Influence of Triazole Substituents of Bis-Heteroleptic Ru(II) Probes toward Selective Sensing of Dihydrogen Phosphate

Article abstract of DOI:10.1021/acs.inorgchem.1c01084

A series of seven new bis-heteroleptic Ru(II) probes (1[PF6]2-7[PF6]2) along with two previously reported probes (8[PF6]2 and 9[PF6]2) containing a similar anion binding triazole unit (hydrogen bond donor) functionalized with various substituents are empl

Full text of DOI:10.1021/acs.inorgchem.1c01084

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Influence of Triazole Substituents of Bis-Heteroleptic Ru(II) Probes
toward Selective Sensing of Dihydrogen Phosphate
Sahidul Mondal, Koushik Sarkar, and Pradyut Ghosh*
Cite This: Inorg. Chem. 2021, 60, 9084−9096
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ABSTRACT: A series of seven new bis-heteroleptic Ru(II) probes (1[PF6]2−7[PF6]2) along with two previously reported probes
(8[PF6]2 and 9[PF6]2) containing a similar anion binding triazole unit (hydrogen bond donor) functionalized with various
−
substituents are employed in a detailed comparative investigation for the development of superior selective probes for H2PO4 .
Various solution- and solid-state studies, such as 1H-DOSY NMR, dynamic light scattering (DLS), single-crystal X-ray
crystallography, and transmission electron microscopy (TEM), have established that the selective sensing of H2PO4− by this series of
3
probes is primarily due to supramolecular aggregation driven enhancement of MLCT emission. Intestingly, 1[PF ]2 and 7[PF ]2,
6
6
−
having an electron-deficient (π-acidic) aromatic pentafluorophenyl substituent are found to be superior probes for H2PO4 in
comparison to the other aryl- and polyaromatic-substituted analogues (2[PF6]2−6[PF6]2, 8[PF6]2, and 9[PF6]2), in terms of a
higher enhancement of the MLCT emission band, a greater binding constant, and a lower detection limit. The superiority of
3
1[PF6]2 and 7[PF6]2 could be due to better supramolecular aggregation properties in the cases of pentafluorophenyl analogues via
both hydrogen bonding and anion−fluorine/anion−π noncovalent interactions.
bonding-based bis-heteroleptic Ru(II) complex with an
iodotriazole-based phosphate sensor that showed metal-
assisted second-sphere phosphate binding through solitary
XB interactions.47 Furthermore, our group has explored
Ru(II)-polypyridyl-based receptors decorated with various
pendant urea moieties for the binding and extraction of
phosphates/carboxylates.24,48,49 In all of the above probes, a
wide range of other basic anions do not show any
photophysical aspect of sensing behavior. Thus, in this class
of probes, the basicity of anions might not govern the anion-
sensing selectivity. Our recent investigation has demonstrated
that the rigidification of probes via the formation of self-
assembly might be responsible for the selective sensing of
phosphates.50 In addition to hydrogen-bonding interactions,
INTRODUCTION
■
Phosphates play vital roles in numerous essential biological as
well as environmental processes.1−14 Thus, the development of
superior selective synthetic probes for phosphates are in
demand in anion recognition chemistry.5,13,15−21 During the
past few years, several different heterocyclic ring systems
containing neutral/cationic N−H/C−H (e.g., urea,22−26
triazole,21,24,27−31 imidazole,32−36 amide,37−40 pyrrole,41−45
etc.) moieties containing receptors have been reported for
the selective recognition and sensing of phosphates. We have
been systematically exploring the ruthenium complexes of
pyridine triazole/iodotriazole and phenanthroline toward the
development of a new class of metal complex based selective
probes and extractants for phosphates.24,27,46−50 In this regard,
initially we developed a bis-heteroleptic Ru(II) probe
containing methyl-substituted pyridyl triazole for selective
−
3−
Received: April 8, 2021
Published: June 9, 2021
sensing of H2PO4 over HP2O7
and other common
inorganic anions through a solitary C−H···anion interaction.27
Then we introduced a bis-heteroleptic trinuclear Ru(II) probe
on a cyanuric acid platform for sensing of higher homologue
phosphates (pyrophosphate, ADP, and ATP) over dihydrogen
phosphate.46 Subsequently, we established a superior halogen-
https://doi.org/10.1021/acs.inorgchem.1c01084
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Scheme 1. Synthetic Scheme of Complexes
other weak interactions such as π−π stacking, anion−π
interactions, etc. also commonly function as noncovalent
interactions for the formation of self-assembled structures.
Thus, at this juncture, we were curious to systematically
develop superior phosphate probes by exploring different
substituents on the triazole backbone of bis-heteroleptic
Ru(II) complex probes. Thus, herein we report a series of
heteroleptic ruthenium probes, (1[PF6]2−9[PF6]2) containing
a pyridyl triazole hydrogen bond donor and different pendant
(pentafluorophenyl, aryl, polyaromatic) units for a detailed
comparative investigation toward the development of superior
and selective Ru(II) complex based H2PO4− probes. Moreover,
we have generalized the different degrees of enhancement-
based selective sensing of phosphate by this series of probes via
the selective formation of phosphate-supported extensive self-
assembled structures in the solid and solution states.
of electron-donating, electron-withdrawing, polyaromatic, and
electron-deficient (π-acidic unit) groups on the triazole moiety
in designing the new probes. Herein we have designed the
series of seven bis-heteroleptic ruthenium(II) probes 1[PF6]2−
7[PF6]2 (Scheme 1), along with the two known complexes
8[PF6]2 and 9[PF6]2 for a detailed comparative investigation
−
toward selective H2PO4 sensing efficiency. Probes 1[PF6]2
and 7[PF6]2 contain the same pendant pentafluorophenyl (π-
acidic)-substituted triazole; however, they differ in the central
core moiety (phenanthroline versus bipyridine). The bis-
heteroleptic Ru(II) probes 1[PF6]2−6[PF6]2) are prepared in
good yields (65−70%) by refluxing of Ru(phen)2Cl2 and
ligands L1−L6 overnight in a binary ethanol/water (2/1)
solvent system followed by PF6− exchange. The probe 7[PF6]2
is synthesized by reacting L1 and Ru(bpy)2Cl2 in a 4/3
ethanol/water mixture and by anion exchange with good yield
(68%) (Scheme 1).
The synthetic procedures of ligands L1−L6 and probes
1[PF6]2−7[PF6]2 are detailed in the Supporting Information
and the Experimental Section. All of the ligands and complexes
have been fully characterized by NMR and mass studies
(Figure S1−S57 in the Supporting Information). The observed
m/z peaks in ESI-MS (+ve) studies are well-matched with the
calculated m/z values for +/2+ charged species of all the
complexes. Further, their experimental isotopic distribution
patterns and the simulated patterns matched well. Single-
crystal X-ray diffraction studies established the structures of all
newly synthesized complexes except for 2[PF6]2, which are
discussed later.
RESULTS AND DISCUSSION
■
Designing Strategy and Synthesis of Probes. We have
previously shown that bis heteroleptic Ru(II) complexes of
triazole ligands (8[PF6]2 and 9[PF6]2; Scheme 1) are efficient
receptors for selective phosphate sensing via the triazole C−
H···anion interaction.27,46,48 Electronic parameters of the
neighboring substituent on the triazole moiety as well as the
assembly properties of the substituents might alter the overall
acidity of the triazole C−H and self-assembly properties via
nonbonding interactions, which might eventually affect the
phosphate recognition efficiency of the probes. To account for
such effects in the sensing of bis-heteroleptic Ru(II)
complexes, we have introduced various substituents comprised
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Table 1. Comparative Photophysical Data of Complexes 1[PF6]2−7[PF6]2
sensing properties
emission
emission intensity enhancement
factor
a
host
anion
none
H2PO4
none
H2PO4
none
absorbance λmax (nm) (ε (M−1 cm−1
400 (13005), 440 (10285)
407 (10775), 449 (9435)
402 (13960), 440 (11445)
402 (11075), 453 (9995)
)
λmax (nm)
Ka (M−1
)
1[PF6]2
589
589
587
591
416
438
590
416
438
590
608
377
2.64 × 106
7.91 × 105
−
−
22
9
2[PF6]2
3[PF6]2
351 (17670), 370 (26595), 391 (34515), 443 (21985)
2.63 × 105
−
H2PO4
none
351 (19990), 370 (23685), 393 (27790), 459 (21085)
8
4[PF6]2
313 (17835), 327 (26985), 343 (35090), 405 (15080),
443 (12325)
395
417
586
377
2.14 × 105
−
H2PO4
313 (15155),327 (24080), 343 (32710), 405 (12920),
443 (10320)
10
395
417
636
587
591
589
589
597
597
590
590
585
590
5[PF6]2
6[PF6]2
7[PF6]2
8[PF6]2
9[PF6]2
none
H2PO4
none
H2PO4
none
H2PO4
none
H2PO4
none
H2PO4
404 (13355), 443 (10925)
415 (13255), 459 (12805)
403 (12915), 443 (10880)
415 (14180), 457 (13340)
412 (8695), 440 (8960)
414 (9560), 456 (9900)
403 (10850), 445 (8637)
8
5
1.83 × 105
4.35 × 104
9.26 × 105
5.28 × 104
5.56 × 104
−
−
−
−
−
19
6
27
47
405 (11750), 445 (9250)
406 (9179), 459 (7873)
6
a
Although the 1:1 (H:G) stoichiometry has been adopted to calculate the binding constants here, consideration of both nucleation and aggregation
processes should be exercised toward calculating the actual binding constants.
