Lanthanide-Based Coordination Polymers for the Size-Selective Detection of Nitroaromatics

Article abstract of DOI:10.1021/acs.cgd.7b00536

Lanthanide coordination polymers (LnCPs), [Eu(HL)₃(CH₃OH)₂]_n (1) and [Tb(HL)₃(CH₃OH)(H₂O)]_n·H₂O (2) (H₂L = 3-(picolinamido)benzoic acid)), have been synthesized and characterized. Single crystal analyses of both LnCPs display that HL ligands not only coordinate to Ln ions but also act as the bridge between them generating one-dimensional (1D) chains. Such 1D chains further pack into three-dimensional (3D) architectures by the mediation of H-bonding interactions. Both LnCPs offer strategically placed exposed Lewis basic sites, which potentially interact with the electron-deficient nitroaromatics, whereas H-bonded 3D architecture having hydrophobic channels allows their facile inclusion within the network. A notable feature is the size-dependent sensing of nitroaromatics potentially governed by the packing of 1D chains into a 3D architecture. Both LnCPs act as the fluorescent sensor for quick, sensitive, and selective detection of nitrobenzene not only in solution but also in the vapor phase suggesting potential applications in the sensing devices for the detection of nitroaromatics.

Full text of DOI:10.1021/acs.cgd.7b00536

Subscriber access provided by CORNELL UNIVERSITY LIBRARY
Article
Lanthanide-based Coordination Polymers for
the Size-selective Detection of Nitroaromatics
Sumit Srivastava, Bipin Kumar Gupta, and Rajeev Gupta
Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 05 Jun 2017
Downloaded from http://pubs.acs.org on June 8, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Crystal Growth & Design is published by the American Chemical Society. 1155
Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 13
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Lanthanide-based Coordination Polymers for the Size-selective Detec-
tion of Nitroaromatics
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
Sumit Srivastava,a Bipin Kumar Guptab and Rajeev Gupta*a
aDepartment of Chemistry, University of Delhi, Delhi-110007, India
bCSIR-National Physical Laboratory (CSIR), Dr K S Krishnan Road, New Delhi-110012, India
ABSTRACT: Lanthanide coordination polymers (LnCPs), [Eu(HL)3(CH3OH)2]n (1) and [Tb(HL)3(CH3OH)(H2O)]n⋅H2O (2) (H2L = 3-
(picolinamido)benzoic acid)), have been synthesized and characterized. Single crystal analyses of both LnCPs display that HL lig-
ands not only coordinate to Ln ions but also act as the bridge between them generating 1D chains. Such 1D chains further pack
into 3D architectures by the mediation of H-bonding interactions. Both LnCPs offer strategically placed exposed Lewis basic sites
which potentially interact with the electron-deficient nitroaromatics whereas H-bonded 3D architecture having hydrophobic
channels allows their facile inclusion within the network. A notable feature is the size-dependent sensing of nitroaromatics poten-
tially governed by the packing of 1D chains into a 3D architecture. Both LnCPs act as the fluorescent sensor for quick, sensitive
and selective detection of nitrobenzene not only in solution but also in the vapour phase suggesting potential applications in the
sensing devices for the detection of nitroaromatics.
Introduction
their explosive qualities but also due to their environmental
hazardous impact.39-49 Although nitroaromatics exhibit strong
UV absorption but their low fluorescence render their direct
detection impractical.32-39 Such a problem necessitates the
use of an alternate strategy and therefore several sensors
have been developed for the detection of nitroaromatics.23-59
In this context, electron-rich sensors have been particularly
notable considering the electron-deficient nature of nitroar-
omatics.15-21,24-39 In this work, we present luminescent one-
dimensional (1D) Eu3+ and Tb3+ based LnCPs which transform
into three-dimensional (3D) architecture held together by H-
bonding interactions for the detection of nitroaromatics. We
illustrate that both LnCPs offering well-defined pores and
channels allow selective detection of smaller nitroaromatics
whereas their 3D polymeric nature enables heterogeneous
sensing of nitroaromatics both in the solution as well as in the
vapor phase.
Coordination polymers (CPs)1-4 are a unique class of mate-
rials that have shown wide variety of notable applications.5-18
Such applications are attributed to their highly crystalline
nature, well-defined pores and channels, and the presence of
functional sites such as open metal sites, acidic, and basic
sites. These features have assisted in developing significant
materials for sorption,5,6 separation,7 heterogeneous cataly-
sis8-14 as well as sensing15,16 and recognition17,18 applications.
Among diverse CPs, luminescent coordination polymers offer
noteworthy applications in sensing, recognition and binding
events with guests and/or substrates.15-19 Under this category,
the ones based on lanthanide metals, i.e., lanthanide coordi-
nation polymers (LnCPs) are particularly interesting materials
for their ability to respond to guests and/or substrates in the
form of large optical signal.20,21 LnCPs based materials with
open metal sites,22,23 hydrogen bonding (H-bonding) sites24,25
and exposed Lewis basic sites26-29 have been particularly suc-
cessful for the recognition of small molecules as well as cati-
ons.30-39
Experimental Section
Materials and Methods. Reagents of analytical grade were
procured from Sigma-Aldrich, Alfa-Aesar, and Spectrochem
and were used without further purification. The solvents
were purified using standard literature methods.50 2-(3-
Ethylbenzoate-carbomyl)pyridine (HL1) was synthesized as
reported in the litrature.51
Nitroaromatics are toxic compounds used extensively as
the explosives32-39 and as the starting materials in various
industrially and commercially important products such as
dyes, pesticides, polyurethane foams, and polymers.40-43 Ni-
troaromatics are obstinate to biological treatment and re-
main in the biosphere, where they constitute a source of pol-
lution due to both toxic and mutagenic effects on microor-
ganisms, aquatic and other organisms, as well as humans.44-49
Exposure of nitroaromatics to humans, particularly the vola-
tile ones, can cause serious health hazards such as cancer,
liver damage and kidney failure.44-49 Therefore, detection of
nitroaromatics is a compelling requirement not only due to
Synthesis of Ligand H2L
2-(3-Ethylbenzoate-carbomyl)pyridine (HL1) (1 g, 3.7 mmol)
was dissolved in a mixture of THF/H2O (3:1, v/v) and treated
with 3 equiv. of NaOH. The reaction mixture was stirred for
12 h at room temperature. The resulting solution was neutral-
ized by using 3 N HCl. Removal of THF under vacuum resulted
in the precipitation of a product which was re-dissolved by
ACS Paragon Plus Environment

