Ruthenium(II) complexes of thiosemicarbazones: Synthesis, X-ray crystal structures, spectroscopy, electrochemistry, DFT studies and fluoride sensing properties

Article abstract of DOI:10.1016/j.ica.2017.01.011

Six Ru(II) complexes with formula [Ru(terpy)(L)]X (L = tridentate N,N,S^?donor thiosemicarbazone ligands, X = PF₆^?) have been synthesized and characterized by using standard analytical and spectroscopic techniques. The X-ray crystal structures of the complexes [Ru(terpy)(L²)]PF₆(2) and [Ru(terpy)(L³)]PF₆(3) have been determined. It was found that during complexation the hydroxyimino functionality of the parent ligands is converted to imine, which participates in coordination through the N-atom. The complexes are found to undergo two quasi-reversible oxidations on the positive side of the potential window (0 to +0.8 V) and three successive quasi-reversible/irreversible reductions on the negative side of the potential window (0 to ?2 V). The fluoride sensing properties of all the complexes have been studied in solution using absorption spectra and¹H NMR studies, as well as by cyclic voltammetric (CV) measurements. From the absorption titration studies the association constants and detection limit values of fluoride by the complexes have been determined. The association constant values were found to be reasonably high (logK_a> 5) for complexes 3–6, and these values are one order of magnitude greater than those observed for the corresponding free thiosemicarbazones. Selective fluoride sensing by these complexes is also signaled by the development of vivid colors, visible with the naked eye.

Full text of DOI:10.1016/j.ica.2017.01.011

Accepted Manuscript
Research paper
Ruthenium(II) complexes of thiosemicarbazones: synthesis, X-ray crystal struc-
tures, spectroscopy, electrochemistry, DFT studies and fluoride sensing prop-
erties
Bipinbihari Ghosh, Piyali Adak, Subhendu Naskar, Bholanath Pakhira, Partha
Mitra, Rupam Dinda, Shyamal Kumar Chattopadhyay
PII:
S0020-1693(17)30058-0
http://dx.doi.org/10.1016/j.ica.2017.01.011
ICA 17404
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
17 June 2016
14 December 2016
11 January 2017
Please cite this article as: B. Ghosh, P. Adak, S. Naskar, B. Pakhira, P. Mitra, R. Dinda, S.K. Chattopadhyay,
Ruthenium(II) complexes of thiosemicarbazones: synthesis, X-ray crystal structures, spectroscopy,
electrochemistry, DFT studies and fluoride sensing properties, Inorganica Chimica Acta (2017), doi: http://
dx.doi.org/10.1016/j.ica.2017.01.011
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Ruthenium(II) complexes of thiosemicarbazones: synthesis, X-ray crystal
structures, spectroscopy, electrochemistry, DFT studies and fluoride sensing
properties
Bipinbihari Ghosh,a Piyali Adak,a Subhendu Naskar,b Bholanath Pakhira,a Partha Mitra,c Rupam
Dinda,d Shyamal Kumar Chattopadhyay*a
aDepartment of Chemistry, Indian Institute of Engineering Science and Technolgy, Shibpur,
Howrah 711103, India
bDepartment of Applied Chemistry, Birla Institute of Technology, Mesra, Ranchi 835215,
Jharkhand, India
cDepartment of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Jadavpur, Kolkata 700032, India
dDepartment of Chemistry, National Institute of Technology, Rourkela 769008, Orissa, India
*Corresponding Author.
E mail address: shch20@hotmail.com (S.K. Chattopadhyay).
Abstract
Six Ru(II) complexes with formula [Ru(terpy)(L)]X (L = tridentate N,N,S− donor
−
thiosemicarbazone ligands, X = PF6 ) have been synthesized and characterized by using standard
analytical and spectroscopic techniques. The X-ray crystal structures of the complexes
[Ru(terpy)(L2)]PF6(2) and [Ru(terpy)(L3)]PF6(3) have been determined. It was found that during
complexation the hydroxyimino functionality of the parent ligands is converted to imine, which
participates in coordination through the N-atom. The complexes are found to undergo two quasi-
reversible oxidations in the positive potential window (0 to +0.8 V) and three successive quasi-
reversible/ irreversible reductions in the negative potential window (0 to −2 V). The fluoride
sensing properties of all the complexes have been studied in solution using absorption spectra
and 1H NMR studies, as well as by cyclic voltammetric (CV) measurements. From the
absorption titration studies the association constants and detection limit values of fluoride by the
complexes have been determined. The association constant values were found to be reasonably
1

high (logKa > 5) for complexes 3-6, and these values are one order of magnitude greater than
those observed for the corresponding free thiosemicarbazones. The selective fluoride sensing
properties of all the complexes have also been signaled by the development of vivid colors
visible with the naked eye.
Keywords: Ru(II) complexes, Thiosemicarbazone, Cyclic voltammetry, X-ray structure, DFT
calculations, F− sensing properties
1. Introduction
Thiosemicarbazones are an important class of N, S-donor ligands, with the free ligands, as well
as their metal complexes showing variety of biological activities, including anticancer,
antibacterial, antimalarial, antifungal and anti-HIV activities [1-10]. Though coordinated
thiosemicarbazones usually form five membered chelate rings [6-12], coordinating through
imine nitrogen and the sulfur atom, there are quite a few examples, mainly involving Ru(II) as
the metal center, where four membered chelate rings are stabilized, the coordinating atoms being
the sulfur and the deprotonated hydrazinic nitrogen [13-17]. The relative stability of the four
membered versus five membered chelate rings have been found to depend on number of factors,
including nature of the coligands, solubility of the complexes, H-bonding interactions and
packing forces[13]. Thus, reaction of Ru(PPh3)3Cl2 with pyridine-2-aldehyde (4-
cyclohexyl)thiosemicarbazone gave [Ru(PPh3)2(H2N^S)2]2+, where H2N^S stands for the
nondeprotonated thiosemicarbazone ligand which coordinates through imine N (N1, see scheme-
1) and thione sulfur, forming five membered chelate ring, whereas reaction of the same Ru(II)
precursor with pyridine-2-aldehyde thiosemicarbazone and pyridine-2-aldehyde (4-
alkyl/aryl)thiosemicarbazones in presence of Et3N gave complexes of type [Ru(PPh3)2(HN^S)2],
where HN^S is monoanionic form of thiosemicarbazone, coordination through deprotonated N2
nitrogen and the sulfur atoms, forming four membered chelate ring [18,19, 20d]. Again,
thiosemicarbazones of thiophen-2-aldehyde as well as benzaldehyde form four membered
chelate rings when the coligands are two cis-PPh3 groups or a bidentate 1,4-
2

bis(diphenylphosphino)butane ligand, but when bi(diphenylphosphino)methane is used as
coligand the same thiosemicarbazones form five membered chelate rings, along with
orthometallation of the heterocyclic/ aromatic ring [13,15,16,20]. It was also shown that
complexes of the type [Ru(PPh3)2(HN^S)2] may act as metallo-ligand and can form oligonuclear
complexes like [(Ph3P)2RuII(N^S)2CuII Cl2], [{(Ph3P)2RuII(N^S)2}4NiII ]4+ (N^S =
2
4
dideprotonated pyridine-2-aldehyde thiosemicarbazone or salicyl aldehyde thiosemicarbazone,
deprotonations occurring from N2 and N4 nitrogen atoms) [14d,19]. Thiosemicarbazides and
thiosemicarbazones are known to be redox non-innocent ligands [7,24,25]. It was also shown
that Ru(II)-thiosemicarbazone complexes possess interesting electronic structures as there are
appreciable mixing between the Ru(II) orbitals and the ligand orbitals in these complexes.
Therefore, thiosemicarabzone complexes of Ru(II) continues to be a fertile area of investigation
with structural diversity and intriguing electronic structures as noted above along with the
revelations of its potential medicinal applications [5-10, 23]. These developments have been
summarized in recent reviews [17, 24].
Anions like acetate, phosphates, and fluoride play important roles in biology [25]. Therefore
design of specific sensors for each of these anions has emerged as an important and active area
of research in recent times [26]. Fluoride ion has important structural role in maintaining
integrity of structures of bones and teeth enamel. However, excess of fluoride, often
contaminated with drinking water, causes health hazard such as fluorosis, urolithiasis, and cystic
fibrosis [27,28]. Compounds containing N-H protons, such as imidazoles, pyrazoles, amides,
thiourea and urea derivatives have been extensively used as chromogenic and fluorogenic
sensors for anions, particularly for fluoride ion [29-33]. This is because of the ability of the N-H
proton to enter into strong hydrogen bonding interaction with anions like F−. 4-aryl substituted
thiosemicarbazones possess two N-H protons in the nondeprotonated state and on deprotonation,
particularly during chelation, one N-H proton remains in the thiosemicarbazide fragment, whose
acidity can be controlled by substitution on the adjacent aromatic ring as well as by changing the
metal ion to which it is coordinated. As a result phenylthiourea derivatives in general, and
thiosemicarbazones in particular, are now subject of intense investigations as anion receptor,
particularly of fluoride [32,33-35]. However, a major problem with many of the reported sensors
of fluoride ions is that they often also sense acetate ions [29b-h, 30c-d, 33b-c, 34, 35]. Therefore,
design of new sensors with high specificity for fluoride ion is a highly desirable goal. In this
3

