Ru(III)-pseudohalide complexes with alkynyl functionalized salicylaldimine ligand and heterocyclic coligand: Synthesis, characterization, electrochemical and luminescence properties

Article abstract of DOI:10.1016/j.ica.2020.119586

A new series of hexa-coordinated Ru(III) complexes of the type [Ru(L)(phen)X₂] (1a-3a) and [Ru(L)(bipy)X₂](1b-3b) [where, X = NCS, N₃, CN] have been prepared by the reaction of RuCl₃·H₂O with 2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)methyl)-4-(2-(4-methoxy phenyl)ethynyl)phenol (L) in presence of 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) as a ligand. The molecular structure of ligand L was confirmed by single crystal X-ray diffraction. All complexes were characterized on the basis of elemental analysis, magnetic moment, TGA, IR, UV–Vis, EPR and mass spectral studies. The EPR spectral data and magnetic susceptibility measurement showed octahedral geometry around Ru(III). The electrochemical properties of all complexes indicate quasireversible redox behaviour corresponding to Ru(III)/Ru(IV) and Ru(III)/Ru(II) couple and are variable to π-acidic character of phen and bipy. All complexes exhibit strong emissions from lowest energy ILCT state with some LMCT character in DMF (10^-4 M) at room temperature indicating that alkynyl functionality on salicylaldimine ligand enhances the emission property of the complexes and varies considerably with quenching ability of pseudohalides.

Full text of DOI:10.1016/j.ica.2020.119586

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Research paper
Ru(III)-pseudohalide complexes with alkynyl functionalized salicylaldimine
ligand and heterocyclic coligand: Synthesis, characterization, electrochemical
and luminescence properties
S.S. Mohite, A.B. Patil-Deshmukh, S.S. Chavan
PII:
DOI:
Reference:
S0020-1693(19)31936-X
https://doi.org/10.1016/j.ica.2020.119586
ICA 119586
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Inorganica Chimica Acta
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Revised Date:
Accepted Date:
11 December 2019
8 March 2020
8 March 2020
Please cite this article as: S.S. Mohite, A.B. Patil-Deshmukh, S.S. Chavan, Ru(III)-pseudohalide complexes with
alkynyl functionalized salicylaldimine ligand and heterocyclic coligand: Synthesis, characterization,
electrochemical and luminescence properties, Inorganica Chimica Acta (2020), doi: https://doi.org/10.1016/j.ica.
2020.119586
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S. S. Mohite, A. B. Patil-Deshmukh, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur (MS) 416004, India
Abstract:
The hexa-coordinated Ru(III)-pseudohalide complexes of the type [Ru(L)(phen)X2] and
[Ru(L)(bipy)X2] [where X=NCS, N3, CN; L=2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)
methyl)-4-(2-(4-methoxyphenyl)ethynyl)phenol, Phen=1,10-phenanthroline, bipy=2,2’- bipyridine]
have been prepared and characterized. The EPR spectra and magnetic susceptibility measurement
indicate octahedral geometry around Ru(III). All complexes exhibit a quasireversible redox behaviour
corresponding to Ru(III)/Ru(IV) and Ru(III)/Ru(II) couple and are variable to -acidic character of
coligands. Room temperature luminescence is observed for all complexes correspond to ILCT with
some LMCT character.
Keywords: Ru(III) complexes, EPR spectra, Cyclic voltammetry, Photoluminescence
Corresponding author: Tel: +91 231 2609381; fax: +91 231 2691533
E-mail: sanjaycha2@rediffmail.com

Ru(III)-pseudohalide complexes with alkynyl functionalized salicylaldimine
ligand and heterocyclic coligand: Synthesis, characterization, electrochemical
and luminescence properties
S. S. Mohite, A. B. Patil-Deshmukh, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur (MS) 416004, India
Abstract
A new series of hexa-coordinated Ru(III) complexes of the type [Ru(L)(phen)X2] (1a-3a) and
[Ru(L)(bipy)X2](1b-3b) [where, X=NCS, N3, CN] have been prepared by the reaction of
RuCl3.H2O with 2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)methyl)-4-(2-(4-methoxy
phenyl)ethynyl)phenol (L) in presence of 1,10-phenanthroline (phen) or 2,2-bipyridine (bipy) as a
ligand. The molecular structure of ligand L was confirmed by single crystal X-ray diffraction.
All complexes were characterized on the basis of elemental analysis, magnetic moment, TGA,
IR, UV-Vis, EPR and mass spectral studies. The EPR spectral data and magnetic susceptibility
measurement showed octahedral geometry around Ru(III). The electrochemical properties of all
complexes indicate quasireversible redox behaviour corresponding to Ru(III)/Ru(IV) and
Ru(III)/Ru(II) couple and are variable to -acidic character of phen and bipy. All complexes exhibit
strong emissions from lowest energy ILCT state with some LMCT character in DMF (10-4 M) at
room temperature indicating that alkynyl functionality on salicylaldimine ligand enhances the
emission property of the complexes and varies considerably with quenching ability of pseudohalides.
Keywords: Ru(III) complexes, EPR spectra, Cyclic voltammetry, Photoluminescence
Corresponding author: Tel: +91 231 2609381; fax: +91 231 2691533