Crystal Growth & Design
Page 2 of 13
adding ethyl acetate. The ethyl acetate layer was separated a Jeol SM 6610 LV instrument. Luminescence measurements
1
2
3
4
5
6
7
8
and dried over anhyd. Na2SO4. Slow evaporation of ethyl ace-
tate solution at room temperature produced a highly crystal-
line product within 2-3 d which was filtered and dried under
vacuum. Yield: 0.75 g (84 %). Anal. Calcd. for C13H10N2O3: C,
64.46%; H, 4.16%; N, 11.56%. Found: C, 64.62%; H, 4.38%; N,
11.54%. 1H NMR spectrum (DMSO-d6, 400 MHz; Figure S1, SI):
δ = 13.00 (s, 1H, COOH), 10.81 (s, 1H, CONH), 8.05-8.02 (d,
2H, H3/H5), 7.47-7.43 (t, 1H, H4), 8.59 (s, 1H, H7), 8.14-8.13
(d, 1H, H10), 7.68-7.63 (m, 2H, H11/H12), 8.71−8.70 (d, 1H,
H13). 13C NMR spectrum (DMSO-d6, 100 MHz; Figure S2, SI): δ
= 167.73 (C1), 129.41 (C2), 125.18 (C3), 131.82 (C4), 127.57
(C5), 138.71 (C6), 121.65 (C7), 163.33 (C8), 150.23 (C9),
123.03 (C10), 139.14 (C11), 125.30 (C12), 148.97 (C13). FTIR
spectrum (Zn-Se ATR, selected peaks; Figure S3, SI): 3332 (N-
Hamide), 2920 (O-Hacid), 1700 (asymmetric C=Oacid), 1666 (sym-
metric C=Oacid), 1594 (C=Oamide) cm-1.
were made either with an Edinburgh Instrument FLS 900 lu-
minescence spectrometer or Cary Eclipse Fluorescence Spec-
trophotometer.
Single Crystal Structure Determination. Single crystals
suitable for the X-ray diffraction studies were grown by the
diffusion of diethyl ether vapours to a DMF solution of the
corresponding product. The intensity data were collected at
293 K with an Oxford XCalibur CCD diffractometer equipped
with a graphite monochromatic Mo-Kα radiation (λ = 0.71073
Å).52 An empirical absorption correction was applied using the
spherical harmonics implemented in the SCALE3 ABSPACK
scaling algorithm.52 The structures were solved by direct
methods using SIR-9253 and refined by the full-matrix least-
squares refinement techniques on F2 using the program
SHELXL-9754 in the WinGX module.55 All hydrogen atoms were
fixed at the calculated positions with isotropic thermal pa-
rameters whereas all non-hydrogen atoms were refined ani-
sotropically. For LnCP 1, some unassigned electron density
was noted very close to the Eu atom (< 1Å) due to the ab-
sorption artifact. This resulted in an A-level alert in checkCIF.
For LnCP 2, A-level alert in checkCIF was due to the observa-
tion of short D…A contacts between the disordered water
molecules (O1w and O2w). Details of the crystallographic
data collection and structure solution parameters are provid-
ed in Table 1.
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
Synthesis of [Eu(HL)3(CH3OH)2]n (LnCP 1)
Solid Eu(NO3)3.5H2O (0.059 g, 0.14 mmol) was added to a
solution containing ligand H2L (0.1 g, 0.42 mmol) and ET3N
(0.043 g, 0.42 mmol) in CH3OH (10 ml) and the reaction mix-
ture was stirred for 1 h. A white product was obtained which
was filtered and dried under vacuum. Crystallization was
achieved by the vapour diffusion of diethyl ether to a DMF
solution of the crude product at room temperature which
afforded a highly crystalline product within 2-3 d. Yield: 0.111
g (85%). Anal. Calcd. for C41H35N6O11Eu: C, 52.40%; H, 3.75%;
N, 8.94%. Found: C, 52.57%; H, 3.48%; N, 8.75%. FTIR spec-
trum (Zn-Se ATR, selected peaks): ν = 3332 (N-Hamide), 1680
(asymmetric C=Oacid), 1635 (symmetric C=Oacid), 1595
(C=Oamide), 1393 (C=N) cm-1.
Fluorescence Experiments. 3 mg of a compound (1 or 2)
was suspended in 3 ml of CHCl3 and the suspension was soni-
cated for 1 h. The resultant suspension was used for PL stud-
ies to maintain the homogeneity of the suspended com-
pound. This suspension was excited at 358 nm and the flo-
rescence spectra were recorded in the range of 450 nm – 750
nm. The quenching experiments were performed by the in-
cremental addition of nitroaromatics to the aforementioned
CHCl3 suspension. To maintain the homogeneity, sample was
sonicated before each run after the addition of nitro com-
pounds.
Synthesis of [(Tb(HL)3(CH3OH)(H2O)]n•H2O (LnCP 2)
This compound was synthesized in a similar manner with
an identical scale as mentioned for
1 except using
Tb(NO3)3.5H2O in place of Eu(NO3)3.5H2O. Yield 0.090 g (70%).
Anal. Calcd. for C40H35N6O12Tb: C, 50.54%; H, 3.71%; N, 8.84%.
Found: C, 50.55%; H, 3.60%; N, 8.78%. FTIR spectrum (Zn-Se
ATR, selected peaks): ν = 3330 (N-Hamide), 1674 (asymmetric
C=Oacid), 1630 (symmetric C=Oacid), 1594 (C=Oamide), 1390
(C=N) cm–1.
Determination of Stern-Volmer constant (Ksv) and Detec-
tion limit.
Stern-Volmer constant (Ksv) were determined by using the
Stern-Volmer equation (1) where I0 and I are the emission
intensity in the presence and absence of quencher (Q), re-
spectively while Ksv is the Stern-Volmer constant.30-39 Detec-
tion limits were calculated by using equation (2) where σ is
defined as the standard deviation of a blank sample and k
represents the slop of the linear calibration plot.30-39
Physical Methods. The FTIR spectra (Zn-Se ATR, 4000−400
cm−1) were recorded with a Perkin-Elmer Spectrum-Two spec-
trometer having Ze-Se ATR. The NMR spectroscopic meas-
urements were carried out with a Jeol 400 MHz spectrome-
ter. The absorption spectra were recorded with either Perkin-
Elmer Lambda 25 or Lambda 35 spectrophotometers. The
elemental analysis data were obtained with an Elementar
Analysen Systeme GmbH Vario EL-III instrument. Thermal
gravimetric analysis (TGA) was performed with a DTG 60 Shi-
madzu at 5 °C min−1 heating rate under the dinitrogen atmos-
phere. X-ray powder diffraction (XRPD) studies were per-
formed either with an X’Pert Pro from Panalytical or a Bruker
AXS D8 Discover instrument (Cu Kα radiation, λ = 1.54184 Å).
The samples were ground and subjected to the range of θ =
5-50 with slow scan rate at room temperature. Scanning elec-
tron microscopic (SEM) measurements were performed with
Io/I = 1 + Ksv [Q]
………………….. (1)
………………….. (2)
Detection limit = 3σ/k
Results and Discussion
Synthesis and Characterization
The ligand H2L, offering both carboxylic acid and pyridine-2-
carboxamide functional groups, was utilized for the synthesis
of LnCPs. We anticipated that Ln(III) metals would preferen-
tially coordinate via Ocarboxylate groups due to their strong ox-
ACS Paragon Plus Environment

