Novel heterocyclic thiosemicarbazones derivatives as colorimetric and "turn on" fluorescent sensors for fluoride anion sensing employing hydrogen bonding

Article abstract of DOI:10.1016/j.saa.2013.04.103

(Chemical Equation Presented) Two novel heterocyclic thiosemicarbazone derivatives have been synthesized, and characterized, by means of spectroscopic and single crystal X-ray diffraction methods. Their chromophoric-fluorogenic response towards anions in

Full text of DOI:10.1016/j.saa.2013.04.103

Accepted Manuscript
Novel Heterocyclic Thiosemicarbazones Derivatives as Colorimetric and “turn
on” Fluorescent Sensors for Fluoride anion sensing employing Hydrogen Bond‐
ing
S.L. Ashok Kumar, M. Saravana Kumar, P.B. Sreeja, A. Sreekanth
PII:
S1386-1425(13)00452-6
http://dx.doi.org/10.1016/j.saa.2013.04.103
SAA 10494
DOI:
Reference:
To appear in:
Spectrochimica Acta Part A: Molecular and Biomo‐
lecular Spectroscopy
Received Date:
Revised Date:
Accepted Date:
8 January 2013
17 April 2013
24 April 2013
Please cite this article as: S.L. Ashok Kumar, M. Saravana Kumar, P.B. Sreeja, A. Sreekanth, Novel Heterocyclic
Thiosemicarbazones Derivatives as Colorimetric and “turn on” Fluorescent Sensors for Fluoride anion sensing
employing Hydrogen Bonding, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2013),
doi: http://dx.doi.org/10.1016/j.saa.2013.04.103
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Novel Heterocyclic Thiosemicarbazones Derivatives as Colorimetric
and “turn on” Fluorescent Sensors for Fluoride anion sensing
employing Hydrogen Bonding
S. L. Ashok Kumara, M. Saravana Kumara, P. B. Sreejab, A. Sreekantha*
aDepartment of Chemistry, Centre of Excellence in Corrosion and Surface Engineering,
National Institute of Technology- Tiruchirappalli, Tiruchirappalli 620015, Tamilnadu, India.
bDepartment of Chemistry, Chirst University, Bangalore- 560029, Karnataka, India.
*1 Corresponding Author
Dr. A. Sreekanth, Assistant Professor, Department of Chemistry, National Institute of
Technology-Tiruchirappalli, Tiruchirappalli-620015, Tamilnadu, India
E-mail: sreekanth@nitt.edu
Tel: +91 431 2503642
Fax: +91 431 2500133
1

Novel Heterocyclic Thiosemicarbazones Derivatives as Colorimetric
and “turn on” Fluorescent Sensors for Fluoride anion sensing
employing Hydrogen Bonding
S. L. Ashok Kumara, M. Saravana Kumara, P. B. Sreejab, A. Sreekantha*
aDepartment of Chemistry, Centre of Excellence in Corrosion and Surface Engineering,
National Institute of Technology- Tiruchirappalli, Tiruchirappalli 620015, Tamilnadu, India.
bDepartment of Chemistry, Chirst University, Bangalore- 560029, Karnataka, India.
Abstract
Two novel heterocyclic thiosemicarbazone derivatives have been synthesized, and
characterized, by means of spectroscopic and single crystal X-ray diffraction methods. Their
chromophoric -fluorogenic response towards anions in competing solvent dimethyl sulfoxide
(DMSO) was studied. The receptor shows selective recognition towards fluoride anion. The
binding affinity of the receptors with fluoride anion was calculated using UV-visible and
fluorescence spectroscopic techniques.
Keywords: Thiosemicarbazone, Heterocyclic, Chromophoric and fluorogenic sensor, Single
Crystal XRD, UV-visible spectroscopy, Deprotonation.
2