regard, we thought that ternary complexes of thiosemicarbazones with preformed Ru(II)-
polypyridyl core are likely to be good chromogenic platform for F− detection, where the
thiosemicarbazone fragment will act as sensor unit and Ru(II)-polypyridyl fragment will be the
reporter unit. Towards this goal, we report in this paper six mixed ligand complexes of Ru(II)
containing terpyridyl and six tridentate thiosemicarbazones and the F− sensing properties of
these Ru(II) complexes.
In recent years we have been investigating in our laboratory the redox non-innocent behavior of
thiosemicarbazones and the extent of coupling of the metal and thiosemicarbzone orbitals in
Ruthenium(II)-thiosemicarbazone complexes [13,15,16]. In this work also, we have devoted
some of our attention to this interesting aspect of Ru(II)-thiosemicarbazone chemistry, apart
from focusing on the primary objective the work of identifying metal complexes of
thiosemicarbazones as fluoride selective sensors. As an interesting aside, we also report here a
relatively rare conversion of oxime functionality of the ligands to metal coordinated imine
moiety.
R2
R1
R1
R
R2
R
N
S
N
1
N
4
+
N
1
4
3
H
3
+
R'
N
2
R'
N
2
S
H
Scheme 1: Protonated and deprotonated forms of thiosemicarbazone ligands along with the atom
numbering scheme.
2. Experimental
2.1. Materials and methods
Diacetyl monooxime was purchased from Aldrich and triethylenetetramine was purchased from
E. Merck. All other chemicals and solvents were of reagent grade and used as such. Ru(terpy)Cl3
was prepared following a published procedure [36]. Solvents for spectroscopic and cyclic
voltammetry studies were of HPLC grade obtained from Merck or Aldrich. Elemental analyses
were performed on a Perkin–Elmer 2400 C, H, N analyzer. Infrared spectra were recorded as
KBr pellets on a JASCO FT-IR-460 spectrophotometer. UV–Vis spectra were recorded using a
JASCO V-530 spectrophotometer. Electrochemical data of 1-2 mM CH3CN solutions of the
4

complexes were collected using a CH1106A potentiostat. A three electrode configuration,
consisting of a glassy carbon working electrode and a Pt-wire auxiliary electrode, Ag/AgCl,
KCl(sat) reference electrode and TEAP as supporting electrolyte, were used. The potentials were
calibrated against the ferrocene/ferrocenium couple (E0 = 0.44 V). 1H and 13C NMR spectra were
recorded on a Bruker AVANCE DPX 400 MHz spectrometer using, Si(CH3)4 as internal
standard. ESI-MS spectra of the samples were recorded on JEOL JMS 600 instrument.
2.2. Synthesis of ligands
The ligands (Scheme 1), (E)-1-(3-hydroxyiminobutan-2-ylidene)-4-p-tolylthiosemicarbazide
(L1H′), (E)-1-(3-hydroxyiminobutan-2-ylidene)-4-phenylthiosemicarbazide (L2H′), (E)-4-(4-
chlorophenyl)-1-(3-hydroxyiminobutan-2-ylidene)thiosemicarbazide (L3H′), (E)-4-(4-
fluorophenyl)-1-(3-hydroxyiminobutan-2-ylidene)thiosemicarbazide (L4H′), (E)-4-(4-
bromophenyl)-1-(3-hydroxyiminobutan-2-ylidene)thiosemicarbazide (L5H′) and (E)-1-(3-
hydroxyiminobutan-2-ylidene)-4-(4-methoxyphenyl)thiosemicarbazide (L6H′) were prepared
using the corresponding aryl amines by the published procedure [37-39].
2.3. Synthesis of Complexes
The complexes (Scheme 2) [Ru(terpy)L1]PF6 (1), [Ru(terpy)L2]PF6·3H2O (2),
[Ru(terpy)L3]PF6·MeOH (3), [Ru(terpy)L4]PF6·2H2O·MeOH (4), [Ru(terpy)L5]PF6·H2O (5) and
[Ru(terpy)L6]PF6.H2O (6) were synthesized following a general procedure outlined below for
complex 1, using the appropriate thiosemicarbazone.
2.3.1. [Ru(terpy)L1]PF6 (1)
To a 50 ml ethanolic solution of the L1H (132.5 mg, 0.5 mmol), Et3N (50 mg, 0.5 mmol) was
added, followed by the addition of solid Ru(terpy)Cl3 (220.25 mg, 0.5 mmol) and the reaction
mixture was refluxed with continuous stirring for 8 hours; the solution was cooled and solid
NH4PF6 was then added to the brown red reaction mixture and filtered. The filtrate was
evaporated to dryness on rotary evaporator. The entire crude product was then purified by silica
gel column chromatography. An intense reddish brown band was eluted with chloroform–
methanol mixture (9:1). Evaporation of the solvent and recrystallization from 1:1 chloroform–
methanol solution leads to deep brown crystals.
Yield: 57%. Anal. Calc. for C27H26F6N7PRuS (Found): C, 44.63 (44.51); H, 3.61 (3.48); N, 13.49
(13.38)%. ESI-MS (positive, MeOH) m/Z = 582.07 (100%) [M−PF6]+. UV−Vis [MeCN; λmax/nm
5

(ε/ M−1 cm−1)]: 271 (81280), 312 (87620), 381 (46736), 498 (37336), 661 (3756). 1H-NMR
(DMSO-d6): δ (ppm) (see Scheme 2 for proton numbering): 9.79 (s, 1H, H1), 9.51 (s, 1H, H2),
8.76 (d, 2H, J=8 Hz, H8), 8.51 (d, 2H, J=8 Hz, H5), 8.13 (m, 3H, 1H3+2H4), 8.02 (m, 2H, H6),
7.68 (d, 2H, J=8.4 Hz, H9), 7.59 (m, 2H, H7), 7.12 (d, 2H, J=8.4 Hz, H10), 2.69 (s, 3H, H11),
2.25 (s, 3H, 4-(CH3)Ph), 2.19 (s, 3H, H12). 13C{1H} NMR (DMSO-d6): δ(ppm): 177.81, 157.54,
154.54, 153.41, 136.6, 133.33, 131.74, 129.33, 128.08, 123.54, 122.59, 120.63, 49.07, 31.16,
22.95, 20.84, 15.87. Selected IR bands (cm-1): 3315 (νN-H), 1596 (νC=N).
2.3.2. [Ru(terpy)L2]PF6·3H2O (2)
Yield: 59%. Anal. Calc. for C26H30F6N7O3PRuS (Found): C, 38.96 (40.28); H, 3.01 (3.21); N,
11.78 (12.05)%. ESI-MS (positive, MeOH) m/Z = 567.79 (100%) [M−PF6−CHCl3]+. UV−Vis
[MeCN; λmax/ nm (ε/ M−1 cm−1)]: 272 (77868), 311 (87210), 374 (48616), 498 (36046), 665
(3362). 1H-NMR (DMSO-d6): δ (ppm): 9.82 (s, 1H, H1), 9.57 (s, 1H, H2), 8.77 (d, 2H, J=8 Hz,
H8), 8.65 (d, 2H, J=8 Hz, H5), 8.11 (m, 3H, 1H3+2H4), 8.02 (m, 2H, H6), 7.82 (d, 2H, J=8 Hz,
H9), 7.59 (m, 2H, H7), 7.32 (m, 2H, H10), 6.97 (m, 1H, 4-(H)Ph), 2.71 (s, 3H, H11), 2.20 (s, 3H,
H12). 13C{1H} NMR (DMSO-d6): δ(ppm): 177.65, 176.84, 157.54, 154.56, 153.45, 141.37,
136.63, 133.33, 128.95, 128.09, 123.55, 122.77, 122.62, 120.52, 79.59, 22.97, 15.91. Selected IR
bands (cm-1): 3421 νO-H, 3315 (νN-H), 1596 (νC=N).
2.3.3. [Ru(terpy)L3]PF6·MeOH (3)
Yield: 57%. Anal. Calc. for C27H26ClF6N7OPRuS (Found): C, 41.64 (41.52); H, 3.34 (3.27); N,
12.59 (12.44)%. ESI-MS (positive, MeOH) m/Z = 601.73 (100%) [M−PF6−MeOH]+. UV−Vis
[MeCN; λmax/ nm (ε/M−1 cm−1)]: 271 (89960), 311 (101196), 375 (59768), 499 (46122), 662
(4170). 1H-NMR (DMSO-d6): δ (ppm): 9.86 (s, 1H, H1), 9.69 (s, 1H, H2), 8.77 (d, 2H, J=8 Hz,
H8), 8.65 (d, 2H, J=8 Hz, H5), 8.14 (m, 3H, 1H3+2H4), 8.02 (m, 2H, H6), 7.84 (d, 2H, J=8.8
Hz, H10), 7.59(m, 2H, H7), 7.37 (d, 2H, J=8.8 Hz, H9), 2.71 (s, 3H, H11), 2.02 (s, 3H, H12).
13C{1H} NMR (DMSO-d6): δ(ppm): 177.77, 157.52, 154.56, 154,153.50, 140.29, 136.69,
133.45, 128.79, 128.12, 126.31, 123.57, 122.64, 121.99, 22.98, 15.97. Selected IR bands (cm-1):
3414 (νO-H), 3310 (νN-H), 1588 (νC=N).
2.3.4. [Ru(terpy)L4]PF6·2H2O·MeOH(4)
Yield: 56%. Anal. Calc. for C27H31F7N7O3PRuS (Found): C, 40.60 (40.49); H, 3.91 (3.83); N,
12.28 (12.19)%. ESI-MS (positive, MeOH) m/Z = 586.01 (100%) [M−PF6−2H2O−MeOH]+.
UV−Vis [MeCN; λmax/ nm (ε/ M−1 cm−1)]: 272 (82900), 311 (99206), 374 (55266), 498
6