E-mail: sanjaycha2@rediffmail.com
1. Introduction
Over the decades, the transition metal complexes containing ruthenium as metal centre have been
the focus of continues research interest because of their rich photocatalytic, photochemical and
electrochemical properties [1-3]. The choice of this metal ion is of interest because it possesses
stable and accessible oxidation states ranging from I to III. Also the photophysical,
photochemical and electrochemical properties of these complexes can be tuned by introducing
specific ligands in a controlled manner. In recent years, considerable research efforts have been
focused on synthesis and properties of ruthenium complexes of hybrid ligands because they can
provide new material with useful properties such as electrochemical, photo-physical, photo-
electrochemical and catalytic properties [4-7]. Of the various ligands, Schiff base containing N, O
donors are interesting ligands that have been widely exploited for the fabrication of this molecular
architecture because of their structural diversity and potential applications in analytical [8], biological
[9] and industrial [10] field. More recently considerable interest has been paid on incorporation of
additional functionalities into Schiff base ligands which are reported to exhibit very interesting
luminescence and optical properties [11, 12]. Addition of alkynyl functionality particularly, with π-
conjugation in Schiff base ligand constitutes an important class of compounds as a luminescent
material due to their advanced structural and electronic properties [13]. These two properties cause a
large –delocalization over the ligand which results into increase in rigidity of the structure and dipole
moment of the complexes [14]. The literature survey reveals that the 1, 10-phenanthroline and 2,2’-
bipyridine have attracted special interest from many researchers in the perspective of their various
structural and chemical properties such as planarity, rigidity, aromaticity, basicity and chelating
capability [15, 16]. All these advantages make them important starting materials for synthesis of
metallodendrimers [17], supramolecular assemblies [18] as well as photoactive materials [19].

Pseudohalides such as thiocynate (NCS), azide (N3) and cyanide (CN) are also versatile building blocks
which can link to one or more metal ions in variety of ways to form different mono-, di- or polynuclear
coordination molecules and supramolecular entities. There is a vast amount of literature available on
numerous transition metal complexes with interesting molecular or supramolecular assemblies by using
organic ligands in combination with pseudohalides [20-22].
Influenced by all these facts, recently we have reported Ru(III)-bypyridyl complexes with 2-((E)-
((4-((4-bromophenyl)ethynyl)phenyl)imino)methyl-4-((E)-phenyldiazenyl)phenol and N3- or NCS- and
anticipated that, the azo chromophore with extended π-conjugation lead to perturb the electronic
properties of the complexes and thus their emission properties [23]. Also, these complexes are
found to be suitable precursor for the preparation of nanoscale structure. Herein we report
synthesis of new series of Ru(III)-pseudohalide complexes by the reaction RuCl3.H2O with alkynyl
functionalized salicylaldimine ligand 2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)methyl)-4-
(2-(4-methoxyphenylethynyl)phenol in presence of 1,10-phenanthroline and 2,2-bipyridine as a
coligand. All the complexes were characterized by elemental analysis, magnetic moment, IR, UV-Vis,
EPR and mass spectral studies. The electrochemical behavior and luminescence properties of the
complexes have also been studied.
2. Experimental
2.1 Materials and General Methods
All chemicals used were of AR grade. Solvents used for synthesis were distilled over appropriate drying
reagents. 4-(-2-(4-methoxyphenyl)ethynyl)benzenamine [24] was prepared according to the literature
procedure. Elemental analyses (C, H and N) were performed on a Thermo Finnigan FLASH EA-112
CHNS analyzer. Electronic spectra were recorded on a Shimadzu UV-Vis-NIR-100 spectrophotometer.
Magnetic susceptibility was measured on Gouy balance at room temperature using a Johnson Matthey

Alfa MKI magnetic susceptibility balance with Hg[Co(SCN)4] as calibrant. The EPR spectra of the
complexes were recorded at room temperature on Varian E-112 spectrometer using TCNE as the
standard. Infrared spectra were recorded on Perkin-Elmer FTIR spectrometer as KBr pellets in the
1
4000-400 cm-1 spectral range. H NMR spectra of the sample was measured on Bruker-300 MHz
instrument using TMS [(CH3)4Si] as an internal standard. ESI mass spectra were recorded using Finnegan
LCQ mass spectrometer. Luminescence properties were measured using a Perkin Elmer LS 55
spectrofluorometer equipped with quartz cuvette of 1 cm path length at room temperature. Luminescence
lifetime measurements were carried out by using time-correlated single photon counting from HORIBA
Jobin Yvon. Thermogravimetric analysis of the complexes was carried out on a Perkin Elmer thermal
analyzer in nitrogen atmosphere at a heating rate of 10 oC min. Cyclic voltammetry measurements were
performed with a CH-400A electrochemical analyzer. A standard three electrode system, consisting of Pt
disk working electrode, Pt wire counter electrode and Ag/AgCl as a reference electrode.
2.2. X-Ray Crystallography
Single crystal X-ray structural study of L was performed on Bruker KAPPA APEX-II diffractometer.
Data were collected in omega and phi scan mode, MoKɑ=0.71073 Å at room temperature with scan
width of 0.3o at θ (0o, 90o and 180o) by keeping the distance at 40 nm between sample to fixed detector
at 24o. The X-ray generator was operated at 50 kV and 30 mA. The details of crystal data, data
collection and refinements are given in Table 1. The X-ray data collection was monitored by SMART
program (Bruker, 2003). All the data were corrected using SAINT and SADABS programs (Bruker,
2003).SHELX-97 was used to solution of structure and full matrix least squares refinement on F2 [25].
Molecular and packing diagram were generated using ORTEP-3and Mercury-3.
2.3. Synthesis of 2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)methyl)-4-(2-(4-methoxy
phenyl)ethynyl)phenol (L)