1. Introduction
The design of host molecules that can recognize and sense anions selectively through
visible, electrochemical and optical responses has received considerable interest in recent years
because of the important roles played by the anions in biological, industrial, and environmental
processes.[1-6] Molecules that possess functional groups such as amides, [7,8] ureas /thioureas,
[9-12] guanidinium [13] and ammonium [14] derivatives have proven to be particularly effective
in this regard as they are able to bind anions using directional hydrogen bonding interactions.
The attachment of such functional groups with a suitable chromophoric part either covalently or
intermolecularly provides a complete receptor that can intimate binding information either by a
color change, fluorescence or both. Several reviews on anion binding in this regard using
luminescent sensors have appeared. [15-17] Despite the significant development in this domain,
the search for new luminescent sensors with structural simplicity and easy synthesis has recently
been of keen interest in molecular recognition research. Thiosemicarbazones are thiourea
derivatives having unique structural properties and chemical properties and have recently gained
interest in the anion sensing. [18] They are easily synthesized in high yields and are found to be
highly specific with low detection limits. We have synthesized two different chemosensors
receptors for fluoride 2-acetlyfuran N(4)-cyclohexyl thiosemicarbazones (H2L1) and 2-
acetlythiophene N(4)-cyclohexyl thiosemicarbazones (H2L2) (Figure 1) which function as dual
mode sensors toward fluoride with much lower detection limits in biologically competing
solvents like DMF and DMSO.
Figure 1
2. Experiment
2.1. Materials and Methods.
2-acetylfuran (Alfa), 2-acetylthiophene (Alfa), cyclohexyl isothiocyanate (Aldrich), and
tetra-n-butylammonium (TBA) salts (Aldrich) were stored in vacuum desiccators containing self-
indicating silica-gel and were used as received. Analytical grade DMSO and other solvents
(Merck) were used without further purification. 1H NMR and 13C NMR spectra were recorded on
a Bruker AVANCE III, 400 MHz in CDCl3 at 298 K with TMS as an internal standard. FT- IR
spectra were measured on a Perkin-Elmer FT-IR spectrometer using KBr pellets. UV- visible and
Fluorescence spectra were recorded in 1 cm path length quartz cell on PG Instrument T90+
3

spectrophotometer and JASCO FP-8300 spectrofluorophotometer, respectively. Elemental
analyses of both the receptor (H2L1 and H2L2) were carried out using Elementar Vario EL III
CHNS.
2.2. General procedure: Ethanolic solutions of cyclohexyl isothiocyanate (0.706 g, 5 mmol)
and hydrazine hydrate (0.250 g, 5 mmol) were mixed with constant stirring. The stirring was
continued for 1 hour and then the white product, N(4)-cyclohexyl thiosemicarbazide formed was
filtered, washed, dried and recrystallized from ethanol.
N(4)-cyclohexyl thiosemicarbazide (0.346 g, 2 mmol) was dissolved in methanol (30
mL) and was added to the appropriate ketones [2–acetylfuron (0.231 g, 2.1 mmol), 2–
acetylthiophene (0.265 g, 2.1 mmol)] dissolved in methanol (5 mL), and the reaction mixture
was continuously refluxed for 6 h after adding a few drops of acetic acid. The reaction mixture
was kept aside for slow evaporation at room temperature. After one week time, the product has
been isolated as a pale yellow solid in both the cases.
Receptor H2L1 (pale yellow). Yield: 89 %, M.P. 132-134⁰ C, Anal. Calc. for C13H19N3S2: C,
58.84; H, 7.22; N, 15.83; S, 12.08. Found: C, 58.57; H, 7.26; N, 15.45; S, 12.65 %. IR data (KBr,
cm–1) 1526 (C=N). 1H NMR (400 MHz, CDCl3, δ ppm) 1.37 (4H, m, -CH2), 1.48 (2H, m, -CH2),
1.75 (4H, m, -CH2), 2.24 (3H, s, CH3), 4.30 (1H, m, -CH), 6.53 (2H, t, Ar), 6.72 (2H, d, Ar),
13
7.50 (2H, d, Ar), 8.47 (1H, br, HC–NH), 10.53 (1H, s, N–NH). C NMR (100 MHz, CDCl3):
176.22, 151.28, 149.15, 144.34, 137.99, 132.77, 53.18, 32.73, 25.52, 24.77, 12.50.
Receptor H2L2 (pale yellow). Fine yellow single crystals obtained upon slow evaporation of a
solution of methanol at room temperature in 6 days were used for single crystal X-ray
diffraction. Yield: 86 %, M.P. 216-218⁰ C, Anal. Calc. for C13H19N3S2: C, 55.59; H, 6.42; N,
14.53; S, 22.06. Found: C, 55.48; H, 6.80; N, 14.93; S, 22.79 %. IR data (KBr, cm–1) 1529
1
(C=N). H NMR (400 MHz, CDCl3, δ ppm) 1.30 (4H, m, -CH2), 1.48 (2H, m, -CH2), 1.75 (4H,
m, -CH2), 2.26 (3H, s, CH3), 4.34 (1H, m, -CH), 7.03 (2H, t, Ar), 7.26 (2H, d, Ar), 7.33 (2H, d,
Ar), 7.47 (1H, br, HC–NH), 8.42 (1H, s, N–NH). 13C NMR (100 MHz, CDCl3): 175.45, 142.75,
142.01, 128.00, 127.59, 127.17, 52.86, 32.52, 25.55, 24.55, 13.61.
2.3 X-ray crystallography.
Crystal H2L2 was mounted on a glass fibre and the intensity data were collected at room
temperature (296 K) on a Bruker Kappa APEXII area-detector diffractometer equipped with
4

graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation. Unit cell dimensions and other
parameters are listed in Table 1. All structures were solved by direct methods and refined by
fullmatrix least-squares calculations with the SHELXTL-PLUS software package [19].
Absorption corrections were employed using SADABS (Tmax 0.9597 and Tmin 0.9404). The non-
hydrogen atoms were refined anisotropically, and all hydrogen atoms were found from the
different Fourier map and refined isotropically.
Table 1
2.4. UV-visible and Fluorescence Titrations.
The stock solutions of receptors (1  10-3 mol L- 1) were prepared in DMSO. The TBA
-
-
salts (F-, Cl-, Br-, I-, ClO4 , H2PO4 , and AcO-) solutions were prepared at a concentration of
-
-
110-2 mol L-1 in DMSO. Different equivalents of TBA salts (F-, Cl-, Br-, I-, ClO4 , H2PO4 , and
AcO-) were added to the receptors and their corresponding UV- visible and fluorescence spectra
were recorded at 298 K.
3. Result and Discussion
The structural formulae of receptors (H2L1 and H2L2) are shown in Figure 1. Both the
receptors were well characterized by various analytical techniques such as, elemental analysis,
1
UV- visible, FT–IR, H, 13C NMR and single crystal X-ray diffraction studies for H2L2. The
elemental analyses found were in good agreement with the calculated values. Receptors were
readily soluble in organic solvents such as DMF and DMSO. IR spectrum of the receptors
showed characteristic stretching frequencies at 1526 (H2L1) and 1529 (H2L2), cm–1 ν(C=N)
indicative of the newly formed azomethine group and stretching frequencies at 1213 (H2L1) and
1
1294 (H2L1) cm–1 ν(C=S) indicating that the thione form is dominating in the solid state. H
NMR spectrum of H2L1 showed two broad singlets at δ 8.47 and δ 10.53 ppm assignable to the
NH protons present in the molecule, which disappears with the addition of D2O. Similarly for
H2L2 the corresponding two NH protons appeared at δ 7.47 and δ 8.42 respectively [20] which
disappear with D2O addition. H2L1 and H2L2 showed singlet protons at δ 2.27 and δ 2.26
corresponding to the ketone methyl group respectively. Receptors (H2L1, H2L2) heterocyclic
aromatic ring protons appeared around δ 6.5–7.7 ppm accounting for two doublet protons and
one triplet proton. The 13C NMR spectrum of H2L1 and H2L2 showed well defined peaks at
5

