Synthesis, characterization, and antimicrobial studies of half-sandwich η6-toluene ruthenium complexes with N,N′-bidentate ligands

Article abstract of DOI:10.1080/00958972.2020.1795146

Nine new complexes [(η⁶-C₆H₅-CH₃)RuLCl]⁺(PF₆)ˉ (where L = N,N′-bidentate ligand; (C₅H₄NCH = N-Ar) where Ar = 4-methylphenyl (C₂₀H₂₀ClF₆N₂PRu, 1); 3,4-dimethylphenyl (C₂₁H₂₂ClF₆N₂PRu, 2); 2,4,6-trimethylphenyl (C₂₁H₂₄ClF₆N₂PRu, 3); 4-bromophenyl (C₁₉H₁₇ClBrF₆N₂PRu, 4); 2,5-dimethylphenyl (C₂₁H₂₂ClF₆N₂PRu, 5); 2-flourophenyl (C₁₉H₁₇ClF₇N₂PRu, 6), (4-methoxyphenyl)methylene (C₂₁H₂₂ClF₆N₂OPRu, 7); phenylmethylene (C₂₀H₂₀ClF₆N₂PRu, 8); and 3,5-dimethylphenyl (C₂₁H₂₂ClF₆N₂PRu, 9) were synthesized by reacting the corresponding N,N′-bidentate ligands with the ruthenium arene dimer in a 2:1 ratio. The compounds were fully characterized via ¹H NMR and ¹³C NMR, IR, and UV-vis spectroscopy and elemental analyses. The molecular structures of representative complexes (1, 7, and 8) were established by single-crystal X-ray diffraction studies. In the molecular structures of the complexes, the ligands coordinate to the Ru(II) centers via the pyridine nitrogen atom and the imine N atom in a bidentate manner. The other coordination sites of the Ru(II) center are occupied by the tolyl system in an η⁶ manner resulting in geometry often referred to as “pseudo-octahedral piano-stool.” All compounds were evaluated for their in?vitro antibacterial activity by the disk diffusion method against a panel of Gram-negative and Gram-positive bacteria. The complexes showed promising bactericidal activity against methicillin-resistant Staphylococcus aureus ATCC 43300.

Full text of DOI:10.1080/00958972.2020.1795146

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis, characterization, and antimicrobial
studies of half-sandwich η6-toluene ruthenium
complexes with N,N′-bidentate ligands
Joel M. Gichumbi , Holger B. Friedrich , Bernard Omondi & Hafizah Y. Chenia
To cite this article: Joel M. Gichumbi , Holger B. Friedrich , Bernard Omondi & Hafizah Y.
Chenia (2020): Synthesis, characterization, and antimicrobial studies of half-sandwich η6-toluene
ruthenium complexes with N,N′-bidentate ligands, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2020.1795146
To link to this article: https://doi.org/10.1080/00958972.2020.1795146
View supplementary material
Published online: 29 Jul 2020.
Submit your article to this journal
Article views: 12
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1795146
Synthesis, characterization, and antimicrobial studies
of half-sandwich g6-toluene ruthenium complexes
with N,N0-bidentate ligands
Joel M. Gichumbia, Holger B. Friedrichb, Bernard Omondic and
Hafizah Y. Cheniad
b
aDepartment of Physical Science, Chuka University, Chuka, Kenya; School of Chemistry, Westville
c
Campus, University of KwaZulu-Natal, Durban, South Africa; School of Chemistry and Physics,
d
Pietermaritzburg Campus, University of KwaZulu-Natal, Scottsville, South Africa; School of Life
Sciences, Westville Campus, University of KwaZulu-Natal, Durban, South Africa
ABSTRACT
ARTICLE HISTORY
Nine new complexes [(g6-C6H5-CH3)RuLCl]þ(PF6)ˉ (where L ¼ N,N0-
bidentate ligand; (C5H4NCH ¼ N-Ar) where Ar ¼ 4-methylphenyl
(C20H20ClF6N2PRu, 1); 3,4-dimethylphenyl (C21H22ClF6N2PRu, 2);
2,4,6-trimethylphenyl (C21H24ClF6N2PRu, 3); 4-bromophenyl
(C19H17ClBrF6N2PRu, 4); 2,5-dimethylphenyl (C21H22ClF6N2PRu, 5);
2-flourophenyl (C19H17ClF7N2PRu, 6), (4-methoxyphenyl)methylene
(C21H22ClF6N2OPRu, 7); phenylmethylene (C20H20ClF6N2PRu, 8);
and 3,5-dimethylphenyl (C21H22ClF6N2PRu, 9) were synthesized by
reacting the corresponding N,N0-bidentate ligands with the ruthe-
nium arene dimer in a 2:1 ratio. The compounds were fully char-
acterized via 1H NMR and 13C NMR, IR, and UV-vis spectroscopy
and elemental analyses. The molecular structures of representa-
tive complexes (1, 7, and 8) were established by single-crystal
X-ray diffraction studies. In the molecular structures of the com-
plexes, the ligands coordinate to the Ru(II) centers via the pyri-
dine nitrogen atom and the imine N atom in a bidentate manner.