Page 3 of 13
Crystal Growth & Design
gesting that the metals are almost linearly arranged. Such a
ophillic nature56 leaving pyridine-2-carboxamide groups un-
ligated. The reaction of H2L with M(NO3)3•5H2O (M = Eu3+ or
Tb3+) in presence of Et3N in CH3OH produced LnCPs,
[Eu(HL)3(CH3OH)2]n (1) and [(Tb(HL)3(CH3OH)(H2O)]n•H2O (2)
(Scheme 1). Both 1 and 2 were crystallized by the diffusion of
diethyl ether vapours to a DMF solution of the respective
product.
fact further justifies the 1D nature of both LnCPs. In both
LnCPs, any Ln3+ ion is eight-coordinated (Figure 2c). In LnCP 1,
two Eu3+ ions are bridged by two arylcarboxylate groups from
1
2
3
4
5
6
7
8
two ligands in syn,syn-η1 η1
: :ꢀ2 bridging mode while every
Eu3+ ion is further coordinated by a carboxylate group in a
bidentate chelating mode in addition to two CH3OH mole-
cules (Figure 2c). LnCP 2 displays an identical coordination
environment around a Tb3+ ion except that two terminal sites
are ligated by a water and a methanol molecule. Interestingly,
in both LnCPs 1 and 2, pyridine-2-carboxamide fragment of a
ligand remains uncoordinated (Figure 2b and 2d).
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
The 1D chains are packed in parallel fashion involving
C=Oamide…H-Carene H-bonding interactions and thus generating
a 3D architecture (Figure 2e). A perspective view of LnCP 1
clearly illustrates the presence of channels propagating along
the c-axis (Figure 2f). Similarly, LnCP 2 displays the presence
of channels as a result of generation of 3D network due to the
C=Oamide…H-Carene H-bonding interactions (Figures 2g and 2h).
Topological analysis58,59 of LnCPs 1 and 2 illustrate that
Eu3+/Tb3+ ions functioned as the 4-connected nodes while
ligands acted as the 2-connected linkers generating 1D chains
with identical point symbol (42)(4)2 (Figure 2i).
Scheme 1. Ligand H2L and its lanthanide coordination polymers
(LnCP) 1 and 2.
The FTIR spectra of LnCPs 1 and 2 exhibited red-shifted
asymmetric as well as symmetric νCOO stretches at 1674-1680
and 1630-1635 cm-1, respectively when compared with the
free ligand H2L (Figures S3 and S4; SI). On the other hand,
nearly unchanged amidic C=O bands were noted at ca. 1595
cm-1. These observations suggest that the Ln3+ ions are coor-
dinated to the arylcarboxylate groups and not to the amidic-O
groups. In addition, a sharp band at ca 3330 cm-1 was due to
the νN-H stretch of the pyridine-2-carboxamide fragment.
Thermogravimetric analysis (TGA) was performed on both 1
and 2 in the temperature range of 35-180 ˚C to shed light on
the nature of lattice as well as coordinated solvent molecules,
decomposition profile and thermal stability of LnCPs. TGA
plots show ca. 7% weight loss for the release of lattice as well
as coordinated solvent molecules.57 TGA plots further exhibit
that both LnCPs are stable up to ca. 400˚C (Figure S5; SI).
Photoluminescence Studies of LnCPs
The photoluminescence (PL) properties of both LnCPs were
carried out at room temperature. The solid-state excitation
and emission spectra of LnCPs 1 and 2 are illustrated in Figure
3. LnCP 1 displays an excitation band at 358 nm and charac-
teristic emission bands of Eu3+ ion at 594, 617 (Intense band,
5
red), 651, and 694 nm, which can be attributed to f-f D0 →
7Fj (j = 1−4) transitions, respectively.36 On the other hand,
LnCP 2 exhibits emission bands for the Tb3+ ion at 487, 542
(Intense band, green), 581 and 620 nm, which can be as-
Crystal Structures
7
signed to f-f 5D4 → Fj (j = 6, 5, 4 and 3) transitions, respec-
tively.25 The emission properties of both LnCPs were also
studied in different solvents as their suspensions. For that
purpose, LnCPs 1 and 2 were suspended in assorted solvents
and their emission spectra were recorded by maintaining an
effective concentration of 3 mg/3 ml. Both LnCPs 1 and 2
exhibited the highest emission intensity in CHCl3 whereas
lowest emission was noted in MeOH (Figure 4). As both LnCPs
behaved nearly identical; 1 was selected as a model system
for further studies in different solvents (CHCl3, CH2Cl2, EtOAc,
hexane, CH3CN, (CH3)2CO, EtOH, THF, H2O, and CH3OH) as well
as assorted reagents such as benzene, toluene, chloroben-
zene, bromobenzene, phenol, aniline, benzaldehyde, nitro-
benzene, nitroethane, 1-nitropropane, 2-nitropropane, and
nitrocyclopentane. Importantly, maximum quenching in the
emission intensity was caused by the electron-deficient spe-
cies such as benzaldehyde and nitrobenzene (Figure 5a). On
the other hand, aliphatic nitro reagents did not result in ap-
preciable change in the emission intensity (Figure 5b).
To understand the solid-state structure and conformation,
ligand H2L as well as both LnCPs were crystallographically
characterized (Tables 1 and S1-S4, SI). The ligand H2L crystal-
lized in monoclinic space group P21/n. Herein, two arene rings
are almost co-planer to each other as revealed by a small
dihedral angle of ca. 5.8˚. Interestingly, ligand H2L exhibited
H-bonding based self-assembly where -OH of the carboxylic
acid functions as the hydrogen bond (H-bond) donor whereas
appended N-pyridyl group acted as the H-bond acceptor (Fig-
ure 1). Topological analysis58,59 of H-bonding based self-
assembly illustrate that the structure is consist of (0 1 0) chain
with point symbol of net (42.6).
Crystal Structures of LnCPs
Single crystal X-ray analysis reveals that the isostructural
LnCPs 1 and 2 crystalize in monoclinic cell with P21/c space
group. The asymmetric unit of 1 and 2 contains one Ln3+ ion
(Ln = Eu and Tb), three mono-anionic HL ligands and two co-
ordinated solvent molecules (methanol and/or water) (Figure
2a). The structures of LnCPs 1 and 2 display that ligands
bridge Ln3+ ions in such a way so as to generate a 1D polymer-
ic chain propagating along the b-axis (Figure 2b). The angle
between any three Ln3+ ions, in a 1D chain, is ca. 174.5o sug-
Sensing of Nitroaromatics
PL studies in different solvents and reagents suggested that
LnCP 1 functioned as a good sensor for the electron-deficient
solvents and/or reagents as well as the ones containing nitro
ACS Paragon Plus Environment