Comparative Phosphate Sensing Properties by
Heteroleptic Ru(II) Polypyridyl Complexes in Solution.
The probes 1[PF6]2−6[PF6]2 having the same chromophoric
unit show photophysical characteristics in acetonitrile at 298 K
similar to those previously observed in 8[PF6]2 and 9[PF6]2.
The UV/vis spectral data of 1[PF6]2−6[PF6]2 are very similar,
having intense broad absorption bands centered in the regions
of λmax 400−405 nm for Ru(dπ) → phenanthroline and 440−
445 nm for Ru(dπ) → pyridine-triazole MLCT charge-transfer
transitions (Figure S58 in the Supporting Information). In the
case of 7[PF6]2, the UV absorption bands are centered at λmax
412 nm (Ru(dπ) → bipyridine) and 440 nm (Ru(dπ) →
pyridine-triazole). In addition, characteristic absorption bands
are observed in probes 3[PF6]2 and 4[PF6]2 at λmax 351, 370,
and 391 nm for anthracene and λmax 313, 327, and 343 nm for
pyrene due to π−π* transitions. Upon excitation at either of
the λmax values of the chromogenic bands, 400 or 445 nm
shows a 3MLCT broad luminescence band. On the other hand,
upon excitation at λmax 391 and 343 nm for probes 3[PF6]2
and 4[PF6]2, luminescence bands are observed at 416, 438,
and 590 nm (for 3[PF6]2) and 377, 395, 417, and 470 nm (for
4[PF6]2) (Figure S58e,g in the Supporting Information). The
absorption and emission spectral data of all the probes in
acetonitrile are given in Table 1.
All of the probes only show perturbation in the absorption
3−
−
and emission bands with HP2O7 and H2PO4 without any
−
−
−
−
observable change for HSO4 , NO3 , CH3CO2 , HCO3 ,
C6H5CO2 , I−, Br−, Cl−, and F− anions in acetonitrile at 298 K
−
(Figure 1 and Figure S59 in the Supporting Information). The
PL titration of receptors with TBAH2PO4 was carried out to
determine the phosphate-binding stoichiometry with the
receptors in acetonitrile at 298 K. The gradual addition of
−
H2PO4 to the probes 1[PF6]2−6[PF6]2 causes significant
perturbations in the emission signal by increasing the intensity
of the emission band at λ 585−597 nm. In probes 3[PF6]2 and
4[PF6]2, emission bands that are red-shifted by 15 and 50 nm,
respectively, are observed. When the acidity of the triazole C−
H is changed by varying the neighboring substituents p-
NO2C6H4, CH3, C6H5, p-OMeC6H4, naphthyl, anthryl, and
pyrenyl in probes 52+, 82+, 92+, 62+, 22+, 32+, and 42+ as their
hexafluorophosphate salts, respectively, the emission intensity
is increased in the range of 5−10-fold only in the presence of
H2PO4 . In cases of probes 22+, 32+, and 42+ as their PF6− salts
−
having different polyaromatic substituents, the enhancement of
3MLCT emission is found to be increased with the increase of
aromatic rings. Interestingly, in the case of 1[PF6]2 having a
pentafluorophenyl substituent, as high as a ∼22-fold increase in
the emission intensity is observed, which differentiates this
probe from the rest of the probes 2[PF6]2−6[PF6]2, 8[PF6]2,
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Figure 1. (a) Changes in the PL spectrum of 1[PF6]2 upon addition of various anions (10 equiv). (b) UV titration of receptors 1[PF6]2 with
−
−
H2PO4 . (c) PL titration of receptors 1[PF6]2 with H2PO4 (Inset (d): anion equivalent plot). (e) Nonlinear fitting of PL titration data for
−
1[PF6]2 with H2PO4 .
and 9[PF6]2 with various substituent groups. Thus, a
pentafluorophenyl ring as the neighboring group substituent
makes the maximum impact toward the phosphate-induced
enhancement of emission intensity. To revalidate the influence
of the pentafluorophenyl moiety, we have designed another
complex, 7[PF6]2, having bipyridine moiety in the central core
unit instead of phenanthroline in 1[PF6]2. Interestingly,
0.018 μM, respectively, among all of the probes studied (Table
S1 in the Supporting Information). All of these results confirm
the superiority of the pentafluorophenyl-substituted triazole
toward the selective sensing of H2PO4 through the highest
fluorescence enhancement, association constants, and sensi-
−
tivity.
−
The 1H NMR experiment of all the receptors with H2PO4 ,
3
in DMSO-d6 at 298 K, shows a sharp singlet peak in the
downfield region, which is recognized as a triazole proton peak.
On the gradual addition of different anions, the acidic triazole
proton of probes 1[PF6]2−6[PF6]2 displays a steady downfield
shift only with 1 equiv of H2PO4− (Figures S63 and S64 in the
7[PF6]2 also shows as high as ∼19-fold growth in MLCT
emission spectra with phosphate. The emission intensity
amplification in all the complexes (1[PF6]2−7[PF6]2) with
phosphates can be justified due to the probe backbone
rigidification assisted by supramolecular self-assembly and
hydrogen-bonding interactions, which are discussed below.
−
Supporting Information). However, competitive HSO4 ,
−
AcO−, F−, Br−, Cl−, NO3 , etc. anions do not display such
−
The binding constants of all the probes with H2PO4 were
visible 1H NMR spectral changes with all of the probes. When
higher amounts (2 equiv or more) of basic anions such as F−
and AcO− are added, slight downfield shifts are noted for the
triazole proton, signifying the requirement of a high analyte
concentration of F− and AcO− for the interaction with a
triazole proton. It is worth mentioning here that the protons of
naphthalene, anthracene, and pyrene units do not show
observable shifts upon complexation with anions (Figure
S64b−d in the Supporting Information). This demonstrates
that the interactions in all of the probes purely occur only
between the triazole proton and phosphate through a
hydrogen-bonding interaction. A Job plot analysis from the
1H NMR experiment of 1[PF6]2 with H2PO4− also shows a 1:1
(H:G) stoichiometric binding complex (Figure S65 in the
Supporting Information).
calculated to demonstrate the binding abilities and the
selectivity of receptors toward the anion. The 1:1 (H:G)
stoichiometric ratios of binding of receptors and phosphates
were confirmed by the Job plot method using PL spectroscopy
(Figure S60 in the Supporting Information). The association
−
constants of 1[PF6]2−7[PF6]2 with H2PO4 were calculated
by a nonlinear fitting of the titration data in the 1:1 binding
model, which show variation in the association constants
ranging from 104 to 106 M−1 (Table 1 and Figure S61 in the
Supporting Information). It is important to note that 1[PF6]2
having a pentafluorophenyl substituent shows the highest
association constant of 2.64 × 106 M−1 among all the probes,
followed by 7[PF6]2 with a value of 9.26 × 105 M−1.
During titration, changes in emission intensity of all the
−
probes with H2PO4 show a linear relationship with the
−
The 31P NMR spectra in DMSO-d6 confirm H2PO4
−
H2PO4 concentration, which resulted in detection limits in
the range of ∼0.013−0.067 μM for probes 1[PF6]2−7[PF6]2,
as calculated by specific quantitative analysis (Table S1 and
Figure S62 in the Supporting Information). Notably, 1[PF6]2
and 7[PF6] also show the lowest detection limit of 0.013 and
binding with the probes, where PPh3 is used as an external
standard. When 1 equiv of 1[PF6]2 and 7[PF6]2 was added to
free phosphate, the 31P resonance at 2.98 ppm shifted upfield
to 1.50 and 2.21 ppm, respectively, which may be due to an
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Table 2. Comparative Data of Diffusion Coefficients D (m2 s−1) Obtained from NMR and Dynamic Light Scattering Recorded
−
for All Complexes (1[PF6]2−7[PF6]2) and with H2PO4 in DMSO-d6 at 298 K
entry
host
1H-DOSY NMR
diffusion coefficient D (m2/S) calcd radius (nm)
dynamic light scattering (DLS)
a
guest
sphere volume ratio (B/A) size d (nm) sphere volume ratio (B/A)
1[PF6]2
(A) none
(B) H2PO4
(A) none
(B) H2PO4
(A) none
(B) H2PO4
(A) none
(B) H2PO4
(A) none
(B) H2PO4
(A) none
(B) H2PO4
(A) none
(B) H2PO4
7.188 × 10−10
1.659 × 10−10
7.365 × 10−10
3.087 × 10−10
3.601 × 10−10
1.684 × 10−10
8.230 × 10−10
3.269 × 10−10
7.953 × 10−10
2.925 × 10−10
8.076 × 10−10
3.585 × 10−10
1.136 × 10−9
2.179 × 10−10
0.1546
0.6700
0.1509
0.3600
0.3087
0.6600
0.1350
0.3400
0.1398
0.3800
0.1376
0.3100
0.0978
0.5100
82.5
14.3
10.2
16.7
20.6
11.8
138.7
143
647
152
383
163
361
196
518
130
374
135
326
141
739
92.8
15.9
10.8
18.4
23.8
14
−
−
−
−
−
−
−
2[PF6]2
3[PF6]2
4[PF6]2
5[PF6]2
6[PF6]2
7[PF6]2
143
a
Using the Stokes−Einstein equation.