176.22, 175.45 assignable to thione carbon (C=S) respectively. Azomethine carbon (–C=N)
peaks appeared at δ 151.28, 142.75 respectively for H2L1 and H2L2.
Figure 1
3.1. Molecular and Crystal Structure of H2L2
The molecular structure of H2L2, along with the atom numbering scheme is given in
Figure 2. The crystal data and structural refinement parameters are given in Table 1 and selected
bond lengths and angles are given in Table 2. The receptor crystallized into a monoclinic lattice
with the space group P21. The molecule exists in the E conformation with respect to the C5–N1
bond. However, the S2 and N1 atoms are in the E conformation with respect to the N2–C7 bond,
and hence the thiosemicarbazone moiety as a whole exists in the EE conformation. This is
contrary to the observations in 3-piperidyl and 3- hexamethyliminyl-di-2-pyridyl ketone
thiosemicarbazones [21], which revealed a ZZ conformation for the thiosemicarbazone moiety.
However, N4-methyl-di-2-pyridyl ketone thiosemicarbazone was observed to be in the ZE
conformation [22]. In H2L1, the thiosemicarbazone moiety comprising of atoms N1, N2, C7, S2
and N3 is almost planar, with a maximum mean plane deviation of 0.0375(1) Å. A torsion angle
of 174.48 (14) corresponding to the S2– C7–N2–N1 moiety implies a trans alignment of the
thiocarbonyl S2 atom in H2L1. The azomethine bond, C5–N1 (1.281 (2) Å) is in conformity with
a formal C=N double bond (1.28Å) and the C7–S2 bond distance of 1.671(2) Å, is very close to
a formal C=S bond length (1.60Å ) [23].
It confirms the existence of the thiosemicarbazone in the thione form in the solid state.
The N2–N1 (1.368 (2)) and N3–C7 (1.322 (3)) bond distances in H2L2 are intermediate between
formal single or double N–N and C–N bonds, giving evidence for an extended π delocalization
along the thiosemicarbazone chain. In the molecule there exist intramolecular hydrogen bonding
interaction, N2–H2A–S2 forming an eight-membered ring as clearly seen from the packing
arrangement of the atoms as shown in Figure 3.
Figure 2, Figure 3, Table 2
3.2. Colorimetric analysis and UV visible spectra studies
The colorimetric analysis were conducted to test the interaction of the receptors (H2L1
and H2L2) with various anions such as fluoride, chloride, bromide, iodide, perchlorate,
6

dihydrogen phosphate and acetate anions were investigated in DMSO solution. Noticeable and
appreciable color changes were observed when the receptors (H2L1 and H2L2) were treated with
the fluoride anion, imparting an immediate color change from colorless to yellow color.
However other anions failed to exhibit color changes on similar condition except, acetate anion
which hardly produces any visible color change on interaction with the receptors as shown in
Figure 4.
Figure 4
The UV-visible behavior of the receptors in DMSO solutions (510-5 mol L- 1) were
studied at 298K in the presence of fluoride, chloride, bromide, iodide, perchlorate, dihydrogen
phosphate and acetate anions. The receptors with addition (up to 3 equiv) of chloride, bromide,
iodide, perchlorate and dihydrogen phosphate induced insignificant changes in the UV-visible
spectra strongly suggesting that no coordination takes place. This behavior contrasts with that
observed in the presence of basic anions, such as fluoride and acetate shown in Figure 5. The
spectral profile of receptors shows the absorption peaks at 258 (H2L1) and 259 (H2L2) nm
attributable to the ππ* transitions. While a second absorption at 323 (H2L1) and 335 (H2L2) nm
was observed which may be attributed to the nπ* transitions. UV-visible titrations of the
receptors (H2L1 and H2L2) with fluoride showed an intensity decrease and a small bathochromic
shift in the absorption band corresponding to the nπ* transitions and also subsequent
formation of a new band appeared at 384 (H2L1) and 402 (H2L2) respectively. Moreover both the
position of the new band and the relative intensity of the absorption band of the receptor with
respect to the band upon addition of fluoride were dependent on the receptor used as shown in
Figure 6. Whereas upon addition of acetate anion to the receptors showed a new peak with a less
intensity at ≈ 360 (H2L1) and ≈ 390 (H2L2) nm.
Figure 5, Figure 6
Continuous variation method was used to determine the stoichiometric ratio of the
receptors (H2L1 and H2L2) to the fluoride anion guest (Job's plot; Figure 7). A Job's plot [24] of
the H2L1 and H2L2 with fluoride anion in DMSO shows the maxima at a molar fraction of 0.5.
This indicates that the H2L1 and H2L2 bind with the fluoride anion in a 1:1 ratio during the initial
stages of the reaction. Considering this result along with the other data, the binding mode of
H2L1 and H2L2 to the fluoride anion is proposed as shown in Figure 8.
7