The other coordination sites of the Ru(II) center are occupied by
the tolyl system in an g6 manner resulting in geometry often
referred to as “pseudo-octahedral piano-stool.” All compounds
were evaluated for their in vitro antibacterial activity by the disk
diffusion method against a panel of Gram-negative and Gram-
positive bacteria. The complexes showed promising bactericidal
activity against methicillin-resistant Staphylococcus aureus ATCC
43300.
Received 14 April 2020
Accepted 22 June 2020
KEYWORDS
Half-sandwich complexes;
bidentate ligands; molecular
structures; antibacterial activity
CONTACT Bernard Omondi
Owaga@Ukzn.ac.za
School of Chemistry and Physics, Pietermaritzburg Campus,
University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1795146.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
J. M. GICHUMBI ET AL.
1. Introduction
Medicinal inorganic chemistry is a field concerned with implementation of metal-based
complexes in therapy or diagnosis of diseases [1, 2]. The use of metal-based drugs
dates back to ancient times when silver was used to treat wounds and ulcers by the
ancient Greeks and gold in China to treat diseases thousands of years ago [3]. The
modern era of metal-based complexes was heralded with the discovery of a square
planar platinum(II) complex, cisplatin, and its clinical success against various types of
cancer such as ovarian, head and neck, lung, testicular, and bladder cancers. This
opened up the way for second and third generation platinum drugs such as carbopla-
tin, oxaliplatin, satraplatin, nedaplatin, and lobaplatin [4]. Therefore, following the clin-
ical success of cisplatin, medicinal inorganic chemistry and the use of metal-based
complexes is a promising approach to treat and diagnose diseases, and metallodrugs
will certainly take a key part of drug development to improve the quality of life of
patients [4].
Ruthenium-based organometallic compounds are progressively gaining importance
as promising aspirants for the design of novel and more effective metal-based drugs.
This is due to the ruthenium complexes having rich synthetic chemistry, redox access-
ible oxidation states, favorable ligand substitution reactions, and diverse coordination
geometries [5]. Organometallic half-sandwich ruthenium compounds are emerging as
a promising class of compounds in inorganic chemistry for anticancer and antimicro-
bial applications [5–7].
There is need for continuous development of new classes of antimicrobial com-
plexes. This is due to widespread use of antibiotics to kill microbes which have seen

JOURNAL OF COORDINATION CHEMISTRY
3
the emergence of drug-resistant populations of microorganisms [6, 7]. Ruthenium-
based complexes have displayed significant biological activity, which has been attrib-
uted to their strong binding capability to nucleic acids and proteins, the prevalence of
two main oxidation states (II and III) and, an iron-mimicking property when bound to
biological molecules [7].