Crystal Growth & Design
Page 4 of 13
group(s). Although no significant PL change was noted for capability to detect vapor-phase nitrobenzene at room tem-
1
2
3
4
5
6
7
8
nitroaliphatic compounds, maximum quenching was observed
for the nitroaromatics (nitrobenzene, 4-nitrophenol, 1,3-
dinitrobenzene, 1-nitronapthalene, 2,4,6-trinitrophenol, 3,5-
dinitrosalicylic acid and 3,5-dinitrobenzyl chloride). Collective-
ly, these results advocate that LnCPs 1 has strong affinity to
sense assorted nitroaromatics although maximum quenching
was noted for the smallest one, nitrobenzene (Figure 6).
perature. In a typical experiment, vacuum-dried LnCP 1 was
exposed to nitrobenzene vapors for a fixed period of time at
room temperature followed by the measurement of its PL
intensity. The fluorescence of 1 was considerably quenched
within 4 h of exposure whereas maximum quenching was
noted after a period of 12 h (Figure 7e and 7f). Such a fact is
further evident by the sample’s optical photographs under
normal and UV light (Figure 7g-7i). These results are notewor-
thy and illustrate that LnCP 1 is also able to sense nitroben-
zene vapors. Remarkably, 1 can be fully regenerated by simp-
ly washing with CHCl3 a couple of times. In fact, its remarka-
ble recyclability suggests its potential use for solid-state sens-
ing applications as only a negligible drop in performance was
noted even after five cycles (Figure S34, SI).
Subsequently, PL studies of 1 as a CHCl3 suspension, was
studied with incremental addition of different nitroaromatics
and percentage of quenching, Ksv values (from Stern–Volmer
analysis), and detection limits were calculated (Figures 7a-7d
and S6-S29 (SI); and Table 2). From these studies, following
quenching efficiency trend was observed: nitrobenzene > 4-
nitrophenol > 1,3-dinitrobenzene > 1-nitronapthalene > 2,4,6-
trinitrophenol > 3,5-dinitrosalicylic acid > 3,5-dinitrobenzyl
chloride. Importantly, such a trend is consistent with the or-
der of the molecular sizes of these nitroaromatics and can be
attributed to the ease in their diffusion abilities within the 3D
network structure of coordination polymers (Figure 6, right
panel and Table S5). The smallest nitrobenzene resulted in
fast diffusion as well as unhindered accessibility to the interi-
ors of the coordination polymer and therefore it caused max-
imum quenching in the emission intensity of LnCP 1. For ex-
ample, a ratio of quenching efficiencies of nitrobenzene and
1-nitronaphthalene yields 1.46 that closely matches to 1.57, a
ratio of volumes of two substrates (cf. Tables 2 and S5, SI).
Such a comparison convincingly infers that the sensing ability
of the present LnCPs is a function of the molecular dimen-
sions of the substrates.
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
Possible Mechanism
In order to elucidate possible mechanism for the observed
PL quenching by the nitroaromatics, powder XRD as well as
scanning electron microscopy (SEM) was employed to moni-
tor the structural and morphological changes during the sens-
ing of nitrobenzene (Figure S35, SI). The powder XRD patterns
of LnCP 1 immersed in nitrobenzene for 15 min and 1 h were
identical to that of pristine 1. Such a fact strongly suggests
that the framework structure remains stable although photo-
luminescence is mostly quenched. Further support came from
the SEM images that additionally inferred that the nitroben-
zene has not caused any morphological changes to the LnCP 1
after 15 min and even 1 h of exposure of nitrobenzene (right
panels; Figure S35, SI). It can be therefore concluded that PL
quenching within a short period of time mainly results from
the electron donor-acceptor mechanism between LnCPs and
nitroaromatics.19,36-39 We therefore propose that the uncoor-
dinated pyridine-2-carboxamide fragments of LnCPs function
as the Lewis basic sites and interact with electron-deficient
nitroaromatics and such an interaction causes the PL quench-
ing.
Sensing of Nitrobenzene
The sensing performance of both LnCPs towards various ni-
troaromatics, particularly volatile nitrobenzene due to its
smallest size is noteworthy as it belongs to a group of sub-
stances known as the volatile organic compounds (VOCs).36-38
Hence, dependency of the degree of luminescence quenching
on the concentration of nitrobenzene was examined. Such a
study revealed that LnCP 1 is quite sensitive towards nitro-
benzene even at very low concentrations. At around 1000 µM
concentration of nitrobenzene, PL intensity is significantly
quenched with a quenching yield of ca. 90% (Figure 7a and
7b). The Stern–Volmer analysis (Ksv) and detection limit of
LnCP 1 with nitrobenzene was found to be 2.38 x 104 and 49
µM, respectively (Figure 7c and 7d). These values illustrate
that LnCp 1 has good sensitivity for detecting even small
amount of nitrobenzene. In fact, such a noteworthy detection
is superior to that of previously reported sensors for detect-
ing nitrobenzene (see Table S6, SI for comparison with litera-
ture examples).36-38 Similar results were obtained when LnCP
2 was used in place of 1 (entry 8, Table 2 and Figures S30-S33,
SI). In this case as well, smaller nitroaromatics resulted in
maximum quenching in comparison to bulkier nitroaromatics
supporting various studies with LnCP 1.
It is well known that nitroaromatics are electron-deficient
molecules19,39 whereas presence of planar aromatic ring al-
lows facile intercalation or stacking.36-39 It is suggested that
once nitroaromatics are able to diffuse inside the channels
present within the interior of the present LnCPs; energy
transfer process from HL to the central Eu/Tb ions is forbid-
den, resulting in fluorescence quenching of LnCPs.60 Im-
portantly, both LnCPs 1 and 2 offer 3D network which is gen-
erated by the operation of H-bonding interactions. Therefore,
size as well as shape of a potential substrate (i.e., nitroaro-
matics) will be a limiting factor that could be related to the
pores and channels created by the H-bonding interactions.
The facile diffusion of a smaller substrate (e.g., nitrobenzene)
is likely to result in the maximum quenching as observed with
the present LnCPs. In fact, such a proposal gets support from
the solvent-dependent PL behavior of both LnCPs 1 and 2. We
believe that any solvent having ability to disrupt the H-
bonding between 1D chains, responsible for the generation of
3D structure, is likely to affect the PL performance of LnCPs.
Indeed, both LnCPs displayed significant solvent dependency
and such a fact is related to the disruption of 3D structure as
Vapor Phase Sensing of Nitrobenzene
The significant ability of both LnCPs 1 and 2 as a CHCl3 sus-
pension to sense nitrobenzene prompted us to study their
ACS Paragon Plus Environment