Figure 7, Figure 8
The binding stoichiometry of H2L1 and H2L2 were calculated in accordance with the
Benesi-Hildebrand equation (shown in figure 9), [16] which was given as follows:



1
1
1

1

A A A  A K [F ]0
0
0


where A0 is the absorbance of free receptor, A is the absorbance with a specific fluoride
concentration, A∞ is the absorbance with excess amount of F-, K is the association constant (M-
1), and [F-]0 is the concentration of F- added (M). The plot of 1/(A-A0) against 1/[F]0 shows a
linear relationship (R = 0.99), indicating that receptors associates with fluoride and acetate in a
1:1 stoichiometry. The association constant (K) of the receptors H2L1 and H2L2 with F- was
determined from the ratio of intercept/slope which is found to be 0.14  104 M-1 (H2L1) and 1.14
 104 M-1 (H2L2), respectively. From the association constant values, it is inferred that H2L2 has
more affinity toward fluoride anion as compared to that of H2L1. The spectra of receptors H2L1
and H2L2 did not show any appreciable change with the addition of other anion (AcO-, Cl-, Br-, I-
-
-
, ClO4 , and H2PO4 ); hence association constants cannot be determined by using the spectra of
both receptors H2L1 and H2L2 with other anions. The changes observed in the UV-visible
spectrum upon fluoride addition were attributed to the formation of hydrogen-bonding
complexes with the thiosemicarbazone groups that eventually resulted in a deprotonation [25-
28]. The formation of hydrogen bonding complexes was reflected in relatively small variations in
the absorption band of the receptor whereas deprotonation processes was related with the
appearance of a new absorption band at longer wavelengths [29]. Moreover a close view of the
results indicated that the final response of the receptors towards the tested anions is dependent on
the heterocyclic ring system attached to the thiosemicarbazone group that modulated the acidity
of the N-H protons.
Figure 9
3.3 Fluorescence spectral studies
The fluorescence behaviors of receptors (H2L1 and H2L2) were studied in DMSO.
Fluorescence experiments were carried out with 384 and 402 nm as excitation wavelength of
H2L1 and H2L2 respectively. When 0 - 3 equiv. of tetrabutylammonium fluoride were added to
8

the solution of receptors a concomitant increase of the fluorescence intensity was observed as
shown in Figure 10. As also seen that the, addition of fluoride anion to H2L1 and H2L2 induced a
slight red shifted emission band at 437 nm and 438 nm respectively. These are clear observations
that the so called fluorescence enhancement comes by the removal of nπ* transitions which
normally mask the ππ* transition which are mainly responsible for the emission behavior.
Hence the recognition of a molecule does not simply involve a color change, but also involves
serious electronic changes within the molecule affecting the HOMO and LUMO interactions
considerably. In the same conditions, no significant spectra changes happened when 20 equiv. of
other tetrabutylammonium anion salt were added.
Figure 10
The stability constant of the complex was calculated by the linear Benesi–Hildebrand
expression [30] (shown in Figure 11).
1
1
1
1


Kass [R] F
I [R] X
where I is the change in the fluorescence intensity at 437 (H2L1) and 438 (H2L2) nm,
Kass is the stability constant, X is the difference of fluorescence quantum yields between the
complex and receptor, and [R] and [F] are the concentrations of receptor and fluoride anion,
respectively. On the basis of the plot of 1/I and 1/[F], the stability constant was determined to
be 6.1 ×105 (H2L1) and 6.8 ×106 (H2L2) M−1 with a good linear relationship (R =0.99), which also
indicates that the formation of the complex occurs with 1:1 stoichiometry . The results suggest
H2L2 have high selective detection fluoride anion.
Figure 11
4. Conclusion
In conclusion, two chromogenic thiosemicarbazone receptors (H2L1 and H2L2) were
synthesized in good yields via diazo coupling and condensation. Among them, the receptor H2L2
exhibits higher sensitive for the fluoride anion and there was a prominent color change in the
system, which can be observed by naked-eye. Both the thiosemicarbazone derivatives have been
designed to provide the anion recognition through H-bonding interactions employing thiourea -
NH groups. However the results show that the deprotonation rather than the H-bonding is the key
9

