune
chemical and physical characteristics of the MOF pores for fur-
ther applications, such as gas storage,[3] separation,[4] and het-
erogeneous catalysis.[5]
Isoreticular synthesis is a powerful method to tune and con-
trol the internal environment of MOFs while retaining the
same framework topologies. This is generally accomplished by
either the functionalization or the extension of organic linkers.
Ligand extension is typically achieved by addition of an ethyn-
yl bridge or a phenylene spacer to a short linker. Maintaining
the same topology and obtaining larger pores by linker expan-
sion is not always easy as expanded linkers often form fragile
frameworks. Also, large void spaces within the crystal frame-
work often encourages interpenetration, where two lattices
10,15-Dihydro-5H-diindolo[3,2-a:3’,2’-c]-carbazole (triazatrux-
ene, Figure 1c) is a C3-symmetric, planar p-conjugated cyclo-
trimer of indole and has three potential sites for functionaliza-
tion at the 5-, 10- and 15-positions.[12] Because of its openness
to modifications, their strong electron donating ability and
emissive characteristics, its derivatives have attracted much at-
tention in supramolecular chemistry, particularly in organic
electronics.[13] Its formyl and amino functionalized derivatives
(Figures 1d, 1e) have been used as building blocks for con-
struction of COFs[14] and molecular polyhedra.[15] However, to
date, triazatruxene based ligands have rarely been studied in
MOF chemistry. To the best of our knowledge, only one car-
boxylic acid functionalized triazatruxene ligand for MOF syn-
thesis has been reported to date in which carboxyl groups
[a] A. Alkas¸, J. Cornelio, Prof. S. G. Telfer
MacDiarmid Institute for Advanced Materials and Nanotechnology
Institute of Fundamental Sciences
Massey University
Palmerston North (New Zealand)
E-mail: s.telfer@massey.ac.nz
Supporting information and the ORCID identification number(s) for the au-
thor(s) of this article can be found under:
https://doi.org/10.1002/asia.201801546.
This manuscript is part of a special issue on chemistry in New Zealand. A
link to the Table of Contents of the special issue will appear here when the
complete issue is published.
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Results and Discussion
Our initial step was to find a convenient method for the trime-
rization of 1H-indole-6-carboxylic acid ethyl ester (Scheme 1).
Trimerization of some substituted indoles has previously been
reported.[19] After modifying the reported conditions, Et3tat was
successfully synthesized by the reaction of 1H-indole-6-carbox-
ylic acid ethyl ester with Br2 in presence of excess formic acid.
The product was obtained directly by precipitation from the
reaction mixture in acceptable purity, as shown by 1H NMR
spectroscopy. This compound was then hydrolyzed to obtain
the parent triazatruxene ligand, H3tat.
Five functional groups were chosen as additional substitu-
ents on the nitrogen atoms of the tat core: ethyl, allyl, butyl,
hexyl and methylcyclohexyl. As outlined in Scheme 1, Et3tat-
ethyl, Et3tat-allyl, Et3tat-butyl, Et3tat-hexyl and Et3tat-cychexyl
were prepared by alkylation of Et3tat. These compounds were
then hydrolyzed to obtain the carboxylic acids H3tat-ethyl,
H3tat-allyl, H3tat-butyl, H3tat-hexyl and H3tat-cychexyl. All sub-
stituted esters and carboxylic acids were obtained in good
yield (65–98%) after purification, where needed, by either re-
crystallization or column chromatography.
A
solvothermal reaction of H3tat-ethyl, H2bpdc, and
H2bdc with Zn(NO3)2 in N,N-diethylformamide (DEF) at 858C af-
forded yellow crystals of MUF-777-ethyl (Figure 2). This is a
quaternary metal-organic framework with the formula
[Zn4O(tat-ethyl)4/3(bpdc)1/2(bdc)1/2]. We determined the struc-
ture of MUF-777-ethyl by single crystal X-ray diffraction
(SCXRD) and confirmed its bulk phase purity by powder X-ray
Figure 1. The structures of a) truxene, b) H3hmtt, c) triazatruxene and its
d) formyl, e) amino and f) carboxylic acid derivatives.
occupy the 3-, 8- and 13-positions (Figure 1 f).[16] Having car- diffraction (PXRD), and 1H NMR spectroscopy of a digested
boxyl groups at these positions changes both the symmetry sample. We note that NMR spectroscopy is a sensitive diagnos-
and the length of ligand arms compared to H3btb. This pre- tic tool for assessing the purity of multicomponent MOFs since
vents it from forming MOFs with the same topology as H3btb the ratio between the ligand integrals is governed by the
and H3hmtt (Figure 1b).
framework stoichiometry. The presence of any side products
Here, we report the synthesis of novel triazatruxene based li- that do not share this stoichiometry is clearly indicated by this
gands in which carboxylic acid groups occupy the 2-, 7- and technique.