Figure 2. Comparative DLS study of (a) 1[PF6]2 and (b) 7[PF6]2 in the absence and presence of phosphates.
anion−π interaction of the pentafluorophenyl group and
phosphate anions (Figure S66 in the Supporting Information).
However, with the addition of receptors 2[PF6]2 and 3[PF6]2
to TBAH2PO4, the 31P peak shifted weakly to the downfield
region. The shifts (downfield or upfield) of the 31P peaks
indicate an interaction of the phosphate oxygen atoms and
probes, as previously reported in the literature.24
7[PF6]2 probes and makes them efficient sensors in
comparison to the others.
Solution-State Aggregation as Well as Macroscopic
Morphological Analysis. To establish the aggregation-
1
induced sensing property of this generation of probes, H-
DOSY NMR experiments of all of the complexes with
−
phosphates (e.g., H2PO4 ) were performed to understand
To understand the superiority of the probes 1[PF6]2 and
the adducts formed between the probes and phosphate in
DMSO-d6 at 298 K (Figure S68 in the Supporting
Information). It has been found that the diffusion coefficients
of all the free probes are reduced considerably in the presence
of 1 equiv of H2PO4− (Table 2). The maximum decrease in the
diffusion coefficient value is observed for phosphate adducts of
the probes 1[PF6]2 and 7[PF6]2. The diffusion coefficient
value decreased from 7.188 × 10−10 to 1.659 × 10−10 m2/S and
from 1.136 × 10−9 to 2.179 × 10−10 m2/S for the phosphate
adducts of 1[PF6]2 and 7[PF6]2, respectively, which may be
due to the formation of larger aggregated species in solution in
comparison to the other probes. Thus, it is clearly evident that
phosphate adduct complexes in solution are considerably
greater in size, dissimilar from free anion complexes. Zapata et
al. has recently reported such supramolecular polymeric
aggregates in solution where the role of cooperative action of
noncommon antielectrostatic anion−anion and halogen-
bonding interactions has been indicated.51 Thus, the supra-
molecular aggregated structure of probes in solution here could
be through hydrogen bonding and uncommon antielectrostatic
anion−anion interactions as well. It may also be noted that
3
7[PF6]2 in terms of enhancement in the MLCT emission
spectra, binding constant, and detection limit, 19F NMR
studies were performed. Two sharp peaks at 71.2 and 73.3 ppm
in 19F NMR spectra were recognized as a fluorine of PF6 in
−
DMSO-d6 at 298 K. The peaks at −143.6, −154.3, and −163.6
ppm were identified as o-, p-, and m-fluorine, respectively, of
the pendant pentafluorophenyl group of probes 1[PF6]2 and
7[PF6]2 (Figure S67 in the Supporting Information). These
distinctive chemical shifts provide a multidimensional spectro-
scopic signature without complexity from overlapping 19F
NMR signals. Binding of H2PO4− to the receptors 1[PF6]2 and
7[PF6]2 yield upfield shifts (−144.1, −155.2, and −164.8 ppm
for 1[PF6]2 and −145.1, − 155.4, and −164.4 ppm for
7[PF6]2; o-, p-, and m-fluorine, respectively) in the 19F NMR
of the pentafluorophenyl group. The upfield shift of 19F peaks
of the pendant pentafluorophenyl group of 1[PF6]2 and
7[PF6]2 indicates a phosphate interaction with the electron-
deficient pentafluorophenyl group in solution, which could be
due to an anion−π interaction. This eventually helps in the
phosphate-assisted extended aggregation of 1[PF6]2 and
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Figure 3. Single-crystal structures of 1[PF6]2 and 3[PF6]2−7[PF6]2. Counteranions, solvent molecules, and all H atoms (except triazole H) are
omitted for clarity. Color code: C, gray; Ru, cyan; N, blue; O, red; H, white; F, green.
such supramolecular aggregates could be assisted by an
anion−π interaction (for 1[PF6]2 and 7[PF6]2) and a π−π
stacking interaction (for 3[PF6]2 and 4[PF6]2) as observed in
literature reports.52
aggregates, which may also be assisted by anion−π or π−π
stacking as reported earlier with different anion-supported
assemblies.50,53
It should be noted that the aggregates stop growing at a
particular size without the availability of capping agents.
Indeed, different types of van der Waal forces of attractions
help the nucleation process for the formation of aggregates.
However, a competition starts between the short-range forces
operating over small distances and the inertial forces which
operate when the particles become larger. This might
eventually help to overcome the attractive van der Waals
forces toward stopping of the growth of aggregates at a
particular size.
Single-Crystal Structures of the Probes and Phos-
phate Complexes of the Probes. Crystals suitable for
single-crystal X-ray diffraction structural analyses of six probes,
1[PF6]2 and 3[PF6]2−7[PF6]2 were obtained from a dichloro-
methane and dimethylformamide/methanol (1/1) solution
mixture of complexes via a slow evaporation method. 1[PF6]2,
4[PF6]2, and 6[PF6]2 crystallize in a triclinic crystal system
The formation of higher-order aggregated species in solution
can also be verified by carrying out DLS experiments of all the
receptors 1[PF6]2−7[PF6]2) in the absence as well as in the
−
presence of H2PO4 in DMSO at 298 K (Figure 2 and Figure
S69 in the Supporting Information). Interestingly, the initial
hydrodynamic diameters of all the free receptors increase
−
significantly in the presence of H2PO4 , which is due to the
formation of supramolecular aggregates of phosphate adducts.
All of the data are given in Table 2. Larger hydrodynamic radii
of 647 and 739 nm are found for adducts of phosphate and
1[PF6]2 and 7[PF6]2, respectively. These data reveal the
formation of higher-order supramolecular self-assembled
structures in the solution. Representative data of the formation
of higher-order supramolecular aggregates in the solution are
shown in Figure 2. Further, a transmission electron microscopy
(TEM) study was performed to support the preliminary
experimental observation of the formation of anion-assisted
supramolecular polymeric aggregates. Spherical types of
micellar/vesicular type morphological structures resulted in
the cases of the free receptors 1[PF6]2, 4[PF6]2, and 5[PF6]2
in the TEM study. On further additions of 1 equiv of
phosphate to the receptors, the spherical micellar/vesicular
structures are transformed to supramolecular aggregates
(Figures S70 and S71 in the Supporting Information). Thus,
the morphological transformation upon addition of phosphate
suggests the formation in solution of supramolecular
̅
with P1 space group, whereas 3[PF6]2, 5[PF6]2, and 7[PF6]2
crystallize in a monoclinic crystal system with P21/n, C2/c, and
P21/c space groups, respectively. An exploration of the crystal
structures of all these probes reveals that the Ru(II) center
adopts a distorted-octahedral geometry in 12+ and 32+−72+,
where four sites are occupied by four coordinating N centers of
two phenanthrolines (bipyridine rings for 72+) and the other
two coordination sites of the distorted octahedra are occupied
by two N atoms of pyridine triazole (Figure 3). The detailed
crystallographic information along with all bond lengths and
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Figure 4. Crystal structures of (a) 1[PF6]2 and (b) 7[PF6]2 showing C−H···F and F···F interactions and showing combined C−H···F and an anion
F−π interaction. Color code: C, gray; Ru, cyan; N, blue; H, white; F, yellowish green; P, orange yellow.
angles are provided in Tables S2−S4 in the Supporting
Information, which is well-matched with the literature
reports.27,47,50 Packing diagrams of all the crystals reveal a
noncovalent 3D network through C−H···F contacts among
triazole C−H and F atom of [PF6]− (Figures S72−S77 in the
Supporting Information). A further exploration of the crystal
structures of 1[PF6]2 and 7[PF6]2 shows that the probes are
associated with the [PF6]− via a C−H···F hydrogen-bonding
contact with the triazole pyridine. The stronger interaction is
found between the hydrogen atom of the triazole pyridine
group (C−H7) and the fluorine atom (F15) of [PF6]− with an
H···F distance of 2.543 Å in the case of 1[PF6]2, whereas that
between the hydrogen atom of the triazole pyridine group (C−
H7) and fluorine atom (F12A) of [PF6]− has an H···F distance
of 2.418 Å in 7[PF6]2. In addition, the fluorine atoms of
[PF6]− have anion···π interactions with C6F5 and triazole units
with the distances C1g···F6 (3.488 Å), C1g···F10 (3.549 Å),
and C2g···F17 (2.984 Å) for 1[PF6]2 and C1g*···F12A (3.403
Å), C1g*···F17A (3.590 Å), and C2g*···F9 (2.975 Å) for
7[PF6]2, where C1g/C1g* and C2g/C2g* are the centroids of
the C6F5 and triazole moiety of 1[PF6]2 and 7[PF6]2,
respectively (Figure 4 and Figures S72 and S77 in the
Supporting Information).54−56 Also, a π−π stacking interaction
is observed between pyrene units for the complex 4[PF6]2 in
the solid state (Figure S74 in the Supporting Information).
