Zn- and Cd-based Coordination Polymers Offering H-Bonding Cavities: Highly Selective Sensing of S2O7 2? and Fe3+ Ions

Article abstract of DOI:10.1002/asia.201901142

We present two Zn^II- and Cd^II-based coordination polymers (CPs), L-Zn and L-Cd, offering H-bonding-based cavities of varying dimensions. Both CPs were used for the highly selective detection of S₂O₇ ^2? and Fe³⁺ ions where H-bonding based cavities played an important role. Fluorescence quenching, competitive binding studies and binding parameters substantiated significant recognition of S₂O₇ ^2? and Fe³⁺ ions by both CPs.

Full text of DOI:10.1002/asia.201901142

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Zn- and Cd-based Coordination Polymers Offering H-Bonding
Cavities: Highly Selective Sensing of S2O72- and Fe3+ Ions
Authors: Rajeev Gupta, Gulshan Kumar, Sanya Pachisia, Pramod
Kumar, and Vijay Kumar
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10.1002/asia.201901142
Chemistry - An Asian Journal
COMMUNICATION
Zn- and Cd-based Coordination Polymers Offering H-Bonding
2-
Cavities: Highly Selective Sensing of S2O7 and Fe3+ Ions
Gulshan Kumar,† Sanya Pachisia,† Pramod Kumar, Vijay Kumar and Rajeev Gupta*
2-
Abstract: We present two Zn(II) and Cd(II) based coordination
polymers (CPs), L-Zn and L-Cd, offering H-bonding based cavities
of varying dimensions. Both CPs were used for the highly selective
detection of S2O72− and Fe3+ ions where H-bonding based cavities
played important role. Fluorescence quenching, competitive binding
studies and binding parameters substantiated significant recognition
of S2O72− and Fe3+ ions by both CPs.
selective detection of S2O7 (pyrosulfate) ion where H-bonding
groups play important roles. In addition, we also show selective
sensing of Fe3+ ion which is accommodated within the pincer
cavity being offered by two CPs. To the best of our knowledge,
this is the first report of utilizing CPs for the selective detection of
S2O72- ion.
H2L
Coordination polymers (CPs) are significant class of porous
crystalline materials with outstanding architectural aspects and
fascinating applications.1 One of the important features that has
made CPs unique is the fact that their architectural aspects can
be fine-tuned by the judicious selection of both connecting
ligands (or linkers) and metal ions or metal clusters.2 Such a
possibility has created manifold opportunities of synthesizing
assorted CPs offering novel structural features and their custom-
made applications. Such applications encompass gas sorption,3
gas storage,4 separation,5 catalysis,6 magnetism,7 drug delivery,8
sensing,9 imaging,10 proton and hydroxide conductivity.11
Out of various CPs, in recent times, luminescent CPs have
shown noteworthy applications in the sensing of small
molecules,12,16 explosives,13,14 metal ions,15 anions,15 dyes,16,17
and even drugs.18 Such remarkable sensing abilities are not only
related to their porous structure but also the fact that their
architecture can be electronically tuned.1,2 Using such strategies,
various luminescent CPs have incorporated electron-rich
aromatic groups that have been found particularly effective for
the sensing of electron-deficient analytes, such as nitro-
aromatics.19,20 A similar strategy has been utilized for the
sensing of metal ions and other cationic species.15 In contrast,
sensing of anionic species is far more challenging as it requires
incorporation of electron-deficient groups within the CPs.21 In
this context, hydrogen bonds (H-bonds) can fill this gap as they
are well-known to interact with anions and other anionic
species.21 However, incorporation of H-bonds within CPs is a
daunting task.22 Not only it is synthetically challenging to
incorporate H-bonds within CPs but equally challenging to orient
them to interact with a targeted guest while preventing other
undesirable interactions.21,22
[{(L)2Zn4(µ3-OH)2(CH3COO)2(H2O)2(DMSO)2}·H2O·DMSO]n
[L-Zn]
[L-Cd]
[{(L)2Cd2(H2O)4(DMSO)}·2DMSO·H2O]n
Scheme 1. Chemical drawings of ligand H2L and its coordination polymers L-
Zn and L-Cd.
CPs L-Zn and L-Cd were synthesized by laying a DMSO
solution of ligand H2L (Figures S1-S5), containing free carboxylic
acid groups, over a solution of M(OAc)2·2H2O salt in water
(Scheme 1). This method produced crystalline CPs: [{(L)2Zn4(µ3-
OH)2(CH3COO)2(H2O)2(DMSO)2}·H2O·DMSO]n
(L-Zn)
and
[{(L)2Cd2(H2O)4(DMSO)}·2DMSO·H2O]n (L-Cd). FTIR spectra of
L-Zn and L-Cd displayed significantly red-shifted bands for the
coordinated carboxylate groups in their anionic form (1560-1585
cm-1) whereas broad features at ca. 3400 cm-1 suggested the
presence of water molecules (Figures S6 and S7).23 TGA
analysis of L-Zn exhibited 6.1% (calcd. 5.8%) weight loss
between 4090 °C for the loss of two hydroxide groups, two
coordinated and one lattice water molecules. Subsequent weight
change between 90210 °C (obs. 23.0%; calcd. 23.3%)
corresponded to the loss of two acetate ions, two coordinated
and one lattice DMSO. L-Cd also displayed weight changes in
two steps: the first one was noted between 3585 °C for the loss
of four ligated and one lattice water molecules (obs. 7.1%; calcd.
