Linker-Induced Structural Diversity and Photophysical Property of MOFs for Selective and Sensitive Detection of Nitroaromatics

Article abstract of DOI:10.1021/acs.inorgchem.5b02645

The linker [1,1′:3′,1″-terphenyl]-4,4′,4″,6′-tetracarboxylic acid (H₄L) was used to construct two three-dimensional (3D) metal-organic frameworks (MOFs), namely, {[Cd₂(L)(L₁)(DMF)(H₂O)](2DMF)(3H₂O)}_n (1) and {[Cd₄(L)₂(L₂)₃(H₂O)₂](8DMF)(8H₂O)}_n (2) (DMF = N,N′-dimethylformamide) in the presence of colinkers 4,4′-bipyridine (L₁) and 2-amino-4,4′-bipyridine (L₂), respectively, under solvothermal condition. A small change in the colinker leads to significant differences in the overall structure of the MOFs. Topological analysis reveals that the framework 1 exhibits 6,4-connected forbidden sub-configuration (FSC) topology, while the framework 2 exhibits twofold interpenetrated and (3,4,4)-connected new network topology with Schl?fli point symbol {4.6²}{4.6⁴.8}{4².6².8²}. The crystallographic investigation reveals the framework 2 having single helix structure, which is further coiled through noncovalent interaction, afforded a double-helix structure similar to DNA. These double helices are further connected through the colinker L₂ to form an overall 3D structure. Besides framework 2 exhibits remarkable fluorescence intensity compared to 1. Framework 2 displayed a strong emission at 457 nm when a sample of 2 was dispersed in ethanol and excited at 334 nm. This emission is selectively and completely quenched in the presence of 2,4,6-trinitrophenol (TNP) allowing its detection in the presence of other nitroaromatic compounds. The quenching constant for TNP was found to be 3.89 × 10⁴ M^-1, which is 26 times higher than that of TNT demonstrating greater and selective quenching ability. The emission is restored to its original value when the sample after collected by filtration is dispersed in fresh ethanol for 1 d. Interestingly, when solid 2 is exposed to different nitroaromatic compounds, its emission is quenched selectively in the presence of nitrobenzene. In this case, the emission is restored upon heating the sample to 150°C for 2 h.

Full text of DOI:10.1021/acs.inorgchem.5b02645

Article
pubs.acs.org/IC
Linker-Induced Structural Diversity and Photophysical Property of
MOFs for Selective and Sensitive Detection of Nitroaromatics
Tapan K. Pal, Nabanita Chatterjee, and Parimal K. Bharadwaj*
Department of Chemistry, Indian Institute of Technology Kanpur 208016, India
S
* Supporting Information
ABSTRACT: The linker [1,1′:3′,1″-terphenyl]-4,4′,4″,6′-tetracarboxylic
acid (H4L) was used to construct two three-dimensional (3D) metal−
organic frameworks (MOFs), namely, {[Cd2(L)(L1)(DMF)(H2O)]-
(2DMF)(3H2O)}n (1) and {[Cd4(L)2(L2)3(H2O)2](8DMF)(8H2O)}n
(2) (DMF = N,N′-dimethylformamide) in the presence of colinkers 4,4′-
bipyridine (L1) and 2-amino-4,4′-bipyridine (L2), respectively, under
solvothermal condition. A small change in the colinker leads to significant
differences in the overall structure of the MOFs. Topological analysis
reveals that the framework 1 exhibits 6,4-connected forbidden sub-configuration (FSC) topology, while the framework 2 exhibits
twofold interpenetrated and (3,4,4)-connected new network topology with Schlafli point symbol {4.62}{4.64.8}{42.62.82}. The
̈
crystallographic investigation reveals the framework 2 having single helix structure, which is further coiled through noncovalent
interaction, afforded a double-helix structure similar to DNA. These double helices are further connected through the colinker L2
to form an overall 3D structure. Besides framework 2 exhibits remarkable fluorescence intensity compared to 1. Framework 2
displayed a strong emission at 457 nm when a sample of 2 was dispersed in ethanol and excited at 334 nm. This emission is
selectively and completely quenched in the presence of 2,4,6-trinitrophenol (TNP) allowing its detection in the presence of other
nitroaromatic compounds. The quenching constant for TNP was found to be 3.89 × 104 M−1, which is 26 times higher than that
of TNT demonstrating greater and selective quenching ability. The emission is restored to its original value when the sample
after collected by filtration is dispersed in fresh ethanol for 1 d. Interestingly, when solid 2 is exposed to different nitroaromatic
compounds, its emission is quenched selectively in the presence of nitrobenzene. In this case, the emission is restored upon
heating the sample to 150 °C for 2 h.