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Figure 5. (a) Single-crystal X-ray structure of 1[H2PO4]2 where a phosphate chain is propagated infinitely via triazole phosphate (C−H···O)
hydrogen bonding as well as an anion−π interaction between fluorine and the C6F5 unit (b) Single-crystal X-ray structure of 2[H2PO4]2
propagated by combined hydrogen bonding and π−π stacking interactions between naphthalene moieties. (c, d) Single-crystal X-ray structures of
4[H2PO4]2 and 5[H2PO4]2 in which phosphate binds with triazole through C−H···O and hydrogen-bonding interactions. Distances are shown in
Å, and all of the H atoms (except triazole C−H) are removed for clarity. Color codes: Ru, cyan; C, gray, green, pink; N, blue; H, white; F, green; P,
orange-yellow; O, red.
To study the phosphate binding of bis-heteroleptic Ru(II)
complexes of triazole probes in the solid state, we have
crystallized the receptors in the presence of H2PO4 . Crystals
electron densities of disordered solvent molecules could not be
accurately modeled and hence were squeezed out. The squeeze
calculation reveals that the electron densities are equivalent to
two DMF molecules. The occluded phosphate anions are
extensively hydrogen bonded among themselves by the usual
extended dimeric phosphate···phosphate hydrogen bonding
interactions (O···H−O), which are in the range between 1.625
and 2.630 Å along with an extra stabilization by hydrogen
bonding with the occluded phosphate methyl ester formed
during the synthesis of the complex. Thus, phosphate anions
form a 2D hydrogen-bonded network by the cumulative
hydrogen bonding described above, which provides an extra
stabilization of the phosphate anions within the crystal lattice.
The packing of the complex offers a continuous channel where
the phosphates and the loosely bound disordered solvent
molecules are located within the channel as well as within the
interstitial space between the arrays of the complex sustained
by H-bonding interactions (Figure S78 in the Supporting
Information). Interestingly, the triazole C−H of 12+ formed a
−
of H2PO4− adducts of 12+, 22+, 42+, and 52+ suitable for single-
crystal X-ray diffraction studies are achieved by slow diffusion
of diethyl ether in DMF/methanol solution of probes 1[PF6]2,
2[PF6]2, 4[PF6]2, and 5[PF6]2, respectively. The crystal
parameters, data collection, and refinement details of the
crystals of 1[H2PO4]2, 2[H2PO4]2, 4[H2PO4]2, and 5-
[H2PO4]2 are summarized in Tables S2 and S3 in the
Supporting Information. All of these complexes are crystallized
̅
in a triclinic crystal system with the P1 space group. The
Ru(II) metal centers of 12+, 22+, 42+, and 52+ units in
phosphate complexes display a distorted-octahedral geometry
wherein four coordination sites of the Ru(II) center are
engaged by two phenanthroline moieties, and the other two
coordination sites are coordinated by different pyridine triazole
units as observed in the cases of PF6− salts of the respective the
bis-heteroleptic Ru(II)-complexes.
−
The asymmetric unit of the complex 1[H2PO4]2 is found to
be comprised of one 12+ unit, two occluded phosphate anions,
and one occluded phosphate methyl ester formed during the
course of the synthesis of the complex, which are all fully
occupied and located on general positions. A few smeared
strong and directional hydrogen-bonding contact with H2PO4
, having a bonding distance (O2···H7) of 2.355 Å and an angle
(∠C−H7···O2) of 160.15°. Anion···π interactions are also
found between the F4 atom and the electron-deficient C6F5
−
ring of 1[H2PO4]2, as well as the oxygen atom of H2PO4
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anion and triazole moiety with the shortest distance C1g···F4
being 3.356 Å and that of C2g···O10 3.340 Å (Figure 5a), as
observed in previously reported systems.27,47,50,56,57 All of
these interactions probably assist the probe rigidification
effectively.
a pentafluorophenyl moiety, 1[PF6]2 and 7[PF6]2, are superior
to all other probes in the series in terms of a large amplification
of emission intensity, an enhanced binding constant, and a
lower detection limit. Such a distinction of the pentafluor-
ophenyl substituent in 1[PF6]2 and 7[PF6]2 has been
correlated with the formation of larger polymeric aggregates
In the case of the complex 2[H2PO4]2, one of the two
phosphates (refined SOF = 0.50944:0.49056) and the
naphthalene moiety (refined SOF = 0.55163:0.44837) of the
ligand are found to be disordered over two positions. Packing
of the complex along the ab plane provides a continuous
channel along the b axis wherein the phosphates are located
and are sustained by dimeric phosphate···phosphate hydrogen-
bonding interactions (Figure S79b in the Supporting
Information). Furthermore, the phosphates are found to
show a weak anion···π interaction (4.08 Å) with the
coordinated phenanthroline moieties. Importantly, strong
hydrogen bonding between the triazole C−H and the oxygen
atom of H2PO4− is found with an O2···H7 distance of 2.414 Å
along with a π−π stacking interaction distance between the
centroid and the centroid (C1g*···C1g*) interligand pendant
naphthalene units of 3.689 Å (C1g*···C1g*) in 2[H2PO4]2
(Figure 5b and Figure S79a in the Supporting Information).58
In the case of the complex 4[H2PO4]2 one 42+ and two
occluded phosphates are all fully occupied and located on
available positions in the asymmetric unit of the complex.
Furthermore, smeared electron densities of disordered solvent
molecules could not be accurately modeled and consequently
were squeezed out. A squeeze calculation reveals the presence
of three disordered methanol molecules in the asymmetric
unit. One of the phosphate anions was found to be disordered
over two positions (refined SOF = 0.81755:0.18245). Packing
of the complex generated a void channel wherein the
phosphates were located and sustained by dimeric 1D
phosphate···phosphate hydrogen bonding (Figure 5c). In the
case of the complex 5[H2PO4]2 one 52+ and two occluded
phosphate anions are all fully occupied and located in general
positions (Figure 5d). The methoxybenzene moiety of the
ligand is found to be disordered over two positions (refined
SOF = 0.52333:0.47667). The phosphates are found to show
fragile anion···π interactions (4.26 Å) with the disordered
methoxybenzene moieties of the ligand. Packing of the
complex generated a void channel wherein the phosphates
were located and sustained by dimeric phosphate···phosphate
hydrogen bonding. Thus, overall strong extensively hydrogen
bonded interactions between triazole and phosphate oxygen
atoms, as well as between the occluded phosphate anions and
solvent molecules, occur in all four phosphate complexes,
1[H2PO4]2, 2[H2PO4]2, 4[H2PO4]2, and 5[H2PO4]2, to
construct the polymeric assembly in the solid state (Figures
S78 and S80 in the Supporting Information).
−
of the probes with H2PO4 in solution, which is evident from
the DOSY and DLS studies, which eventually rigidified the
system more effectively. We envisaged that such an under-
standing of the phosphate sensing pathways in Ru(II)
polypyridyl based receptors might be advantageous in planning
better sensors for various anions.
EXPERIMENTAL SECTION
■
Materials. All of the reactions were performed under an inert
atmospheric environment, followed by an ambient conditions workup.
Acetonitrile was refluxed over calcium hydride and was collected afore
use. RuCl3·xH2O, 1,10-phenanthroline, deuterated solvents, tetrabu-
−
−
−
−
tylammonium salts of the anions HSO4 , NO3 , CH3CO2 , HCO3 ,
−
−
C6H5CO2 , I−, Br−, Cl−, F−, H2PO4 , and HP2O73−, zinc perchlorate,
and potassium hexafluorophosphate were purchased from Sigma-
Aldrich and were used as received. Ethanol was procured from
Spectrochem Private Limited. All physical studies were carried out by
using spectroscopy-grade solvents. Distilled and well-degassed
ethanol/water mixtures (2/1 v/v and 3/4 v/v respectively) were
used for the synthesis of probes.
Methods. A Shimadzu FTIR-8400S infrared spectrophotometer
was used for recording FTIR. Elemental analysis was performed on a
PerkinElmer 2500 series II elemental analyzer (PerkinElmer, USA).
HRMS analysis was done on a QToF-Micro YA 263 mass
spectrometer in ESI (+ve) mode. A Bruker FT-NMR DPX 500/
400/300 MHz NMR spectrometer was used to record all types of
1
NMR data. The chemical shift (δ) values for H, 13C, 31P, and 19F
NMR are reported in parts per million (ppm), and the peak positions
were calibrated using TMS as an internal standard. All 31P NMR
experiments were carried out in the presence of triphenylphosphine
(used as an external standard). A PerkinElmer Lambda 900 UV/vis/
NIR spectrometer (with 1 cm path length of the quartz cuvette) was
used to record absorption spectra, whereas a FluoroMax-3
spectrophotometer (Horiba-JobinYvon) was used to record emission
spectra.
Caution! Perchlorate salts and organic azide(I) are potentially
explosive under certain conditions. These materials should be used with
proper precaution. However, we did not face any difficulty in handling
these materials.