6.6%) whereas the second weight change was related to the
loss of one ligated and two lattice DMSO molecules between
85220 °C (obs. 17.7%; calcd. 17.2%) (Figures S8 and S9).
Both CPs were also characterized by the powder XRD
experiments to establish the phase purity of the bulk samples. In
both cases, Le Bail refinements, done by using the lattice
parameter obtained from the single crystal diffraction data,
exhibited good match (Figures S10 and S11).
Single crystal X-ray diffraction studies revealed that L-Zn
crystallized in triclinic cell with P space group (Tables S1 – S6).
The asymmetric unit of L-Zn is consisted of one dianionic ligand
L2-, two Zn(II) ions, one bridging hydroxide group, one acetate
ion, one coordinated DMSO, one coordinated water and a
molecule each of DMSO and water in the lattice (Figure S12).
Every dianionic ligand L2- provides two negative charges through
its two anionic carboxylate groups; one negative charge is
contributed each by an acetate and an hydroxide group. As a
result, an overall 4 charge is balanced by two Zn2+ ions. In L-
Zn, two Zn(II) ions exhibited two different coordination territories
Herein, we present two CPs, L-Zn and L-Cd, offering
hydrogen bonding (H-bonding) based cavities of varying
dimensions. Both CPs illustrate prominent emission in the visible
window after being excited at ca. 300 nm. These CPs exhibited
Dr. G. Kumar, S. Pachisia, Dr. P. Kumar, V. Kumar, Prof. (Dr.) R. Gupta
Department of Chemistry
University of Delhi
Delhi – 110007, India
E-mail: rgupta@chemistry.du.ac.in
Web site: http://people.du.ac.in/~rgupta
Supporting information for this article is available on the WWW under
https://doi.org/10....
†Both authors have contributed equally.
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COMMUNICATION
(Figure S13). Zn1 shows a four-coordinated geometry where two
coordinations come from Ocarboxylate from two different ligands,
one from Oacetate and one from bridging Ohydroxide. Zn2 illustrates a
six-coordinated distorted octahedral geometry where basal
plane is constituted by one Ocarboxylate, two bridging Ohydroxide
groups and one Owater while two axial sites are occupied by an
Oacetate and a DMSO molecule (Figure 1a). Collectively, a
secondary building unit (SBU) is constituted of four Zn(II) ions
that are bridged by two 3-OH groups while additional sites are
occupied by four carboxylate groups originating from four
different ligands and two acetate ions. Further, both octahedral
DMSO, one lattice water and two lattice DMSO molecules
(Figure S14). Two dianinic ligands, L2-, provide four negative
charges via anionic carboxylate groups which is balanced by two
Cd(II) ions. The Cd(II) ions in L-Cd show two types of
coordination spheres (Figure S15). The Cd1 atom exhibits
seven-coordinated geometry where five sites are occupied by
three different ligands via two bidentate and one bridging
carboxylate groups whereas two sites are satisfied by the water
molecules (Figure 1d). The Cd2 atom illustrates six-coordinated
distorted octahedral geometry where three sites come from two
different ligands, one from DMSO and two from water molecules.
In L-Cd, ligands are arranged in criss-cross fashion resulting
into parpendicularly oriented cavities of 27.05  10.54 Å2
dimension (Figures 1e and 1f). Herein, a SBU is constituted of
two Cd(II) ions that are bridged by a carboxylate group emerging
from a ligand and three carboxylate groups present in 1:1
mode with the following composition: [Cd2(-1,3-COO)(-
COO)3(H2O)4(DMSO)] (Figure S15). In this case also, lattice
DMSO molecules were forming H-bonds with the N-H groups of
the amide-based ligands with N…O heteroatom separations
being 2.972 and 3.053 Å; and 2.996 and 2.997 Å for two DMSO
molecules present in alternate cavities. The presence of such
solvent molecules favorably interacting with the N-H groups
being offered by the complex-cavity advocates encouraging
possibilities for the sensing of a suitable analyte (vide infra).21
The topology of L-Cd was examined using TOPOS simplification
approach24 where Cd-based SBUs acted as the three-connected
nodes linked through the amide-based ligands that resulted in
uninodal, three connected and 2(3)2/2-plane minimal net with
{82.10} point symbol (Figure 1g).
Zn(II) ions additionally receive two coordinations from
a
molecule each of DMSO and water. As a result, the composition
of SBU is as follows: [Zn4(-OH)2(-COO)4(CH3COO)2
(H2O)2(DMSO)2] (Figure S13). Two Zn(II)-based SBUs assemble
two amide-based ligands in end-on fashion creating a large
cavity with dimension of 15.91

14.75 Å2 (Figure 1b).
Interestingly, all amidic groups remain intact or protonated and
their N-H hydrogen atoms are directed towards the center of the
cavity. Notably, the lattice DMSO molecules form H-bonds with
the N-H groups being offered by the cavity. In particular, O-atom
of DMSO forms two H-bonds with both the N-H groups with
N…O heteroatom separations of 3.022 and 3.092 Å. Such a
unique structural feature creates opportunities for the recognition
of a suitable analyte (vide infra).21 A combination of Zn-based
SBUs and ligands generate a one dimensional (1D) chain.