(43960), 664 (4106). 1H-NMR (DMSO-d6): δ (ppm): 9.83 (s, 1H, H1), 9.61 (s, 1H, H2), 8.77 (d,
2H, J=8 Hz, H8), 8.65 (d, 2H, J=8.4 Hz, H5), 8.14 (m, 3H, 1H3+2H4), 8.02 (m, 2H, H6), 7.82
(m, 2H, J=8.4 Hz, H10), 7.59 (m, 2H, H7), 7.18 (m, 2H, H9), 2.70 (s, 3H, H11), 2.20 (s, 3H,
H12). 13C{1H} NMR (DMSO-d6): δ(ppm): 177.65, 157.54, 154.58, 153.46, 137.90, 136.64,
133.36, 128.09, 123.55, 122.62, 122.12, 115.55, 115.33, 79.59, 21.95, 15.90. Selected IR bands
(cm-1): 3453 (νO-H), 3315 (νN-H), 1605 (νC=N).
2.3.5. [Ru(terpy)L5]PF6·H2O (5)
Yield: 61%. Anal. Calc. for C26H25BrF6N7OPRuS (Found): C, 38.58 (38.46); H, 3.11 (3.01); N,
12.11 (12.01)%. ESI-MS (positive, MeOH) m/Z = 547.98 (100%) [M−PF6−H2O]+. UV−Vis
[MeCN; λmax/ nm (ε/ M−1 cm−1)]: 270 (88848), 312 (95246), 375 (56356), 498 (42670), 659
(3860). 1H-NMR (DMSO-d6): δ (ppm): 9.85 (s, 1H, H1), 9.67 (s, 1H, H2), 8.76 (d, 2H, J=8.4 Hz,
H8), 8.65 (d, 2H, J=8 Hz, H5), 8.13 (m, 3H, 1H3+2H4), 8.02 (m, 2H, H6), 7.78 (d, 2H, J=8.8
Hz, H10), 7.59(m, 2H, H7), 7.49 (d, 2H, J=8.8 Hz, H9), 2.71 (s, 3H, H11), 2.25 (s, 3H, H12),
2.20 (s, 3H). 13C{1H} NMR (DMSO-d6): δ(ppm): 207.24, 177.78, 157.51, 154.56,153.50,
140.69, 136.70, 133.46, 131.68, 128.12, 123.57, 122.64, 122.42, 114.35, 31.15, 22.98, 15.96.
Selected IR bands (cm-1): 3408 (νO-H), 3315 (νN-H), 1599 (νC=N).
2.3.6. [Ru(terpy)L6]PF6·H2O (6)
Yield: 59%. Anal. Calc. for C27H28F6N7O2PRuS (Found): C, 42.63 (42.55); H, 3.71 (3.62); N,
12.89 (12.77)%. ESI-MS (positive, MeOH) m/Z = 598.08 (100%) [M−PF6−H2O]+. UV−Vis
[MeCN; λmax/ nm (ε/ M−1 cm−1)]: 271 (98758), 312 (10678), 386 (59510), 498 (50466), 664
(4666). 1H-NMR (DMSO-d6): δ (ppm): 9.78 (s, 1H, H1), 9.49 (s, 1H, H2), 8.78 (d, 2H, J=8 Hz,
H8), 8.67 (d, 2H, J=8 Hz, H5), 8.15 (m, 3H, 1H3+2H4), 8.04 (m, 2H, H6), 7.74 (d, 2H, J=8 Hz,
H10), 7.61 (m, 2H, H7), 6.92 (d, 2H, J=9.2 Hz, H9), 3.74 (s, 3H, 4-(OCH3)Ph), 2.74 (s, 3H, H11)
, 2.21 (s, 3H, H12). 13C{1H} NMR (DMSO-d6): δ(ppm): 177.48, 157.57, 155.21, 154.60, 153.36,
136.55, 134.83, 133.18, 128.04, 123.51, 122.56, 120.10, 114.07, 79.72, 55.68, 22.92, 15.81.
Selected IR bands (cm-1): 3421 (νO-H), 3286 (νN-H), 1593 (νC=N).
2.4. X-ray crystallography
Single crystal X-ray data were collected for 2 and 3 at 150 (2) and 293(2) K respectively, on a
Bruker AXS SMART APEX-II CCD area detector diffractometer using graphite monochromated
Mo-Kα radiation. Data were corrected for absorption effects using the numerical method
SADABS [40], solved by direct methods and refined by full matrix least squares on F2 using
7

SHELX-97 [41]. All non-hydrogen atoms were refined with anisotropic displacement
parameters. A summary of the crystallographic data is presented in Table 1. Important bond
distances and bond angles are collected in Table 2. Crystallographic data has been deposited at
CCDC with deposition no. 1448038 for 2 and 1448039 for 3.
Table 1. Crystal data and structure refinement parameters for 2 and 3.
Compounds
Formula
Formula weight
Wavelength (Å)
Temperature
Crystal system
Space group
a (Å)
b (Å)
c(Å)
α(°)
β(°)
2
3
C27 H25 Cl3 F6 N7 P Ru S
831.99
0.71073
150(2)
triclinic
C27 H26 Cl F6 N7 O P Ru S
778.10
0.71073
293(2)
triclinic
P -1
P -1
8.685(4)
12.008(5)
16.603(7)
72.086(8)
85.233(9)
82.114(9)
11.1857(19)
12.259(2)
12.351(2)
79.834(4)
70.415(4)
84.421(4)
1.647, 2
γ(°)
Density (calculated) (g cm-3), Z 1.695, 2
µ(mm-1)
0.906
0.773
F(000)
832
782
Reflections collected: total,
unique
15403, 5745
15199, 5527
Max. and min. transmission
Observed data [ I>2σ(I)]
R(int)
0.897, 0.850
5088
0.0237
0.884, 0.857
4592
0.0378
R1, wR2 [I>2σ(I)]
R1, wR2 (all data)
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
0.0531,0.1521
0.0593, 0.1598
5745/0/417
1.030
0.0385,0.0900
0.0497, 0.0969
5527/0/410
1.05
Largest difference in peak and −0.893, 1.197
−0.498, 0.658
hole (e Å-3)
2.5. Computational Details
DFT calculations were performed using Gaussian 03 package (Revision A.02) [42]. The
molecular orbitals were visualized using Gauss View software. Geometry optimizations, single
point calculations, and population analysis of the molecular orbitals were carried out at the
density functional theory (DFT) level with B3LYP hybrid exchange functional [43] and the
nonlocal correlation provided by the Lee and the Vosko et al. For H, C, N, and O atoms 6-31G*+
8

basis set [44] were used. The LANL2DZ [45] basis set and LANL2DZ pseudopotentials of Hay
and Wadt [46] were used for the Ru atom. The initial geometry of the complexes 2 and 3 were
taken from their crystal structures and they were optimized without any symmetry constraints, in
MeCN solvent, using CPCM model [47].
For time dependent density functional theory (TD-DFT) calculations, same basis set with the
CPCM model were used, taking acetonitrile as the solvent. Singlet excited states were calculated
based on the singlet ground-state geometry. The lowest 40 singlet excited states, with oscillator
strengths greater than 0.01, were considered for TD-DFT calculations.
2.6. Anion Binding Studies
All the solvents were of HPLC grade and were used without any further purification. The anions
used for the titrations were in the form of their tetrabutylammonium salts. Stock solutions of the
complexes (5×10−4M), free ligands (1×10−3M) and of tetrabutylammonium salts of the respective
anions (2×10−4M) were prepared in HPLC grade acetonitrile and were stored in dark. For
absorption measurements, the stock solutions of the complexes and ligands were diluted to
1×10−5M and 5×10−5M respectively. The titration experiments were performed at room
temperature (298 K) by placing 2 mL solution of a complex or a ligand in a quartz cuvette of 1-
cm path length and various amounts of anions were added incrementally from a micropipette.
The association constant of the anion with the complex in the solution was estimated by using
the equation (1) and (2) [48,49]
[Ru(terpy)(L)]+ + F−
[[Ru(terpy)(L)]+.F−]
[[Ru(terpy)(L)]+ ⋅F- ]
K =
(1)
[Ru(terpy)(L)]+ +[F- ]
∆ε ([S]+[G]+1/ Ka ) (∆ε 2([S]+[G]+1/ Ka )2 − 4∆ε 2[S][G])1/2
∆A =
(2)
2
In eqn (2), ∆A represents the change in the initial absorbance of the complexes at 535 nm upon
each addition of the fluoride ion and [S] and [G] are the concentrations of the complex and
fluoride ion respectively, during the spectrophotometric titrations. The association constant (Ka)
and the change in the molar extinction coefficient (∆ε) at each concentration of F− for the
complexes are evaluated by the nonlinear curve fitting procedure. The association constants (Ka)
9

for the complexes are given in Table 7, whereas those for the free ligands are given in Fig. S35
and Table S2.
The cyclic voltammetric (CV) and differential pulse voltammetric (DPV) titrations
measurements were carried out at 298 K in HPLC grade degassed acetonitrile solution of the
complex 3 (2×10-4M), which was taken as a representative example, and the concentration of the
supporting electrolyte (TEAP) was maintained at 0.1 M. For electrochemical titrations, 20 µL
aliquots of a tetrabutylammonium salt of the anions (5×10−3 M in acetonitrile) were added to a 5
mL solution of 3.
3. Results and discussions
3.1. Synthesis
The thiosemicarbazone ligands L1H′–L6H′ were prepared by a procedure described earlier
(scheme 2). The syntheses of Ru(II) complexes 1-6 were achieved by refluxing equimolar
amounts of the corresponding thiosemicarbazone ligand with Ru(terpy)Cl3 (terpy: 2,2′:6′,2′′-
terpyridine) and triethylamine in ethanolic solution for 8 hours, followed by anion exchange with
ammonium hexafluorophosphate (scheme 3). The crude products were then purified by column
chromatography over silica gel using chloroform–methanol (9:1) mixture as the eluent. The
compounds were finally recrystallized from chloroform-methanol (1:1) mixture. All the
compounds have been characterized by their elemental (C, H, and N) analyses, ESI-MS, IR, UV-
vis, 1H- and 13C-NMR spectroscopic measurements, and the results are given in the Experimental
Section. Single crystals suitable for X-ray crystallography of 2 and 3 were obtained from the
slow evaporation of 1:1 chloroform–methanol mixture.
OH
NH2
N
CH3
CH3
R=CH3 for L1H'
R=H for L2H'
R=Cl for L3H'
R=F for L4H'
R=Br for L5H'
R=OCH3 for L6H'
S
NH
CH3
CH3
O
(1:1)/MeOH
+
N
N
2-3 drops HCl
Stirr, 3 hours
H
N
S
NH
OH
R
N
H
R
Scheme 2: Schematic representation for the synthesis of the Ligands.
10