Calculation of Association Constants. Associations between
−
probes 1[PF6]2−7[PF6]2 and H2PO4 were calculated using PL
titration data. The emission spectra of probes increased progressively
due to the binding of the phosphate anion to the receptor. The
corresponding association constant (Ka) was determined by a
nonlinear fitting of curves that was obtained by plotting the changes
in emission (ΔI) at a fixed wavelength against the concentration of
the anions added. All of the PL titration data were fitted to eq 1 for
1:1 binding
l
o
o
o
|
o
o
o
o
CONCLUSION
2
■
i
j
y
i
j
j
j
j
j
y
z
z
z
z
z
I
2H
1
Ka
1
Ka
i
j
y
z
o
z j
z
2
ΔI = j
z j
m H
+
X
+
z −
z
H
+ X +
+
4HX}
Studies on a series of nine bis-heteroleptic Ru(II) receptors
having a pyridine triazole moiety as an anion-binding unit with
various substituents on the triazole have established this series
of metal complexes as selective probes for dihydrogen
phosphate. Further, we have determined that enhancement-
based selective sensing is via the selective formation of
phosphate-supported extensive self-assembled structures. It has
also been found that the change in the aromaticity or
electronic parameter of the substituents on the probes
2[PF6]2−6[PF6]2, 8[PF6]2, and 9[PF6]2 moderately influences
j
z j
o
o
o
o
o
o
o
o
j
z
k
{
k
{
k
{
n
~
(1)
where I = emission intensity of the probes upon each addition of the
H2PO4− anion, ΔI = I − I0, H = probe concentration, and X =
−
H2PO4 concentration.59,60
Calculation of Detection Limit. The detection limit (DL) was
calculated using eq 2
3SD
DL =
−
slope
(2)
the effective sensing of H2PO4 . Significantly, the probes with
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where SD corresponds to the standard deviation of the value of
luminescence intensity of the blank sample, measured for 10
consecutive scans. The slope was calculated from the linear fit plot
of the change in emission intensity vs the concentration of the anion.
X-ray Crystallographic Refinement Details. The crystallo-
graphic details of the probes are given in Table S2 in the Supporting
Information. A Bruker SMART APEX diffractometer having Mo Kα
(λ = 0.7107 Å) radiation was used to collect intensity data of the
crystal, and the instrument was equipped with a CCD area detector.
SAINT61 software was used for the integration and reduction of data.
SADABS62 was applied for an empirical absorption correction to the
collected reflections. SHELXTL63 and SHELXL-201464 were utilized
to solve the structure and refined on F2 by the full-matrix least-squares
technique, respectively. Graphics were created with the help of
PLATON-9765 and MERCURY 3.7.66 The PLATON/SQUEEZE
program was applied to account for some disordered solvent
molecules that we have not been able to assign properly. The
CCDC file numbers of the crystal structures (2048424−2048433)
contains the crystallographic data for this paper.
8.25 (d, J = 5.2 Hz, 1H), 8.02 (t, J = 8 Hz, 1H), 7.98−7.91 (m, 4H),
7.85 (d, J = 5.6 Hz, 1H), 7.79 (dd, J = 8.2, 5.6 Hz, 1H) 7.72 (dd J = 8,
5.2 Hz, 1H), 7.61 (d, J = 8.4 Hz, 1H), 7.53 (t, J = 8 Hz, 1H), 7.46 (d,
J = 5.2 Hz, 2H) 7.30−7.22 (m, 2H), 6.10 (q, J = 6.8 Hz, 2H) ppm.
13C NMR (100 MHz, acetone-d6): δ 154.2, 154.1, 154.0, 153.7, 153.1,
152.2, 149.4, 149.2, 149.05, 149.01, 148.9, 139.1, 137.8, 137.7, 137.5,
134.8, 132.02, 132.01, 131.7, 131.6, 131.0, 130.2, 129.8, 129.3, 129.1,
129.07, 129.02, 128.7, 127.9, 127.7, 127.1, 127.09, 127.03, 126.8,
126.4, 126.3, 123.6, 123.2, 55.6 ppm.
3[PF6]2. Anal. Calcd for C46H32N8RuP2F12 (Mw = 1088.1077): C,
50.79; H, 2.97; N, 10.30. Found: C, 50.78; H, 2.95; N, 10.27. FTIR in
KBr disk (ν/cm−1): 3434, 2923, 1724, 1548, 1427, 1122, 840, 723.
ESI-MS: for [C46H32N8RuPF6]+, calcd m/z 943.1430, found m/z
943.1432. 1H NMR (500 MHz, acetone-d6): δ 8.91 (s, 1H), 8.84 (d, J
= 6.8 Hz, 1H), 8.78−8.74 (m, 2H), 8.72−8.69 (m, 2H), 8.50 (d, J =
4.6 Hz, 2H), 8.47 (d, J = 4.6 Hz, 1H), 8.42−8.36 (m, 5H), 8.21 (t, J =
4.8 Hz, 2H), 8.16 (dd, J = 6.8, 2.8 Hz, 4H), 7.96−7.94 (m, 1H),
7.93−7.89 (m, 1H), 7.85 (dd, J = 6.4, 4 Hz, 1H), 7.81 (d, J = 4.4 Hz,
1H), 7.78 (dd, J = 6.6, 4.4 Hz, 1H), 7.70 (dd, J = 6.6, 4.4 Hz, 1H),
7.56 (t, J = 5.2 Hz, 2H), 7.44 (t, J = 7.6 Hz, 2H), 7.24 (t, J = 4.8 Hz,
1H), 6.66 (q, J = 12.4 Hz, 2H) ppm. 13C NMR (125 MHz, acetone-
d6): δ 154.2, 154.0, 153.9, 153.6, 153.0, 152.1, 149.3, 149.0, 148.97,
148.9, 139.0, 137.8, 137.7, 137.4, 132.3, 131.99, 131.97, 131.56, 131.5,
131.3, 131.1, 130.2, 129.09, 129.04, 128.9, 128.6, 128.3, 127.1, 126.99,
126.9, 126.8, 126.4, 126.2, 124.2, 123.7, 123.6, 49.0 ppm.
4[PF6]2. Anal. Calcd for C48H32N8RuP2F12 (Mw = 1112.1077): C,
51.85; H, 2.90; N, 10.08. Found: C, 51.84; H, 2.89; N, 10.04. FTIR in
KBr disk (ν/cm−1): 3047, 1620, 1454, 1427, 1344, 1122, 1054, 840,
721. ESI-MS: for [C48H32N8RuPF6]+, calcd m/z 967.1430, found m/z
967.1441. 1H NMR (400 MHz, acetone-d6): δ 9.13 (s, 1H), 8.84 (d, J
=8 Hz, 1H), 8.75 (d, J =8 Hz, 1H), 8.64 (d, J =5.6 Hz, 1H), 8.60 (t, J
=8.8 Hz, 2H), 8.49 (d, J =5.6 Hz, 1H), 8.46 (d, J =5.2 Hz, 1H), 8.43−
8.37 (m, 4H), 8.28 (d, J =8.8 Hz, 2H), 8.23−8.18 (m, 4H), 8.07 (d,, J
=8.6 Hz, 1H), 8.03−7.99 (m, 3H), 7.94−7.88 (m, 3H), 7.85−7.81
(m, 2H), 7.77 (dd, J =8, 5.2 Hz, 1H), 7.67 (dd, J =8, 5.2 Hz, 1H),
7.27 (t, J =7.2 Hz, 1H), 6.39 (q, J =14.8 Hz, 2H) ppm. 13C NMR
(100 MHz, acetone-d6): δ 154.2,154.1, 153.9, 153.5, 153.0, 152.2,
149.2, 149.0, 148.9, 148.87, 148.8, 139.1, 137.8, 137.7, 137.6, 137.3,
131.97, 131.96, 131.38, 131.3, 129.27, 129.20, 129.05, 129.0, 128.5,
128.3, 128.2, 127.5, 127.4, 127.1, 126.95, 126.9, 126.8, 126.2, 125.8,
123.6, 122.6, 54.7 ppm.
Synthesis. The ligands L1−L6 were synthesized and then were
used in synthesizing complexes (details of ligand synthesis are given in
the experimental section in the Supporting Information).
General Synthetic Procedure of the Complexes. cis-[Ru-
(phen)2Cl2] and cis-[Ru(bpy)2Cl2] were synthesized by a reported
procedure.67 Further, they were used for the synthesis of complexes. L
(0.28 mmol) and cis-[Ru(phen)2Cl2]/cis-[Ru(phen)2Cl2] (0.28
mmol) were placed in a 100 mL three-neck round-bottom (RB)
flask. The flask was degassed and purged with argon several times.
After that 40 mL of a well-degassed ethanol/water mixture (2/1 v/v
and 3/4 v/v, respectively) was placed in the flask through a septum
under an argon atmosphere. The mixture was heated to reflux under
an argon atmosphere for 24 h. After evaporation of ethanol, the
reaction mixture was cooled to room temperature. Then a saturated
solution of KPF6 (450 mg) was added to the reaction mixture, and
this mixture was stirred for up to 30 min to complete the
precipitation. The orange-red or yellow-orange precipitate was
dissolved in dichloromethane. The organic phase was washed with
brine solution followed by distilled water. The organic layer was
evaporated to obtain a crude yellow-orange solid, which was further
purified through column chromatography using 60−120 mesh silica
gel and CH3CN/H2O/KNO3 (90/9.5/0.5) as eluent. During column
chromatography in the dark, the orange band was collected as the
nitrate salt of the complex. The collected portion was concentrated
and treated with excess KPF6 salt dissolved in water. After addition, an
orange-red/yellow-orange precipitate was formed, which was filtered,
washed with water, and dried under vacuum to give the desired
crystalline solid product.