Page 5 of 13
Crystal Growth & Design
(3) Cook, T. R.; Stang, P. J. Recent Developments in the Preparation
a result of a solvent’s polarity (e.g., MeOH) or its swelling
efficiency (e.g, THF, CH2Cl2).61
1
and Chemistry of Metallacycles and Metallacages via Coordina-
tion. Chem. Rev. 2015, 115, 7001-7045.
2
3
4
5
6
7
8
9
(4) Schoedel, A.; Li, M.; Li, D.; O’Keeffe, M.; Yaghi, O. M. Structures
of Metal-Organic Frameworks with Rod Secondary Building
Units. Chem. Rev. 2016, 116, 12466−12535.
(5) Kumar, K. V.; Preuss, K.; Titirici, M.-M.; Rodríguez-Reinoso, F.
Nanoporous Materials for the Onboard Storage of Natural Gas.
Chem. Rev. 2017, 117, 1796−1825.
(6) Maspoch, D.; Ruiz-Molina, D.; Veciana, J. Old materials with
new tricks: Multifunctional open-framework materials. Chem.
Soc. Rev.2007, 36, 770-818.
(7) Li, J. R.; Kuppler, R. J.; Zhou, H. C. Selective gas adsorption and
separation in metal-organic frameworks. Chem. Soc. Rev. 2009,
38, 1477-1504.
(8) Srivastava, S.; Kumar, V.; Gupta R. A Carboxylate-Rich Metal-
loligand and Its Heterometallic Coordination Polymers: Synthe-
ses, Structures, Topologies, and Heterogeneous Catalysis. Cryst.
Growth Des. 2016, 16, 2874-2886.
(9) Srivastava, S.; Aggarwal, H.; Gupta, R. Three-Dimensional Het-
erometallic Coordination Networks: Syntheses, Crystal Struc-
tures, Topologies, and Heterogeneous Catalysis. Cryst. Growth
Des. 2015, 15, 4110-4122.
Conclusions
In this work, two lanthanide coordination polymers (LnCPs)
have been synthesized and characterized. Both LnCPs illus-
trated 1D chain-like structure which was further extended to
3D architecture due to the involvement of H-bonding interac-
tions. Both LnCPs were successfully used for the sensing of
various nitroaromatics although maximum emission quench-
ing was noted for the smallest nitrobenzene. Both LnCPs of-
fered strategically placed exposed Lewis basic sites which
potentially interacted with the electron-deficient nitroaro-
matics whereas H-bonded 3D architecture having hydropho-
bic channels allowed their facile inclusion within the network.
An important observation was the size-dependent sensing of
nitroaromatics potentially governed by the packing of 1D
chains into a 3D architecture. Importantly, vapor-phase de-
tection of nitrobenzene as well as recyclability of LnCPs sug-
gests their potential applications in the sensing devices for
the detection of nitroaromatics.
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
(10) Singh, A. P.; Ali, A.; Gupta, R. Cobalt complexes as the building
blocks: {Co3+–Zn2+} heterobimetallic networks and their proper-
ties. Dalton Trans. 2010, 39, 8135-8138.
ASSOCIATED CONTENT
(11) Singh, A. P.; Kumar, G.; Gupta, R. Two-dimensional {Co3+–Zn2+}
and {Co3+–Cd2+} networks and their applications in heterogene-
ous and solvent-free ring opening reactions. Dalton Trans. 2011,
40, 12454-12461.
Supporting Information. Figures for NMR, FTIR, and absorption
spectra, TGA, titration plots, spectral fittings, powder XRD and
SEM micrographs; and tables of bond distances, bond angles, H-
bonding parameters; size and percentage quenching efficiency of
nitroaromatics; and a comparative table with literature examples
for the sensing of nitroaromatics. This material is available free of
charge via the Internet at http://pubs.acs.org.
(12) Kumar, G.; Gupta, R. Cobalt Complexes Appended with p- and
m-Carboxylates: Two Unique {Co3+−Cd2+} Networks and Their
Regioselective and Size Selective Heterogeneous Catalysis. In-
org. Chem. 2012, 51, 5497-5499.
(13) Kumar, G.; Gupta, R. Three-Dimensional {Co3+−Zn2+} and
{Co3+−Cd2+} Networks Originated from Carboxylate-rich Building
Blocks: Syntheses, Structures, and Heterogeneous Catalysis. In-
org. Chem. 2013, 52, 10773-10787.
(14) Kumar, G.; Kumar, G.; Gupta, R. Manganese- and Cobalt-Based
Coordination Networks as Promising Heterogeneous Catalysts
for Olefin Epoxidation Reactions. Inorg. Chem. 2015, 54, 2603-
2615.
(15) Zhou, X.; Lee, S.; Xu, Z.; Yoon, J. Recent Progress on the Devel-
opment of Chemosensors for Gases. Chem. Rev. 2015, 115,
7944-8000.
(16) Wagner, T.; Haffer, S.; Weinberger, C.; Klaus, D.; Tiemann, M.
Mesoporous Materials as Gas Sensors. Chem. Soc. Rev. 2013,
42, 4036
(17) Chen, B.; Xiang, S.; Qian, G. Metal-Organic Frameworks with
Functional Pores for Recognition of Small Molecules. Acc. Chem.
Res. 2010, 43, 1115-1124.
(18) Chen, B.; Wang, L.; Zapata, F.; Qian, G.; Lobkovsky, E. B. A Lumi-
nescent Microporous Metal-Organic Framework for the Recog-
nition and Sensing of Anions. J. Am. Chem. Soc., 2008, 130,
6718-6719.
(19) Hu, Z. C.; Deibert, B. J.; Li, J. Luminescent Metal-Organic
Frameworks for Chemical Sensing and Explosive Detection.
Chem. Soc. Rev. 2014, 43, 5815-5840.
AUTHOR INFORMATION
Corresponding Author
*Fax: +91-11-27666605; Email: rgupta@chemistry.du.ac.in. Web-
site: http://people.du.ac.in/~rgupta/.
ORCID: 0000-0003-2454-6705
Author Contributions
The manuscript was written through contributions of all authors.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
RG acknowledges financial support from the Science and Engi-
neering Research Board (SERB), New Delhi. SS thanks UGC, New
Delhi for the SRF fellowship. Authors thank CIF-USIC of this uni-
versity for the instrumental facilities including X-ray data collec-
tion and CSIR-NPL, New Delhi for the solid-state PL measure-
ments.
(20) Guo, Z.; Xu, H.; Su, S.; Cai, J.; Dang, S.; Xiang, S.; Qian, G.; Zhang,
H.; O’ Keeffe, M.; Chen, B. A robust near infrared luminescent
ytterbium metal–organic framework for sensing of small mole-
cules. Chem. Commun., 2011, 47, 5551-5553.
(21) Salinas, Y.; M.-M., R.; Marcos, M. D.; Sancenon, F.; Costero, A.
M.; Parra, M.; Gil, S. Optical chemosensors and reagents to de-
tect explosives. Chem. Soc. Rev., 2012, 41, 1261-1296.
(22) Chen, B.; Yang, Y.; Zapata, F.; Lin, G.; Qian, G.; Lobkovsky, E. B.
Luminescent Open Metal Sites within a Metal-Organic Frame-
REFERENCES
(1) Kumar, G.; Gupta, R. Molecularly designed architectures - the
metalloligand way. Chem. Soc. Rev. 2013, 42, 9403-9453.
(2) Srivastava, S.; Gupta, R. Metalloligands to material: design
strategies and network topologies. CrystEngComm, 2016, 18,
9185-9208.
ACS Paragon Plus Environment