12-positions. Their structural similarity to truxene-based ligands
SCXRD was carried on a desolvated MUF-777-ethyl crystal at
provides an opportunity to employ them as building blocks for 133 K. A good X-ray diffraction pattern was obtained to a reso-
multicomponent frameworks. We have focused on MOFs built lution of around 1.1 ꢁ. The data reveal that MUF-777-ethyl
up using three topologically distinct carboxylate ligands and crystallizes in the cubic space group Pm-3 and has an ith-d
Zn4O clusters. We have previously synthesized several exam- topology which is identical to the MUF-77 framework,
ples of such quaternary MOFs, including MUF-7 and MUF-77 [Zn4O(hmtt)4/3(bpdc)1/2(bdc)1/2].
(MUF=Massey University Framework), that are based on btb
The three ligands are linked by six-connected Zn4O SBUs. At
and hmtt.[11b,17] Other quaternary frameworks prepared by simi- each SBU carboxyl group donors from four tritopic ligands
lar bottom-up methods have emerged in the literature.[18] One occupy the equatorial positions. Carboxyl groups from one
advantage of these multicomponent MOFs is that the ligands bpdc and one bdc ligand fill the axial sites. The framework has
occupy specific positions in the MOF structure, rather than be- a low crystallographic density (0.46 gcmÀ3) and high calculat-
coming scrambled by disorder. Programming pore environ- ed[20] porosity (void fraction of 82%). Three types of cavity in
ments becomes possible by installing different functionalities MUF-777-ethyl are highlighted in Figure 2. The large dodecahe-
appended to the linkers. Using triazatruxene based ligands, we dral cavity is defined by 12Zn4O clusters, eight tat-ethyl ligands
prepared a new family of quaternary MOFs, which is termed and three pairs of bpdc ligands. The widest distance in this
MUF-777. One useful aspect of the triazatruxene core is that it cavity is between two Zn4O clusters that are facing each other
can be symmetrically-substituted with various functionalities to and is nearly 34.5 ꢁ. The cavity can accommodate a sphere
systematically create MOFs that feature different pore sizes, with a diameter of around 18.5 ꢁ. In the smaller dodecahedral
shapes and chemical properties.
cavity bdc ligands replace the bpdc ligands. The small tetrahe-
dral cavity, on the other hand, is surrounded by four Zn4O clus-
ters, two pairs of tat-ethyl ligands, a bpdc ligand and a bdc
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Scheme 1. Synthetic route to the tat-based ligands.
ligand. Taking advantage of their uniform and complex chemi-
cal environments, our group previously showed that these
cavities can be designed to modulate asymmetric organocata-
lysis.[17a] These concepts are being applied to tat-based frame-
works in ongoing work.