2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)methyl)-4-(2-(4-methoxyphenyl)ethynyl)
phenol (L) was prepared by mixing of methanolic solution (10 ml) of 2-hydroxy-5-(2-(4-
methoxyphenylethynyl)benzaldehyde (1.500 g, 5.937 mmol) with methanolic solution (10 ml) of
4-(-2-(4-methoxyphenyl)ethynyl)benzenamine (1.327 g, 5.946 mmol). The resulting mixture was
o
refluxed for 3h at 80 C. The separated brick red coloured solid was collected by filtration,
washed with diethyl ether and recrystallized from ethanol.
Yield: 82%. (2.536 g, 5.561 mmol); Elemental analysis (C, H, N, wt %) Anal. Calc. for
C31H23NO3: C, 81.38; H, 5.07; N, 3.06; Found: C, 81.12; H, 4.88; N, 3.30 %; IR (KBr, cm-1):
1
3064 ʋ(O-H), 2067 ʋ(C≡C), 1623 ʋ(HC=N), 1273, ʋ(C-O); H NMR (CDCl3; 300 MHz): δ 8.62
(s, 1H, HC=N), δ 13.35 (s, 1H, OH), δ 3.83 (s, 6H, OCH3), 6.86-7.59 (m,15H Ar): ESI-MS:
Found m/z = 457.51 (M+) (calculated m/z = 457.70 for M+).
2.4. Synthesis of [Ru(L)(phen)X2] (1a-3a)
To a stirring solution of RuCl3.H2O (1 mmol, 0.270 g) in methanol (10 ml) was added a solution
of 1, 10 phenanthroline (1mmol, 0.180 g) and solution of two equivalent of appropriate
pseudohalides (2 mmol, 0.152 g, NH4SCN; 2 mmol, 0.129 g, NaN3; 2 mmol, 0.130 g, KCN) in
methanol (10 ml). After half an hour solution of 2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenyl
imino)methyl)-4-(2-(4-methoxyphenyl)ethynyl)phenol (L) (0.457 g, 1 mmol) in dichloromethane
(10 ml) was added drop wise. The resulting solution was refluxed for 4h at 80 oC. The solid
complex precipitated was collected by filtration, washed with 1:1 ethanol: water mixture and
dried under vacuum over CaCl2.
1a: Yield: 79%. (0.405 g, 4.747 mmol); Elemental analysis (C, H, N, wt%) Anal. Calc for
C45H30N5O3S2Ru: C, 63.29; H, 3.54; N, 8.20% Found: C, 63.05; H, 3.41; N, 8.40%; IR (KBr cm-1):
2067, ʋ(C≡C); 2149, ʋ(NCS); 1609, ʋ(HC=N), 1281, ʋ(C-O); ESI-MS: 877 ([Ru(L)(phen)
(NCS)2+Na]+, 22), 457 ([L]+, 100), 397 ([Ru(phen)(NCS)2]+, 41). 2a:Yield: 82%. (0.417 g, 5.075

mmol); Elemental analysis (C, H, N, wt%) Anal. Calc for C43H30N9O3Ru: C, 62.84; H, 3.68; N,
15.34% Found: C, 62.56; H, 3.45; N, 15.56%; IR (KBr cm-1): 2067, ʋ(C≡C); 2040, ʋ(N3); 1606,
ʋ(HC=N); 1278, ʋ(C-O);. ESI-MS: Found: 845 ([Ru(L)(phen)(N3)2+Na]+, 24), 457 ([L]+, 100), 365
([Ru(phen)(N3)2]+, 43). 3a:Yield: 84%. (0.426 g, 5.398 mmol); Elemental analysis (C, H, N, wt%)
Anal. Calc for C45H30N5O3Ru: C, 68.43; H, 3.83; N, 8.87 % Found: C, 68.12; H, 3.57; N, 9.05%; IR
-1
(KBr cm ): 2067, ʋ(C≡C); 2093, ʋ(CN); 1607, ʋ(HC=N); 1279, ʋ(C-O); ESI-MS: 813 ([Ru(L)
(phen)(CN)2+Na]+, 22), 457 ([L]+, 100), 333 ([Ru(phen)(CN)2]+, 45).
2.5. Synthesis of [Ru(L)(bipy)X2] (1b-3b)
To a stirring solution of RuCl3.H2O (1 mmol, 0.270 g) in methanol (10 ml) was added a solution of
2,2’-bypyridine (1mmol, 0.156 g) and solution of two equivalents of appropriate pseudohalides (2
mmol, 0.152 g, NH4SCN; 2 mmol, 0.129 g, NaN3; 2 mmol, 0.130 g, KCN) in methanol (10 ml). After
half an hour solution of 2-((E)-(4-(2-(4-methoxyphenyl)ethynyl)phenylimino)methyl)-4-(2-(4-
methoxyphenyl)ethynyl)phenol (L) (0.457 g, 1 mmol) in dichloromethane (10 ml) was added drop
wise. The resulting solution was refluxed for 4h at 80 oC. The solid complex precipitated was collected
by filtration, washed with 1:1 ethanol: water mixture and dried under vacuum over CaCl2.
1b: Yield: 83%. (0.409 g, 4.924 mmol); Elemental analysis (C, H, N,wt%) Anal. Calc for
-1
C43H30N5O3S2Ru: C, 62.23; H, 3.64; N, 8.44% Found: C, 61.97; H, 3.49; N, 8.63%; IR (KBr cm ):
2067, ʋ(C≡C); 2153 ʋ(NCS), 2148; 1611, ʋ(HC=N); 1280, ʋ(C-O); ESI-MS: 853 ([Ru(L)(bipy)
(NCS)2+Na]+, 20), 457 ([L]+, 100), 373 ([Ru(bipy)(NCS)2]+, 40). 2b: Yield: 85%. (0.410 g, 5.137
mmol); Elemental analysis (C, H, N, wt%) Anal. Calc for C41H30N9O3Ru: C, 61.72; H, 3.79;
N, 15.80 % Found: C, 61.54; H, 3.57; N, 15.98%; IR (KBr cm-1): 2067, ʋ(C≡C); 2039, ʋ(N3);
1613, ʋ(HC=N); 1278, ʋ(C-O); ESI-MS: 821 ([Ru(L)(bipy)(N3)2+Na]+, 22), 457 ([L]+, 100), 341
([Ru(bipy)(N3)2]+, 43). 3b: Yield: 81%. (0.390 g, 5.101 mmol); Elemental analysis (C, H, N,
wt%) Anal. Calc for C43H30N5O3Ru: C, 67.44; H, 3.95; N, 9.15 % Found: C, 67.22; H, 3.69; N, 9.38%;