Further, various 1D chains are stacked via an array of H-bonds
between Oamide groups and hydrogen atoms of the coordinated
water molecules (Figure 1c).
L-Cd crystallized in monoclinic cell with P21 space group.
The asymmetric unit contains two dianionic ligands (L2-), two
Cd(II) ions, four coordinated water molecules, one coordinated
(a)
(b)
(c)
N2
N3
N1
O6
I
Zn2
Zn1
O5
Zn1
II
O9
Zn2
O12
I = 15.90 Å
II = 14.75 Å
N1-H1…O12 = 3.022 Å
N3-H3A…O12 = 3.092 Å
(g)
(e)
(f)
(d)
N3
N2
O101 N1
Cd2
Cd1
III
N1-H1…O101 = 2.972 Å
N3-H3A…O101 = 3.053 Å
III = 27.41 Å
IV = 10.54 Å
N6
O13
IV
N5
N4
N4-H4A…O13 = 2.996 Å
N6-H6A…O13 = 2.997 Å
Figure 1. (a) Crystal structure of L-Zn, shown in capped stick fashion; lattice DMSO molecules are shown in purple colors for distinction; (b) Spacefil diagram of
L-Zn displaying the cavity structure and its dimentions; (c) 1D chain structure of L-Zn and their stacking through H-bonding interactions. (d) Cystal structure of L-
Cd, shown in capped stick fashion; lattice DMSO molecules are shown in purple colors for distinction; (e) spacefil diagram of L-Cd displaying the cavity structure
and its dimentions; (f) Partial 2D sheet-like structure of L-Cd; (g) Topological representation of L-Cd where yellow and green nodes respectively represent SBUs
and ligands.
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500
400
300
200
100
0
250
200
150
100
50
(b)
(a)
Both CPs, L-Zn and L-Cd, were used for I2 adsorption
studies.6 For a 10 mg evacuated sample of CPs, 2.0 mg (ca.
17%) and 1.5 mg (ca. 13%) weight gain was noted for L-Zn and
L-Cd, respectively, accompanying with color change from white
to organe (Figure S16).6 The I2 adsorption process was
completely reversible as the original white color of CPs was
regained by leaving the organge sample in open atmosphere for
L-Cd and
other anions
L-Zn and
other anions
S2O72-
S2O72-
0
350
400
450
500
550
600
650
400
500
600
700
a
few minutes. Importantly, FTIR spectra in both cases
Wavelength (nm)
Wavelength (nm)
50
40
30
20
10
0
illustrated unchanged nature of stretches suggesting non-
invasive nature of adsorption (Figures S17 and S18).
(d)
(e)
400
300
200
100
0
(f)
-0.004
-0.008
-0.012
L-Zn
L-Cd
L-Zn
L-Cd
The presence of closed-shell d10 metal ions in L-Zn and L-
Cd suggested their potential emission properties. Indeed, both
L-Zn and L-Cd25 exhibited prominent emission at 438 nm and
475 nm respectively upon excitation at ca. 300 nm as CH3OH
suspension. The emission properties of both CPs were further
studied in different solvents (THF, MeCN, CHCl3, H2O, CH3OH,
DMF and DMSO) as their suspensions (Figure S19); however,
CH3OH was found to be the best in terms of intensity. For
comparison, solid samples of L-Zn and L-Cd displayed emission
at 440 nm 454 nm, respectively, after excitation at 300 nm
(Figure S20) while both CPs exhibited absorption maxima at ca.
250 nm in the solid-state (Figure S20).
L-Zn
-0.016
L-Cd
0
50
100
150
200
0
20
40
60
80
100
[S2O72- ] (M)
[S2O72-] (M)
-0.020
0
10000 20000 30000 40000 50000
2-
1/[S2O7
]
Figure 2. Change in emission spectra of (a) L-Zn (25 mg/100 mL) and (b) L-
Cd (25 mg/100 mL) with different anions (200 µM) in CH3OH. (c) Bar diagram
showing change in emission at 438 nm for L-Zn (blue bars) and at 475 nm for
L-Cd (green bars) in presence of different anions (200 µM) in CH3OH. 1 =
SCN−, 2 = SO42−, 3 = HSO4−, 4 = SO32−, 5 = HSO3−, 6 = S2O82−, 7 = S2−, 8 =
S2O32−, 9 = C2O42−, 10 = CH3COO−, 11 = CO3−, 12 = HCO3−, 13 = F−, 14 = Cl−,
15 = Br−, 16 = I−, 17 = IO4−, 18 = NO3−, 19 = NO2−, 20 = P2O72−, 21 = HPO4
−
and 22 = S2O72−. (d) Stern-Volmer plots for the detection of S2O72− ion by L-Zn
and L-Cd. (e) Determination of detection limit of S2O72− ion by L-Zn and L-Cd
(Concentration was linear from 0 - 30 μM). (f) Benesi-Hildebrand plots for the
detection of S2O72− ion by L-Zn and L-Cd.