available on the detection of TNT and TNP7 it is still a
INTRODUCTION
■
challenge to selectively detect TNP, as both of them have
The design and synthesis of metal−organic frameworks
(MOFs) have attracted enormous interest owing to the
capability these frameworks have of forming diverse structural
extremely strong electron affinity.8 We show here that TNP is
selectively capable of quenching fluorescence. However,
architectures and a wide range of potential applications.1 The
nitrobenzene is a highly toxic substance, and its continued
exposure even in trace quantities can lead to severe health
natures of organic linkers/ligands and metal ions play an
problems. Therefore, rapid and sensitive detection of these
important role in directing the structure (dimentionality/
topology) and desired properties of the resulting MOFs.2 The
materials is of extreme importance. Nitroaromatic compounds
are electron-deficient in nature and can possibly enter the voids
porous features and capability of host−guest interactions make
them as promising candidates like chemical sensors.3
of a porous luminescent MOF that provides electron-rich
environment for efficient host−guest interactions leading to
Particularly, detection of explosive compounds or their
modulation of emission.9 Li and co-workers reported10 a highly
precursors in a nondestructive manner is of considerable
importance in the present-day security environments.4 Organic
luminescent MOF whose emission is quenched in the presence
of traces of nitroaromatic compounds 2,4-DNT and 2,3-
nitrocompounds 2,4,6-trinitrotoluene (TNT), 2,4-dinitroto-
dimethyl-2,3-dinitrobutane (DMNB). In a recent paper, an
luene (2,4-DNT), 2,4,6-trinitrophenol (TNP), and 2,6-
amine-functionalized linker was used to construct a porous
dinitrotoluene (2,6-DNT) are explosive in nature and are
luminescent MOF that detects TNP in aqueous medium.11 To
extensively used in the manufacture of explosive devices.
Among them TNP is considered to be a powerful explosive and
is used extensively for making explosive devices and land-
have porous MOFs with electron-rich interior, a symmetrical π-
electron-rich tetracarboxylic acid linker (H4L) was used with
mines.5 Additionally, TNP effect on human health and its usage
colinkers L1 and L2 (Scheme 1) for the construction of two
MOFs with Cd(II) ion {[Cd2(L)(L1)(DMF)(H2O)](2DMF)-
in the chemical industry may lead to fatal environmental
(3H2O)}n (1) and {[Cd4(L)2(L2)3(H2O)2](8DMF)(8H2O)}n
Received: November 16, 2015
consequences. TNP metabolism gives the byproduct picramic
acid (2-amino-4,6-dinitrophenol), which shows 10 times more
mutagenic activity than TNP.6 Thus, quick and judicious
detection of TNP is very imperative. Although literature is
© XXXX American Chemical Society
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interpenetrated three-dimensional (3D) MOF {[Cd2(L)(L1)-
(DMF)(H2O)](2DMF)(3H2O)}n (1; L4− = L). The bulk-
phase purity of the sample is confirmed by comparing the
experimental powder X-ray diffraction (PXRD) pattern with
the simulated one obtained from the single-crystal data (Figure
S5, Supporting Information). Single-crystal study reveals the
complex crystallizes in the monoclinic space group P21/c
(Table S1, Supporting Information), and the asymmetric unit
contains two crystallographically independent Cd(II) ions, one
L4− ligand, one L1 ligand, one water molecule, and one DMF
molecule (Figure S6, Supporting Information). The structure of
1 consists of a dimeric Cd2 secondary building unit (SBU)
composed from one syn−syn bridging carboxylate, one
bridging carboxylate, one terminal chelating carboxylate, and
one chelating as well as bridging carboxylate from four different
L4− units (Figure 1a). The Cd1 further connected by one L1
Scheme 1. Ligands Used for the Construction of Metal−
Organic Frameworks
(2), respectively (DMF = N,N′-dimethylformamide). It is
observed that the presence of the amine group in the colinker
L2 has a profound effect on the overall structure of 2 compared
to 1 and results in an unknown network structure for 2.