-1
IR (KBr cm ): 2067, ʋ(C≡C); 2092, ʋ(CN); 1612, ʋ(HC=N); 1282, ʋ(C-O); ESI-MS: 798
([Ru(L)(bipy)(CN)2+Na]+, 21), 457 ([L]+, 100), 309 [Ru(bipy)(CN)2]+, 42).
3. Results and discussion
3.1 Synthesis of L and Ru(III) complexes
Initially, 5-ethynylsalicylaldehyde was prepared by Sonogashira PdCl2(PPh3)2/CuI catalyzed coupling
of 5-bromosalicylaldehyde with trimethylsilylacetylene followed by treatment with KOH in methanol
according to the procedure reported earlier [26]. The reaction of 5-ethynylsalicylaldehyde with
4-iodoanisole yielded 2-hydroxy-5-(-2-(4-methoxyphenylethynyl)benzaldehyde in good yield. Further
condensation of 2-hydroxy-5-(-2-(4-methoxyphenylethynyl)benzaldehyde with 4-(-2-(4-methoxy
phenyl)ethynyl)benzenamine in methanol afforded corresponding Schiff base ligand 2-((E)-(4-(2-(4-
methoxyphenyl)ethynyl)phenylimino)methyl)-4-(2-(4-methoxyphenyl)ethynyl)phenol (L) in excellent
yield (Scheme 1). The Ru(III) complexes [Ru(L)(phen)X2] [X=NCS (1a), N3 (2a), CN (3a) and
[Ru(L)(bipy)X2] [X=NCS (1b), N3 (2b), CN (3b) were prepared by the reaction of L with
RuCl3.H2O in presence of 1,10-phenanthroline and 2,2’-bipyridine followed by addition of
NH4SCN, NaN3 and KCN in CH2Cl2:MeOH (1:1) mixture, respectively, All complexes are
coloured, moisture insensitive and insoluble in common organic solvents but shows maximum
solubility in DMF and DMSO. The results of elemental analyses (C, H and N) which are given in
section 2 confirm the assigned composition of the complexes (Fig.1)
3.2 X-ray structure of L
Single crystal of ligand L suitable for X-ray diffraction was obtained by slow evaporation of
saturated solution of L in dichloromethane. The ligand L crystallizes in a monoclinic system
with the space group Pc and Z=2. The molecular structure of L along with atom numbering
scheme is illustrated in Fig. 2 and the selected bond lengths and bond angles are summarized in
Table 2. The crystal and molecular structure of L reveals some interesting findings. First the

structure exhibits a strong intramolecular (O2-H2A-N1) hydrogen bond between the nitrogen
atom of -HC=N- of Schiff base and hydrogen atom of the -OH group of salicylaldehyde ring
with a distance of 2.581(9) Å which is in good agreement with the values reported in the
literature [27]. Individually, each benzene ring in the molecule is almost planar in which the C3,
C14 and C20 atom from each benzene ring has best plane by 0.042(3), 0.036(2) and 0.037(2) Å.
The molecular packing of the structure is stabilized by C-H-O intermolecular hydrogen bond. All bond
lengths and angles in (C1-C6), (C9-C14), (C16-C21) and (C24-C29) benzene rings have normal
values 1.375(12), 1.376(13), 1.394(11) and 1.404(13) Å, respectively. The two benzene rings
along with HC=N displayed the trans configuration and torsion angles of N(1)-C(16)-C(17)-C(18) is
177.2(8)°, C(14)-C(13)-C(15)-N(1) is −177.0(8)°. These angles are reported in the literature with
values of 175.5(2)° and −176.8(2)° [28]. The bond distance C(7)-C(8) 1.188(12) Å and C(22)-C(23)
1.189 Å is smaller due to presence of C≡C. These results are comparable with those of the
ligands reported earlier containing the similar moiety [29].
3.3 IR and NMR Spectra
The IR spectra of selected groups in the spectra of L and their 1a-3a and 1b-3b complexes are
given in section 2. The IR spectrum of L and representative spectrum of 1a are depicted in Fig 3
and 4, respectively. In the IR spectrum of L a broad band observed at 3064 cm-1 is assigned to
(OH) vibration associated intramolecularly with the nitrogen atom of -HC=N- group. This band
disappeared in 1a-3a and 1b-3b confirmed the coordination of phenolic oxygen to Ru(III)
centers. Another medium intensity band observed at ca 2067 cm-1 due to internal triple bond
(C≡C) and ca 1160 cm-1 due to OCH3 group remain unaltered in all Ru(III) complexes. A strong
absorption at 1623 cm-1 observed in the spectrum of L is slightly shifted to lower frequency at
1606-1609 cm-1 in 1a-3a and 1611-1613 cm-1 for 1b-3b. This change in frequency indicating