Subsequently, emission spectra of L-Zn and L-Cd were
2−
studied after the addition of various anions: SCN--, SO42–,SO3
,
2−
−
–
−
Interestingly, addition of S2O7 ion to a suspension of L-
Zn and L-Cd resulted in an immediate generation of a colorless
and transparent solution. Such a fact infers interaction of S2O7
ion with CPs that has plausibly resulted in the dissolution of CPs
(Figure S24). Notably, in presence of other twenty-one anions,
the suspensions of CPs remained stable suggesting that only
pyrosulfate ion acted differently (vide infra).30
HSO4 , HSO3 , S2O82−, S2−, S2O32−, C2O42−, CH3COO−, CO3 ,
−
−
−
−
−
HCO3 , F−, Cl−, Br−, I−, IO4 , NO3 , NO2 P2O72−, and HPO4
2−
(Figure 2). Importantly, presence of these twenty-one assorted
anions did not result in any significant change in the emission
spectra of both CPs. More importantly, introduction of S2O72− ion
resulted in nearly complete emission quenching (Figures 2a-2c).
Such a fact suggests that both CPs were highly selective for the
pyrosulfate ion.
Pyridine-2,6-dicarboxamide fragment based ligands have
been found very successful in accommodating assorted metal
ions.32 Such a fact is due to the presence of a N3-pincer cavity
that effectively holds a metal ion supported with two anionic
Namidate groups.32 The presence of pyridine-2,6-dicarboxamide
fragment based pincer cavities in the present CPs suggested
their potential application in the detection of suitable metal
ions.32 Therefore, both CPs were investigated towards assorted
metal ions: Na+, K+, Mg2+, Ca2+, Cr3+, Mn2+, Mn3+, Fe2+, Co2+, Ni2+,
Cu2+, Zn2+, Cd2+, Hg2+, Ag+ and Pb2+. Addition of these metal
ions to a suspension of CPs in CH3OH resulted in insignificant
change in the emision spectra of both L-Zn and L-Cd; therefore,
ruling out their interaction with CPs. Importantly, addition of Fe3+
ion showed nearly 90% quenching with hypsochromic shift
(Figures 3a-3c).33 Subsequently, binding parameters were
determined by the concentration variation of Fe3+ ion (Figures
S25 and S26).27-31 The Stern-Volmer constants were found to be
1.63  105 M-1 and 1.15  105 M-1 for L-Zn and L-Cd,
respectively (Figure 3d). Detection limits for Fe3+ ion were
calculated to be 0.091 µM and 0.21 µM for L-Zn and L-Cd,
respectively by 3σ/slope method (Figure 3e).27-30 Binding
constants (Kb) were 8.02  104 M−1 and 3.49  104 M−1 for L-Zn
and L-Cd, respectively (Figure 3f). These parameters illustrate
notable detection of Fe3+ ion by two CPs.
We then performed fluorescent spectral titrations for L-Zn
2−
and L-Cd towards S2O7 ion (Figures S21 and S22).26 These
titrations allowed us to calculate Stern–Volmer constants (KSV),
detection limits and binding constant (Kb).27-31 The Stern–Volmer
plots for L-Zn and L-Cd, shown in Figure 2d, resulted in KSV
values of 2.25  105 M−1 and 8.69  104 M−1, respectively. These
2−
numbers assert high selectivity of both CPs toward the S2O7
ion. Both CPs, L-Zn and L-Cd, further illustrated high detection
limits of 0.26 µM and 0.77 µM, respectively (Figure 2e).27-30 Such
detection limits are impressive considering the sensing of
pyrosulfate ion in the solid-state suspension form.30 The binding
constant (Kb) for L-Zn and L-Cd towards S2O72− ion were found
to be 2.18 x 104 M−1 and 6.5 x 103 M−1, respectively (Figure 2f).27-
31
It is clear from these binding parameters that L-Zn shows
better selectivity towards S2O72− ion as compared to L-Cd.
Subsequently, selectivity studies were performed to
understand possible interference from other anions during the
2−
detection of S2O7 ion. For such studies, an equimolar amount
of S2O72− ion and other anions was added to a suspension of L-
Zn and L-Cd in CH3OH. Notably, none of the twenty-one anions
2−
interfered in the detection of S2O7 ion (Figure S23). Therefore,
both CPs L-Zn and L-Cd acted as the highly selective and
effective sensors for the detection of S2O72− ion even in presence
of other assorted anions.
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500
(a)
250
200
150
100
50
(b)
the PXRD pattern and FTIR spectrum of the regenerated CP to
that of pristine one confirms its formation (Figures S34 and S35).
As expected, a cycle of dissolution, induced by S2O7 ion, and
L-Zn and
other metal ion
L-Cd and
other metal ion
400
2−
300
200
precipitation, due to M(OAc)2 salt, can be easily accomplished.30
In case of detection of Fe3+ ion by two CPs, generation of
an identical bright yellow solution suggested the formation of a
similar species, as both CPs contain an identical ligand H2L.
ESI+ mass spectrum of this solution exhbited peaks at m/z
605.1223 and 605.1215 corresponding to [H2L-2H++ Fe3+ + 2
DMF]+ for L-Zn + FeCl3 and L-Cd + FeCl3, respectively (Figures
S36 and S37). These results infer the formation of a discrete
Fe(III) complex of ligand H2L. This prompted us to perform a
stoichiometric reaction of ligand H2L with Et4N[FeCl4] in CH3OH.