Besides, 2 is highly luminescent compare to 1, can selectively
and reversibly detect TNP when dispersed in ethanol medium,
and can also detect nitrobenzene vapors in the solid state.
EXPERIMENTAL SECTION
■
Materials and Method. Reagent-grade Cd(NO3)2·4H2O, 4,4′-
bipyridine (L1), trifluoroacetic anhydride, sodium metabisulfite, 4-
bromotoluene, and trimethyl borate were purchased from Sigma-
Aldrich and used as received. All the solvents were procured from S. D.
Fine Chemicals, India, and were purified prior to use.
Physical Measurements. All physical measurements were
performed as described earlier.12 The UV−vis spectra were recorded
on a Shimadzu 2450 UV−vis spectrophotometer in ethanol at 298 K.
Steady-state emission spectra were obtained using a PerkinElmer LS
50B Luminescence spectrometer at 293 K with excitation and emission
band-pass of 2.5 nm. In the solid state, the luminescence studies were
performed on a Jobin Yvon Horiba Fluorolog-3 spectrofluorimeter at
room temperature.
Figure 1. Perspective view of (a) coordination environment around
Cd2 SBU and (b) linker L1 connected between the two layers in 1
leads to the formation of 3D structure.
X-ray Structural Studies. Single-crystal X-ray data of the
compounds were collected at 100 K on a Bruker SMART APEX
CCD diffractometer using graphite monochromated Mo Kα radiation
(λ = 0.710 73 Å). Details of the structure solution and refinements are
given in the Supporting Information. Lattice parameters of the
compounds, data collection, and refinement parameters are
summarized in Table S1, and selected bond distances and bond
angles are given in Table S4.
linker gives rise to seventh coordination, while Cd2 apart from
L1 linker additionally connected by one water and DMF
molecules afforded a total of six coordination at the metal
center (Figure S6, Supporting Information). The Cd−O
(2.201(2)−2.495(3)) and Cd−N (2.290(4)−2.322(4)) bond
distances are comparable to those reported earlier.15 The
carboxylate groups bind to the metal ions in different fashion,
μ7:η1:η1:η1:η1:η1:η2:η2:η0 (Figure S7, Supporting Information)
in complex 1.
Synthesis of Ligands. Synthesis of the tetra-acid linker H4L
(Scheme S1) was reported by us earlier.13 The colinker L2 was
synthesized following a literature method.14
Synthesis of {[Cd2(L)(L1)(DMF)(H2O)](2DMF)(3H2O)}n(1). A mixture
containing H4L (20 mg, 0.05 mmol), L1 (7.68 mg, 0.05 mmol), and
Cd(NO3)2·4H2O (30 mg, 0.1 mmol) in DMF (2 mL) and ethanol (1
mL) was heated at 100 °C under autogenous pressure in a Teflon-
lined stainless-steel autoclave for 72 h, followed by cooling to room
temperature at the rate of 5 °C h−1. Compound 1 was isolated as
colorless block-shaped crystals in ∼45% yield. Anal. Calcd for
C41H47N5O15Cd2: C, 45.82; H, 4.41; N, 6.52%. Found: C, 45.40 ;
H, 4.81 N, 6.24. FT-IR (KBr pellets, cm−1): 3446 br, 2937 w, 1659 s,
1359 s, 1096 m, 775 w, 700 w.