imine nitrogen coordination [30]. The characteristic band appeared at 1273 cm-1 in L has been
ascribed to the phenolic C-O stretch. On complexation, this band shifted to higher frequency by
ca 7-9 cm-1 in 1a-3a and ca 8-11 cm-1 in 1b-3b relative to L suggesting involvement of C-O
moiety in coordination. In addition to this, the bands at ca 1500, 805 and 735 cm-1 due to phen in
1a-3a and bands at ca 760 and 740 cm-1 due to bipy in 1b-3b confirmed the coordination of
these ligands with Ru(III). The complexes 2a, 2b exhibit bands at around 2039 cm-1 and strong
band at 1348 cm-1 assigned to ʋa and ʋs vibration of the coordinated azido group [31]. The cynide
complexes 3a, 3b exhibit band at around 2094, 2065 cm-1 [32] whereas, thiocyanato complexes
1a, 1b shows a strong band at around 2148 cm-1, a weak band at 771 and 484 cm-1 which can be
1
attributed to ʋ(CN), ʋ(CS) and ʋ(NCS), respectively. The H NMR spectrum of L exhibit
hydroxyl proton and the imine proton as a singlet at δ 13.35 and 8.62 ppm, respectively. The
resonance due to aromatic protons appeared as a multiplet in the region δ 6.86-7.59 ppm.
Moreover, a signal of two methoxy protons is observed at δ 3.83 ppm.
3.4 Magnetic moment and EPR spectra
The room temperature (300 K) magnetic moment of 1a-3a and 1b-3b in the powdered phase are
in the range 1.82-1.94 μB, and are listed in Table.3. These values are consistent with the low spin
character and S = ½ ground state of metal ion, which corresponds to unpaired electron (low spin
5
RuIII, t2g ) in an octahedral environment [33]. To obtain further information about the
stereochemistry and the site of the metal-ligand bonding and to determine the magnetic
interaction in the complexes, the X-band EPR spectra of 1a-3a and 1b-3b complexes were
recorded in polycrystalline state at room temperature. The g values obtained are given in Table 3 and
a representative spectrum of 1a is shown in Fig 5. The EPR spectra of all complexes exhibit two
different g values (gx=gy≠gz) with g at 2.47-2.66 and g at 1.99-2.11 indicating octahedral field with

tetragonal distortion. Two g values indicate an axial symmetry and hence trans positions are
assigned to the pseudohalide group in these complexes. Overall, the position of lines and nature of
the EPR spectra of the complexes are characteristic of low spin Ru(III) octahedral complexes. These
results are consistent with those obtained for other similar octahedral Ru(III) complexes [34].
3.5 Electrochemical Properties
The electrochemical properties of 1a-3a and 1b-3b were screened cyclic voltammetrically in 10-3 M
DMF solution containing 0.05 M n-Bu4NClO4 as supporting electrolyte. The electrochemical
data are listed in Table 4 and the representative cyclic voltammogram of 1a and 2b is shown in
Fig 6 (A and B). Cyclic voltammogram of all complexes displayed a quasireversible oxidation
(RuIV/RuIII) and reduction (RuIII/RuII) at the scan rate of 100 mV s-1. All the complexes showed
well-defined waves E1/2 lies at +0.20 to +0.28 V (RuIII/RuIV) and -0.36 to -0.48 V (RuIII/RuII). The
large peak-to-peak separation (ΔEp) of 120-180 mV in 1a-3a and 100-130 mV in 1b-3b and the
current height measurement revel one electron redox processes [35]. It was observed that, the
electrochemical properties of all the complexes are highly sensitive to the nature of coligand. The,
redox processes for 1a-3a appeared at more positive potential by 0.010-0.019 V as compared to those
for corresponding 1b-3b. These results could be attributed to better stabilization of the phen based
complexes as compared to bipy based complexes as a consequence of their strong π-acidic character [36].
Further, the redox process for Ru(III) thiocynato complexes (1a, 1b) appeared at less positive potential
(140 V) as compared to those for corresponding azido (2a, 2b) and cyano (3a, 3b) complexes (167 V).
This is might be due to the differences between π-acidic characters of the pseudohalides [37].
3.6 Thermogravimetric (TG) analysis
The thermal stabilities of 1a-3a and 1b-3b were investigated by thermogravimetric analysis (TGA)
o
under flowing nitrogen to 800 C. Typical TG curve of 1a is presented in Fig. 7 and thermal
analysis data is depicted in Table 5. TGA data suggest that, complexes 1a-3a is stable up to 162 oC