factor triggering the chromogenic effect. Sensing ability and binding affinity of both the
receptors towards fluoride was examined using techniques UV-visible and fluorescence
spectroscopy. It has also been found that the receptors were highly sensitive and selective
towards fluoride even in a biologically competing solvent like DMSO.
5. Supplementary information
Crystallographic data for the structural analysis has been deposited with the Cambridge
Crystallographic Data Centre, CCDC 892725 for the H2L2. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 IEZ, UK
(fax: +44-1223- 336-033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Acknowledgements:
AS
acknowledge
the
DAE-BRNS,
Department
of
Atomic
Energy
(NO.2010/20/37C/10/BRNS/2494) for a young scientist award. SLA, acknowledges MHRD,
Govt of India, for a research fellowship. The authors are also thankful to SAIF at IIT-Madras,
Chennai-600036, Tamil Nadu, India for NMR as well as single crystal X-ray data.
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List of Figure Captions
Figure 1: Structural formulae of the receptor (H2L1 and H2L2)
Figure 2: ORTEP of H2L2 showing the atom-numbering scheme.
Figure 3: Representing hydrogen bonding interactions in H2L2.
Figure 4: Color change of H2L1 and H2L2 (5 × 10–5 mol L–1) in DMSO solution with the addition
–
–
3 eq. of TBA anions. A= Receptor, B = F–, C = Cl–, D = Br–, E = I–, F = ClO4 ,
G = H2PO4 ,
H = AcO– at 298 ± 0.1 K.
Figure 5: Absorption spectra of receptor with addition of different anions (3 eq.) as their TBA
salts (a) H2L1 (b) H2L2
Figure 6: Absorption spectra of receptor with addition (0 – 3 eq.) of standard solution fluoride
(a) H2L1 (b) H2L2
Figure 7: Job plot for complexation of receptor with F– determined by absorption spectra, [H4L]
+ [anion] = 1×10–4 mol L–1 (a) H2L1 (b) H2L2
Figure 8: The proposed host–guest binding mode with fluoride anion in solution.
Figure 9: Benesi-Hildebrand plot UV-visible titration result receptor with F– in DMSO (a) H2L1
(b) H2L2
Figure 10: Fluorescence spectra for receptor in DMSO solution with the addition (0- 3 eq.) of
fluoride anion (a) H2L1 (b) H2L1.
Figure 11: Benesi-Hildebrand plot photo luminance titration result receptor with F– in DMSO
(a) H2L1 (b) H2L2.
12

Figure 1: Structural formulae of the receptor (H2L1 & H2L2)
13

Figure 2: ORTEP of H2L2 showing the atom-numbering scheme.
14

Figure 3: The crystal packing of (H2L2). Hydrogen bonds are shown as dashed lines of H2L2.
15

Figure 4: Color change of H2L1 and H2L2 (5 × 10–5 mol L–1) in DMSO solution with the addition
–
–
3 eq. of TBA anions. A= Receptor, B = F–, C = Cl–, D = Br–, E = I–, F = ClO4 ,
G = H2PO4 ,
H = AcO– at 298 ± 0.1 K.
16

Figure 5: Absorption spectra of receptor with addition of different anions (3 eq.) as their TBA
salts (a) H2L1 (b) H2L2
17

Figure 6: Absorption spectra of receptor with addition (0 – 3 eq.) of standard solution fluoride
(a) H2L1 (b) H2L2
18

Figure 7: Job plot for complexation of receptor with F– determined by absorption spectra, [H4L]
+ [anion] = 1×10–4 mol L–1 (a) H2L1 (b) H2L2
19

Figure 8: The proposed host–guest binding mode with fluoride anion in solution.
20