H3
H4
H4
OH
N
H5
H8
H5
CH3
CH3
H6
H7
H1
R=CH3 for 1
R=H for 2
R=Cl for 3
R=F for 4
R=Br for 5
R=OCH3 for 6
N
H6
H7
N
N
N
Ru
[Ru(terpy)Cl3]/Et3N
EtOH/Reflux, 8 hours
H
H8
S
N
S
NH
N
H2
H
CH3
H12
N
N
N
H
H3C
H11
H9
H10
H9
H10
R
R
Scheme 3: Schematic representation for the synthesis of the Ru(II) complexes.
During the synthesis of the complexes, ruthenium which was present in +3 oxidation state in the
precursor Ru(terpy)Cl3 is reduced to +2 oxidation state by the ligands. Thiosemicarbazones are
known to be good reducing agents and such reduction of Ru(III) to Ru(II) by thisoemicarbazides
and thiosemicarbazones have been previously noticed [3-5, 11,12]. The n.m.r. spectra of the
complexes indicate that the oxime moiety that is present in the ligands are absent in the
complexes. This is further confirmed by the determination of X-ray crystal structures of two of
the complexes. Conversion of oximes to imines, and isolation and X-ray structural
characterization of the resultant imine complexes was reported earlier where oximes of
salicylaldehyde, 2-hydroxy acetophenone and 2-hydroxy napthylaldehyde or aryl azo-oximes
were converted to the corresponding imine complexes of Ru(III) and Re(V) [50,51].
Deoxygenation/ reduction of oximes has been found to be effected by oxophilic species like
PPh3, CO, Re(I), Re(III), SOCl2 or reducing agents like citric acid [50-52]. Low-valent electron
rich metal ions are also known to convert oxime to imines [53,54]. Thus, in the present case, a
combination of electron rich Ru(II) and moderately strong reducing agent thiosemicarbazone,
probably act synergistically to reduce the oxime moiety to imine. As a plausible mechanism it
may be thought that the initially formed Ru(II) oxime complex undergoes two electron transfer
from Ru(II) to oxime forming the Ru(IV) imine complex, which rapidly undergoes reduction by
the free thiosemicarabzone ligand to form the Ru(II) imine complex. The relatively low
Ru(III)/Ru(II) and Ru(IV)/Ru(III) potentials observed in our complexes (see section 3.7) add
strength to our above mechanistic proposition.
11

3.2. Description of X-ray crystal structure
The molecular structures of complexes 2 and 3 along with the atom numbering schemes are
shown in Figs. 1 and 2 respectively. In both the complexes Ru(II) is in a distorted octahedral
geometry, coordinated by a tridentate N,N,S-donor thiosemicarbazone ligand and a terpyridyl
moiety. In each of these two structures the largest trans angle (174.39(14)° for 2 and 173.43(11)°
for 3) observed involves the endo-nitrogen atom of terpyridyl chelate ring and the hydrazone
nitrogen of the thiosemicarbazone moiety (N3-Ru1-N5). The other two trans angles involving
the terminal nitrogen atoms of the terpyridyl (N1-Ru1-N2) or the terminal sulfur and imine
nitrogen atoms of the thiosemicarbazone ligand (S1-Ru1-N4) lie between 157.58(19)-159.23(9) °.
The best least square plane consists of Ru1, S1, N3, N4 and N5, with the r.m.s deviations of the
constituent atoms being 0.047(7) Å for 2 and 0.019(3) Å for 3. The C(26)–S(1) bond distance is
1.747(5) and 1.763(3) Å in complex 2 and 3 respectively, and the corresponding thioamido
C(26)–N(6) bond distance is 1.305(6) and 1.313(4) Å for 2 and 3 respectively, which may be
compared with the corresponding C-S and C-N bond distances of 1.673(2) and 1.373(2) Å in the
free ligand diacetyl monoxime (4-phenyl)thiosemicarabzone [39], clearly indicating that
thiosemicarabzone is coordinated in deprotonated thioamide form. The metal ligand bond
distances in the thiosemicarbazone fragment is very similar to those observed earlier for Ru(II)
complexes of tridentate thiosemicarbazone ligands [6,12,24,55]. The most interesting
observation obtained from the X-ray crystal structures is the revelation that the hydroxyimino
fragment has been converted to a ketone imine and the later is coordinated to Ru(II) through the
imine nitrogen. N-unsubstituted imines, particularly of ketones, are generally unstable and prone
to rapid hydrolysis [56] As a result, complexes of such ketone imines are relatively rare in
number [12,52,57]. In the DFT optimized structure of the monoanioinic tridentate ligand found
in complex 2 (see Fig. S37 and Table S3 in SI), the ketone imine bond distance (C1-N1 distance)
is 1.284 Å, while the C1-C2 distance is 1.492 Å. This may be compared with the observed values
of the corresponding C22-N4 distances at 1.290(6) Å and 1.295(4) Å in complexes 2 and 3
respectively and C22-C24 distances at 1.446(6) Å in the complex 2 and 1.456 (5) Å in complex
3, indicating back donation from Ru(II) filled dπ-orbitals to the vacant π*-orbital of the imine
ligand. The change in bond lengths in the thiosemicarbazone fragment of the complexes
compared to that of the free ligand is indicative of extensive π-delocalization over the ligand
backbone.
12

Fig. 1
Fig. 2
Table 2. Selected bond distances (Å) and angles (°) for 2 and 3.
2
3
Bond distances
Ru1–N1
Ru1–N2
Ru1–N3
Ru1–N4
2.061(4)
2.056(4)
1.974(4)
2.035(4)
1.997(4)
2.350(1)
Ru1–N1
Ru1–N2
Ru1–N3
Ru1–N4
Ru1–N5
Ru1–S1
2.063(3)
2.061(3)
1.974(3)
2.047(3)
2.004(3)
2.378(1)
Ru1–N5
Ru1–S1
Bond angles
N3–Ru1–N5
N3–Ru1–N4
N5–Ru1–N4
N3–Ru1–N1
N5–Ru1–N1
N4–Ru1–N1
N3–Ru1–N2
N5–Ru1–N2
N4–Ru1–N2
N1–Ru1–N2
N3–Ru1–S1
N5–Ru1–S1
N4–Ru1–S1
N1–Ru1–S1
N2–Ru1–S1
174.39(14)
97.96(15)
76.81(15)
78.64(19)
103.16(17)
89.67(15)
79.04(18)
99.26(16)
95.47(15)
157.58(19)
103.34(11)
82.01(10)
158.42(12)
91.14(11)
91.95(12)
N3–Ru1–N5
N3–Ru1–N4
N5–Ru1–N4
N3–Ru1–N1
N5–Ru1–N1
N4–Ru1–N1
N3–Ru1–N2
N5–Ru1–N2
N4–Ru1–N2
N1–Ru1–N2
N3–Ru1–S1
N5–Ru1–S1
N4–Ru1–S1
N1–Ru1–S1
N2–Ru1–S1
173.43(11)
96.09(11)
77.42(11)
79.02(12)
102.04(12)
92.00(12)
79.27(12)
99.76(11)
92.30(11)
158.20(12)
104.65(8)
81.86(8)
159.23(9)
90.74(8)
92.76(8)
3.3. 1H and 13C NMR Spectra
1H and 13C NMR spectra for complexes 1−6 were recorded in DMSO-d6 at room temperature to
confirm the molecular structures of the complexes in solution, and their chemical shift values are
given in the Experimental Section and the 1H NMR spectra for complexes 1−6 are shown in Fig.
S19. In all the Ru(II) complexes (1-6), imine (=N-H) protons and N-H adjacent to the phenyl
ring (4-(R)Ph-NH-) are observed at 9.7-9.8 ppm and 9.5-9.6 ppm respectively. The appearance
of imime (=N-H) proton as a singlet confirms the conversion of oxime to imine during
complexation. Two sets of doublets and three sets of multiplets are observed for coordinated
terpyridine group, with almost same chemical shift in all the complexes. Methyl protons of 4-
(CH3)Ph and 4-(OCH3)Ph, appeared as a singlet at δ2.25 ppm and δ3.74 ppm respectively. Two
13

methyl protons of diacetyl group observed as singlets at 2.7 ppm and 2.2 ppm, and 4-Phenyl
protons show as a multiplet at δ6.97 ppm.
In 13C NMR spectra of all the complexes (1-6), twelve non equivalent aromatic carbon atoms
along with three aliphatic (C=N) carbon atoms are observed in the region 177.8-79.6 ppm. Two
methyl carbon of diacetyl group are found at 22.9 ppm and 15.9 ppm, whereas para- substituted
methyl and methoxy carbon atom of 1 and 6 are observed at 22.95 ppm and 55.68 ppm
respectively.
3.4. DFT calculations
It was mentioned in the introductory remarks that Ru(II)-thiosemicarbazones possess interesting
electronic structures and there is appreciable mixing of Ru(II) dπ-orbitals with
thiosemicarabzone orbitals. This makes assigment of oxidation state of the metal ion in these
compounds ambiguous. Again, imine complexes, where the imine N is unsubstituted, also show
intriguing electronic structures [58-60]. To understand the electronic structures of the complexes
as well as to understand the natures of the electronic transitions observed experimentally DFT
and TD-DFT calculations were performed on complexes 2 and 3 on their optimized structures in
MeCN solution. It was observed that the optimized structures of both the complexes are very
similar to those obtained by X-ray crystallography (see Table S4 in SI), except for the fact in the
optimized structures in MeCN solution the Ru-N bond lengths are on an average 0.04-0.05Å
longer and the Ru-S bond length is about 0.1Å longer than the values observed in the X-ray
structures, similar to our earlier observation [61]. The frontier orbitals of both the complexes are
very similar and hence the frontier orbitals for complex 2 are shown in Fig. 3, while those for
complex 3 are depicted in Fig. S38 (SI). The HOMO contains 47% contribution from Ru(dπ) and
28% contribution from the S(pπ) orbitals, besides some small contribution from imine π-orbital.
The HOMO−1 and HOMO−3 also have major contributions from Ru(dπ) orbitlas (62% and 69%
respectively), whereas HOMO−2 is predominantly a thiosemicarabzone based π-orbital. The
LUMO is a π*-orbital, mainly centered on dimine fragment of the thiosemicarabzone ligand. The
LUMO+1 to LUMO+6 are all terpyridine based π*-orbitals. It has been argued that percentage
contribution of ruthenium dπ orbitals towards LUMO or LUMO+1, is a measure of metal to
ligand back bonding [62-64]. For complexes 2 and 3 it is observed that LUMO has more than
8%, LUMO +1 has more than 7% contribution from the Ru-orbitals, indicating substantial metal
to ligand back bonding.
14