o
revealing the absence of either water or solvent molecule. In the temperature range of 162-474 C,
the complexes 1a-3a underwent complicated multiple weight loss with total loss of 35.05 (1a), 32.60
(2a), 36.16 (3a)%, (Calcd. 35.96 (1a), 33.18 (2a), 36.81 (3a)%) which corresponds to loss of
azido/thiocynato/cynato ion along with phen ligand. All the complexes collapse due to release of
ligand L which occurs between 475-576oC with an observed weight loss of 49.57(1a), 53.70 (2a),
52.70 (3a)% (Calcd.50.14 (1a), 54.23 (2a), 53.13 (3a)%). The complexes 1b-3b shows slight
changes in their thermal behaviour as compare to 1a-3a, once again indicating absence of water
o
or solvent molecule and decomposition ranges from 164 to 460 C. The rapid and significant
weight loss observed of 33.15 (1b), 31.64 (2b), 34.11 (3b)% (Calcd 33.82 (1b), 31.09 (2b),
34.61 (3b)%) which are presumably due to collapse of azido/thiocynato/cynato ion along with
o
bipy ligand. The weight loss due to L in temperature range 461-562 C observed at about
51.90 (1b), 55.48 (2b), 53.19 (3b)% (Calcd 52.23 (1b), 56.00 (2b), 53.73 (3b)%). From the
thermogravimetric profile, it is clear that phen based complexes are found to be thermally more
stable as compared to bipy based complexes.
3.7 Photophysical properties
The UV-Vis absorption spectra of free ligand L and its complexes 1a-3a and 1b-3b were carried
out in DMF solution (10-4 M) at room temperature and resulting data are summarized in Table 6.
In DMF, ligand L exhibit two absorption bands at max 233 and 341 nm (Fig. 8) are due to intra-
ligand π- π* and n- π* transitions. These peaks shows bathochromic shift in 1a-3a and 1b-3b and
observed at 246-256, 241-247 nm and 354-361, 352-367 nm, respectively which support the
coordination of L to Ru(III) ion. Besides the π-π* and n-π* transitions, 1a-3a exhibit an intense
absorption at max 421-448 nm whereas, 1b-3b exhibit absorption at max 412-438 nm which can
be attributed to charge transfer (CT) transitions. In a d5 system and especially Ru(III) which has
relatively high oxidizing properties, the charge transfer bands of the type Lπy→t2g are prominent

in the low energy region which obscure the weaker bands due to d-d transitions. However, low
energy absorption bands observed at max 637-658 nm in 1a-3a and max 621-643 nm in 1b-3b
are attributed to d-d transition (2T2g→2A2g) which is in conformity with the assignment made for
similar octahedral ruthenium(III) complexes [38]. Low value of d-d transition observed in phen
complexes (1a-3a) indicating that, in these complexes basel planes are comparatively more
distorted than the bipy complexes (1b-3b). Also, d-d transition of cyano complexes (3a, 3b) are blue
shifted by 13-15 nm as compared to thiocynato (1a and 1b) and azido (2a, 2b) complexes.
Moreover, the high intensity of cyano complexes may be suggestive of stronger distortion
compared to thiocynato and azido complexes. These results are consistent with the higher ligand
field factor of N-coordinated –CN than -NCS and -N3 [39].
The emission and corresponding excitation spectra of L and its 1a-3a and 1b-3b complexes were
systematically investigated in DMF solution (10-4M) at room temperature. The excitation and
emission spectra of representative complex 1a is shown in Fig. 9 and the resulting data are
summarized in Table 6. The ligand L exhibit emission at max 558 nm (Fig. 8) upon excitation at
399 nm with stoke shift of 159 nm. The emission observed in L is due to emission stemming from
a ligand centered π-π* transition. In contrast, 1a-3a and 1b-3b shows steady state marked
differences in their emission behaviour in DMF solution. The spectra of 1a-3a exhibit a broad
emission profile at max 654-669 nm with life time 6.74-7.01 ns upon excitation at max 420-445
nm. Whereas, 1b-3b shows emission profile at max 645-658 nm with life time 6.49-6.86 ns upon
excitation of max 410-435 nm resulting in higher stokes shifts. The emission observed in these
complexes can be attributed to π→π* intra-ligand charge transfer (ILCT) fluorescence in
combination with some ligand to metal charge transfer (LMCT) character. The enhancement of
fluorescence efficiency in all these complexes can be attributed to coordination of the ligands to
Ru(III) ion which effectively increases the rigidity of the ligands and reduces loss of energy via

radiation less thermal vibration decay [40]. It was observed that, all the complexes under study
offer an extra conjugated back bone resulting in significantly increase in fluorescence efficiency as
compare to previously reported similar Ru(III) complexes [23]. It was also observed that, the
emission efficiency of phen complexes (1a-3a) appear at longer wavelength with enhanced
intensity and large stoke shifts as compared to bipy complexes (1b-3b). This may be due to non-
radiative decay process which is more effective in bipy complexes as compared to Phen
complexes [41]. Moreover, cyano complexes (3a and 3b) shows high emissivity as compare to
thiocynato (1a and 1b) and azido 2a and 2b) complexes and fallow the path N3<NCS<CN due to
better quenching ability of pseudohalides [42]. The fluorescence quantum yield (ϕ) of all the
complexes was determined with reference to quinine sulfate (ϕ=0.52 at 298 K) and appeared at
0.082-0.089 for 1a-3a and 0.066-0.077 for 1b-3b which are in good agreement with those are
reported in the literature [43]. The observed emission decay of all the complexes are fit well with
single exponential decay with average life time of 1a-3a is longer than those observed for 1b-3b.
These results could be attributed due to red shifted emission and decreased emission intensity
observed in 1b-3b as compare to 1a-3a. The experimentally measured τ and ϕ values were used to
calculate the radiative Kr and the non radiative Knr rate constant. The Kr values of 1a-3a are slightly
greater whereas, Knr values are slightly lower than the 1b-3b. All these results are in good agreement
with those values reported in the literature [44].
4. Conclusion
Some new Ru(III)-pseudohalide complexes of the type [Ru(L)(phen)X2] (1a-3a) and
[Ru(L)(bipy)X2] (1b-3b) [where; X=NCS, N3, CN; phen = 1,10-phenanthroline, bipy = 2,2-
bipyridine] have been prepared and characterized. Based on magnetic susceptibility and EPR spectra,
an octahedral structure was confirmed for the new complexes. All complexes exhibit quasireversible
redox behaviour corresponding to Ru(III)/Ru(IV) and Ru(III)/Ru(II) couple. Further, significant