Arene-ruthenium complexes play an important role in organometallic chemistry
among various metal complexes. They have been shown to exhibit antimicrobial activ-
ity against drug-resistant pathogenic microorganism [5, 8, 9]. The increased activity of
these ruthenium complexes in antimicrobial, antibiotic, and anticancer applications
has greatly contributed to the interest in synthesizing new ruthenium complexes and
investigating their possible uses [5, 8, 9]. Although a large number of Ru(II)-arene com-
pounds have been developed and extensively investigated, most studies have focused
on [(g6-arene)RuCl(L)Cl]þ (where arene is g6-C6H6, p-cymene, and L the ligand) type
complexes [8]. This work therefore is a contribution to half-sandwich ruthenium com-
plexes where arene is g6-C6H5-CH3. Toluene was chosen because it has properties
between benzene and p-cymene. This was expected to have an influence on the prop-
erties when compared to benzene and p-cymene; due to the presence of one methyl
group it has a different ability to provide electron density to the ruthenium metal ion.
Nitrogenous monodentate and bidentate heterocyclic compounds have been syn-
thesized due to a number showing a wide range of biological activities [10]. Much
attention has been paid to the synthesis of heterocyclic compounds bearing nitrogen
containing ring systems, mainly due to their higher pharmacological activity. In add-
ition, the nitrogenous ligands are very attractive in coordination chemistry because of
their simplicity and availability. Also, the steric and electronic properties around the
metal centers can easily be modified through the ligands [10].
This work is part of our continuing investigations into the development of anti-
microbial and anticancer activities of half-sandwich metal complexes [11–15]. This has
been motivated by the emergence of drug-resistant populations of microorganisms
which have been resistant to commonly used antibiotics. In this article, we report the
synthesis and characterization of [(g6-C6H5-CH3)RuCl(C5H4NCH ¼ NAr)](PF6) where Ar ¼
4-methylphenyl (1); 3,4-dimethylphenyl (2); 2,4,6-trimethylphenyl (3); 4-bromophenyl
(4); 2,5-dimethylphenyl (5); 2-flourophenyl (6); (4-methoxyphenyl)methylene (7); phe-
nylmethylene (8); and 3,5-dimethylphenyl (9). The compounds were fully characterized
1
by H NMR, 13C NMR, UV-vis, IR, HRMS, and elemental analysis. Moreover, to confirm
the structures of the synthesized complexes, the molecular structures of 1, 7, and 8
have been determined by single-crystal XRD. Antimicrobial susceptibility tests were
carried out against antimicrobial resistant and antimicrobial susceptible Gram-positive
and Gram-negative bacteria to determine their antibacterial potential.
2. Experimental
2.1. Materials and methods
All manipulations were carried out under nitrogen atmosphere using Schlenk techni-
ques. All reagents and solvents were purchased commercially from Sigma-Aldrich.
Solvents were dried using standard techniques and stored over 4 Å molecular sieves.

4
J. M. GICHUMBI ET AL.
NMR spectra were recorded using a Bruker topspin 400 MHz spectrometer. Deuterated
solvent DMSO-d6 (Aldrich) was used as purchased. Melting points were measured on
an Ernest Leitz Wetzlar hot stage microscope. Elemental analyses were performed
using a Thermal-Scientific Flash 2000 CHNS/O analyzer. Infrared spectra were recorded
using an ATR Perkin-Elmer Spectrum 100 spectrophotometer between 4000 and
400 cmꢀ1 in the solid state. Mass spectra were recorded via a Waters Micromass LCT
Premier TOF-MS and ESI in the positive mode. Ruthenium trichloride was received
from DLD-scientific. The Ru(II)-arene dimeric precursor [(g6-C6H6-CH3)Ru(l-Cl)Cl]2 was
synthesized according to a reported literature procedure [16].
2.2. Synthesis of the ligands L1–L9
The imino-pyridine ligands were synthesized by a method adopted from Zai et al. [17].
A solution of 2-pyridinecarboxaldehyde in 30 mL ethanol was added to a solution of
substituted aniline in 1.0 equivalent ratio and a few drops of formic acid were added.
The solution was stirred for 5 h at 60 ꢁC, followed by solvent removal, and the solid
obtained recrystallized from hexane. The ligands were fully characterized and gave
good elemental results.