Synthesis of {[Cd4(L)2(L2)3(H2O)2](8DMF)(8H2O)}n (2). A mixture
containing H4L (20 mg, 0.05 mmol), L2 (8.5 mg, 0.05 mmol), and
Cd(NO3)2·4H2O (30 mg, 0.1 mmol) in DMF (2 mL) and ethanol (1
mL) was heated at 100 °C under autogenous pressure in a Teflon-
lined stainless-steel autoclave for 72 h. When cooled to room
temperature at the rate of 5 °C h−1 compound 2 was obtained as
colorless block-shaped crystals in ∼40% yield. Anal. Calcd for
C98H118N17O34Cd4: C, 46.57; H, 4.71; N, 9.42%. Found: C, 46.40 ;
H, 4.80 N, 10.05. FT-IR (KBr pellets, cm−1): 3441br, 2937w, 1653 s,
1391w, 1102 m, 706 s.
This connectivity initially leads to the formation of two-
dimensional (2D) layers, and each 2D layer is further
connected by the colinker L1 to an overall non-interpenetrated
3D neutral architecture (Figure 1b). Topological analysis16
shows the SBU Cd2(CO2)4(L1)2 is connected by four
carboxylate groups and two L1 colinkers. So it is six-connected
node, while the ligand is connected to four SBUs and behaves
as a four-connected node. Hence, the structure has a 6,4-
connected net, and the framework contains forbidden sub-
configuration (FSC) topology (Figure 2). The cavity of the
framework is occupied by disordered solvent molecules, and
hence exact solvent composition is evaluated by the
combination of TGA and elemental analysis and agreement
with PLATON17 calculated solvent-accessible void volume
(1520 Å3, 34.50%).
When colinker L2 is in place of L1, the complex 2 is formed.
Interestingly, presence of an amine group in the colinker L2
makes the overall structure of 2 very different compared to 1.
The phase purity of the bulk material is confirmed by matching
the PXRD pattern of bulk material with that of the simulated
pattern (Figure S8, Supporting Information). Single-crystal X-
ray analysis reveals that 2 crystallizes in the monoclinic space
RESULTS AND DISCUSSION
Under solvothermal conditions, ligand H4L reacts with
Cd(NO3)2·4H2O in the presence of colinker L1 to form non-
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leading to a twofold interpenetrated 3D architecture (Figure
4c).
Topological simplification shows that the framework is 3,4,4-
c net forming a new network topology with Schlafli point
̈
symbol {4.62}{4.64.8}{42.62.82} (Figure 5). The solvent
molecules in the cavity are disordered, and hence the exact
solvent composition is evaluated by the combination of
thermogravimetric analysis (TGA), elemental analysis, and
agreement with PLATON17 accessible void volume of 2997 Å3
or 51.32% of the unit cell volume. The channel dimension
along the a direction is 8.799 × 7.751 Å2 and in the b direction
is 6.010 × 5.975 Å2, and these channels are decorated with the
amine moiety of the linker.
