Optical detection of sodium salts of fluoride, acetate and phosphate by a diacylhydrazine ligand by the formation of a colour alkali metal complex

Article abstract of DOI:10.1007/s12039-011-0154-8

A solution of N, N'-diacylhydrazine ligand in organic solvent is potential for colourimetric detection of F^-/AcO^-/PO ^3-₄ via -NH deprotonation, tautomerization and its stabilization as a colour alkali metal comp

Full text of DOI:10.1007/s12039-011-0154-8

c
J. Chem. Sci. Vol. 123, No. 6, November 2011, pp. 869–874. ꢀ Indian Academy of Sciences.
Optical detection of sodium salts of fluoride, acetate and phosphate
by a diacylhydrazine ligand by the formation of a colour alkali metal
complex
PURNANDHU BOSE, RANJAN DUTTA, I RAVIKUMAR and PRADYUT GHOSH∗
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
2A and 2B Raja S C Mullick Road, Kolkata 700032, India
e-mail: icpg@iacs.res.in
Abstract. A solution of N, Nꢁ-diacylhydrazine ligand in organic solvent is potential for colourimetric detec-
tion of F−/AcO−/PO34− via -NH deprotonation, tautomerization and its stabilization as a colour alkali metal
complex.
Keywords. Anion sensing; colourimetric detection; alkali metal complex; single crystal X-ray;
deprotonation.
1. Introduction
2. Experimental
Anions like fluoride, acetate and phosphate play an 2.1 Materials and methods
important roles in a wide range of chemical and biologi-
1H NMR and 13C NMR spectra for L and complex 1
cal systems and they are also of health concern.1,2 Many
synthetic chromogenic and/or fluorogenic sensors for
fluoride, acetate and phosphate have been reported in
recent years.3 Colourimetric sensing of anions by these
systems are mostly explained via deprotonated recep-
tors and their stabilization upon delocalization. Thus,
most of the above sensors are not suitable for colouri-
metric sensing of these anions even in the presence
of a trace quantity of water in the system and are
not applicable in many bio-analytical applications. Of
course, colourimetric detection of fluoride in aqueous
medium through chemodosimetric approach has been
reported scarcely.4 Gunnlaugsson and other group have
also developed few systems which are capable of bind-
ing acetate in competitive solvent like water along
with ‘naked eye’ colour change.5 To the best of our
knowledge colourimetric detection of fluoride or phos-
phate via deprotonation mechanism in the presence of
water is not known. Here, we describe a new approach
for the colourimetric detection of fluoride, acetate and
phosphate via deprotonation, tautomerization followed
by complex formation which is established by single
crystal X-ray structural analysis.6
were recorded on Bruker 300 MHz FT-NMR spectro-
meter (model: DPX-300) in DMSO-d6 at 25◦C. HRMS
measurements were carried out on QTof-Micro YA
263 instruments. Elemental analyses were performed
on a CHN 2400 Ser II Elemental Analyzer. UV/Vis
spectra were recorded on a Perkin–Elmer Lambda
950 UV/Vis Spectrometer and with a quartz cuvette
(path length: 1 cm). Acetonitrile (MeCN), dimethyl for-
mamide (DMF) and all the sodium salts were purchased
1
from Spectrochem Ltd., India. Chemical shifts for H
and 13C NMR were reported in parts per million (ppm),
calibrated to the residual solvent peak set, with coupling
constants reported in Hertz (Hz).
2.2 Synthesis of ligand, L
L was synthesized by a modified literature procedure
(scheme 1).7 To a solution of hydrazine hydrate (0.4 ml)
in dry THF was added triethylamine (3.2 ml) in ice
cold condition and the solution stirred for 15 min. To
the stirred solution 4-nitrobenzoyl chloride (3 g) in dry
THF was added, a yellow precipitate appeared after
sometime and the solution was stirred overnight and
finally refluxed for 3 h. The whole solution was then
evaporated in vacuo and thoroughly washed with H2O
to remove triethylammonium chloride and excess acid
∗For correspondence
869