Fig. 3
3.5. IR Spectra
IR spectra of all the complexes are given in Fig S20 and selected i.r. bands are listed in
experimental section. Oxime to imine conversion occurs during complexation with Ru(terpy)Cl3,
so a broad band ~3410 cm−1 in most of the complexes is due to the νO-H vibration of the water
molecule or MeOH in the crystal lattice. A sharp band ~3315 cm−1 overlapping with the broad
band mentioned above in all the complexes indicates the presence of N–H bond in the
coordinated imine fragment [65]. Bands at ~840-850 cm−1 in all the complexes are attributed to
[PF6]−. The νC=N stretching frequency is found at 1590 cm−1 in all the Ru(II) complexes (1-6).
3.6. Electronic Spectra
The electronic spectra of the complexes consist of several intense bands in the visible and UV
region (Fig. 4). Two very strong bands at 270 and 311 nm, with molar extinction coefficients
grater that 80,000 M−1 cm−1 are assigned to ligand centered transitions. Two less intense bands at
381 and 498 nm are assigned to metal to terpy charge transfer transitions. A broad shoulder
centered on 660 nm is probably due to a MLCT transition involving diimine fragment of the
thiosemicarbazone ligand.
Fig. 4
Table 3. Electronic spectral data for the complexes
Complex
λ/nm (ε/M−1 cm−1)
271 (81280), 312 (87620), 381 (46736), 498 (37336), 661 (3756)
272 (77868), 311 (87210), 374 (48616), 498 (36046), 665 (3362)
271 (89960), 311 (101196), 375 (59768), 499 (46122), 662 (4170)
272 (82900), 311 (99206), 374 (55266), 498 (43960), 664 (4106)
270 (88848), 312 (95246), 375 (56356), 498 (42670), 659 (3860)
271 (98758), 312 (10678), 386 (59510), 498 (50466), 664 (4666)
1
2
3
4
5
6
TD-DFT calculations on complexes 2 and 3 were performed for better understanding of the
nature of the transitions responsible for the observed electronic spectra. The results of the TD-
DFT calculations are given in Table 4. The broad shoulder at around 660 nm has contribution
from HOMO to LUMO transition and the calculated peak position is at 635 and 638 nm for
complex 2 and 3 respectively; it also has contribution from HOMO to LUMO+1, with calculated
peaks at 611 nm (for 2) and 606 nm (for 3). Since LUMO is a diimine based π*-orbital of the
15

thiosemicarabzone ligand and HOMO is predominantly a Ru dπ-orbital with appreciable
contribution from Spπ-orbital, so the HOMO to LUMO transition is mainly MLCT (involving
π*-diimine of thiosemicarbazone) in nature with some degree of ILCT (intra-ligand charge
transfer involving Spπ to diimine-π* fragment of thiosemicarbazone) character. The HOMO to
LUMO+1 transition is similarly mainly MLCT (involving π*-terpy orbiltal) and to some extent
LLCT (ligand to ligand charge tranfer involving Spπ to π*-terpy) transition. The band observed
at 498 nm is mainly due to HOMO−1 to LUMO+1 transition, and hence it can be described as
MLCT transition involving π*-terpy orbital. The major contribution towards the intensity of the
band at 380 nm is due to HOMO−2 to LUMO transition, though it has also contributions from
HOMO−2 to LUMO+2 (for 2) and HOMO to LUMO+3 (for 3) transitions. The HOMO−2 to
LUMO transition should be considred as ILCT (aromatic amine-π fragment to diimine-π*
fragment of the thiosemicarbazone ligand), while HOMO−2 to LUMO+2 is a ligand to ligand
charge transfer transition (LLCT from thiosemicarbazone to terpy) and HOMO to LUMO+3 is
made up of MLCT involving π*-terpy orbiltal and to some extent LLCT (involving charge
tranfer from Spπ-thiosemicrabazone to π*-terpy).
Table 4. Vertical excitations with band position, oscillator strength and character assignment
Complex Experimental
wave length
Calculated
Oscillator Contributing
Percentage
(%)
wave length strength
orbital(s)
(nm)
(nm)
(f)
H-6 L+2
H-5 L+2
H-6 L+1
H L+5
25%
56%
34%
47%
37%
41%
94%
74%
77%
90%
98%
272
278.85
0.0716
300.73
301.93
0.2553
0.1818
311
H-6 L+1
H L+5
2
376.88
389.61
448.28
513.34
611.32
0.0592
0.2704
0.2119
0.0005
0.0087
H-2 L+2
H-2 L
374
H-1 L+1
H-1 L
498
665
H L+1
16

634.70
278.56
283.31
299.74
301.39
308.12
373.47
389.02
447.18
516.68
606.54
638.39
0.0046
0.0943
0.0179
0.1161
0.3299
0.0318
0.0438
0.3315
0.2325
0.0005
0.0088
0.0048
H L
92%
75%
54%
75%
61%
65%
97%
76%
75%
93%
98%
94%
H-5 L+2
H-6 L+2
H L+7
H-5 L+1
H-3 L+4
H L+3
H-2 L
271
311
3
375
499
662
H-1 L+1
H-1 L
H L+1
H L
3.7. Electrochemical studies
On the positive side of the Ag/AgCl electrode, complexes 1-6 show two quasi-reversible
oxidations at 0.5 V and 0.7 V (Fig. 5, Table 5) which are assigned to Ru(III)/Ru(II) and
Ru(IV)/Ru(III) couples respectively. Both the couples have ∆Ep value of approximately 65-95
mV and ip.a./ip.c value 1.4-1.6, indicating electrochemical and chemical quasi-reversibility of
these couples. Since the DFT calculations show there is appreciable metal-ligand mixing in the
HOMO and HOMO−1, so it should be kept in mind that the above mentioned oxidations cannot
be pure metal based oxidations and they involve appreciable charge transfer from the ligand as
well. At more positive potential, at around 1.4-1.7 V, two more irreversible oxidations with
much higher anodic peak current is observed, which might be attributed to ligand centred
oxidations. On the negative side of the reference electrode there are three quasi-reversible/
irreversible reductions at −1.40, −1.60 V and −1.90 V, the first peak is assigned to addition of
electron to the diimine fragment of the thiosemicarbazone ligand, whereas the other two peaks
are due to electron addition to the π*-orbitals of terpy.
Fig. 5
Table 5. Cyclic voltammetry and differential pulse voltammetry data[a] of complexes 1-6 in
MeCN solutions.
Complex
E0/V (∆Ep/mV) values[b]
DPV
17

0.49(66), 0.73(72), 1.47,
1.72, -1.39, -1.65, -1.98
0.48(75), 0.71(91), 1.45,
1.67, -1.37, -1.61, -1.95
0.52(65), 0.71(75), 1.45,
1.64, -1.38, -1.60, -1.95
0.50(65), 0.74(69), 1.43,
1.63, -1.33, -1.59, -1.94
0.52(70), 0.71(80), 1.44,
1.64, -1.33, -1.57, -1.94
0.48(62), 0.71(65), 1.29,
1.65, -1.36, -1.70, -1.99
0.47, 0.71, 1.37, 1.71,
-1.49, -1.62, -1.92
0.45, 0.68, 1.33, 1.58,
-1.52, -1.88
0.49, 0.68, 1.35, 1.55,
-1.27, -1.56, -1.89
0.47, 0.71, 1.32, 1.53,
-1.42, -1.62, -1.92
0.49, 0.69, 1.34, 1.54,
-1.33, -1.60, -1.92
0.45, 0.68, 1.19, 1.55,
-1.41, -1.60, -1.91
1
2
3
4
5
6
[a] Scan rate is 100 mV/s. [b] Potentials are referred against Ag/AgCl electrode.
4. Anion-Sensing Studies
4.1. Color Changes of the Receptors in Solution upon Interaction with Anions
The initial assessment of anion sensing abilities of the complexes (1-6) were on a qualitative
basis by visual examination of the anion-induced color changes in acetonitrile solutions (5×10−5
−
M) before and after the addition of an anions such as F−, Cl−, Br−, I−, OAc−, SCN−, HSO4 and
−
H2PO4 . Tetrabutylammonium salts of the anions were used to observe the visual color changes.
The photograph in Fig. 6 shows the dramatic colour changes of complex 3 in the presence of one
equivalent of fluoride ion, in contrast the other anions (up to 5 equivalents) induce almost no
change in colour. The other three complexes 4, 5 and 6 also show similar type of color changes
with fluoride ion but somewhat less intense color is obtained in case of complexes 1 and 2. This
implies that the complexes 3-6 are particularly effective as F− ion selective colorimetric sensors.
Fig. 6
4.2. 1H NMR Spectral Changes of the Receptors upon Interaction with Anions
To prove the interaction of the complexes (1-6) with fluoride ion, 1H NMR titrations of 3 were
carried out with additions of increasing amounts of tetrabutyl ammonium fluoride (TBAF) to
DMSO solution. Typically a 5.0 × 10−3 M solutions of 3 in DMSO-d6 were titrated with F− ion up
to 2 equivalents. Fig. 7 shows that the two N−H protons, imine (=N–H) and secondary amine
adjacent to the phenyl ring (4-(Cl)Ph-NH-) appeared as a singlet at 9.86 ppm and 9.69 ppm
respectively in the 1H NMR spectrum of the complex. Upon gradual addition of TBAF, the
signal due to the NH proton of secondary amine becomes broadened and finally vanished when
almost 1 equivalent of F− was added. When F− ion was added beyond 1 equivalent, deprotonation
18