higher than that of MUF-77-ethyl which found to be
1004 cm3 gÀ1 (Figure 3a). On basis of the N2 adsorption iso-
therm, the Brunauer-Emmett-Teller (BET) surface area and pore
volume of MUF-777-ethyl were calculated to be 3640 m2 gÀ1
and 1.80 cm3 gÀ1, respectively. CO2, CH4, C2H6 and C2H4 iso-
therms were measured at both 273 K and 298 K (Figure S15–
S16). MUF-777-ethyl displays near-linear adsorption behavior
with no appreciable hysteresis for these gases, as expected on
the basis of its wide pore windows. The adsorption amounts of
MUF-777-ethyl reach up to 49.8 and 23.1 cm3 gÀ1 for CO2 at
273 and 298 K, respectively. MUF-777-ethyl can take up a large
amount of C2H6 (56.4 cm3 gÀ1) and C2H4 (40.7 cm3 gÀ1), and, as
expected, a smaller amount of CH4 (6.9 cm3 gÀ1) at 298 K. It ex-
hibits an adsorption capacity of 128.3, 84.8 and 16.1 cm3 gÀ1
for C2H6, C2H4 and CH4 at 298 K, respectively. The high C2H6
and C2H4 adsorption capacity of MUF-777-ethyl as compared
to CH4 is in line with the larger size and polarizability of C2H6
and C2H4 relative to CH4.[22]
The bulk identity and thermal stability of MUF-777-ethyl
were investigated by PXRD measurements and thermogravi-
metric analysis (TGA). The TGA curve shows that, after removal
of guest solvent molecules filled in the pores, the framework is
thermally stable up to 3508C (Figure S20). To obtain the fully
desolvated framework, the as-synthesized MUF-777-ethyl
sample was first washed with anhydrous N,N-dimethylforma-
mide (DMF) and then with anhydrous acetone. The sample
then was evacuated under high vacuum at 808C for 20 hours.
PXRD experiments shows that the simulated pattern from the
SCXRD model matches both the experimental patterns of as-
synthesized and desolvated samples (Figure 3b). This result
demonstrates that the single crystal is representative of the
pure bulk sample, and the framework retains its crystallinity
after removal of guest molecules.
After characterization of MUF-777-ethyl, we set about pre-
paring an isoreticular family of MOFs using the ligands H3tat,
H3tat-allyl, H3tat-butyl and H3tat-hexyl and H3tat-cychexyl in
place of H3tat-ethyl (Scheme 2). On the basis of the isoreticular
principle, we anticipated that these ligands could form quater-
nary MOFs which are isostructural to MUF-777-ethyl since the
tritopic linkers have the same size and symmetry in each case.
Under solvothermal conditions, we found that H3tat and H3tat-
allyl formed phase-pure MUF-777 and MUF-777-allyl, respec-
The porous nature of MUF-777-ethyl was examined by per-
forming low-pressure N2 adsorption measurements at 77 K
(Figure 3a and Figure S13). The isotherm shows a two-step
steep rise in gas uptake below P/Po =0.1 which is characteristic
of materials that have both micropores (pore diameter<2 nm)
and mesopores (2ꢀpore diameterꢀ50 nm).[21] Its capacity for
taking up N2 at 77 K is 1160 cm3 gÀ1 (Figure 3a). This value is
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Figure 2. a) The constituents of MUF-777-ethyl and the synthetic route to it. Views of the SCXRD structure of MUF-777-ethyl highlighting the presence of all
three organic linkers and b) the larger dodecahedral cavity, c) the smaller dodecahedral cavity and d) the tetrahedral cavity. Hydrogen atoms are omitted for
clarity.
tively. These frameworks have the same overall ith-d topology
as MUF-777-ethyl, as evidenced by SCXRD and PXRD analyses.
Their TGA plots show a thermal stability up to 3508C. A signifi-
cant decrease in the TGA trace of MUF-777-allyl between
3508C and 4508C has a value of 12.5 wt%, which corresponds
the expulsion of a C3H4 fragment (Figure S20). This is presuma-
bly the allyl groups that depart as allene gas to leave behind
MUF-777 with the tat ligand. The thermolytic expulsion of
small ligand fragments can also be observed from other frame-
works.[23] The capacity of MUF-777 and MUF-777-allyl for taking
up N2 at 77 K was found to be 1170 cm3 gÀ1 and 1030 cm3 gÀ1,
respectively, which lead to BET surface areas well in excess of
3000 m2 gÀ1 (Figure S12 and S14).
1H NMR spectroscopic analysis of a digested sample of MUF-
777 showed that the integrals of the peaks corresponding to
the H3tat linker was lower than the expected value by about
15%. Some additional peaks were also observed in the spec-
trum, especially in the chemical shift range of the NH proton.
These results indicate that some undesired reactions occur at
the NH site under the solvothermal MOF synthesis conditions.