870
Purnandhu Bose et al.
Scheme 1. Synthesis of L.
chloride and finally washed with diethyl ether. Mole- treated anisotropically. Wherever possible, the hydro-
cular receptor L was obtained as a pale yellow colour gen atoms are located on a difference Fourier map
1
solid (90% yield). H NMR (300 MHz, DMSO-d6): and refined. In other cases, the hydrogen atoms are
11.00 (s, -NH), 8.38 (d, J = 8.58 Hz, 4H), 8.15 geometrically fixed. Crystallographic data for complex
(d, J = 8.61 Hz, 4H).13C (75 MHz, DMSO-d6) 164.69, 1: Triclinic, P-1, a = 7.761(9)Å, b = 9.182(11)Å,
149.91, 138.31, 129.44, 124.24. HRMS: 331 (M+H+), c = 13.791(17)Å, α = 73.221(11)◦, β = 86.963(12)◦,
353.3573 (M+Na+), 369.3293 (M+K+). Anal. Calcd. γ = 74.063(12)◦, V = 904.4(19)Å3, Z = 1, Dc =
for C14H10N4O6: C, 50.66; H, 3.13; N, 16.77. Found: C, 1.558 g/cm3, T = 120 (2) K, μ = 0.153 mm−1, GOF
50.92; H, 3.13; N, 16.96.
on F2 = 1.080, R = 0.0699, wR = 0.2052 [I > 2σ(I)].
CCDC 781918 contains the supplementary crystallo-
graphic data for complex 1.
2.3 Synthesis of complex, 1
To a DMF (10 ml) solution of molecular receptor L
(50 mg), aqueous solution of Na2CO3 (100 mg in 10 ml
water) was added. The solution immediately turned to
reddish colour. It was then filtered and kept for crystal-
lization; pink colour crystal was obtained within 24 h
3. Results and discussion
The molecular receptor L was synthesized and char-
acterized by NMR, ESI-MS and elemental analyses.
Complex 1 was synthesized by the reaction of L with
Na2CO3 in a DMF solution. Pink coloured single crys-
tals of complex 1 suitable for X-ray crystallographic
analysis is obtained after slow evaporation of the sol-
vent. All compounds were obtained in good yield. The
detailed solution and structural analysis of the complex
was described below.
1
(65% yield). H NMR (300 MHz, DMSO-d6): 10.66
(br, -NH), 8.32 (d, J = 10.53 Hz, 4H), 8.11 (d, J =
8.07 Hz, 4H). Anal. Calcd. for C28H34N8O20Na2: C,
39.63; H, 4.04; N, 13.20. Found: C, 39.39; H, 3.94;
N, 12.76.
Here, we explored L for colourimetric sensing of
different inorganic anions in a semi-aqueous solvent
2.4 X-ray crystallographic analyses
The crystallographic data and data collection details for system. Colourimetric and UV-Vis experiments were
complex 1 was given below. A crystal of suitable size carried out with different anions as their sodium salts.
was selected from the mother liquor and immersed in When 0.3 ml of 10−2 (M) anions in water was added
partone oil, then mounted on the tip of a glass fibre and to 2.7 ml solution of L (1 × 10−4 M) in MeCN/DMF
cemented using epoxy resin. Intensity data for the crys- (4.9 : 0.1)(v/v), colour changes from colourless to
tal were collected using Mo Kα (l = 0.7107 Å) radiation yellow in cases of fluoride, acetate and phosphate
on a Bruker SMART APEX diffractometer equipped (figure 1), whereas the other anions induced negligi-
with CCD area detector at 120 K. The data integra- ble responses. In cases of fluoride, acetate and phos-
tion and reduction were processed with SAINT8a soft- phate a new absorption peak at 401 nm appear with
ware. An empirical absorption correction was applied molar extinction coefficient (ε401 nm) values of 5,050,
to the collected reflections with SADABS.8b The struc- 9,000 and 17,365 M−1 cm−1, respectively (figure 1). It
ture was solved by direct methods using SHELXTL9 was important to note that yellow colour persists even
and was refined on F2 by the full-matrix least-squares in the presence of significant amount of water in the
technique using the SHELXL-9710 program package. system. To determine the detection limit and selectivi-
Graphics are generated using PLATON,11 MERCURY ty of these anions further UV-Vis as well as colouri-
2.212 and ORTEP3v2. The non-hydrogen atoms are metric experiments for fluoride, acetate and phosphate