1[PF6]2. Anal. Calcd for C38H23N8RuP2F17 (Mw = 1078.0293) C,
42.35; H, 2.15; N, 10.40. Found: C, 42.33; H, 2.12; N, 10.39. FTIR in
KBr disk (ν/cm−1): 3421, 1660, 1512, 1429, 1357, 11128, 1026, 842,
720. ESI-MS: for [C38H23N8RuPF11]+, calcd m/z 933.0646, found m/
z 933.0646; for [C38H23N8RuPF5]2+, calcd m/z 394.0499, found m/z
394.0469; 1H NMR (400 MHz, acetone-d6): δ 9.24 (s, 1H), 8.83 (d, J
= 8.4 Hz, 2H), 8.75 (d, J = 9.2 Hz, 1H), 8.70 (d, J = 9.2 Hz, 1H), 8.61
(d, J = 5.2 Hz, 1H), 8.58 (d, J = 5.2 Hz, 1H), 8.46 (d, J = 5.2 Hz, 1H),
8.40−8.33 (m, 5H), 8.22 (d, J = 6.4 Hz, 1H), 8.08 (t, J = 6.4 Hz, 1H),
7.99−7.92 (m, 2H), 7.87 (d, J = 5.6 Hz, 1H), 7.78 (dd, J = 8.2, 5.2
Hz, 1H), 7.69 (dd, J = 8, 5.2 Hz, 1H), 7.31 (t, J = 7.2 Hz, 1H), 5.82
(s, 2H) ppm. 13C NMR (100 MHz, acetone-d6): δ 154.2, 154.18,
154.16, 153.9, 153.1, 152.0, 149.4, 149.0, 148.9, 148.8, 139.2, 137.9,
137.86, 137.82, 137.4, 132.0, 131.9, 131.6, 131.3, 129.0, 128.8, 128.6,
127.2, 127.1, 127.06, 127.01, 126.3, 123.7, 43.8 ppm.
5[PF6]2. Anal. Calcd for C39H30ON8RuP2F12 (Mw = 1018.0870): C,
46.03; H, 2.97; N, 11.01. Found: C, 46.02; H, 2.95; N, 10.99. FTIR in
KBr disk (ν/cm−1): 3454, 1724, 1514, 1427, 1251, 1178, 842, 775,
723. ESI-MS: for [C39H30ON8RuPF6]+, calcd m/z 873.1222, found
m/z 873.1227; for [C39H30ON8Ru]2+, calcd m/z 364.0788, found m/z
1
364.0747. H NMR (400 MHz, acetone-d6): δ 9.07 (s, 1H), 8.86−
8.82 (m, 2H), 8.74 (d, J =8.4 Hz, 1H), 8.69 (d, J =8.4 Hz, 1H), 8.60−
8.57 (m, 2H), 8.42−8.34 (m, 6H), 8.23 (d, J =5.2 Hz, 1H), 8.06 (t, J
=8.2 Hz, 1H), 7.97 (d, J =5.2 Hz, 1H), 7.95 (d, J =5.2 Hz, 1H), 7.85
(d, J =5.2 Hz, 1H), 7.77 (dd, J =8.2, 5.2 Hz, 1H), 7.69 (dd, J =8.2, 5.2
Hz, 1H), 7.30 (t, J =7.2 Hz, 1H), 7.11(d, J =8.4 Hz, 2H), 6.84 (d, J
=8.4 Hz, 2H), 5.53 (q, J =14.8 Hz, 2H) ppm. 13C NMR (100 MHz,
acetone-d6): δ 161.1, 154.1, 153.8, 153.1, 152.3, 149.4, 149.2, 149.1,
149.0, 148.9, 139.2, 137.88, 137.8, 137.5, 132.0, 130.7, 129.1, 129.0,
128.8, 127.2, 127.1, 127.0, 126.6, 126.4, 115.2, 55.9, 55.7 ppm.
6[PF6]2. Anal. Calcd for C38H27O2N9RuP2F12 (Mw = 1033.0615):
C, 44.20; H, 2.64; N, 12.21. Found: C, 44.19; H, 2.61; N, 12.18. FTIR
in KBr disk (ν/cm−1): 3411, 3087, 1724, 1604, 1523, 1427, 1346,
1122, 1053, 840, 777, 721. ESI-MS: for [C38H27O2N9RuPF6]+, calcd
m/z 888.0968, found m/z 888.0953; for [C38H27O2N9Ru]2+, calcd m/
z 371.5660, found m/z 371.5664. 1H NMR (400 MHz, acetone-d6): δ
9.35 (s, 1H), 8.85 (t, J =7.6 Hz, 2H), 8.75 (d, J =8.4 Hz, 1H), 8.64 (d,
J =8 Hz, 1H), 8.42−8.37 (m, 4H), 8.34−8.28 (m, 3H), 8.15 (d, J =8.4
Hz, 3H), 8.08 (t, J =7.6 Hz, 1H), 8.00−7.93 (m, 3H), 7.74 (dd, J =8,
5.2 Hz, 1H), 7.62 (dd, J =8, 5.2 Hz, 1H), 7.55 (d, J =5.6 Hz, 1H),
7.30 (d, J =8 Hz, 3H), 5.78 (q, J =15.6 Hz, 2H) ppm. 13C NMR (100
MHz, acetone-d6): δ 152.9, 152.6, 151.7, 150.5, 147.7, 147.6, 147.4,
147.3, 147.2, 147.1, 141.3, 138.2, 137.6, 136.8, 136.4, 130.4, 130.1,
2[PF6]2. Anal. Calcd for C42H30N8RuP2F12 (Mw = 1038.0921) C,
48.61; H, 2.91; N, 10.80. Found: C, 48.60; H, 2.89; N, 10.79. FTIR in
KBr disk (ν/cm−1): 1623, 1512, 1429, 1027, 840, 721. ESI-MS: for
[C42H30N8RuPF6]+, calcd m/z 893.1273, found m/z 893.1274; for
[C42H30N8Ru]2+, calcd m/z 374.0813, found m/z 374.0812. 1H NMR
(400 MHz, acetone-d6): δ 9.07 (s, 1H), 8.85 (d, J = 8.4 Hz, 2H), 8.76
(d, J = 7.6 Hz, 1H), 8.72 (d, J = 8 Hz, 1H), 8.55 (t, d, J = 4 Hz, 2H),
8.47 (d, J = 5.2 Hz, 1H), 8.44−8.37 (m, 4H), 8.30 (d, J = 8 Hz, 1H),
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129.8, 129.1, 127.9, 127.8, 127.6, 126.9, 126.8, 126.3, 125.6, 123.8,
123.7, 122.6, 123.0, 122.9, 53.7 ppm.
an SRF. The authors especially thank Dr. Bijit Chowdhury, Dr.
Tamal Kanti Ghosh, and Dr. Abu Saleh Musha Islam for
fruitful discussions during this work.
7[PF6]2. Anal. Calcd for C34H23N8RuP2F17 (Mw = 1030.0293): C,
39.66; H, 2.25; N, 10.88. Found: C, 39.64; H, 2.24; N, 10.83. FTIR in
KBr disk (ν/cm−1): 3454, 3132, 1604, 1514, 1446, 1357, 1128, 1026,
842, 765, 663. ESI-MS: for [C34H23N8RuPF11]+, calcd m/z 885.0651,
REFERENCES
■
1
found m/z 885.0647. H NMR (500 MHz, DMSO-d6): δ 9.38 (s,
(1) Nyren, P. Enzymic method for continuous monitoring of DNA
polymerase activity. Anal. Biochem. 1987, 167, 235−8.
1H), 8.85 (dd, J =8.5, 3 Hz, 2H), 8.77 (d, J =8 Hz, 1H), 8.74 (d, J =8
Hz, 1H), 8.35 (d, J =8 Hz, 1H), 8.18 (q, J =8 Hz, 3H), 8.13 (t, J =7.9
Hz, 2H), 7.89 (d, J =5.5 Hz, 1H), 7.86 (dd, J =9, 5.5 Hz, 2H), 7.74
(d, J =5.5 Hz, 1H), 7.63 (d, J =6 Hz, 1H), 7.58−7.52 (m, 3H), 7.47
(t, J =7 Hz, 1H), 7.44 (t, J =7 Hz, 1H), 5.86 (s, 2H) ppm.13C NMR
(125 MHz, DMSO-d6): δ 157.2, 156.87, 156.8, 156.5, 151.8, 151.7,
151.6, 151.4, 151.3, 150.1, 147.4, 138.4, 137.98, 137.9, 137.6, 127.7,
127.1, 126.6, 126.4, 124.5, 124.4, 123.9, 123.6, 122.7, 107.9, 42.8
ppm.
(2) Hargrove, A. E.; Nieto, S.; Zhang, T.; Sessler, J. L.; Anslyn, E. V.
Artificial Receptors for the Recognition of Phosphorylated Molecules.
Chem. Rev. (Washington, DC, U. S.) 2011, 111, 6603−6782.