2.3. Synthesis of 1–9
The complexes were prepared using a modified method from Gichumbi et al. [12]. To
a suspension of [(g6-C6H5-CH3)Ru(l-Cl)Cl]2 (0.2 mmol) in methanol (20 mL) was added
the ligand (0.42 mmol). The mixture was stirred at room temperature for 3 h followed
by a reduction in the volume of the solvent in vacuo to about 10 mL before adding
NH4PF6 (0.42 mmol). The mixture was then cooled in an ice-bath while stirring for 2 h,
leading to a precipitate which was collected by filtration. The filtrate was washed with
diethyl ether and dried in vacuo.
2.3.1. Complex 1
1
Orange powder, yield 80%, m.p. 200 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.59 (d, JHH¼5.24 Hz, 1H, py); 8.87 (s, 1H, CH ¼ N); 8.31 (m, 2H, Py); 7.87 (t, 1H,
JHH¼5.76, py); 7.70 (d, 2H, JHH¼8.08 Hz, Ar); 7.44 (d, 2H, JHH¼8.0 Hz, Ar); 6.12 (t, 1H,
JHH¼5.6 Hz, Ar); 5.79 (m, 3H, Ar); 5.57 (d, 1H, JHH¼5.72 Hz, Ar); 2.43 (s, 3H, CH3); 2.10
(s, 3H, CH3). 13C NMR (400 MHz, DMSO-d6), d (ppm): 167.06 (CH ¼ N); 156.01 (py);
154.72 (py); 149.36 (py); 139.88 (py); 129.78 (py); 129.63 (Ar); 128.60 (Ar); 122.34 (Ar);
105.11(Ar); 90.57 (Ar); 90.19 (Ar); 84.12 (Ar); 84.09 (Ar); 80.8 (Ar); 20.76 (CH3); 18.53
(CH3). IR (KBr), (cmꢀ1): ꢀ(C ¼ N) 1601.74. Anal. Calcd for C20H20ClN2RuPF6: C, 42.15; H,
3.14; N, 4.92. Found: C, 42.11; H, 3.44; N, 5.03%. Found: MS (ESI, m/z): 425.03
[C20H20ClN2Ru]þ.
2.3.2. Complex 2
1
Orange powder, yield 84%, m.p. 178 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.58 (d, JHH¼5.44 Hz, 1H, py); 8.86 (s, 1H, CH ¼ N); 8.30 (m, 2H, py); 7.87 (t, 1H,
JHH¼4.04 Hz, py); 7.55 (t, 2H, JHH¼7.12 Hz, Py); 7.38 (d, 1H, JHH ¼7.88 Hz, Ar); 7.38

JOURNAL OF COORDINATION CHEMISTRY
5
(d, 1H, JHH¼7.88 Hz, Ar); 6.1 (t, 1H, JHHH¼4.84 Hz, Ar); 5.80 (m, 3H, Ar); 5.56 (d, 1H,
JHHH¼5.96 Hz, Ar), 2.36 (d, 6H, JHH¼7.00 Hz, 2CH3); 2.11 (s, 3H, CH3). 13C NMR (400 MHz,
DMSO-d6), d (ppm): 167.0 (CH ¼ N); 156.00 (py); 154.73 (py); 149.64 (py); 139.87 (py);
138.48 (py); 130.47 (py); 129.56 (Ar); 128.56 (Ar); 122.82 (Ar); 120.14 (Ar); 104.83 (Ar);
90.37 (Ar); 90.37(Ar); 89.9 (Ar); 84.45 (Ar); 84.31 (Ar); 80.94 (Ar); 19.52 (CH3); 19.16 (CH3);
18.53 (CH3). IR (KBr), (cmꢀ1): ꢀ(C ¼ N) 1601.60; ꢀ(P-F) 833.59. Anal. Calcd for
C21H22ClN2RuPF6: C, 43.20; H, 3.80; N, 4.80. Found: C, 43.20; H, 3.90; N, 4.82%. MS (ESI,
m/z): 439.05 [C21H22ClN2Ru]þ.