1
To prevent this and obtain a clean H NMR spectrum indicative
of phase purity of the framework, we developed another pro-
cedure for synthesis of MUF-777. In this procedure, zinc ace-
tate was added to a solution of H3tat, H2bpdc and H2bdc in
DMF at room temperature. After optimization of the feed ratio
of the three ligands, phase pure MUF-777 was obtained as
nanocrystals. PXRD indicates that the architecture of nanocrys-
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Scheme 2. Two different synthesis conditions used for new MOFs. Route A
Figure 3. a) Nitrogen adsorption (filled circles) and desorption (open circles)
isotherms of MUF-77-ethyl, MUF-777, MUF-777-ethyl and MUF-777-allyl mea-
sured at 77 K. b) powder X-ray diffraction patterns (Cua radiation) of MUF-
777-ethyl; freshly synthesized and desolvated samples and MUF-77-ethyl.
produces large crystals while Route B produces nanocrystals.
cence turn-on behavior towards electron rich arenes.[14] Related
light emission was also observed in a triazatruxene containing
conjugated microporous polymer.[24] Moreover, researchers
have reported triazatruxene-containing molecules and their
use in the detection of vapors of nitroaromatic explosives.[25]
Compared to these COF and polymer materials above, the
high BET surface area of MUF-777 and its available free NH
sites may be useful for detection of guests that can act as H-
bonding acceptors.
talline MUF-777 is identical to that seen in the large crystals
that is, the lattice adopts an ith-d topology with a stoichiome-
try of [Zn4O(tat)4/3(bpdc)1/2(bdc)1/2].
Unlike the three ligands discussed so far, H3tat-butyl, H3tat-
hexyl and H3tat-cychexyl ligands produced a second phase
along with the desired multicomponent product under solvo-
thermal conditions. A series of adjustments in conditions in-
cluding using modulators, different solvents and changing the
feed ratio of the ligands could not prevent the formation of
this second phase. However, with the same procedure that
formed phase-pure MUF-777 nanocrystals, MUF-777-butyl,
MUF-777-hexyl and MUF-777-cychexyl were prepared as nano-
crystals (Scheme 2, Route B). Their structure matches MUF-777-
ethyl, as determined by PXRD (Figure S11). 1H NMR spectro-
scopic analysis of digested samples of these MOFs demonstrat-
ed that the ratio of the ligand integrals matches the [Zn4O(tat-
X)4/3(bpdc)1/2(bdc)1/2] stoichiometry (Figure S4–S6). This demon-
strates the purity of the nanocrystalline frameworks.
Upon recording emission spectra with an excitation wave-
length of 390 nm, we noted that all of the triazatruxene li-
gands displayed a unique blue luminescence. H3tat showed a
relatively strong emission band at 475 nm. The emission
maxima for other ligands were observed in a range between
425 and 475 nm (Figure S22). H2bpdc and H2bdc are non-emis-
sive linkers upon 390 nm excitation prior to incorporation in
MOFs. The Zn4O cluster is also non-emissive and the diamag-
netic nature of ZnII generally does not have a decisive impact
on the emission behavior of the linkers.[26] The emission spec-
tra of the [Zn4O(tat-X)4/3(bpdc)1/2(bdc)1/2] MOFs were observed
between 430 and 490 nm, which correlated closely with the
spectral output of the triazatruxene ligands (Figure S23). This
information together with the emission spectra of MOFs indi-
cate that the emission profile largely originates from triazatrux-
ene based ligands.
The electron rich nature of triazatruxene derivatives endows
them with interesting fluorescence properties which have po-
tential uses in chemical sensing and photon harvesting and
conversion. A luminescent COF based on a triazatruxene deriv-
ative has recently been reported which shows sensitive fluores-
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To explore the reponse of the emission profile to added
guest molecules, titrations were carried out with the gradual
addition of the guest to MUF-777 dispersed in dichlorome-
thane while a series of guests were chosen to reveal the un-
derlying mechanism of the framework-guest interaction. Upon
the addition of benzaldehyde (PhCHO), the fluorescence inten-
sity of MUF-777 decreased significantly until the point where
approximately one equivalent guest molecule per NH site was
reached (Figure 4). Beyond this point the fluorescence intensity
continued to drop with a much more limited quenching effect.
This result indicates that the quenching effect occurs by hydro-
gen bonding between the NH groups of the tat linker and the
benzaldehyde guest molecules. This hypothesis was tested by
the addition of nitrobenzene (PhNO2) and benzonitrile (PhCN).