(3) Katayev, E. A.; Ustynyuk, Y. A.; Sessler, J. L. Receptors for
tetrahedral oxyanions. Coord. Chem. Rev. 2006, 250, 3004−3037.
(4) Pal, S.; Ghosh, T. K.; Ghosh, R.; Mondal, S.; Ghosh, P. Recent
advances in recognition, sensing and extraction of phosphates: 2015
onwards. Coord. Chem. Rev. 2020, 405, 213128.
(5) Beer, P. D.; Gale, P. A. Anion Recognition and Sensing: The
State of the Art and Future Perspectives. Angew. Chem., Int. Ed. 2001,
40, 486−516.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01084.
■
sı
(6) Hirsch, A. K. H.; Fischer, F. R.; Diederich, F. Phosphate
recognition in structural biology. Angew. Chem., Int. Ed. 2007, 46,
338−352.
Detailed syntheses of all ligands and characterization
spectra of synthesized compounds, solution-state 1H
NMR, X-ray crystallographic data of complexes 1[PF6]2,
1[H2PO4]2, 2[H2PO4]2, 3[PF6]2, 4[PF6]2, 4[H2PO4]2,
5[PF6]2, 5[H2PO4]2, 6[PF6]2,and 7[PF6]2, solution-
(7) Lee, D. H.; Kim, S. Y.; Hong, J.-I. Fluorescent sensors: A
fluorescent pyrophosphate sensor with high selectivity over ATP in
water. Angew. Chem., Int. Ed. 2004, 43, 4777−4780.
(8) Schmidtchen, F. P.; Berger, M. Artificial Organic Host Molecules
for Anions. Chem. Rev. (Washington, DC, U. S.) 1997, 97, 1609−1646.
(9) Lee, C.-H.; Na, H.-K.; Yoon, D.-W.; Won, D.-H.; Cho, W.-S.;
Lynch, V. M.; Shevchuk, S. V.; Sessler, J. L. Single Side Strapping: A
New Approach to Fine Tuning the Anion Recognition Properties of
Calix[4]pyrroles. J. Am. Chem. Soc. 2003, 125, 7301−7306.
(10) Khatua, S.; Choi, S. H.; Lee, J.; Kim, K.; Do, Y.; Churchill, D.
G. Aqueous Fluorometric and Colorimetric Sensing of Phosphate
Ions by a Fluorescent Dinuclear Zinc Complex. Inorg. Chem. 2009, 48,
2993−2999.
state studies (PL, UV, TCSPC, H NMR, 19F and 31P)
1
of all probes with anions in solution, solution-state
aggregation as well as macroscopic morphological
analysis data (PDF)
Accession Codes
CCDC 2048424−2048433 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(11) Gale, P. A. Anion receptor chemistry. Chem. Commun.
(Cambridge, U. K.) 2011, 47, 82−86.
(12) Das, P.; Bhattacharya, S.; Mishra, S.; Das, A. Zn(II) and
Cd(II)-based complexes for probing the enzymatic hydrolysis of
Na4P2O7 by alkaline phosphatase in physiological conditions. Chem.
Commun. (Cambridge, U. K.) 2011, 47, 8118−8120.
(13) Kim, S. K.; Lee, D. H.; Hong, J.-I.; Yoon, J. Chemosensors for
Pyrophosphate. Acc. Chem. Res. 2009, 42, 23−31.
(14) Tabary, T.; Ju, L.-Y.; Cohen, J. H. M. Homogeneous phase
pyrophosphate (PPi) measurement (H3PIM) A non-radioactive,
quantitative detection system for nucleic acid specific hybridization
methodologies including gene amplification. J. Immunol. Methods
1992, 156, 55−60.
(15) Marcus, Y. A simple empirical model describing the
thermodynamics of hydration of ions of widely varying charges,
sizes, and shapes. Biophys. Chem. 1994, 51, 111−27.
(16) Bowman-James, K. Alfred Werner Revisited: The Coordination
Chemistry of Anions. Acc. Chem. Res. 2005, 38, 671−678.
(17) Gale, P. A.; Garcia-Garrido, S. E.; Garric, J. Anion receptors
based on organic frameworks: highlights from 2005 and 2006. Chem.
Soc. Rev. 2008, 37, 151−190.
AUTHOR INFORMATION
Corresponding Author
Pradyut Ghosh − School of Chemical Sciences, Indian
Association for the Cultivation of Science, Kolkata 700032,
India; orcid.org/0000-0002-5503-6428; Email: icpg@
iacs.res.in
■
Authors
Sahidul Mondal − School of Chemical Sciences, Indian
Association for the Cultivation of Science, Kolkata 700032,
India
Koushik Sarkar − School of Chemical Sciences, Indian
Association for the Cultivation of Science, Kolkata 700032,
India
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.1c01084
(18) Ramakrishnam Raju, M. V.; Harris, S. M.; Pierre, V. C. Design
and applications of metal-based molecular receptors and probes for
inorganic phosphate. Chem. Soc. Rev. 2020, 49, 1090−1108.
(19) Sturbelle, R. T.; Farias da Costa de Avila, L.; Roos, T. B.;
Borchardt, J. L.; de Cassia dos Santos da Conceicao, R.; Dellagostin,
O. A.; Leite, F. P. L. The role of quorum sensing in Escherichia coli
(ETEC) virulence factors. Vet. Microbiol. 2015, 180, 245−252.
(20) Kubik, S. Amino acid containing anion receptors. Chem. Soc.
Rev. 2009, 38, 585−605.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
P.G. gratefully acknowledges the Science and Engineering
Research Board (SERB; EMR/2016/000900), India, for
financial support and the Alexander von Humboldt Foundation
for donating a fluorimeter. S.M. gratefully thanks the CSIR for
(21) Hua, Y.; Flood, A. H. Click chemistry generates privileged CH
hydrogen-bonding triazoles: the latest addition to anion supra-
molecular chemistry. Chem. Soc. Rev. 2010, 39, 1262−1271.
9094
https://doi.org/10.1021/acs.inorgchem.1c01084
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Inorganic Chemistry
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Article
(22) Garcia-Garrido, S. E.; Caltagirone, C.; Light, M. E.; Gale, P. A.
Acridinone-based anion receptors and sensors. Chem. Commun.
(Cambridge, U. K.) 2007, 1450−1452.
(42) Yano, M.; Tong, C. C.; Light, M. E.; Schmidtchen, F. P.; Gale,
P. A. Calix[4]pyrrole-based anion transporters with tuneable transport
properties. Org. Biomol. Chem. 2010, 8, 4356−4363.
(43) Park, J.-Y.; Skonieczny, K.; Aratani, N.; Osuka, A.; Gryko, D.
T.; Lee, C.-H. Calix[4]pyrroles bearing proximally meso-meso linking
straps: synthesis and anion binding properties. Chem. Commun.
(Cambridge, U. K.) 2012, 48, 8060−8062.
(44) Sokkalingam, P.; Hong, S.-J.; Aydogan, A.; Sessler, J. L.; Lee,
C.-H. Decoration of Gold Nanoparticles by a Double-Armed
Calix[4]pyrrole: A Receptor-Decorated Nanoensemble for Anion
Sensing and Extraction. Chem. - Eur. J. 2013, 19, 5860−5867.
(45) Sokkalingam, P.; Kim, D. S.; Hwang, H.; Sessler, J. L.; Lee, C.-
H. A dicationic calix[4]pyrrole derivative and its use for the selective
recognition and displacement-based sensing of pyrophosphate. Chem.
Sci. 2012, 3, 1819−1824.
(46) Chowdhury, B.; Dutta, R.; Khatua, S.; Ghosh, P. A Cyanuric
Acid Platform Based Tripodal Bis-heteroleptic Ru(II) Complex of
Click Generated Ligand for Selective Sensing of Phosphates via C-H···
Anion Interaction. Inorg. Chem. 2016, 55, 259−271.
(47) Chowdhury, B.; Sinha, S.; Ghosh, P. Selective Sensing of
Phosphates by a New Bis-heteroleptic RuII Complex through
Halogen Bonding: A Superior Sensor over Its Hydrogen-Bonding
Analogue. Chem. - Eur. J. 2016, 22, 18051−18059.
(48) Ghosh, T. K.; Ghosh, P. Balancing the acidity of the pendant
urea arm of bis-heteroleptic ruthenium(II) complex containing
pyridyl triazole for improved oxyanion recognition. Dalton Trans.
2018, 47, 7561−7570.
(49) Ghosh, T. K.; Mondal, S.; Bej, S.; Nandi, M.; Ghosh, P. An
integrated urea and halogen bond donor based receptor for superior
and selective sensing of phosphates. Dalton Trans. 2019, 48, 4538−
4546.
(50) Mondal, S.; Ghosh, T. K.; Chowdhury, B.; Ghosh, P.
Supramolecular Self-Assembly Driven Selective Sensing of Phos-
phates. Inorg. Chem. 2019, 58, 15993−16003.
(51) Zapata, F.; Gonzalez, L.; Bastida, A.; Bautista, D.; Caballero, A.
Formation of self-assembled supramolecular polymers by anti-
electrostatic anion-anion and halogen bonding interactions. Chem.
Commun. (Cambridge, U. K.) 2020, 56, 7084−7087.