Crystal Growth & Design
Page 6 of 13
work for Sensing Small Molecules. Adv. Mater., 2007, 19, 1693-
(39) Shanmugaraju, S.; Mukherjee, P. S. π-Electron rich small mole-
1
2
3
4
5
6
7
8
1696.
cule sensors for the recognition of nitroaromatics. Chem. Com-
mun., 2015, 51, 16014-16032.
(40) Germain, M. E.; Knapp, M. J. Optical explosives detection: from
color changes to fluorescence turn-on. Chem. Soc. Rev., 2009,
38, 2543-2555.
(41) Germain, M. E.; Vargo, T. R.; Khalifah, P. G.; Knapp, M. J. Fluo-
rescent Detection of Nitroaromatics and 2,3-Dimethyl- 2,3-
dinitrobutane (DMNB) by a Zinc Complex: (salophen)Zn. Inorg.
Chem., 2007, 46, 4422-4429.
(23) Zhang, Z.; Xiang, S.; Rao, X.; Zheng, Q.; Fronczek, F. R.; Qian, G.;
Chen, B. A rod packing microporous metal–organic framework
with open metal sites for selective guest sorption and sensing of
nitrobenzene. Chem. Commun., 2010, 46, 7205-7207.
(24) Wang, Z.-J.; Qin, L.; Chen, J.-X.; Zheng, H.-G. H‑Bonding Interac-
tions Induced Two Isostructural Cd(II) Metal-Organic Frame-
works Showing Different Selective Detection of Nitroaromatic
Explosives. Inorg. Chem. 2016, 55, 10999-11005.
9
(42) He, G.; Peng, H.; Liu, T.; Yang, M.; Zhang, Y.; Fang, Y. A novel
picric acid film sensor via combination of the surface enrich-
ment effect of chitosan films and the aggregation-induced
emission effect of siloles. J. Mater. Chem., 2009, 19, 7347-7353.
(43) Pimienta, V.; Etchenique, R.; Buhse, T. On the Origin of Electro-
chemical Oscillations in the Picric Acid/CTAB Two-Phase System.
J. Phys. Chem. A, 2001, 105, 10037-10044.
(44) Sylvia, J. M.; Janni, J. A.; Klein, J.; Spencer, K. M. Surface-
Enhanced Raman Detection of 2,4-Dinitrotoluene Impurity Va-
por as a Marker To Locate Landmines. Anal. Chem. 2000, 72,
5834-5840.
(45) Wallenborg, S. R.; Bailey, C. G. Separation and Detection of
Explosives on a Microchip Using Micellar Electrokinetic Chroma-
tography and Indirect Laser-Induced Fluorescence. Anal. Chem.
2000, 72, 1872-1878.
(46) Kandpal, M.; Bandela, A. K.; Hinge, V. K.; Rao, V. R.; Rao, C. P.
Fluorescence and Piezoresistive Cantilever Sensing of Trinitro-
toluene by an Upper-Rim Tetrabenzimidazole Conjugate of Ca-
lix[4]arene and Delineation of the Features of the Complex by
Molecular Dynamics. ACS Appl. Mater. Interfaces, 2013, 5,
13448-13456.
(47) Zu, B.; Guo, Y.; Dou, X. Nanostructure-based optoelectronic
sensing of vapor phase explosives – a promising but challenging
method. Nanoscale, 2013, 5, 10693-10701.
(48) Toal, S. J.; Trogler, W. C. Polymer sensors for nitroaromatic
explosives detection. J. Mater. Chem., 2006, 16, 2871-2883.
(49) Vij, V.; Bhalla, V.; Kumar, M. Attogram Detection of Picric Acid
by Hexa-peri-Hexabenzocoronene-Based Chemosensors by
Controlled Aggregation-Induced Emission Enhancement. ACS
Appl. Mater. Interfaces, 2013, 5, 5373-5380.
(50) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, Pergamon Press, Oxford, 1980. Purifica-
tion of Laboratory Chemicals, Pergamon Press, Oxford, 1980.
(51) Kumar, G.; Aggarwal, H.; Gupta, R. Cobalt Complexes Appended
with para- and meta-Arylcarboxylic Acids: Influence of Cation,
Solvent, and Symmetry on Hydrogen-Bonded Assemblies. Cryst.
Growth. Des. 2013, 13, 74-90.
(52) CrysAlisPro, Oxford Diffraction Ltd., version 1.171.33.49b
(2009).
(53) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. Com-
pletion and refinement of crystal structures with sir92. J. Appl.
Crystallogr. 1993, 26, 343-350.
(54) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sec.
A 2008, 64, 112-122.
(55) Farrugia, L. J. WinGX version 1.70, An Integrated System of
Windows Programs for the Solution, Refinement and Analysis of
Single-Crystal X-ray Diffraction Data; Department of Chemistry,
University of Glasgow, 2003.
(56) Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O’Keeffe M.;
Yaghi, O. M. Secondary building units, nets and bonding in the
chemistry of metal–organic frameworks. Chem. Soc. Rev., 2009,
38, 1257-1283.
(57) For LnCP 1, Obs. weight change: 6.7%; Calc.: 6.8% for the loss of
two MeOH molecules. For LnCP 2, Obs. weight change: 7.4%;
Calc.: 7.1% for the loss of one MeOH and two water molecules.
(25) Pal, S.; Bharadwaj, P. K. A Luminescent Terbium MOF Contain-
ing Hydroxyl Groups Exhibits Selective Sensing of Nitroaromatic
Compounds and Fe(III) Ions. Cryst. Growth Des. 2016, 16, 5852-
5858.
(26) Joarder, B.; Desai, A. V.; Samanta, P.; Mukherjee, S.; Ghosh, S. K.
Selective and Sensitive Aqueous-Phase Detection of 2,4,6- Trini-
trophenol (TNP) by an Amine-Functionalized Metal–Organic
Framework. Chem. Eur. J. 2015, 21, 965-969.
(27) Mukherjee, S.; Desai, A. V.; Manna, B.; Inamdar, A. I.; Ghosh, S.
K. Exploitation of Guest Accessible Aliphatic Amine Functionality
of a Metal−Organic Framework for Selecꢀve Detecꢀon of 2,4,6-
Trinitrophenol (TNP) in Water. Cryst. Growth Des. 2015, 15,
4627-4634.
(28) Nagarkar, S. S.; Desai, A. V.; Samanta, P.; Ghosh, S. K. Aqueous
phase selective detection of 2,4,6-trinitrophenol using a fluo-
rescent metal-organic framework with a pendant recognition
site. Dalton Trans., 2015, 44, 15175-15180.
(29) Tang, Q.; Liu, S.; Liu, Y.; Miao, J.; Li, S.; Zhang, L.; Shi, Z.; Zheng,
Z. Cation Sensing by a Luminescent Metal-Organic Framework
with Multiple Lewis Basic Sites. Inorg. Chem. 2013, 52, 2799-
2801.
(30) Hao, Z.; Song, X.; Zhu, M.; Meng, X.; Zhao, S.; Su, S.; Yang, W.;
Song, S.; Zhang, H. One-dimensional channel-structured Eu-
MOF for sensing small organic molecules and Cu2+ ion. J. Mater.
Chem. A, 2013, 1, 11043-11050.
(31) Zhu, Y.-M.; Zeng, C.-H.; Chu, T.-S.; Wang, H.-M; Yang, Y.-Y.;
Tong, Y.-X.; Su, C.-Y.; Wong, W.-T. A novel highly luminescent
LnMOF film: a convenient sensor for Hg2+ detecting. J. Mater.
Chem. A, 2013, 1, 11312-11319.
(32) Gole, B.; Bar, A. K.; Mukherjee, P. S. Fluorescent metal–organic
framework for selective sensing of nitroaromatic explosives.
Chem. Commun., 2011, 47, 12137-12139.
(33) Hu, X.-L.; Liu, F.-H.; Qin, C.; Shao, K.-Z.; Su, Z.-M. A 2D bilayered
metal–organic framework as a fluorescent sensor for highly se-
lective sensing of nitro explosives. Dalton Trans., 2015, 44,
7822-7827.
(34) Zhou, X.; Li, H.; Xiao, H.; Li, L.; Zhao, Q.; Yang, T.; Zuo, J.; Huang,
W. A microporous luminescent europium metal-organic frame-
work for nitro explosive sensing. Dalton Trans., 2013, 42, 5718-
5723.
(35) Banerjee, D.; Hu, Z.; Li, J. Luminescent metal-organic frame-
works as explosive sensors. Dalton Trans., 2014, 43, 10668-
10685.
(36) Gao, R.-C.; Guo, F.-S.; Bai, N.-N.; Wu, Y.-L.; Yang, F.; Liang, J.-Y.;
Li, Z.-J.; Wang, Y.-Y. Two 3D Isostructural Ln(III)-MOFs: Display-
ing the Slow Magnetic Relaxation and Luminescence Properties
in Detection of Nitrobenzene and Cr2O72-. Inorg. Chem. 2016,
55, 11323-11330.
(37) Xia, Y.-P.; Li, Y.-W.; Li, D.-C.; Yao, Q.-X.; Du, Y.-C.; Dou, J.-M. A
new Cd(II)-based metal–organic framework for highly sensitive
fluorescence sensing of nitrobenzene. CrystEngComm, 2015,
17, 2459-2463.
(38) Wang, R.; Liu, X.; Huang, A.; Wang, W.; Xiao, Z.; Zhang, L.; Dai,
F.; Sun, D. Unprecedented Solvent-Dependent Sensitivities in
Highly Efficient Detection of Metal Ions and Nitroaromatic
Compounds by a Fluorescent Barium Metal-Organic Frame-
work. Inorg. Chem. 2016, 55, 1782-1787.
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
ACS Paragon Plus Environment