This reaction afforded a bright yellow solid and the FTIR
spectrum showed the disappearance of N-H stretches and red-
shifted C=Oamide features (Figure S38). These spectral features
suggest the coordination of Fe(III) ion by anionic Namidate groups
within the N3-pincer cavity of ligand. Based on mass and FTIR
spectra, we propose the following composition of the bright
yellow species: [Fe(H2L2H+)Cl(DMF)2] (Figure 4c). 32,35
Fe3+
Fe3+
100
0
0
400
500
600
400
500
Wavelength (nm)
600
Wavelength (nm)
400
300
200
100
(e)
(d)
(f)
8
6
4
2
0
-0.004
L-Zn
L-Cd
-0.008
-0.012
-0.016
-0.020
L-Zn
L-Cd
L-Zn
L-Cd
0
10
20
[Fe3+
30
40
50
0
5
10
15
20
25
30
[Fe3+] (M)
]
(M)
0
50000
100000 150000 200000
1/[Fe3+
]
Figure 3. Change in emission spectra of (a) L-Zn and (b) L-Cd with different
metal ions (50 µM) in CH3OH (λex = 300 nm). (c) Bar diagram showing change
in emission for L-Zn (red bars; at 438 nm) and for L-Cd (purple bars, at 475
nm) in presence of different metal ions (50 µM) in CH3OH. 1 = Cd2+, 2 = K+, 3
= Ag+, 4 = Ca2+, 5 = Cr3+, 6 = Mn3+, 7 = Fe2+, 8 = Cu2+, 9 = Na+, 10 = Hg2+, 11 =
Mg2+, 12 = Al3+, 13 = Co2+, 14 = Ni2+, 15 = Pb2+, 16 = Zn2+, 17 = Mn2+ and 18 =
Fe3+. (d) Stern-Volmer plots for the detection of Fe3+ ion by L-Zn and L-Cd. (e)
Determination of detection limit of Fe3+ ion by L-Zn and L-Cd (Concentration
was linear from 0 - 30 μM). (f) Benesi-Hildebrand plots for the detection of Fe3+
ion by L-Zn and L-Cd CPs.
Interestingly, after the insertion of Fe(III) ion to the pincer
cavity, Zn(II) and Cd(II) ions are expelled out from their CPs.30
Furthermore, once [Fe(H2L2H+)Cl(DMF)2] is generated in
solution, both CPs, L-Zn and L-Cd, were not regenerated by the
reaction with additional zinc or cadmium salts. Such a fact
suggests the stable nature of [Fe(H2L2H+)Cl(DMF)2] once
formed. In fact, our laboratory has reported several similar
mono-nuclear complexes including their crystal structures,
supporting the present mononuclear Fe(III) complex.37,38 Based
on all available results, a regeneration cycle is presented in
Figure 4a.
The detection of Fe3+ ion was further evaluated by simple
colorimetric method. Both CPs, L-Zn and L-Cd, showed
unchanged suspension in CH3OH in presence of other tested
metal ions. Notably, a bright yellow colored clear solution was
observed in presence of Fe3+ ion (Figure S27). To check
interference from other metal ions during the detection of Fe3+
ion, an equimolar amount of both Fe3+ ion and other metal ions
was used.32,34,35 Gratifyingly, none of the cations interfered in the
detection of Fe3+ ion (Figure S28). Therefore, both CPs, L-Zn
and L-Cd, functioned as the selective sensors for the Fe3+ ion
even in presence of other interfering metal ions.
(a)
(b)
(c)
2-
S2O7
Fe3+
Both L-Zn and L-Cd were able to detect S2O72− and Fe3+
ions by dissolving the respective coordination polymers.30 In
L-Fe
L
L-Zn
or
L
L-Cd
2−
Zn2+ or Cd2+
case of detection of S2O7 ion, a clear transparent solution
Zn2+ or Cd2+
resulted (Figure 4a). ESI+ mass spectrum of such a CH3OH
solution showed signals at m/z 406.1038, 428.0854 and
444.0587 corresponding to [H2L + H+]+, [H2L +Na+]+ and [H2L +
K+]+, respectively (Figure S29). In case of L-Cd, after the
addition of S2O72− ion, a peak at m/z 406.1046 was noted that
correlates to [H2L + H+] (Figure S30). Further, in both cases of L-
Zn and L-Cd, a white product was isolated from the transparent
solution after routine workup. FTIR and proton NMR spectral
characterization of this product confirmed it as the ligand H2L
only (Figures S31 and S32). Finally, colorless needle-shaped
crystals were obtained by the slow evaporation of a solution
generated by adding Na2S2O7 to a CH3OH suspension of L-Zn.
The crystal structure substantiated it as a free ligand H2L (Figure
4b). On the other hand, FTIR spectra of the metal salt isolated
after the addition of Na2S2O7 to a CH3OH suspension of L-Zn
and L-Cd, confirmed them as ZnSO4xH2O and CdSO4xH2O,
Figure 4. (a) Color change of CPs L-Zn or L-Cd in CH3OH in presence of Fe3+
and S2O72− ions and their reversibility in presence of Zn2+ and Cd2+ salts. (b)
Crystal structure of isolated product (H2L) from the reaction of L-Zn with
Na2S2O7 in CH3OH. (c) Proposed chemical structure of [Fe(L2H+)Cl(DMF)2].