effect of phen/bipy coligands on redox state of metal in complexes has been examined. The phen
(1a-3a) complexes are thermally more stable than the bipy (1b-3b) complexes. At room temperature
all complexes shows large stokes shift and act as fluorescent in blue-green region due to π-π* intra-
ligand charge transfer (ILCT) transition with some ligand to metal charge transfer (LMCT) character.
Moreover, cyano (3a and 3b) complexes shows high emissivity as compare to thiocynato (1a and
1b) and azido (2a and 2b) complexes and fallow the path N3<NCS<CN due to better quenching
ability of pseudohalides.
Supplementary material
CCDC 1945674 contain the supplementary crystallographic data 2-((E)-(4-(2-(4-methoxyphenyl)
ethynyl)phenylimino)methyl)-4-(2-(4-methoxyphenyl)ethynyl)phenol (L)
Acknowledgments
We gratefully acknowledge Head, Sophisticated Analytical Instrument Facility Center, IIT, Madras,
India for providing single crystal X-ray facilities. One of the authors (SSM) is thankful to UGC-SAP-
SRF, New Delhi for awarding UGC Research fellowship in Sciences for Meritorious Students.

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Figure captions:
Scheme. 1 Synthetic route to the preparation of L
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Proposed molecular structure of the complexes (I) 1a-3a and (II)1b-3b
Single crystal X-ray diffraction of L
IR spectrum of L
IR spectrum of 1a
EPR spectrum of [Ru(L)phen(NCS)2] (1a)
Cyclic voltammogram of (A) 1a and (B) 2b
Thermogram of 1a
Absorption and Emission Spectra of L
Excitation (red line) and Emission (blue line) spectra of 1a
Table.1. Crystal data and structure refinement details for L
Empirical formula
C31 H23 N O3
Formula weight
457.50

Crystal system
Space group
a (Å)
Monoclinic
Pc
26.489(3)
7.2195(7)
6.2098(6)
90
b (Å)
c (Å)
ɑ (o)
β (o)
b= 93.279(5)°
90
γ (o)
V (A3)
1185.6(2)
2
Z
Density (mg/m3)
μ (M0Kɑ)(mm-1)
F (000)
1.282 Mg/m3
0.656
480
Data collection
Temperature (K)
θ mini-maxi (deg)
Data set [h k l]
Total unique data Rint
Extinction coefficient
Refinement
No of reflection collected
Data / restraints / parameters
R1, R1
3.342 to 65.986°
296 (2)
0.7536 and 0.5441
-30/31, -8/8, -7/7
10184 [R(int) = ?]
0.010(4)
Full-matrix least-square on F2
10184
10184 / 2 / 318
0.0732, 0.1220
0.1781, 0.2045
1.023
wR2, wR2
Goodness-of-fit
Table.2. Selected bond lengths (Å) and bond angles (o) for L

Bond length
C(1)-O(1)
(Å)
Bond angle
C(7)-O(8)-C(9)
(o)
174.7(10)
121.2(8)
177.2(10)
176.5(10)
115.5(9)
118.1(7)
109.5
1.373(11)
1.188(12)
1.462(11)
1.276(10)
1.403(11)
1.189(12)
1.370(11)
1.422(12)
C(7)-C(8)
N(1)-C(15)-C(13)
C(23)-C(22)-C(19)
C(22)-C(23)-C(24)
O(3)-C(27)-C(28)
C(1)-O(1)-C(31)
C(12)-O(2)-H(2A)
C(27)-O(3)-C(30)
C(13)-C(15)
C(15)-N(1)
C(16)-N(1)
C(22)-C(23)
C(27)-O(3)
C(30)-O(3)
118.2(8)
Table.3. EPR and magnetic susceptibility data of 1a-3a and 1b-3b
Complexes
gx
gy
gz
(g)*
2.69
2.77
2.79
2.88
3.06
2.96
µeff(BM)
1.82
1.90
1.88
1.94
1.87
1.81
1a
2a
3a
1b
2b
3b
2.47
2.54
2.52
2.57
2.66
2.63
2.47
2.54
2.52
2.57
2.66
2.63
2.04
1.99
2.07
2.08
2.11
2.06
< g >* = [ 1/3gx2 + 1/3gy2 + 1/3gz2]1/2