Luminescence Behavior and Sensing Properties. The
MOFs are built by d10 metal ions, and different π-conjugated
organic ligands are expected to be promising candidates for
luminescent materials.3 To examine the luminescence behavior,
both the complexes are dispersed in ethanol medium, and their
emission spectra are recorded at room temperature (RT; Figure
6). Upon excitation at 270 nm, 1 emits at 374 nm, while 2
emits at 457 nm when excited at 334 nm (Figure S12,
Supporting Information). Such a red shift in the emission peak
of the complex 2 is due to the strong synergistic effect between
the neighboring ligands and metal units.19 The luminescent
intensity of complex 2 is much greater than that of 1 in both
solid (Figure S13, Supporting Information) and solution
medium (Figure 6; 1 mg of each complex in 20 mL ethanol)
under the same experimental conditions. The linker L2 is found
to be more fluorescent compared to that of L1. Also, a close
examination of the structures of 1 and 2 reveal that the colinker
L2 is more strongly bound to the metal compared to the
binding of colinker L1 to the metal (Table S4) hindering
deactivation in 2. Thus, 2 is more fluorescent compared to 1.
The luminescent property of 2 was investigated and invariant
in different solvents like N,N′-dimethylacetamide (DMA),
DMF, methanol (MeOH), ethanol (EtOH), acetonitrile,
acetone, dioxane, and tetrahydrofuran. Interestingly, when we
used nitrobenzene (NB) as a solvent the, however, the emission
quenches (Figure 7a and Figure S14, Supporting Information)
and remains unperturbed by the other solvents (Figure 7b).
Thus, aforesaid observation clearly manifested complex 2 is
potential candidate for the detection of NB. Enthused from
such an important outcome we further explore the detection of
other nitroaromatic compounds (congener of NB), which are
explosive in nature.
Fluorescence titrations were performed with different
nitroaromatic compounds such as TNP, TNT, 2,6-DNT, 2,4-
DNT, 2,4-dinitrochlorobenzene (DNCB), and NB (Figures
S15−S19, Supporting Information). Addition of the same
amount of analytes (400 μL) results different extent
fluorescence quenching takes place. The quenching efficiency
was calculated by using the equation (I0 − I)/I0 × 100%, where
I0 and I are the luminescence intensities of 2 before and after
the addition of the analyte, respectively. It was observed that all
the analytes quench the fluorescence to some extent except
TNP, which shows highly sensitive as well as significant
quenching of the fluorescence (94.28%; Figure 8). The
quenching efficiency by all the analytes is in the following
order: TNP ≫ TNT > 2,6-DNT > NB > 2,4-DNT > DNCB
(Figure 9a). To understand such a high sensitivity of complex 2
toward TNP a quenching mechanism was thoroughly
investigated. To comprehend the sensing ability of 2 for
TNP, the emission spectra were recorded by a gradual addition
Figure 2. Topological representation, 6,4-connected net with FSC
topology of 1.
group P2/m (Table S1, Supporting Information). The
asymmetric unit contains two crystallographically independent
Cd(II) ions, one L4− ligand, L2 ligand (one and half
occupancy), and one water molecule (Figure 3a). Both metal
Figure 3. (a) A perspective view of the dimeric unit in 2 and (b)
space-filling model of 2 viewed along the b axis.
ions exhibit distorted octahedral coordination geometry (Figure
S9, Supporting Information). The Cd1 is ligated by four oxygen
atoms of two bridging carboxylates from two L4− ligands and
two N atoms from two L2 colinkers. The Cd2 is connected to
five oxygen atoms, four from two carboxylate groups of two L4−
ligands and one oxygen atom from water molecule, and six
coordination is satisfied by one nitrogen atom from colinker L2
(Figure S9, Supporting Information). In complex 2 the four
carboxylate groups of L4− bonded to the metal in chelating
mode μ4:η1:η1:η1:η1:η1:η1:η1:η1 (Figure S10, Supporting In-
formation). All bond distances are comparable to those
reported earlier.15
The combination of such carboxylate binding mode and that
of the colinker L2 with Cd(II) ions leads to the formation of
single helical chains extending along the crystallographic b axis
(Figure 4a). Two such helices wrap each other around the same
axis through noncovalent interaction (N5−H···π, dN‑π
=
3.733(2) Å and N4−H···π, dN‑π = 3.819(3) Å) and N5···H−
C, dN−H = 3.902(2) Å and N4···H−C, dN−C = 4.023(3) Å) to
form a double helix (Figure 4b and Figure S11 Supporting
Information) like in DNA. MOFs having double helical
structure are very rarely reported in the literature.18 The
pitch of double helix is 20.48 Å, and the radius is 2.5 Å. The
stability of the final helical structure relies on the coordinate
bonds that each metal makes with the ligand. Each double helix
connects to the adjacent double helix through the colinker L2
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Figure 4. A perspective view of (a) single helical chain in 2, (b) double helical chain (c) colinker L2 connected double helices to the interpenetrated
3D framework, and (d) its space-filling model.