At this stage, it became essential to understand how
pyrosulfate ion has interacted with both the CPs. For such a
purpose, FTIR and emission spectra of solid samples of L-Zn
and L-Cd were measured after the incremental addition (1–5
equiv.) of solid Na2S2O7. For these studies, vacuum-dried
samples of L-Zn and L-Cd were used to insure that most of the
adventitious water/moisture is removed. In the FTIR spectra,
notable changes were observed for the N-H stretches for both
the CPs. For example, in case of L-Zn, broad stretches were
noted at ca. 3280 and 3110 cm-1. Not only have such stretches
become much broader after the addition of one equiv. of
Na2S2O7 but shifted to lower energy (ca. 3250 cm-1).39 Such a
fact clearly establishes the interaction of S2O72− ion with the N-H
groups of L-Zn. With further incremental addition of Na2S2O7, N-
H stretches nearly disappeared (Figure S39). In contrast, broad
N-H stretches, centered at ca. 3285 cm-1 for L-Cd, shifted to ca.
2900 cm-1 with a large shift of ca. 385 cm-1, asserting their
2−
respectively (Figure S33). It is suggested that the S2O7 ion
2-
decomposes to SO4 ion after abstracting proton from the CPs,
followed by its hydrolysis.36
Importantly, addition of Zn(OAc)2 or Cd(OAc)2 to a clear
and transparent solution, generated after the dissolution of CPs
2−
by S2O7 ion, again produced the corresponding CPs (Figure
2−
interaction with the S2O7 ion.39 However, in this case, N-H
4a). Taking L-Zn as a representative example, regenerated L-
Zn was isolated and characterized. Notably, a close similarity in
stretches do not disappear but are only shifted (Figure S40).
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2−
These experiments support that the S2O7 ion has interacted
with N-H groups of both the CPs. It is important to mention that
the remaining part of the FTIR spectra of CPs remained largely
Fe3+ ion was noted to coordinate within the N3-pincer cavity
offered by CPs and in the process CPs were collapsed. These
results are noteworthy and not only illustrate that H-bonding
groups can be judiciously incorporated within the polymeric CPs
but can also participate in the recognition events.
2−
unchanged, suggesting that S2O7 ion has not interfered with
other functional groups of both CPs.
In order to further substantiate, we prepared a deuterated
analogue of L-Zn by potentially replacing amidic N-H groups
with N-D. Such a sample was prepared by sealing an evacuated
solid sample of L-Zn in a sealed environment containing D2O for
24 h. Such an exercise provided sample with partial N-D groups
that were observed at ca. 2545, 2465, 2410, 2370 cm-1. When
such a solid sample, having N-D groups, was treated with
Na2S2O7; N-D stretches were found to shift to lower energies
followed with their diminished intensity (Figure S41). This
Acknowledgements
RG acknowledges financial support from the Science and
Engineering Research Board (SERB), New Delhi, India [Grant
No: EMR/2016/000888]. SP and VK thank UGC, New Delhi,
India, for their fellowships. PK thanks CSIR, New Delhi, India, for
the SRA “Scientists’ Pool Scheme” (IA-27577). Authors thank
CIF-USIC at the University of Delhi for the instrumental facilities
including crystallographic data collection.
2−
experiment confirms that S2O7 ion has indeed interacted with
the N-H groups of a CP.
For both CPs, solid samples after treating with Na2S2O7
were further investigated with the fluorescence spectral
measurements. As anticipated, addition of one equiv. of
Na2S2O7 caused substantial quenching of the emission intensity
of both L-Zn and L-Cd (Figure S42). Such a fact further confirms
Keywords: Coordination polymers • H-bonds • Fluorescence •
Sensor • Pyrosulfate • Iron
[1] G. Kumar, R. Gupta, Chem. Soc. Rev. 2013, 42, 9403–9453.
[2] S.R. Batten, S.M. Neville, D.R. Turner, Coordination Polymers: Design,
Analysis and Application. The Royal Society of Chemistry, 2009, pp.1-190.
[3] J.B. Lin, J.P. Zhang, X.M. Chen, J. Am. Chem. Soc. 2010, 132, 6654-6656.
[4] K. V. Kumar, K. Preuss, M. M. Titirici, F. R. Rodriguez, Chem. Rev. 2017,
117, 1796–1825.
[5] J. R. Li, R. J. Kuppler, H. C. Zhou, Chem. Soc. Rev. 2009, 38, 1477–1504.
[6] a) G. Kumar, F. Hussain, R. Gupta, Dalton Trans. 2017, 46, 15023 –
15031; b) G. Kumar, F. Hussain, R. Gupta, Dalton Trans. 2018, 47, 16985 –
16994.
[7] X. N. Cheng, W. X. Zhang, Y. Y. Lin, Y. Z. Zheng, X. M. Chen, Adv. Mater.
2007, 19, 1494–1498.
[8] M. X. Wu, Y. W. Yang, Adv. Mater. 2017, 29, 1606134–1606154.
[9] a) W.P. Lustig, S. Mukherjee, N.D. Rudd, A.V. Desai, J. Li , S. K. Ghosh,
Chem. Soc. Rev. 2017, 46, 3242—3285; b) Q. Q. Xiao, D. Liu, Y.L. Wei, G. H.