2.3.3. Complex 3
1
Orange powder, yield 80%, m.p. 174 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.59 (d, JHH¼5.36 Hz, 1H, py); 8.82 (s, 1H, CH ¼ N); 8.31 (t, JHHH¼7.56 Hz, 1H, py); 8.21
(d, 1H, JHH¼7.44 Hz, py); 7.92 (t, 1H, JHH¼6.36 Hz,Py); 7.15 (s, 1H, Ar); 7.09 (s, 1H, Ar);
6.17 (t, 1H, JHHH¼5.84 Hz, Ar); 5.89 (t, 1H, JHH¼5.92 Hz, Ar); 5.79 (d, 1H, JHHH¼5.6 Hz,
Ar), 5.41(d, 1H, JHH¼6.0 Hz, Ar); 5.26 (t, 1H, JHH¼5.8 Hz, Ar); 2.35 (s,3H, CH3), 2.30 (s, 3H,
CH3), 2.12 (s, 6H, 2CH3). 13C NMR (400 MHz, DMSO-d6), d (ppm): 173.27 (CH ¼ N);
156.07 (py); 154.00 (py) 148.57 (py); 139.97 (py); 137.40 (py); 130.90 (Ar); 129.80 (Ar);
129.1 (Ar); 128.97 (Ar); 128.53 (Ar); 105.55 (Ar); 89.99 (Ar); 89.91 (Ar); 84.5 (Ar); 84.23
(Ar); 81.03 (Ar); 20.43 (CH3); 19.5 5(CH3); 18.61 (CH3); 18.02 (CH3). IR (KBr), (cmꢀ1):
ꢀ(C ¼ N) 1607; ꢀ(P-F) 835.88. Anal. Calcd for C22H24ClN2RuPF6: C, 44.19; H, 4.05; N, 4.69.
Found: C, 44.20; H, 4.10; N, 4.70%. MS (ESI, m/z): 453.07 [C22H24 ClN2Ru]þ.
2.3.4. Complex 4
1
Orange powder, yield 81%, m.p. 182 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.61 (d, JHH¼5.44 Hz, 1H, py); 8.92 (s, 1H, CH ¼ N); 8.32 (m, 2H, py); 7.90 (m, 3H, py);
7.76 (d, 2H, JHH¼8.68 Hz, Ar); 6.15 (m, 1H, Ar); 5.83 (m, 1H, Ar); 5.77 (m, 2H, Ar); 5.59 (d,
1H, JHH¼3.64 Hz, Ar); 2.12 (s, 3H, CH3). 13C NMR (400 MHz, DMSO-d6), d (ppm): 168.43
(CH ¼ N); 156.14 (py); 150.76 (py); 139.96 (py); 132.39 (py); 130.04 (py); 128.88 (Ar);
124.56 (Ar); 122.53 (Ar); 105.30 (Ar); 105.30 (Ar); 90.62 (Ar); 90.09 (Ar); 84.13 (Ar);
84.01(Ar); 80.91 (Ar); 18.59 (CH3). IR (KBr), (cmꢀ1): ꢀ(C ¼ N) 1614.59; ꢀ(P-F) 821.00. Anal.
Calcd for [C19H17ClN2BrRuPF6: C, 35.95; H, 2.70; N, 4.41. Found: C, 36.00; H, 2.80; N,
4.42%. MS (ESI, m/z): 488.93 [C19H17ClN2BrRu]þ.
2.3.5. Complex 5
1
Orange powder, yield 87%, m.p. 181 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.62 (d, 1H, JHH¼5.32 Hz, py); 8.82 (s, 1H, CH ¼ N); 8.32 (m, 2H, py); 7.91 (m, 1H, py);
7.88 (s, 1H, Ar); 7.32 (m, 2H, Ar), 6.12 (s, 1H, Ar); 5.90 (d, 1H, JHH¼5.92 Hz, Ar); 5.84 (t,
1H, JHHH¼5.52 Hz, Ar); 5.51(s, 1H, Ar); 5.33 (s, 1H, Ar); 2.41 (s, 3H,CH3), 2.26 (s, 3H, CH3);
2.07(s, 3H, CH3). 13C NMR (400 MHz, DMSO-d6), d (ppm): 172.23 (CH ¼ N); 155.31 (py);
140.07 (py); 138.73 (py); 138.62 (py); 131.00 (py); 130.55 (Ar); 129.33 (Ar); 125.7 6(Ar);
117.06 (Ar); 105.05 (Ar); 90.23 (Ar); 89.74 (Ar); 84.74 (Ar); 84.34 (Ar); 81.30 (Ar); 55.99
(CH3); 18.47 (CH3). IR (KBr) (cmꢀ1): ꢀ(C ¼ N) 1601.1; ꢀ(P-F) 832.98. Anal. Calcd for
C21H22ClN2RuPF6: C, 43.20; H, 3.80; N, 4.80. Found: C, 43.15; H, 3.90; N, 4.90%. MS (ESI,
m/z): 439.05 [C21H22ClN2Ru]þ.