quenching performances were calculated and estimated to be
42.82% for 100 μL, 76.11% for 200 μL, 83.99% for 300 μL, and
94.28% for 400 μL.
Such diversity in quenching efficiency can be clearly
interpreted by using the Stern−Volmer (SV) equation (I0/I)
= KSV[A] + 1, where I0 represents the initial intensity of the of 2
in absence of analyte, I is the fluorescence intensity in the
presence of analyte with molar concentration [A], and KSV is
the quenching constant (M−1).20 The SV plot for TNP deviates
from linearity at low concentration and bending upward upon
incremental addition of TNP (Figure 9b), while other analytes
give linear variation with concentration in their corresponding
SV plot (Figure S20, Supporting Information). This nonlinear
nature in the SV plot supports dynamic quenching processes or
energy transfer between TNP and the host.21 Additionally, the
Figure 5. A representation of the new 3,4,4-c net of 2.
electronic features of the analytes will help us to rationalize the
reason behind this sensing ability. Generally, the conduction
band (CB) of MOFs lies above the lowest unoccupied
molecular orbital (LUMO) of these electron deficient
analytes.22
Upon excitation photoinduced electron transfer takes place
from the CB band of 2 to LUMO of the analyte leading to the
quenching effect.23 The highest occupied molecular orbital
(HOMO)−LUMO energies of the given analytes were
calculated by density functional theory by using the B3LYP/
6-31G* method with Gaussian 09,24 and the obtained results
support the maximum quenching for TNP as observed22
(Figure 10b). Such an electron-transfer phenomena is not the
sole mechanism behind the reason for high degree of
fluorescence quenching efficiency. It has been well-established
that when the absorption band of the analytes overlaps with the
emission band of the fluorophore (here complex 2) then
resonance energy can occur adequately. The extent of
resonance energy transfer depends on the spectral overlap
between analytes absorption band and emission band of 2. The
Figure 6. Emission spectra of 1 and 2 dispersed in ethanol medium
(left) and (right) complex 1 and 2 were subjected to the UV light
under the same experimental condition.
of TNP. As shown in Figure 8 the fluorescence intensity of 2 is
deliberately decreased with increasing amount of TNP. The
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Figure 7. (a) The emission spectra of 2 in the presence of different solvent and (b) fluorescence intensity ratio histograms of 2 dispersed in different
solvents (red) and subsequent addition of nitrobenzene (black).
MOFs.9 The compound 2 can sense the TNP at very low
concentration with a detection limit 1.98 ppm (Figure S21,
Supporting Information).
Inspiring of these worthy denouement, next we verified the
selectivity of TNP in the presence of other nitro compounds.
The selectivity of TNP in the presence of other nitroaromatic
compounds was also probed. In a typical experiment, the
fluorescence spectrum of 2 was monitored upon addition of
each analyte (400 μL) separately and allowed to stand for 5 h at
RT. The spectra showed insignificant changes. Upon addition
of TNP (400 μL) the fluorescence shows considerable
quenching in 30 min at RT (Figure 11).