Figure 9: Benesi-Hildebrand plot UV-visible titration result receptor with F– in DMSO (a) H2L1
(b) H2L2
21

Figure 10: Fluorescence spectra for receptor in DMSO solution with the addition (0- 3 eq.) of
fluoride anion (a) H2L1 (b) H2L1
22

Figure 11: Benesi-Hildebrand plot photo luminance titration result receptor with F– in DMSO
(a) H2L1 (b) H2L2.
23

Table 1: Crystal data and structure refinement information for H2L2.
H2L2
Empirical formula
Formula weight
C13 H19 N3 S2
281.43
Temperature
293(2) K
Wavelength
0.71073 Å
Crystal system, space group
Unit cell dimensions
Monoclinic, P12/c1
a = 13.0370(5) Å
alpha = 90 deg.
b = 5.7580(2) Å
beta = 96.7000(10) deg.
c = 19.9200(6) Å
gamma = 90 deg.
1485.12(9) A^3
4, 1.259 Mg/m^3
0.346 mm^-1
600
Volume
Z, Calculated density
Absorption coefficient
F(000)
Crystal size
Theta range for data
collection
0.30 x 0.20 x 0.20 mm
2.06 to 25.00 deg.
-15<=h<=15, -6<=k<=4, -
23<=l<=23
Limiting indices
13464 / 2599 [R(int) = 0.0282]
Reflections collected / unique
Completeness to theta
Absorption correction
Max. and min. transmission
Refinement method
= 25.00
99.2 %
Semi-empirical from equivalents
0.9863 and 0.9031
Full-matrix least-squares on F^2
2599 / 198 / 241
Data / restraints / parameters
Goodness-of-fit on F^2
Final R indices [I>2sigma(I)]
R indices (all data)
1.036
R1 = 0.0347, wR2 = 0.0859
R1 = 0.0540, wR2 = 0.1002
0.217 and -0.138 e.A^-3
Largest diff. peak and hole
Table 2: Selected bond lengths (Å) and bond angles (°) for H2L2
24

Selected bonds
Value (Å)
Selected angles
(°)
C(2)-S(1')
C(4)-S(1')
C(4)-S(1)
C(5)-N(1)
C(7)-N(3)
C(7)-N(2)
C(7)-S(2)
C(8)-N(3)
N(1)-N(2)
N(2)-H(2A)
N(3)-H(3A)
1.637(3)
1.587(7)
1.649(6)
1.687(3)
1.281(2)
1.322(3)
1.362(2)
1.671(2)
1.455(2)
1.368(2)
0.859(15)
C(1)-C(2)-S(1')
S(1')-C(4)-S(1)
C(1)-S(1)-C(4)
C(2)-S(1')-C(4)
N(1)-C(5)-C(4)
N(1)-C(5)-C(6)
C(4)-C(5)-C(6)
H(6A)-C(6)-H(6B)
N(3)-C(7)-N(2)
N(3)-C(7)-S(2)
N(2)-C(7)-S(2)
N(3)-C(8)-C(9)
N(3)-C(8)-C(13)
N(3)-C(8)-C(9')
N(3)-C(8)-H(8)
C(5)-N(1)-N(2)
C(7)-N(2)-N(1)
C(7)-N(2)-H(2A)
N(1)-N(2)-H(2A)
C(7)-N(3)-C(8)
C(7)-N(3)-H(3A)
C(8)-N(3)-H(3A)
120.1(3)
117.2(3)
92.74(16)
93.3(4)
115.15(17)
125.05(18)
119.79(16)
109.5
114.94(18)
124.76(15)
120.29(15)
115.2(3)
108.7(3)
103.2(5)
103.9(15)
119.80(16)
117.83(17)
115.9(13)
125.8(13)
126.00(19)
117.4(15)
116.6(15)
25

3

Research highlights
ꢀ New heterocyclic thiosemicarbazone derivatives have been prepared and characterized.
ꢀ It is a very good naked eye detection sensor for the fluoride anion
ꢀ The Chemosensor is novel with sensing unit directly attached to the signaling unit for
easy signaling.
4