Optical detection of fluoride, acetate and phosphate by a diacylhydrazine ligand
871
2.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
3-
AcO-
F-
PO4
2.0
1.5
1.0
0.5
0.0
Cl-
SO4
2-
-
AcO-
PO4
3-
F-
NO3
L
PO43-
-5
3-
5x10 (M) PO
4
AcO-
F-
SO42-
-5
-
-
NO3-,Cl-
5x10 (M) AcO ,F
L
300
400
500
600
Wavelength(nm)
300
400
500
600
Wavelength(nm)
Figure 3. UV-Vis spectra and colour changes (inset)
observed upon addition of 0.3 ml 5 × 10−4 M aqueous solu-
tion of anions to the solution of L (10−4 M) in MeCN/DMF
(4.9:0.1 v/v, 2.7 ml).
Figure 1. UV-Vis spectra and colour changes (inset)
observed upon addition of 0.3 ml of 10−2 M aqueous solu-
tion of anions to the solution of L (10−4 M) in MeCN/DMF
(4.9:0.1 v/v, 2.7 ml).
final anion concentration is 20 times dilute and water
content is 10 times less than the previous case.
were carried out in two different experimental condi-
tions where final anion concentration and the amount
of water play important roles. Figure 2 showed UV-Vis
and colourimetric experimental results when 0.03 ml of
5 × 10−3(M) anion solution was added to 2.97 ml of
10−4 (M) solution of L. In this case a yellow coloura-
tion was observed only for acetate and phosphate where
Keeping the final anion concentration fixed and upon
increasing the water content by 10 times with respect
to figure 2, only phosphate ion showed selective colour
and spectral change (figure 3). Further we have carried
out experiment where the colour sustainability and
selectivity even in the presence of 20% water was
obtained via distinct and selective colour change for
phosphate (figure S1). It was clear from above three
experiments that in a particular condition, absorption
maxima for all the anions were same with different
molar extinction coefficient values. This clearly indi-
cates that the origin of colour appearance could be the
3.0
2.5
3-
AcO-
F-
PO4
2.0
1.5
1.0
0.5
0.0
O2N
O2N
NaX/H2O
O
O
H
N
N
N
H
L
-5
5x10 (M) PO
3-
N
H
X = OH, F, AcO, PO4
4
O
O
NO2
NO2
Deprotonation
-5
-
5x10 (M) AcO
-5
O
O2N
H
N
-
Tautomerization
5x10 (M) F
N
O2N
NO2
O
O
Na
H
O
N
H
H
H
H
N
H
Na
O
O
300
400
500
600
O2N
NO2
N
Stabilization
N
H
Wavelength(nm)
NO2
O
Figure 2. UV-Vis spectra and colour changes (inset)
observed upon addition of 0.03 ml 5 × 10−3 M aqueous solu-
tion of anions to the solution of L (10−4 M) in MeCN/DMF
(4.9:0.1 v/v, 2.97 ml).
Complex Formation
Scheme 2. The proposed mechanism for complex forma-
tion in aqueous solution.

872
Purnandhu Bose et al.
L
L+NaF
L+NaOAc
L+Na3PO4
Figure 5. Colour changes observed upon grinding 4 equi-
valents of NaF, NaOAc and Na3PO4 with L.
015
C14
O28’
O26
N13
N12
O11
O28
Na25
O27
C10
needle-like crystal of complex 1 in case of Na2CO3
was isolated and characterized by single crystal X-ray,
1H-NMR and elemental analyses. X-ray crystal struc-
tural analysis of complex 1 clearly showed the evi-
_
dence of NH deprotonation which further stabilizes
upon tautomerization and followed by alkali metal com-
plex formation. Single crystal X-ray structural analy-
sis (figure 4) reveals complex 1 as a di-sodium aquo-
bridged complex of L where each sodium ion was in
six-coordination state and showed a distorted octahe-
dral geometry around the metal centre (table 1). Two
water molecules bridge two Na+ with a Na...Na sepa-
ration of 5.341 Å. Deprotonated _NH in the complex 1
was identified from the N–C and C–O bond distances.
Figure 4. Single crystal X-ray structure of complex 1; inset
shows the crystal of complex 1 (orange:Na; black:C; red: O;
deep blue: N; white: H.).
same for these three anions and that could be due to The C(10)-N(12) and C(14)-O(15) bond distances are
the proton dissociation equilibrium. To test this phe- 1.306 Å and 1.253 Å which are significantly shorter
nomenon, NaOH/Na2CO3 solution was added to the than the C(14)-N(13) and C(10)-O(11) bond distances
solution of L (figure S2) in similar experimental con- 1.315 Å and 1.301 Å, respectively.
ditions and a similar colour change was also observed.
Shorter distances in C(10)-N(12) and C(14)-O(15)
This indeed indicates deprotonated species of the recep- can be explained due to the partial double bond charac-
tor must be involved for the colour generation. Sus- ter after deprotonation and its delocalization. From the
tainability of the colour in the presence of significant solution and single crystal X-ray analysis, we propose
amount of water suggests stabilization of the deproto- the possible mechanism (scheme 2) for the persistence
nated species in aqueous medium via tautomerization of colour even in the presence of water in the system
(scheme 2). Efforts have been made to isolate the crys- as diacylhydrazine ligand. Interestingly, this system can
tals of the colour complexes of the chemosensor with also be used for colourimetric detection of phosphate
sodium salts of fluoride, acetate, phosphate, carbonate ion in the solid phase. When a 1:4 mixture of molecular
and hydroxide in DMF-water mixture. A pink colour receptor, L and sodium salts of respective anions were
Table 1. Hydrogen bonding interactions in complex 1.
D-H· · ·A
D-H (Å)
H· · ·A (Å)
D· · ·A (Å)
∠D-H· · ·A (◦)
N13-H1...O26
0.788
0.915
0.764
0.902
0.692
0.818
0.909
0.805
0.837
2.275
1.873
2.037
1.978
2.387
2.149
2.041
1.968
2.239
3.043(5)
2.762(6)
2.799(6)
2.797
3.068
2.951
2.891
2.725
3.067
165.17
163.21
174.82
150.13
168.37
166.73
155.07
156.53
170.16
O26-H26A· · ·O11
O26-H26B· · ·O29
O27-H27A· · ·O15
O27-H27B· · ·O1
O28-H28A· · ·O29
O28-H28B· · ·O11
O29-H29A· · ·O11
O29-H29B· · ·O23