of the N−H protons and subsequent delocalization of the negative charge throughout the
aromatic ring occurs, this process is facilitated due to the presence of electron withdrawing
substituent at the para position to the phenyl ring. It is also seen that during the titration of the F−
ion, the N-H proton signal of the coordinated imine fragment at about 9.86 ppm remains almost
stable up to 1 equivalent and it gets slightly broadened, with almost same chemical shift, when
excess of F− was added, indicating a very weak hydrogen bonding interaction with this imine
(=N−H) proton. The chemical shift values of all the other aromatic protons remain unaltered
during the titration.
Fig. 7
4.3. Absorption Spectral Changes of the Receptors upon Interaction with Anions
Changes in the Uv-vis spectra of the complexes in MeCN solution on addition of successively
increasing amount of TBAF is shown in Fig. 8 and the changes observed during the titration is
tabulated in Table 6. Complexes 1 and 2 show only minor changes on addition of TBAF, but the
other four complexes (3-6) show appreciable spectral modifications, with generation of three
isosbestic points at 390 nm, 485 nm and 510 nm. The Job’s plot shown in the inset of the figures
show that for all the four complexes F− binds in 1:1 molar ratio. The association constants
derived from non-linear curve fitting using equation (2) (Fig. S33) are given in Table 7. The
association constant values were found to be reasonably high (logKa > 5) for complexes 3-6,
with complex 5 and 6 having the highest and lowest value respectively of the association
constant. These values are one order of magnitude greater than those observed for free
thiosemicarbazone ligands (Table S2) and the later results are consistent with some earlier
reports [33b,34]. The detection limits were calculated to be of the order of 10−8(M) for 3, 5 and 6
and 10−7(M) for 4 (Fig. S34, Table S1), and thus these four complexes can act as highly sensitive
reagent for detection of F−. The detection limits obtained for complexes 3, 5 and 6 are much
smaller than some of the free thiosemicarbazones and thus these Ru(II) complexes are more
sensitive sensors of F− than free thiosemicarbazones [35,67].
Fig. 8
Fig. 9
There are few reports of thiosemicarbazones or its complexes being used as sensor of fluoride
ion and it is worthwhile to compare these results with that of ours. Thiosemicarbazones of
19

thiophen-2-aldehyde, furan-2-aldehydes and their various substituted derivatives have been
found to behave as sensors of F− with binding constants varying between 0.16-3.3×105 M−1 for
the thiophen based molecules and 2.88-36.31×103 M−1 for furan based molecules, the former
values being slightly greater and the latter an order of magnitude lower than those of our free
thiosemicarbazone values [33b,34]. However, in both these works the sensing behaviour
thiosemicarbazone molecules were not found to be F− specific, rather they also act as sensors for
acetate, cyanide and dihydrogen phosphate. A fluoride specific sensor behaviour was observed
for napthaldehyde thiosemicarabzone in DMSO solution [35].Though the binding constant value
is not reported in this case but the detection limit was reported to be 2.2×10−5 M, which is one
thousand parts less than our Ru(II) complexes. In situ formed Fe(III) complex of napthaldehyde
thiosemicarabzone was also shown to have specific binding affinity for F− with the detection
limit of 140µM [33a]. Selective sensing of F− was also reported for bis(thiocrabohydrazone)
with thiophen-2-aldehyde and furan-2-aldehyde in DMSO solution [33c] with the binding
constant values being 2.91×105 and 5.5 ×104 M−1 respectively. Both F− and CN− in preference to
other anions were detected by 4-(phenyl)thiosemicarabzone of 3,5-diodosalicylaldehyde, but
unfortunately neither the binding constant values nor the detection limits were reported [32c].
Two thiosemicarabzone molecules appended to thioxanthone were found to be selective sensors
for F− and Hg2+ with detection limit in the range of 10−7 M [66]. From the above discussion it
seems clear that our Ru(II) complexes are superior to other thisomicarbazone derivatives
reported in the literature both in respect of binding constant values and detection limits as well as
in terms of greater selectivity for F−.
Table 6. Absorption Spectral Data for the Complexes in Acetonitrile
Complex
1
λ
max, nm(ε/M−1 cm−1)
without added anion
with 1 equiv. of added
fluoride ion
∆λ, nm
271 (81280)
312 (87620)
381 (46736)
498 (37336)
661 (3756)
NA
NA
20

272 (77868)
311 (87210)
374 (48616)
498 (36046)
665 (3362)
2
3
4
5
6
NA
NA
271 (89960)
311 (101196)
375 (59768)
499 (46122)
662 (4170)
275(86115)
311(89536)
412(55926)
532(35810)
785(6677)
37(375 412)
33(499 532)
123(662 785)
272 (82900)
311 (99206)
374 (55266)
498 (43960)
664 (4106)
276(81191)
311(83565)
404(49335)
541(26518)
792(3141)
30(374 404)
43(498 541)
128(664 792)
270 (88848)
312 (95246)
375 (56356)
498 (42670)
659 (3860)
278(82509)
311(84689)
416(53901)
531(35383)
783(3838)
41(375 416)
33(498 531)
124(659 783)
271 (98758)
312 (10678)
386 (59510)
498 (50466)
664 (4666)
273(93449)
311(93729)
400(52921)
543(26845)
790(3127)
14(386 400)
45(498 543)
126(664 790)
Table 7. Association constants (Ka/M−1) for 1−6 toward fluoride in Acetonitrile at 298K
Complex
From Absorption Spectra
NA
NA
1
2
3
4
5
6
2.89×105
2.19×105
4.90×105
1.39×105
4.4. Changes in the Electrochemical Behaviour of the Receptors upon Interaction with Anions
The electrochemical anion recognition and sensing features of 1-6 have also been evaluated by
following the change in redox potential of the oxidation processes (Fig. 10) as a function of the
addition of different anions using cyclic and differential pulse voltammetric techniques. With the
21

progressive addition of F− to 3, negative shift of the initial Ru(III)/Ru(II) potential, at 0.52 V to
0.17 V occurs. As the F− ion concentration reaches 1 equivalent, the couple at 0.52 V is
completely replaced by the new couple at 0.16 V, but no further change in the E° value was
observed on further addition of F− up to 5 equivalents. The ligand based reduction potentials of
the complexes remain almost constant on addition of F− up to 5 equivalents, as shown in Fig.
S27. However, no identifiable shift in E° values occurs on the addition of other anions (Cl−, Br−,
−
−
I−, OAc−, SCN−, HSO4 and H2PO4 ) up to 8 equivalents in the acetonitrile solution of complex
3. All the other complexes also show very similar type of response with fluoride. The strong
hydrogen bonding of the free NH proton of thiourea group in the thiosemicarbazone ligands in 1-
6 under the influence of the strongly basic F− ion increases the electron density on the metal
centre, which in turn decreases the metal centered oxidation potentials. Thus, in accordance with
the colorimetric observations (see above), all the complexes (1-6) can also function as excellent
electrochemical receptors for the selective recognition of F−.
Fig. 11
4.5. Nature of Receptor-Anion Interaction
The observations made above from colorimetric, electrochemical and 1H NMR measurements
clearly suggest that F− ion interacts strongly with the complexes (1-6) in 1:1 stoichiometry.
−
−
Anion basicity in acetonitrile is expected to follow the order F−> OAc−> H2PO4 , Cl−, HSO4 ,
SCN−, Br−, I− in agreement with the Hofmeister series [67,68]. Thus, fluoride as the most basic
anion, induced spectroscopic changes for complexes 1-6. It is also noted that except F− ion such
−
−
interaction is very weak for other anions like Cl−, Br−, I−, OAc−, SCN−, HSO4 and H2PO4 .
Close resemblance of absorption spectrum of 3 in the presence of OH– (Fig. S32), to that in the
presence of F− ion, suggests that metal coordinated phenyl thiosemicarbazone ligands in 1-6 get
strongly hydrogen bonded with F− ion and finally deprotonated to form mono-negative species in
the presence of an excess of F− ions (Scheme 3). The fact that the NMR signals of the free
complex are very similar to the NMR signals in presence of excess F−, except one of the N-H
signal which is involved in the interaction, clearly show that the thiosemicarbazone ligand
remains undissociated from the complex during its interaction with the F−. Moreover, both Uv-
vis spectroscopy studies show that when complex 3 is first deprotonated by addition of aliquots
of tetrabutylammonium hydroxide, and then to this mixture triflic acid is added gradually, the
22

spectral change is reversed and finally the spectrum of the parent complex is obtained (Figs S36),
clearly demonstrating the reversibility of the deprotonation process.
N
N
N
N
N
N
N
N
N
Ru
Ru
-
Ru
F-
F-
+
HF2
H
H
H
N
N
N
S
S
S
F-
N
N
H
N
H
CH3
CH3
N
CH3
N
N
N
N
N
H3C
H3C
H3C
R
R
R
Scheme 3. Fluoride-Induced Coordination/Deprotonation Process of the complexes (1-6).
Conclusions
In this work we show that based on MLCT emission of RuII(trpy) as reporting unit and tridentate
thiosemicarbazones as sensor unit very efficient multichannel fluoride detecting platforms can be
designed. The fluoride ion can be estimated by Uv-Vis spectroscopy or by voltammtery. We also
report here an interesting transformation of the parent hydroxyimino thiosemicarbzone to imino
thiosemicarbazone during complexation with Ru(terpy)3+. Though conversion of an oxime to
imine during complexation has been previously reported in literature [50,51], most of them
involve aldoxime and to our knowledge only one ligand system is known where a metal
stabilized ketone imine complex was reported to be formed from the parent ketoxime [52,6].
Thus the present report is an important and interesting addition to the list of scarcely obtained
ketone imine complexes generated from the corresponding ketoxime.
Acknowledgements
B.G. thanks Indian Institute of Engineering Science and Technology (IIEST) for an Institute
fellowship. The authors acknowledge the All India Council for Technical Education (AICTE) for
funding the purchase of a CH1106A potentiostat. The authors also acknowledge Saswati and
Satabdi Roy, National Institute of Technology (NIT), Rourkela for the help in the NMR
spectroscopy study.
23