These guests caused a weaker decline in the emission (Figur-
es S24, S25). This is consistent with benzaldehyde’s quenching
effect being largely due to H-bonding because nitro and nitrile
groups are much poorer H-bond acceptors than formyl
groups.[27] The small amount of fluorescence quenching that is
observed in the latter cases may be due to p–p interactions of
these electron-deficient guests with the electron-rich tat linker.
To further confirm that the fluorescent quenching is caused by
hydrogen bonding with NH sites in MUF-777 the titrations of
the three guests were carried out on MUF-777-hexyl. Here, the
hydrogen bonding sites of the triazatruxene linker are blocked
by the hexyl group. As expected, only small changes in the
fluorescence intensity of MUF-777-hexyl were observed with
the titration of benzaldehyde and nitrobenzene while there
was no change with addition of benzonitrile (Figures S26–S28).
In this light, MUF-777 frameworks join their MUF-77 counter-
parts in a class of multicomponent materials with rich photo-
physcial properties.[28]
Conclusions
In summary, we have prepared six new tritopic ligands based
on a rigid, electron-rich C3-symmetric triazatruxene core. Using
these triazatruxene ligands along with bpdc and bdc a series
of multicomponent MOFs was synthesized. MUF-777, MUF-
777-ethyl and MUF-777-allyl were obtained under solvothermal
conditions and their structures determined by SCXRD analysis.
These materials are well ordered with each of their three link-
ers positioned in precise locations in the lattice without disor-
der or defects. TGA and gas adsorption measurements showed
that these materials are stable and porous after removal of
guest molecules. Additionally, MUF-777-butyl, MUF-777-hexyl
and MUF-777-cychexyl were synthesized at room temperature
by using zinc acetate instead of zinc nitrate to form nanocrys-
talline materials. PXRD and 1H NMR spectroscopic analyses
reveal that these MUF-777 MOFs define an isoreticular series
which differ by the functional group introduced on the N
atom sites of the triazatruxene linker. The parent MUF-777 ma-
terial can form hydrogen bonds with guest molecules through
its NH sites. This may be useful for the detection of proton ac-
ceptors by luminescence quenching. Benefitting from the
straightforward derivatization of H3tat, new ligands containing
further substituents with different electronic and steric proper-
ties can be prepared to tune MOF features such as catalytic ac-
tivity, gas adsorption and fluorescence output in a programma-
ble way.[17b]
Experimental Section
Et3 tat: 1H-Indole-6-carboxylic acid (1.28 g, 6.79 mmol) was dis-
solved in formic acid (130 mL). To this solution, Br2 (1.24 g,
7.77 mmol) in formic acid (70 mL) was added slowly over 3 mi-
nutes. The mixture was stirred at room temperature overnight. The
green solid formed was filtered, washed with formic acid, water
and dried under vacuum. Although a minor impurity was detected
1
by H NMR spectroscopy, this mixture was used for the next step
without further purification. Yield: 575 mg (45%). 1H NMR
(500 MHz, [D6]DMSO): d=12.44 (s, 3H), 8.75 (d, J=8.2 Hz, 3H), 8.40
(s, 3H), 8.02 (d, J=8.2 Hz, 3H), 4.42 (q, J=7.1 Hz, 6H), 1.44 ppm (t,
J=7.1 Hz, 9H). 13C NMR (125 MHz, [D6]DMSO): d=167.02, 138.40,
136.98, 126.11, 124.35, 121.02, 119.86, 113.00, 101.13, 60.97,
14.82 ppm.
Figure 4. a) Emission spectra of MUF-777 with addition of benzaldehye, and
b) corresponding curve showing the reduction in meission intensity with
added benzaldehye. The point at which approximately one equivalent of
guest per NH site on the MOF has been added is highlighted.