Optical detection of fluoride, acetate and phosphate by a diacylhydrazine ligand
873
grinded, a distinct red colour appeared only for phos-
phate ion whereas, yellowish colour was detected for
acetate ion (figure 5).
O’Brien J E and Glynn M 2002 Org. Lett. 4 2449;
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2. (a) Fitzmaurice R J, Kyne G M, Douheret D, Kilburn J
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4344
In summary, we have described a simple N, Nꢁ-
diacylhydrazine molecular receptor which can detect
fluoride, acetate and phosphate colourimetrically in
a semi-aqueous solvent system and it shows selec-
tivity towards phosphate at lower concentration. Fur-
ther, single crystal X-ray structural analysis confirms
–NH deprotonation in the presence of basic anions
and its stabilization through tautomerization in aqueous
medium and subsequent formation of a colour alkali
metal complex. It has been found that in the case of
phosphate the colour intensity is maximum among the
anions. This could be due to the most basic nature of
tri-negative phosphate anion which could deprotonate
L easily and effectively. Consequently, the formation
of the disodium complex 1 (i.e., concentration of 1) in
solution becomes maxima in the case of phosphate.
3. Representative examples: (a) Lee D H, Lee K H, Hong
J I 2001 Org. Lett. 3 5; (b) Camiolo S, Gale P A,
Hursthouse M B, Light M E, Shi A J 2002 Chem.
Commun. 758; (c) Camiolo S, Gale P A, Hursthouse
M B, Light M E 2003 Org. Biomol. Chem. 1 741;
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(l) Amendola V, Esteban-Gómez D, Fabbrizzi L,
Licchelli M 2006 Acc. Chem. Res. 39 343; (m) Jun
E J, Swamy K M K, Bang H, Kim S-J, Yoon J
2006 Tetrahedron Lett. 47 3103; (n) Wu Y, Peng
X, Fan J, Gao S, Tian M, Zhao J, Sun S 2007 J.
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(p) Caltagirone C, Gale P A, Hiscock J R, Brooks S
J, Hursthouse M B, Light M E 2008 Chem. Commun.
3007; (q) Amendola V, Fabbrizzi L 2009 Chem. Com-
mun. 513; (r) Gale P A, Hiscock J R, Moore S J,
Caltagirone C, Hursthouse M B, Light M E 2010
Chem.–Asian J. 5 555; (s) Bose P, Ghosh P 2010 Chem.
Commun. 46 2962; (t) Wang Q, Xie Y, Ding Y, Li X, Zhu
W 2010 Chem. Commun. 46 3669; (u) Bose P, Ahamed
B N, Ghosh P 2011 Org. Biomol. Chem. 9 1972
4. (a) Kim S Y, Hong J I 2007 Org. Lett. 9 3109; (b) Kim
S Y, Park J, Koh M, Park S B, Hong J-I 2009 Chem.
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Chem. Soc. 131 3363; (d) Hu R, Feng J, Hu D, Wang
S, Li S, Li Y, Yang G 2010 Angew. Chem. Int. Ed. 49
4915
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Ali H D, Hussey G M 2005 J. Org. Chem. 70 10875;
(b) Yu X, Lin H, Caia Z, Lina H 2007 Tetrahedron Lett.
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Supplementary data
Experimental section and spectral data (1H, 13C NMR
and ESI-MS) for L and (1H NMR) complex 1 are
provided. Crystallographic table, selected geometric
parameter and hydrogen bonding table for complex 1
are also provided for reference. The electronic sup-
plementary information can be seen in www.ias.ac.in/
chemsci.
Acknowledgements
PG gratefully acknowledges the Department of Science
and Technology (DST), New Delhi, India for finan-
cial support; PB and RD would like to acknowledge
Council of Scientific and Industrial Research (CSIR),
New Delhi, India for fellowships. X-Ray crystallogra-
phy was performed at the Facility in the Department
of Inorganic Chemistry, IACS. DST-funded National
Single Crystal X-ray Diffraction.
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