Cui, Polyhedron 2019, 158, 342-351.
2−
that S2O7 ion has interacted with CPs. Collectively, both FTIR
and emission spectral studies infer that both CPs were efficiently
able to recognize S2O72− ion in the solid state. We, therefore,
propose that S2O72− ion first interacts with the N-H groups of CPs
via H-bonds followed by their polarization and subsequent
deprotonation. The deprotonation of N-H groups led to the
decomposition of CPs as observed by their dissolution in CH3OH.
Similar solid-state FTIR and emission spectral studies
were performed for L-Zn after treating with solid Et4N[FeCl4].
FTIR spectral experiment exhibited complete disappearance of
the N-H stretches, originally present at 3280 and 3110 cm-1,
suggesting potential insertion of Fe(III) ion within the N3-pincer
cavity (Figure S43).40 Along the same direction, florescence
spectra also illustrated emission quenching of both the CPs
(Figure S44), as was also noted with S2O72− ion.
[10] F. S. Gallis, L. E. S. Rohwer, M. A. Rodriguez, M. C. Barnhart-Dailey, K. S.
Butler, T. S. Luk, J. A. Timlin, K. W. Chapman, ACS Appl. Mater. Interfaces.
2017, 9, 22268–22277.
[11] L. Liu, Z. Yao, Y. Ye, Q. Lin, S. Chen, Z. Zhang, S. Xiang, Cryst. Growth
Des. 2018, 18, 3724–3728.
[12] Y. Cui, J. Zhang, H. He, G. Qian, Chem. Soc. Rev. 2018, 47, 5740–5785.
[13]a) L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. V. Duyne, J. T.
Hupp, Chem. Rev. 2012, 112, 1105–1125; b) C. Zhang, Y. Yan, Q. Pan, L.
Sun, H. He, Y. Liu, Z. Liang, J. Li, Dalton Trans., 2015,44, 13340-13346; c) C.
Yu, X. Sun, L. Zou, G. Li, L. Zhang, Y. Liu, Inorg. Chem. 2019, 58,
4026−4032; d) W. H. Huang, J. Ren, Y.H. Yang, X.M. Li, Q. Wang, N. Jiang, J.
Q. Yu, F. Wang, J. Zhang, Inorg. Chem. 2019, 58, 48 − 49 .
[14] a) B. Gole, S. Shanmugaraju, A. K. Bar, P. S. Mukherjee. Chem. Commun.
2011,47, 10046-10048 ; b) X. Zhao, S. Wang, L. Zhang, S. Liu, G. Yuan, Inorg.
Chem. 2019, 58, 2444−2453; c) Z.Q. Shi, Z. J. Guoa, H. Zheng, Chem.
Commun., 2015, 51, 8300-8303.
[15] a) C. Chen, X. Zhang, P. Gao, M. Hu, J. Solid State Chem. 2018, 258,86-
92; b) X.J. Wei, D. Liu, Y.H. Li, G.H. Cui, Polyhedron. 2019, 158, 357-364; c)
X.J. Wei, D. Liu, Y. H. Li, G. H. Cui, J. Solid State Chem., 2019, 272, 138-147.
[16] Li−Li Lv, Jin Yang, Hong-Mei Zhang, Ying-Ying Liu, and Jian-Fang Ma,
Inorg. Chem. 2015, 54, 744− 755.
As pyrosulfate ion is expected to change pH of the medium,
pH-dependent investigations were performed for both CPs. For
these studies, CPs were suspended in buffer solutions of
varying pH (4, 5, 6, 9 and 10) for 24 h. Subsequently, CPs were
isolated by filtration, washed with water and vacuum dried
before analysing by FTIR spectral and PXRD studies. For both
CPs, negligible changes in their FTIR spectra (Figures S45 and
S46) and PXRD patterns (using L-Cd as a representative case;
Figure S47) asserted their structural stability under different pHs.
Finally, as all studies were done in CH3OH, it became essential
to ascertain the chemical stability and crystallinity of CPs as the
sensing material in CH3OH. For such a purpose, L-Cd was
soaked in CH3OH for 48 h, subsequently isolated and analyzed
with PXRD studies. The PXRD pattern of CH3OH-soaked L-CD
was in excellent agreement to that of pristine sample
establishing its chemical robustness (Figure S48).
[17] a) T. Wen, D.X. Zhang, J. Zhang, Inorg. Chem. 2013, 52, 2− 4; b) X.J.
Wei, Y. H. Li, Z.-B. Qin, G. H. Cui, J. Mol. Struct. 2019, 1175, 253-260.
[18] Y. Yan, J. Zhang, L. Rend, C. Tang, Chem. Soc. Rev. 2016, 45, 5232-
5263.
[19] M. Arici, New J. Chem. 2019, 43, 3690–3697.
[20] S. Srivastava, R. Gupta, Cryst. Growth Des. 2017, 17, 3907−39 6.
[21] S. O. Kang, R. A. Begum, K. B. James, Angew. Chem. Int. Ed. 2006, 45,
7882–7894.
[22] S. Kitagawa, K. Uemura, Chem. Soc. Rev. 2005, 34, 109–119.