References
[1] A. R. Cowley, J. R. Dilworth, P. S. Donnelly, A. D. Gee, J. M. Heslop, Dalton Trans. (2004)
2404.
[2] R. Pedrido, M. R. Bermejo, M. J. Romero, M. Vazquez, A. M. Gonzalez-Noya, M. Maneiro,
M. J. Rodrıguez, M. I. Fernandez, Dalton Trans. (2005) 572.
[3] S. K. Chattopadhyay, S. Ghosh, Inorg. Chim. Acta. 131 (1987) 15.
[4] S. K. Chattopadhyay, S. Ghosh, Inorg. Chim. Acta. 163 (1989) 245.
[5] F. Bregant, S. Pacor, S. Ghosh, S. K. Chattopadhyay, G. Sava, Anticancer Res. 13 (1993)
1007.
[6] S. Grguric-Sipka, C. R. Kowol, S. M. Valiahdi, R. Eichinger, M. A. Jakupec, A. Roller, S.
Shova, V. B. Arion, B. K. Keppler, Eur. J. Inorg. Chem. (2007) 2870.
[7] C. R. Kowol, E. Reisner, I. Chiorescu, V. B. Arion, M. Galanski, D. V. Deubel, B. K.
Keppler, Inorg. Chem. 47 (2008) 11032.
[8] F. A. Beckford, M. Shaloski, Jr., G. Leblanc, J. Thessing, L. C. Lewis-Alleyne, A. A. Holder,
L. Li, N. P. Seeram, Dalton Trans. (2009) 10764.
[9] B. Demoro, C. Sarniguet, R. Sánchez-Delgado, M. Rossi, D. Liebowitz, F. Caruso, C. Olea-
Azar, V. Moreno, A. Medeiros, M. A. Comini, L. Otero, D. Gambino, Dalton Trans. 41 (2012)
1534.
[10] B. Demoro, R. F. M. de Almeida, F. Marques, C. P. Matos, L. Otero, J. C. Pessoa, I. Santos,
A. Rodríguez, V. Moreno, J. Lorenzo, D. Gambino, A. I. Tomaz, Dalton Trans., 42 (2013) 7131
[11] M. Maji, M. Chatterjee, S. Ghosh, S. K. Chattopadhyay, B. M. Wu, Thomas C. W. Mak, J.
Chem. Soc., Dalton Trans. (1999) 135.
[12] M. Maji, S. Ghosh, S. K. Chattopadhyay, T. C. W. Mak, Inorg. Chem. 36 (1997) 2938.
[13] D. Mishra, S. Naskar, Michael G. B. Drew, S. K. Chattopadhyay, Polyhedron 24 (2005)
1861.
[14] (a) F. Basuli, S. -M. Peng, S. Bhattacharya, Inorg. Chem. 36 (1997) 5645; (b) F. Basuli, M.
Ruf, C. G. Pierpont, S. Bhattacharya, Inorg. Chem. 37 (1998) 6113; (c) F. Basuli, S. M. Peng, S.
Bhattacharya, Inorg. Chem. 39 (2000) 1120; (d) I. Pal, F. Basuli, T. C. W. Mak, S. Bhattacharya,
Angew. Chem. 113 (2001) 15.
[15] D. Mishra, S. Naskar, Michael G. B. Drew, S. K. Chattopadhyay, Inorg. Chim. Acta. 359
(2006) 585.
24

[16] S. Naskar, S. Naskar, Mike G.B. Drew, Serge I. Gorelsky, B. L. Kaiser, A. Aukauloo, D.
Mishra, S. K. Chattopadhyay, Polyhedron 28 (2009) 4101.
[17] T. S. Lobana, R. Sharma, G. Bawa, S. Khanna, Coord. Chem. Rev. 253 (2009) 977.
[18] P. Sengupta, R. Dinda, S. Ghosh, W. S. Sheldrick, Polyhedron 22 (2003) 447.
[19] T. S. Lobana, G. Bawa, R. J. Butcher, Inorg. Chem. 47 (2008) 1488.
[20] (a) T. S. Lobana, G. Bawa, A. Castineiras, R. J. Butcher, M. Zeller, Organometallics 27
(2008) 175; (b) T. S. Lobana, G. Bawa, R. J. Butcher, B. -J. Liaw, C. W. Liu, Polyhedron 25
(2006) 2897; (c) T. S. Lobana, G. Bawa, R. J. Butcher, C. W. Liu Z. Anorg. Allg. Chem. 2009,
635 (2009) 355.
[21] S. Blanchard, E. Bill, T. Weyhermüller, K. Wieghardt, Inorg. Chem. 43 (2004) 2324.
[22] S. Blanchard, F. Neese, E. Bothe, E. Bill, T. Weyhermüller, K. Wieghardt, Inorg. Chem. 44
(2005) 3636.
[23] G. S. Smith, B. Therrien, Dalton Trans. 40 (2011) 10793.
[24] S. K. Chattopadhyay, Ruthenium thiosemicarbazone complexes in Ruthenium: Properties,
Production and Applications, D. B. Watson (ed) Nova Science Publishers, Inc., New York,
(2011) pp293-310.
[25] (a) X. Y. Liu, D. R. Bai, S. N. Wang, Angew. Chem. Int. Ed. 45 (2006) 5475; (b) W. J. Xu,
S. J. Liu, X. Y. Zhao, S. Sun, S. Cheng, T. C. Ma, H. B. Sun, Q. Zhao, W. Huang, Chem. –Eur.
J. 16 (2010) 7125; (c) P. Gamez, T. J. Mooibroek, S. J. Teat, J. Reedijk, Acc. Chem. Res. 40
(2007) 435; (d) M. Arunachalam, I. Ravikumar, P. Ghosh, J. Org. Chem. 73 (2008) 9144; (e) R.
Dutzler, E. B. Campbell, M. Cadene, B. T. Chait, R. MacKinnon, Nature 415 (2002) 287; (f) H.
Maeda, Y. Ito, Inorg. Chem. 45 (2006) 8205; (g) M. Arunachalam, P. Ghosh, Org. Lett. 12
(2010) 328; (h) F. Zapata, A. Caballero, A. Tárraga, P. Molina, J. Org. Chem. 75 (2010) 162; (i)
X.-F. Shang, X.-F. Xu, BioSystems 96 (2009)165.
[26] (a) V. B. Bregović, N. Basarić, K. M. Majerski, Coord. Chem. Rev. 295 (2015) 80; (b) R.
M. Manez, F. Sancenon, Chem. Rev. 103 (2003) 4419; (c) A. E. Hargrove, S. Nieto, T. Zhang, J.
L. Sessler, E. V. Anslyn, Chem. Rev. 111 (2011) 6603; (d) V. Vajpayee, Y. H. Song, M. H. Lee,
H. Kim, M. Wang, P. J. Stang, K.-W. Chi, Chem. Eur. J. 17 (2011) 7837; (e) P. A. Gale, Coord.
Chem. Rev. 213 (2001) 79; (f) C. R. Bondy, S. J. Loeb, Coord. Chem. Rev. 240 (2003) 77; (g) P.
D. Beer, P. A. Gale, Angew. Chem., Int. Ed. 40 (2001) 486; (h ) A. Chakraborty, R. Gunupuru,
D. Maity, S. Patra, E. Suresh, P. Paul, Inorg. Chem. Commun. 13 (2010) 1522; (i) A. Ghosh, B.
25