(52) Zapata, F.; Gonzalez, L.; Caballero, A.; Bastida, A.; Bautista, D.;
Molina, P. Interlocked Supramolecular Polymers Created by
Combination of Halogen- and Hydrogen-Bonding Interactions
through Anion-Template Self-Assembly. J. Am. Chem. Soc. 2018,
140, 2041−2045.
(53) Naskar, S.; Dalal, C.; Ghosh, P. Ion-pair coordination driven
stimuli-responsive one-dimensional supramolecular helicate. Chem.
Commun. (Cambridge, U. K.) 2017, 53, 2487−2490.
(54) Lakshminarayanan, P. S.; Ravikumar, I.; Suresh, E.; Ghosh, P.
Trapped inorganic phosphate dimer. Chem. Commun. (Cambridge, U.
K.) 2007, 5214−5216.
(55) Lakshminarayanan, P. S.; Ravikumar, I.; Suresh, E.; Ghosh, P.
Encapsulation of Halides within the Cavity of a Pentafluorophenyl-
Substituted Tripodal Amine Receptor. Inorg. Chem. 2007, 46, 4769−
4771.
(23) dos Santos, C. M. G.; McCabe, T.; Gunnlaugsson, T. Selective
fluorescent sensing of chloride. Tetrahedron Lett. 2007, 48, 3135−
3139.
(24) Ghosh, T. K.; Chakraborty, S.; Chowdhury, B.; Ghosh, P. Bis-
Heteroleptic Ruthenium(II) Complex of Pendant Urea Function-
alized Pyridyl Triazole and Phenanthroline for Recognition, Sensing,
and Extraction of Oxyanions. Inorg. Chem. 2017, 56, 5371−5382.
(25) Ghosh, A.; Ganguly, B.; Das, A. Urea-based ruthenium(II)-
polypyridyl complex as an optical sensor for anions: synthesis,
characterization, and binding studies. Inorg. Chem. 2007, 46, 9912−
9918.
(26) Wu, Y.; Peng, X.; Fan, J.; Gao, S.; Tian, M.; Zhao, J.; Sun, S.
Fluorescence Sensing of Anions Based on Inhibition of Excited-State
Intramolecular Proton Transfer. J. Org. Chem. 2007, 72, 62−70.
(27) Chowdhury, B.; Khatua, S.; Dutta, R.; Chakraborty, S.; Ghosh,
P. Bis-Heteroleptic Ruthenium(II) Complex of a Triazole Ligand as a
Selective Probe for Phosphates. Inorg. Chem. 2014, 53, 8061−8070.
(28) Zapata, F.; Gonzalez, L.; Caballero, A.; Alkorta, I.; Elguero, J.;
Molina, P. Dual Role of the 1,2,3-Triazolium Ring as a Hydrogen-
Bond Donor and Anion-π Receptor in Anion-Recognition Processes.
Chem. - Eur. J. 2015, 21, 9797−9808.
(29) Romero, T.; Caballero, A.; Tarraga, A.; Molina, P. A Click-
Generated Triazole Tethered Ferrocene-Pyrene Dyad for Dual-Mode
Recognition of the Pyrophosphate Anion. Org. Lett. 2009, 11, 3466−
3469.
(30) Schulze, B.; Schubert, U. S. Beyond click chemistry -
supramolecular interactions of 1,2,3-triazoles. Chem. Soc. Rev. 2014,
43, 2522−2571.
(31) Curiel, D.; Cowley, A.; Beer, P. D. Indolocarbazoles: a new
family of anion sensors. Chem. Commun. (Cambridge, U. K.) 2005,
236−238.
(32) Yoon, J.; Kim, S. K.; Singh, N. J.; Kim, K. S. Imidazolium
receptors for the recognition of anions. Chem. Soc. Rev. 2006, 35,
355−360.
(33) Molina, P.; Tarraga, A.; Oton, F. Imidazole derivatives: A
comprehensive survey of their recognition properties. Org. Biomol.
Chem. 2012, 10, 1711−1724.
(34) Zapata, F.; Caballero, A.; Espinosa, A.; Tarraga, A.; Molina, P.
Cation coordination induced modulation of the anion sensing
properties of a ferrocene-imidazophenanthroline Dyad: Multichannel
recognition from phosphate-related to chloride anions. J. Org. Chem.
2008, 73, 4034−4044.
(35) Alfonso, M.; Espinosa, A.; Tarraga, A.; Molina, P. A Simple but
Effective Dual Redox and Fluorescent Ion Pair Receptor Based on a
Ferrocene-Imidazopyrene Dyad. Org. Lett. 2011, 13, 2078−2081.
(36) Zapata, F.; Caballero, A.; Tarraga, A.; Molina, P. Ferrocene-
Substituted Nitrogen-Rich Ring Systems as Multichannel Molecular
Chemosensors for Anions in Aqueous Environment. J. Org. Chem.
2010, 75, 162−169.
(37) Chmielewski, M. J.; Jurczak, J. Anion binding versus
intramolecular hydrogen bonding in neutral macrocyclic amides.
Chem. - Eur. J. 2006, 12, 7652−7667.
(38) Hossain, M. A.; Kang, S. O.; Powell, D.; Bowman-James, K.
Anion Receptors: A New Class of Amide/Quaternized Amine
Macrocycles and the Chelate Effect. Inorg. Chem. 2003, 42, 1397−
1399.
(39) Choi, J. K.; Kim, S. H.; Yoon, J.; Lee, K.-H.; Bartsch, R. A.;
Kim, J. S. A PCT-Based, Pyrene-Armed Calix[4]crown Fluoroiono-
phore. J. Org. Chem. 2006, 71, 8011−8015.
(40) Mondal, S.; Ghosh, K. Naphthalimide-linked bispyridinium
clefts in selective aqueous sensing of triphosphate and triphosphate-
based biomolecules. Anal. Methods 2019, 11, 5864−5871.
(41) Fisher, M. G.; Gale, P. A.; Hiscock, J. R.; Hursthouse, M. B.;
Light, M. E.; Schmidtchen, F. P.; Tong, C. C. 1,2,3-Triazole-strapped
calix[4]pyrrole: a new membrane transporter for chloride. Chem.
Commun. (Cambridge, U. K.) 2009, 3017−3019.
(56) Dutta, R.; Ghosh, P. Encapsulation of Fluoride/Chloride in the
C3v-Symmetric Cleft of a Pentafluorophenyl-Functionalized Cyanuric
Acid Platform Based Tripodal Amide: Solid and Solution-State Anion-
Binding Studies. Eur. J. Inorg. Chem. 2012, 2012, 3456−3462.
(57) Ravikumar, I.; Lakshminarayanan, P. S.; Arunachalam, M.;
Suresh, E.; Ghosh, P. Anion complexation of a pentafluorophenyl-
substituted tripodal urea receptor in solution and the solid state:
Selectivity toward phosphate. Dalton Trans. 2009, 4160−4168.
(58) Janiak, C. A critical account on π−π stacking in metal
complexes with aromatic nitrogen-containing ligands. J. Chem. Soc.,
Dalton Trans. 2000, 3885−3896.
(59) Thordarson, P. Determining association constants from
titration experiments in supramolecular chemistry. Chem. Soc. Rev.
2011, 40, 1305−1323.
(60) Brynn Hibbert, D.; Thordarson, P. The death of the Job plot,
transparency, open science and online tools, uncertainty estimation
9095
https://doi.org/10.1021/acs.inorgchem.1c01084
Inorg. Chem. 2021, 60, 9084−9096

Inorganic Chemistry
pubs.acs.org/IC
Article
methods and other developments in supramolecular chemistry data
analysis. Chem. Commun. (Cambridge, U. K.) 2016, 52, 12792−12805.
(61) SAINT - Software for the Integration of CCD Detector System
Bruker Analytical X-ray Systems; Bruker AXS: Madison, WI, 1995.
(62) Sheldrick, G. M. SADABS, Empirical Absorption Correction
̈
̈
Program; University of Gottingen: Gottingen, Germany, 1997.
(63) Sheldrick, G. M. SHELXS97. Program for Crystal Structure
̈
̈
Solution and Refinement; University of Gottingen: Gottingen,
Germany, 1997.
(64) Sheldrick, G. M. SHELXL v. 2014, Program for Crystal Structure
̈
̈
Refinement; University of Gottingen, Gottingen, Germany, 2014.
(65) Spek, A. L. PLATON-97; University of Utrecht: Utrecht, the
Netherlands, 1997.
(66) Mercury, version 3.7, supplied with Cambridge Structural
Database, CCDC, Cambridge, U.K., 2003−2004.
(67) Collins, J. E.; Lamba, J. J. S.; Love, J. C.; McAlvin, J. E.; Ng, C.;
Peters, B. P.; Wu, X.; Fraser, C. L. Ruthenium(II) α-Diimine
Complexes with One, Two, and Three 4,4′-Bis(hydroxymethyl)-2,2′-
bipyridine and 4,4′-Bis(chloromethyl)-2,2′-bipyridine Ligands: Useful
Starting Materials for Further Derivatization. Inorg. Chem. 1999, 38,
2020−2024.
9096
https://doi.org/10.1021/acs.inorgchem.1c01084
Inorg. Chem. 2021, 60, 9084−9096