The visual recognition of TNP is also probed due to its
relevance in terms of security threats, environmental pollution,
Figure 8. Emission spectra of 2 dispersed in ethanol upon incremental
addition of TNP solution (1 mM) in ethanol.
and so on. With the addition of 2−3 drops of ethanolic solution
of TNP (1 × 10−3 M) to a dispersion of 2 in ethanol monitored
under UV light, the bright fluorescence completely vanished
within 3 min by naked eye detection (Figure 12). The
detection ability of 2 can be revived at least to three cycles by
centrifuging the dispersed solution after use and washing it
several times with ethanol (Figure S22, Supporting Informa-
tion). The PXRD pattern after three cycles exactly matches
with the initial sample proving its structural integrity (Figure
S23, Supporting Information). In a different experiment, when
solid 2 is exposed to different nitroaromatic compounds listed
above at RT, only NB is able to quench the emission intensity
Figure 10a depicts a substantial spectral overlap between the
absorption spectrum of TNP and the emission spectrum of 2,
and almost negligible overlap happens in all other analytes.
These observations clearly support the highest quenching
efficiency by TNP compare to the other nitroanalytes. The
quenching constant (KSV) value for TNP was calculated and
found to be 3.89 × 104 M−1, which indicates strong interaction
between TNP and framework 2. It is worth mentioning that
this quenching constant value is higher than the many reported
Figure 9. (a) Quenching efficiency of 2 for different nitroaromatics in ethanol and (b) SV plot of 2 upon incremental addition of TNP solution (1
mM) in ethanol.
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Figure 10. (a) Spectral overlap between the absorption band of the analytes and the emission band of 2 and (b) HOMO and LUMO energies of
electron-deficient nitroaromatics.
structure similar to DNA and forms a new network topology.
The luminescent intensity of 2 is high and is found to be useful
in the selective and sensitive detection of TNP. The favorable
energy transfer between the electron-deficient TNP and
electron-rich 2 efficiently quenches its emission intensity. The
construction of different MOFs helps the idea of crystal
engineering through the design of linkers to tune their
properties.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b02645.
Details of syntheses, including illustrated schemes for
synthetic routes to H4L and L2; table for selected bonds
and distances for complexes 1 and 2; complete data for
Figure 11. Emission intensity of 2 after the addition of an analytes
IR, TGA analysis, and PXRD; NMR, UV−vis, and
separately followed by addition of same amount of TNP. In each set,
luminescence spectra; perspective drawings including the
(a, black) = initial intensity of 2, (b, red) = intensity of 2 after addition
asymmetric unit in complex 1, the coordination environ-
of an analyte, (c, blue) = after addition of TNP.
ment around metal centers Cd1 and Cd2, and the
carboxylate binding mode of ligand H4L in complex 2,
among others. (PDF)
X-ray crystallographic data in CIF format. (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: pkb@iitk.ac.in.
■
Notes
The authors declare no competing financial interest.
Figure 12. Response of 2 to various analytes in ethanol monitored
under UV light (left to right) 2 and 2 in the presence of TNT, NB,
DNCB, 2,6-DNT, 2,4-DNT, and TNP.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the financial support from the
Department of Science and Technology, New Delhi, India (J.
C. Bose National Fellowship to P.K.B.). T.K.P. and N.C. thank
CSIR for SRF fellowship.
of 2 due to its higher vapor pressure (Figure S24 and Table S2,
Supporting Information). Like in case of solution, this solid-
state phenomenon is also reversible (Figure S24, Supporting
Information).
REFERENCES
■
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G. A.; Yaghi, O. M. J. Am. Chem. Soc. 2015, 137, 7810−7816.
CONCLUSIONS
■
In summary, the introduction of amine functional moiety in the
linker tailored the structure and the photophysical property of
MOF. Importantly the framework 2 showed a double helical
(c) Muller, P.; Wisser, F. M.; Bon, V.; Grunker, R.; Senkovska, I.;
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DOI: 10.1021/acs.inorgchem.5b02645
Inorg. Chem. XXXX, XXX, XXX−XXX