Ganguly, A. Das, Inorg. Chem.46 (2007) 9912 (j) L. S. Evans, P. A. Gale, M. E. Light, R.
Quesada, Chem. Commun. (2006) 965.
[27] (a) Y. Bao, B. Liu, H. Wang, J. Tian, R. Bai, Chem. Commun. (2011) 3597; (b) S. Guha, S.
Saha, J. Am. Chem. Soc. 132 (2010) 17674; F. M. Ashcroft, Ion Channels and Disease,
Academic Press, San Diego, CA, 2000.
[28] (a) K. L. Kirk, Biochemistry of the halogens and inorganic halides, Springer, Berlin. (1991)
58; (b) M. Kleerkoper, Metab. Clin. North Am. 27 (1998) 441; (c) C.D. Geddes, Meas. Sci.
Technol. 12 (2001) 53–58; (d) E. Kissa, Clin. Chem. 33 (1987) 253; (e) J. Aaseth, M. Shimshi, J.
L. Gabrilove, G. J. Støa Birketvedt, Trace Elem. Exp. Med. 17 (2004) 83; (f) Y. Xie, B. N.
Popov, Anal. Chem. 72 (2000) 2075.
[29] (a) D. Saha, S. Das, S. Mardanya, S, Baitalik, Dalton Trans. 41 (2012) 8886; (b) S. Das, D.
Saha, C. Bhaumik, S. Dutta, S. Baitalik, Dalton Trans. 39 (2010) 4162; (c) D. Saha, S. Das, D.
Maity, S. Dutta, S. Baitalik, Inorg. Chem. 50 (2011) 46; (d) D. Saha, S. Das, C. Bhaumik, S.
Dutta, S. Baitalik, Inorg. Chem. 49 (2010) 2334; (e) C. Bhaumik, S. Das, D. Saha, S. Dutta, S.
Baitalik, Inorg. Chem. 49 (2010) 5049; (f) C. Bhaumik, D. Saha, S. Das, S. Baitalik, Inorg.
Chem. 50 (2011) 12586; (g) D. Maity, S. Das, S. Mardanya, S. Baitalik, Inorg. Chem. 52 (2013)
6820; (h) C. Bhaumik, D. Maity, S. Das, S. Baitalik, Polyhedron 52 (2013) 890.
[30] (a) A. Das, H. Agarwala, T. Kundu, P. Ghosh, S. Mondal, S. M. Mobin, G. K. Lahiri,
Dalton Trans. 43 (2014) 13932; (b) A. Das, T. Kundu, S. M. Mobin, J. L. Priego, R. J. Aparicio,
G. K. Lahiri, Dalton Trans. 42 (2013) 13733; (c) T. Kundu, A. Dutta Chowdhury, D. De, S. M.
Mobin, V. G. Puranik, A. Datta, G. K. Lahiri, Dalton Trans. 41 (2012) 4484; (d) T. Kundu, S. M.
Mobin, G. K. Lahiri, Dalton Trans. 39 (2010) 4232.
[31] (a) C. Saravanan, S. Easwaramoorthi, C. Y. Hsiow, K. Wang, M. Hayashi, L. Wang, Org.
Lett. 16 (2014) 354; (b) A. Ghosh, B. Ganguly, A. Das, Inorg. Chem. 46 (2007) 9912; (c) D. A.
Jose, P. Kar, D. Koley, B. Ganguly, W. Thiel, H. N. Ghosh, A. Das, Inorg. Chem. 46 (2007)
5576.
[32] (a) X. Peng, Y. Wu, J. Fan, M. Tian, K. Han, J. Org. Chem. 70 (2005) 10524; (b) Y. Wu, X.
Peng, J. Fan, S. Gao, M. Tian, J. Zhao, S. Sun, J. Org. Chem. 72 (2007) 62; (c) S. Mathan
Kumar, K. Dhahagani, J. Rajesh, K. Nehru, J. Annaraj, G. Chakkaravarthi, G. Rajagopal,
Polyhedron. 85 (2015) 830; (d) A. Misra, M. Shahid, P. Dwivedi, Talanta 80 (2009) 532.
26

[33] (a) W. Lu, H. Jiang, F. Hu, L. Jiang, Z. Shen, Tetrahedron 67 (2011) 7909; (b) L. E. Santos-
Figueroa, M. E. Moragues, M. M. M. Raposo, R. M. F. Batista, S. P. G. Costa, R. C. M. Ferreira,
F. Sancenón, R. Martínez-Máñez, J. V. Ros-Lisa, J. Sotoa, Org. Biomol. Chem. 10 (2012) 7418;
(c) S. L. A. Kumar, R. Tamilarasan, M. S. Kumar, A. Sreekanth, Ind. Eng. Chem. Res. 50 (2011)
12379.
[34] M. M. M. Raposo, B. Garcıa-Acosta, T. Abalos, P. Calero, R. Martınez-Manez, J. V. Ros-
Lis, J. Soto, J. Org. Chem. 75 (2010) 2922.
[35] W. Lu, M. Zhang, K. Liu, B. Fan, Z. Xia, L. Jiang, Sens. Actuators B, 160 (2011) 1005.
[36] R. A. Leising, S. A. Kubow, M. R. Churchill, L. A. Buttrey, J. W. Ziller, K. J. Takeuchi,
Inorg. Chem. 29 (1990) 1306.
[37] S. Ghosh, P. K. Ray, S. R. Saha, A. P. Koley, Ind. J. Chem. 23A (1984) 745.
[38] A. K. Nandi, S. Chaudhuri, S. K. Majumder, S. Ghosh, Acta Crystallogr. Sect. C. 40 (1984)
1193.
[39] S. Naskar, S. Naskar, H. Mayer-Figge, W. S. Sheldrick, M. Corbella, J. Tercero, S. K.
Chattopadhyay, Polyhedron 35 (2012) 77.
[40] SADABS, version 2.03; Bruker AXS Inc.: Madison, WI, (2002).
[41] G. M. Sheldrick, Acta Crystallogr. Sect. A 64 (2008) 112.
[42] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K.
N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C.
Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J.
Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
[43] D. Becke, J. Chem. Phys. 98 (1993) 5648.
[44] G. A. Petersson, M. A. Al-Laham, J. Chem. Phys. 94 (1991) 6081.
[45] P. J. Hay, W. R. Wadt, J. Chem. Phys. 82 (1985) 299.
27

[46] P. J. Hay, W. R. Wadt, J. Chem. Phys. 82 (1985) 270.
[47] Y. Takano, K.N. Houk, J. Chem. Theory Comput. 1 (2005) 70.
[48] Y. Cui, H. -J. Mo, J. -C. Chen, Y. -L. Niu, Y. -R. Zhong, K. -C. Zheng, B. -H. Ye, Inorg.
Chem. 46 (2007) 6427.
[49] (a) Y. Liu, B. -H. Han, Y. -T. Chen, J. Phys. Chem. B 106 (2002) 4678; (b) Y. Liu, B.-H.
Han, S. -X. Sun, T. Wada, Y. Inoue, J. Org. Chem. 64 (1999) 1487; (c) C. Basu, S. Biswas, A. P.
Chattopadhyay, H. Stoeckli-Evans, S. Mukherjee, Eur. J. Inorg. Chem. (2008) 4927; (d) L.
Wang, X. -J. Zhu, W. -Y. Wong, J. -P. Guo, W.-K. Wong, Z. -Y. Li, Dalton Trans. (2005) 3235;
(e) B. Valeur, J. Pouget, J. Bouson, M. Kaschke, N. P. Ernsting, J. Phys. Chem. 96 (1992) 6545;
(f) Y. Liu, B. Li, C. -C. You, T. Wada, Y. Inoue, J. Org. Chem. 66 (2001) 225.
[50] A. K. Das, S.-M.Peng, S. Bhattacharya, J. Chem. Soc., Dalton Trans. (2000) 181.
[51] (a) I. Chakraborty, B. K. Panda, J. Gangopadhyay, A. Chakravorty, Inorg. Chem. 44
(2005)1054; (b) C. K. Pal, S. Chattopadhyay, C. Sinha, A. Chakravorty, Inorg. Chem. 35
(1996)2442.
[52] S. K. Singh, S. Sharma, S. D. Dwivedi, R. -Q. Zou, Q. Xu, D. S. Pandey, Inorg. Chem. 47
(2008) 11942.
[53] (a) V. Y. Kukushkin, D. Tudela, A. J. L. Pombeiro, Coord. Chem. Rev. 156 (1996) 333; (b)
V. Y. Kukushkin, A. J. L. Pombeiro, Coord. Chem. Rev. 181 (1999) 147.
[54] A. J. L. Pombeiro, V.Y. Kukushkin in Comprehensive Coordination Chemistry II, Vol 1,
pp 631-637; A. B. P. Lever (Editor), J. A. McCleverty, T. J. Meyer (Eds. In Chief), Elsevier,
Amsterdam, 2005.
[55] A. E. Graminha, A. A. Batista, J. Ellena, E. E. Castellano, L. R. Teixeira, I. C. Mendes, H.
Beraldo, J. Mol. Str. 875 (2008) 219.
[56] M. B. Smith, J. March, March’s Advanced Organic Chemistry: Reactions, Mechanisms and
Structure, sixth edition, Wiley Interscience (2007) 1263.
[57] A. R. Cowley, J. R. Dilworth, P. S. Donnely, J. W. Shore, Dalton Trans. (2003) 748.
[58] S. C. Bart, K. Chłopek, E. Bill, M. W. Bouwkamp, E. Lobkovsky, F. Neese, K. Wieghardt,
P. J. Chirik, J. Am. Chem. Soc. 128 (2006) 13901.
[59] B. de Bruin, E. Bill, E. Bothe, T. Weyhermuller, K. Wieghardt, Inorg. Chem. 39 (2000)
2936.
28

[60] P. H. M. Budzelaar, B. de Bruin, A. W. Gal, K. Wieghardt, J. H. van Lenthe, Inorg. Chem.
40 (2001) 4649.
[61] S. Naskar, B. Pakhira, D. Mishra, P. Mitra, S. K. Chattopadhyay, S. Naskar, Polyhedron 100
(2015) 170.
[62] S. I. Gorelsky, E. S. Dodsworth, A. B. P. Lever, A. A. Vlcek, Coord. Chem. Rev. 174
(1998) 469.
[63] S. I. Gorelsky, A. B. P Lever, J. Organomet. Chem. 635 (2001) 187.
[64] A. B. P. Lever, S. I. Gorelsky, Coord. Chem. Rev. 208 (2000) 153.
[65] J.R. Dyer, Application of Absorption Spectroscopy of Organic Compounds, Prentice-Hall of
India Pvt. Ltd., New Delhi. (1989) 37.
[66] L. Ding, M. Wu, Y. Li, Y. Chen, J. Su, Tetrahedron Lett. 55 (2014) 4711.
[67] F. Hofmeister, Arch. Exp. Pathol. Pharmakol. 24 (1888) 247.
[68] W. Kunz, J. Henle, B. W. Ninham, Curr. Opin. Colloid Interface Sci. 9 (2004) 19.
[69] M. Trivedi, S. K. Singh, D. S. Pandey, R.-Q. Zou, M. Chandra, Q. Xu, J. Mol. Str. 886
(2008) 136.
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