Page 7 of 13
Crystal Growth & Design
(58) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. Topos 3.2: a
new version of the program package for multipurpose crystal-
1
chemical analysis. J. Appl. Crystallogr. 2000, 33, 1193.
(59) Blatov, V. A.; O’Keefee, M.; Proserpio, D. M. Vertex-, face-,
point-, Schlafli-, and Delaney-symbols in nets, polyhedra and til-
ings: recommended terminology. CrystEngComm. 2010, 12, 44-
48.
(60) A typical fluorescence probe contains a receptor unit (antenna),
a luminescence center, and a linker.19 In the present LnCPs,
Eu/Tb ion is the luminescence center, while ligand functions
both as a linker and a receptor.
2
3
4
5
6
7
8
9
(61) Miller-Chou, B. A.; Koenig, J. L. A review of polymer dissolution.
Prog. Polym. Sci. 2003, 28, 1223-1270.
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
Table 1. Crystallographic Data Collection and Structure Refinement Parameters for Ligand H2L and LnCPs 1 and 2.
H2L
C13H10N2O3
242.23
1
C41H35EuN6O11
937.69
293(2)
Monoclinic
P21/c
28.082 (2)
14.6148 (14)
9.7461 (6)
90
96.049 (7)
90
2
C40H35TbN6O12
945.63
293(2)
Monoclinic
P21/c
28.0524(12)
14.7147(9)
9.7408(4)
90
96.216 (4)
90
Molecular formula
Fw
T(K)
293(2)
Crystal system
Space group
Monoclinic
P21/n
a
b
c
13.240 (7)
4.988 (2)
17.127 (14)
90
97.56 (6)
90
α
β
γ
ACS Paragon Plus Environment

Crystal Growth & Design
Page 8 of 13
V (Å3)
Z
1121.3 (12)
4
3977.7 (6)
4
1.566
3977.2(3)
4
1.571
1
2
ρ (g cm-3)
1.435
3
4
5
6
7
8
9
F (000)
504.0
0.104
6323
1961(0.1071)
994
1888
1.646
28873
6991(0.1878)
4008
1892
1.840
45715
7026(0.1076)
5129
µ (Mo Kα) (mm-1)
collected reflections
unique reflections
no. of observations
Goodness of fit (F2)
0.988
0.992
1.143
R1 , wR2b [I >2σ(I)]
0.0772, 0.1721
0.1455, 0.2158
1544542
0.0954, 0.2375
0.1542, 0.3124
1544543
0.0646, 0.1101
0.0939, 0.1190
1544544
a
R1 , wR2b [all data]
a
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
CCDC No.
[a]R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = {Σ[w(/Fo/2 – /Fc/2 )2]/Σ[wFo4]}1/2
.
Table 2. Summary of percentage quenching efficiency, Stern-Volmer constant (Ksv) and detection limit for LnCP 1 with various
nitroaromatics.
Entry
Nitroaromatic
Nitrobenzene
% Quenching Efficiency
Ksv (M-1)
2.38 x 104
2.54 x 103
2.o1 x 103
9.88 x 102
8.951 x 102
5.462 x 102
4.272 x 102
1.728 x 104
Detection Limit (µM)
1
2
98
82
80
67
64
52
45
96
49
66
4-nitrophenol
3
88
1,3-dinitrobenzene
1-nitronapthalene
2,4,6-trinitrophenol
3,5-dinitrosalicylic acid
3,5-dinitrobenzyl chloride
Nitrobenzene
4
90
5
98
6
130
134
53
7
8a
aUsing LnCP 2.
Figure 1. ORTEP representation of the crystal structure of ligand H2L (30% probability level) (left); Color code: blue, N; red,
O; gray, C; white, H; H-bonding (COO-Hacid…Npyridine and C=Oacid…Harene) between individual molecules (middle); and topology
of the hydrogen bonded network (right).
8
ACS Paragon Plus Environment