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Et3 tat-ethyl: Et3tat (562 mg, 1 mmol) and K2CO3 (2.07 g) were com-
bined in DMSO (5 mL) under an argon atmosphere and stirred at
room temperature for 15 minutes. Ethyl bromide (746 mL, 10 mmol)
was then added and the reaction mixture stirred at room tempera-
ture overnight. The mixture was poured into cold water and stirred
for 30 mins. The yellow solid was filtered off, washed with water
and dried under vacuum. This crude product was recrystallized
from a mixture of ethyl acetate and hexane (1:3). Yield: 538 mg
Keywords: hydrogen bonding · ligand design · metal-organic
frameworks · triazatruxene · tritopic ligands
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1
(83%). H NMR (500 MHz, CDCl3): d=8.39 (s, 3H), 8.33 (d, J=8.5 Hz,
3H), 8.10 (d, J=8.4 Hz, 3H), 5.07 (q, J=6.9 Hz, 6H), 4.53 (q, J=
7.1 Hz, 6H), 1.65 (t, J=7.1 Hz, 9H), 1.52 ppm (t, J=7.1 Hz, 9H).
13C NMR (125 MHz, CDCl3): d=167.29, 140.80, 139.94, 126.74,
124.94, 121.52, 120.80, 112.03, 103.15, 61.01, 41.91, 15.68,
14.53 ppm. ESI (positive mode, CH3OH): m/z=668.2721
([C39H39N3O6Na]+, calcd 668.2731).
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H3 tat-ethyl: Et3tat-ethyl (527 mg, 0.82 mmol) was dissolved in
20 mL of 1:1 (V/V) dioxane/KOH (aq., 1m) and the solution was re-
fluxed overnight. Dioxane was removed under reduced pressure
and the reaction mixture then was acidified with aqueous 1m HCl
while it was kept on an ice bath. The pH was adjusted to around
1, and the mixture was stirred for one hour. The yellow solid was
filtered off, washed with water and dried under vacuum. Yield:
451 mg (98%). 1H NMR (500 MHz, [D6]DMSO): d=12.83 (br, 3H),
8.42–8.40 (m, 6H), 8.01 (d, J=8.8 Hz, 3H), 5.11 (q, J=6.7 Hz, 6H),
1.50 ppm (t, J=7.0 Hz, 9H). 13C NMR (125 MHz, [D6]DMSO): d=
168.33, 140.41, 139.85, 126.15, 125.83, 122.03, 121.56, 112.51,
102.87, 41.97, 15.76 ppm. ESI (negative mode, CH3OH): m/z=
560.1838 ([C33H26N3O6]À, calcd 560.1900).
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MUF-777-ethyl, [Zn4O(tat-ethyl)4/3(bpdc)1/2(bdc)1/2]: H3tat-ethyl
(4.2 mg, 7.5 mmol), biphenyl-4,4’-dicarboxylic acid (2.3 mg,
9.6 mmol), terephthalic acid (1.2 mg, 7.0 mmol) and Zn(NO3)2·4H2O
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water (35 mL) in a 4 mL vial. The reaction mixture was sonicated for
1 minute, then heated in an 858C isothermal oven for 17 hours to
obtain yellow crystals. For the yield calculation, TGA and NMR anal-
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DMF. The solvent was then replaced with fresh anhydrous DMF
(2 times) and anhydrous acetone (5 times). After acetone was deca-
nted, the crystals were dried under vacuum. The synthesis can be
scaled up by combining H3tat-ethyl (21.8 mg, 38.9 mmol), biphenyl-
4,4’-dicarboxylic acid (12.3 mg, 51.5 mmol), terephthalic acid
(7.2 mg, 42.0 mmol), Zn(NO3)2·4H2O (70 mg, 267.8 mmol), DEF (5 mL)
and water (175 mL) in a 20 mL scintillation vial at 858C. Yield:
23 mg.
Detailed synthesis and characterization of all other compounds are
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We are grateful to the RSNZ Marsden Fund for supporting this
study (contract 14-MAU-024). A.A. would like to thank to Dr.
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Conflict of interest
The authors declare no conflict of interest.
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Manuscript received: October 20, 2018
Revised manuscript received: November 20, 2018
Version of record online: && &&, 0000
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FULL PAPER
Supramolecular Chemistry
A range of new tritopic ligands with a
triazatruxene core were synthesized and
successfully introduced into a series of
multicomponent Zn4O-carboxylate
MOFs in conjunction with two linear li-
gands. The emission spectra of these
MOFs are responsive to H-bonding
guest molecules.
Adil Alkas¸, Joel Cornelio, Shane G. Telfer*
&& – &&
Tritopic Triazatruxene Ligands for
Multicomponent Metal-Organic
Frameworks
Chem. Asian J. 2018, 00, 0 – 0
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ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