Table.4 Electrochemical data of 1a-3a and 1b-3b in DMF (10-3M)
Complexes
RuIII - RuIV
RuIII - RuII
Band
gap
EA
IP
Band
gap
EA
IP
Epa
(V)
Epc
(V)
ΔEp
(mV)
200
E1/2
(V)
Epa
Epc
(V)
ΔEp
(mV)
120
E1/2
(V)
(V)
1a
2a
3a
1b
2b
3b
0.45
0.25
0.35
0.20 -0.125 -4.875 -0.42
0.11 -0.095 -4.815 -0.47
0.14 -0.135 -4.805 -0.50
0.18 -0.155 -4.825 -0.45
0.22 -0.125 -4.895 -0.40
0.16 -0.175 -4.785 -0.55
-0.30
-0.36
-0.12 -0.675 -4.005
-0.19 -0.655 -3.955
-0.18 -0.695 -3.925
-0.11 -0.715 -3.975
-0.01 -0.765 -4.025
0.39
0.38
0.40
0.47
0.36
0.28
0.24
0.22
0.25
0.20
110
140
180
220
160
0.33
0.31
0.31
0.36
0.28
-0.28
-0.32
-0.34
-0.39
-0.42
190
180
100
110
130
-0.37
-0.41
-0.39
-0.39
-0.48
-0.13
0.795
-3.875
Supporting electrolyte: n-Bu4NClO4 (0.05 M); complex: 0.001 M; solvent: DMF; E1/2 = ½(Epa + Epc); scan rate: 100 mV s1.

Table.5 Thermoanalytical data of 1a-3a and 1b-3b
Complex Thermogravimetric (TG) Mass loss (%)
Decomposition product
loss
Stage
Temp range(oC)
162-474
475-576
165-473
474-574
164-470
471-575
164-460
461-562
167-458
459-560
165-558
559-560
Found
35.05
49.57
32.60
53.70
36.16
52.70
33.15
51.90
32.64
55.48
34.11
53.19
Calc
35.96
50.14
33.18
54.23
36.81
53.13
33.82
52.23
31.09
56.00
34.61
53.73
1a
2a
3a
1b
2b
3b
I
II
I
C14H8N4S2
C30H23NO3
C12H8N8
II
I
C30H23NO3
C14H8N4
II
I
C30H23NO3
C12H8N4S2
C30H23NO3
C10H8N8
II
I
II
I
C30H23NO3
C12H8N4
II
C30H23NO3
Table.6 Absorption and Emission data of L and 1a-3a and 1b-3b in DMF (10-4 M)
λmax(nm)
(ε x103, M_1 cm_1)
233, 341
Stoks
Shift
159
242
209
233
223
235
223
Compound
λex
λem
ϕ
τ
(ns)
Kr(S-1/107) Knr(S-1/109)
L
399
420
445
436
428
558
662
654
669
651
645
658
0.061 4.87
0.084 6.74
0.082 6.76
0.089 7.01
0.068 6.49
0.066 6.51
0.077 6.86
1.21
1.23
1.21
1.25
1.05
1.01
1.12
0.1992
0.1506
0.1479
0.1408
0.1555
0.1536
0.1457
1a
2a
3a
1b
2b
3b
246, 356, 438, 649
251, 354, 448, 658
256, 361, 421, 637
246, 352, 429, 631
241, 359, 438, 643 410
247, 367, 412, 621 435

Research Highlights:
 Synthesis of Ru(III)-pseudohalide complexes.
 Characterization by elemental analyses, IR, EPR and mass spectral studies.
 Room temperature luminescence is observed for all complexes.
SHIVAJI UNIVERSITY, KOLHAPUR
DEPARTMENT OF CHEMISTRY
Vidyanagar, Kolhapur-416004 (India)
‘A’ Reaccredited by
NAAC
Phone: +91 231 2609381(O), +91 9881647064 (Cell)
Fax: +91 231 2692333
Prof. (Dr.) S. S. Chavan
BOYSCAST (India) and ENDEAVOUR (Australia) Fellow
Email: sanjaycha2@rediffmail.com
2 February 2020
To
Editor,
Inorganica Chimica Acta
Dear Sir,
We have revised the manuscript titled ‘Ru(III)-pseudohalides complexes with alkynyl functionalized
salicylaldimine ligand and heterocyclic coligand: Synthesis, characterization electrochemical and

luminescence properties’ by taking into consideration the suggestions made by the respected
reviewers. The work presented in the manuscript contributes examining the structural aspects as
well as luminescence properties of new Ru(III) complexes. The data and ideas of the prepared
complexes are of our own and are not under consideration for publication elsewhere, and that all
authors are aware of the submission and agree to its publication. I hope that the manuscript will
be worth for publication in your esteemed journal
Thanking you
Yours faithfully
Prof. (Dr.) Sanjay Chavan
Scheme 1.
CHO
OH
CHO
OH
CHO
OH
CSi(CH3)3
HC
PdCl2(PPh3)2, CuI
KOH
MeOH + CH2Cl2
(H3C)3Si
H
Br
OCH3
I
PdCl2(PPh3)2,
CuI
NEt3
OCH3
N
CHO
OH
H2N
OCH3
H3CO
OH
H3CO
MeOH
L
Fig. 1.

OCH3
OCH3
X
N
X
N
N
N
N
N
Ru
Ru
H3CO
O
H3CO
O
X
X
1b-3b
(II)
1a-3a
(I)
X = NCS, N3, CN
Fig. 2.
Fig. 3.

Fig. 4.

Fig. 5.
Fig. 6.
(A)
(B)

Fig. 7.
Fig. 8.
Fig. 9.