Page 9 of 13
Crystal Growth & Design
1
2
3
4
5
6
7
8
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
Figure 2. (a) Asymmetric unit cell of LnCP 1; color code: yellow, Eu; blue, N; red, O; purple, Omethanol; gray, C; hydrogen atoms
are omitted for clarity. (b) Capped sticks representation of 1 along b-axis showing exposed amide and pyridyl groups. (c) A
closer view of 1 only displaying Eu3+ ions and their coordination environment generating a 1D chain (d) A view of 1D chain
along the c-axis exhibiting exposed amide and pyridyl groups. (e) An extended view of several 1D chains held together by H-
bonds as explained in the text in a view along the c-axis. (f) A line-diagram perspective view of LnCP 1. (g) An extended off-
set view the along c-axis of several 1D chains of LnCP 2. (h) A ball and stick perspective view of LnCP 2. (i) A representative
topological diagram of LnCP 1 showing Eu atoms as the 4-connected nodes (yellow balls) and ligand as the 2-connected
linkers (green balls).
9
ACS Paragon Plus Environment

Crystal Growth & Design
Page 10 of 13
1
2
3
4
5
6
7
8
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
Figure 3. (a) Solid-state excitation spectrum of LnCP
mal light (left) and UV light of wavelength 350 nm (right). (b) Solid-state emission spectrum of LnCP
1
at 617 nm whereas insets show powder sample under nor-
1 at excitation
wavelength of 358 nm whereas inset shows the CIE chromaticity diagram x = 0.61, y = 0.34. (c) Solid-state excita-
tion spectrum of LnCP at 542 nm whereas insets show powder sample under normal light (left) and UV light of
2
wavelength 350 nm (right). (d) Solid-state emission spectrum of LnCP
whereas shows the CIE chromaticity diagram x = 0.35, y = 0.55.
2
at excitation wavelength of 358 nm
100
(b)100
THF (1)
CH3OH (2)
(a)
CH3CH2OH (3)
CH3CN (4)
80
60
40
20
0
80
60
40
20
0
Acetone (5)
CHCl3 (6)
Ethylacetate (7)
Hexane (8)
CH2Cl2 (9)
H2O (10)
550
600
650
700
750
6
4
5
3
7
10
1
9
8
2
Wavelength (nm)
100
80
60
40
20
0
(d)100
(c)
THF (1)
CH3OH (2)
CH3CH2OH (3)
CH3CN (4)
80
Acetone (5)
CHCl3(6)
60
40
20
0
Ethylacetate (7)
Hexane (8)
CH2Cl2 (9)
H2O (10)
450
500
550
600
650
700
4
1
6
5
10
2
8
7
3
9
Wavelength (nm)
Figure 4. Photoluminescence spectra of LnCPs
1
1
sions. Both LnCPs and 2 show maximum intensity in CHCl3.
(a, b) and
2
(c, d) obtained in different solvents as their suspen-
10
ACS Paragon Plus Environment

Page 11 of 13
Crystal Growth & Design
1
2
3
4
5
6
7
8
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
Figure 5. Photoluminescence spectra of LnCP
(b) nitroaliphatics.
1
in different solvents as their suspensions: (a) nitroaromatics, and
100
80
60
40
20
0
100
80
60
40
20
0
0
500
1000
1500
2000
Concentration (ꢀM)
Size
Figure 6. (Left) Photoluminescence quenching efficiency of LnCP in different nitroaromatics varying their ꢀM
concentrations: nitrobenzene ( ); para-nitrophenol ( ); 1,3-dinitrobenzene ( ); 1-nitronapthalene ( ), 2,4,6-
1
trinitrophenol ( ); 3,5-dinitrosalicilic acid ( ); 3,5-dinitrobenzylchloride ( ). (Right) Photoluminescence quenching
efficiency of LnCP
1
plotted against the molecular dimensions of assorted nitroaromatics.
11
ACS Paragon Plus Environment

Crystal Growth & Design
Page 12 of 13
1
2
3
4
5
6
7
8
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
Figure 7. (a) Photoluminescence spectra of LnCP 1 as a CHCl3 suspension after the incremental addition of nitrobenzene. (b)
Photoluminescence spectra of 1 as a CHCl3 suspension after the incremental addition of nitrobenzene by observing
5D0→7F2 transition at 617 nm. (c) Stern–Volmer analysis of 1 as a function of nitrobenzene concentration. (d) A plot for the
calculation of detection limit of 1 as a function of nitrobenzene concentration. Solid-state time-dependent (e) excitation
spectrum and (f) emission spectrum of LnCP 1 as a result of vapour-phase exposure of nitrobenzene: red trace after 0 h
exposure; blue trace after 4 h exposure; and green trace after 12 h exposure. Optical photographs under normal light (left)
and UV light of wavelength 350 nm (right) taken at 0 h (red trace in Figure 7 e/f); after 4 h (blue trace in Figure 7 e/f); and
after 12 h of vapour-phase exposure of nitrobenzene (green trace in Figure 7 e/f).
12
ACS Paragon Plus Environment

Page 13 of 13
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
For Table of Contents Use Only
Manuscript Title: Lanthanideꢀbased Coordination Polymers for the Sizeꢀselective Detection of Niꢀ
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
troaromatics
Authors: Sumit Srivastava,a Bipin Kumar Guptab and Rajeev Gupta*a
TOC Graphic:
Synopsis:
Luminescent
coordination
polymers,
[Eu(HL)3(CH3OH)2]n
(1)
and
[Tb(HL)3(CH3OH)(H2O)]n⋅H2O (2), illustrate detection of nitroaromatics in general and sizeꢀselective
detection of nitrobenzene in particular via a fluorescence TurnꢀOff mechanism.
13
ACS Paragon Plus Environment