[23] a) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds: Part A: Theory and Applications in Inorganic
Chemistry, Sixth Edition. 2008. b) Nakamoto, K. Infrared and Raman Spectra
of Inorganic and Coordination Compounds: Part B: Theory and Applications in
Inorganic Chemistry, Sixth Edition. 2008.
[24] V. A. Blatov, A. P. Shevchenko, D. M. Proserpio, Cryst. Growth Des. 2014,
14, 3576–3586.
[25] In the emission spectrum of L-Cd, signal at ca. 350 nm is tentatively
assigned to charge transfer, commonly observed in metal-organic frameworks,
In conclusion, coordination polymers L-Zn and L-Cd,
offering H-bonding cavities, were synthesized and structurally
characterized. Both CPs offered large cavities that provide H-
bonding functional groups. Both CPs were used for the detection
of an anion, S2O72−, as well as a cation, Fe3+, by fluorescence
and colorimetric methods. H-bonding containing groups were
2−
found to interact with the S2O7 ion, followed by their
deprotonation that led to the decomposition of CPs. In contrast,
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and arise from ligands having π-conjugated backbones; see a) M. D. Allendorf,
C. A. Bauer, R. K. Bhaktaa, R. J. T. Houk, Chem. Soc. Rev., 2009, 38, 1330–
1352; b) Q. Fang, G. Zhu, X. Shi, G. Wu, G. Tian, R. Wang, S. Qiu, J. Solid
State Chem., 2004, 177, 1060–1066; c) J.C. Dai, X. T. Wu, Z.Y. Fu, C.P. Cui,
S.M. Hu, W. X. Du, L.M. Wu, H.H. Zhang, R. Q. Sun, Inorg. Chem., 2002, 41,
1391-1396; d) J. C. Dai, S. M. Hu, X. T. Wu, Z. Y. Fu, W. X. Du, H. H. Zhang,
R. Q. Sun, New J. Chem., 2003, 27, 914–918; e) C. Gogoi, S. Biswas, Dalton
Trans., 2018, 47, 14696-14705; f) C. Gogoi, M. Yousufuddin, S. Biswas,
Dalton Trans., 2019, 48, 1766-1773.
[29] P. Kumar, V. Kumar, R. Gupta, RSC Adv. 2017, 7, 7734–7741.
[30] S. Pandey, P. Kumar, R. Gupta, Dalton Trans. 2018, 47, 14686–14695.
[31] H. A. Benesi, J. A. Hildebrand, J. Am. Chem. Soc. 1949, 71, 2703–2707.
[32] P. Kumar, R. Gupta, Dalton Trans. 2016, 45, 18769 –18783.
[33] The hypsochromic shift for Fe3+ ion can be explained by photo-induced
charge transfer (PCT) where Fe3+ ion binds within the pincer cavity of CPs by
deprotonating the amidic N–H groups that reduce the conjugation within the
ligand; see, B. Valeur and I. Leray, Coord. Chem. Rev., 2000, 205, 3-40.
[34] V. Kumar, P. Kumar, R. Gupta, RSC Adv. 2017, 7, 23127–23135.
[35] P. Kumar, V. Kumar, S. Pandey, R. Gupta, Dalton trans. 2018, 47, 9536–
9545.
[26] The hypsochromic shift with S2O72- ion can be explained on the basis of
intramolecular charge transfer (ICT), due to the reduction in the extent of
charge transfer of receptor molecule (–N-H groups) in the presence of a
negatively charged guest (S2O72- ion); see, A. Kovalchuk, J. L. Bricks, G. Reck,
K. Rurack, B. Schulz, A. Szumnac , H. Weißhoff, Chem. Commun. 2004, 47,
1946-1947.
[36] H. K. Hofmeister, J. R. V. Wazer, Inorg. Chem. 1962, 1, 811 – 812.
[37] D. Bansal, R. Gupta, Dalton Trans. 2016, 45, 502–507.
[38] D. Bansal, G. Kumar, G. Hundal, R. Gupta, Dalton Trans. 2014, 43,
14865–14875.
[27] a) P. Kumar, V. Kumar, R. Gupta, RSC Adv. 2015, 5, 97874–97882; b) S.
Kumar, R. Kishan, P. Kumar, S. Pachisia, R. Gupta, Inorg. Chem. 2018,
57, 1693–1697.
[39] M. Sarkar, K. Biradha, Cryst, Growth & Des., 2007, 7, 1318–1331.
[40] a) D. Zhao, Y. Cui, Y. Yang, G. Qian, CrystEngComm, 2016, 18, 3746–
3759; b) H. Tan, B. Liu, Y. Chen, ACS Nano. 2012, 6, 10505-10511.
[28] P. Kumar, V. Kumar, R. Gupta, Dalton Trans. 2017, 46, 10205–10209.
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Entry for the Table of Contents
COMMUNICATION
Luminescent Coordination Polymers
Gulshan Kumar, Sanya Pachisia,
Pramod Kumar, Vijay Kumar and
Rajeev Gupta*
2
S2O7
2-
S2O7
400
500
600
Wavelength (nm)
Page No. – Page No.
Zn- and Cd-based Coordination
Polymers Offering H-Bonding
Cavities: Highly Selective Sensing
of S2O72- and Fe3+ Ions
Fe3+
Fe3+
400
500
600
Wavelength (nm)
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