6
J. M. GICHUMBI ET AL.
2.3.6. Complex 6
1
Orange powder, yield 82%, m.p. 183 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.64 (d, 1H, JHH¼5.48 Hz, py); 9.05 (s, 1H, CH ¼ N); 8.32 (d, 2H, JHH¼4.36 Hz, py); 7.94
(m, 2H, py); 7.61 (m, 2H, Ar); 7.47 (m, 1H, Ar), 6.20 (t, 1H, JHH¼5.88 Hz, Ar); 5.88 (t, 2H,
JHH¼8.0 Hz, Ar); 5.75 (t, 1H, JHHH¼5.88 Hz, Ar); 5.88 (t, 2H, JHH¼8.0 Hz, Ar); 5.75(t, 1H,
JHH¼5.88 Hz, Ar); 5.55 (d, 1H, JHH¼6.00 Hz, Ar); 2.10 (s, 3H, CH3). 13C NMR (400 MHz,
DMSO-d6), d (ppm): 170.87 (CH ¼ N); 156.10 (py); 154.37 (py); 139.93 (Ar); 138.51 (Ar);
129.69 (Ar); 128.85 (Ar); 125.97 (Ar); 84.59 (Ar); 81.26 (Ar); 18.48 (CH3). IR (KBr), (cmꢀ1):
ꢀ(C ¼ N) 1610.1; ꢀ(P-F) 832.98. Anal. Calcd for C19H17FN2RuPF6: C, 39.77; H, 2.99; N,
4.88. Found: C, 39.80; H, 3.00; N, 4.88%. MS (ESI, m/z): 429.01 [C19H17FN2Ru]þ.
2.3.7. Complex 7
1
Orange powder, yield 86%, m.p. 176 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.54 (d, 1H, JHH¼5.48 Hz, py); 8.30 (s, 1H, CH ¼ N); 8.19 (d, 2H, JHH¼4.28 Hz, py); 7.78
(m, 1H, py); 7.38 (d, 2H, JHH¼8.52 Hz, Ar); 6.26 (d, 1H, JHH¼8.56 Hz, Ar), 6.19 (m, 1H, Ar);
5.97 (m, 1H, Ar); 5.74 (m, 2H, Ar); 5.40 (s, 1H, Ar); 3.32 (s, 3H, CH3); 2.2 (s, 3H, CH3). 13C
NMR (400 MHz, DMSO-d6), d (ppm): 166.21 (CH ¼ N); 159.46 (py); 155.88 (py); 154.65
(py); 139.57 (py); 131.32 (py); 129.07 (Ar); 127.90 (Ar); 126.20 (Ar); 114.42 (Ar); 104.79
(Ar); 89.25 (Ar); 87.9 (Ar); 84.7 (Ar); 84.2 (Ar); 80.59 (Ar); 67.98 (Ar); 55.13 (CH2); 18.78
(CH3). IR (KBr), (cmꢀ1): ꢀ(C ¼ N) 1611.18; ꢀ(P-F) 825.52. Anal. Calcd for
C21H22N2OClRuPF6: C, 42.05; H, 3.70; N, 4.88. Found: C, 42.10; H, 3.80; N, 4.90%. MS
(ESI, m/z): 455.05 [C21H22N2OClRu]þ.
2.3.8. Complex 8
1
Orange powder, yield 80%, m.p. 179 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.55 (d, 1H, JHH¼5.48 Hz, Ph); 8.39 (s, 1H, CH ¼ N); 8.20 (d, 2H, JHH¼4.16 Hz, Py); 7.48 (d,
5H, JHH¼2.24 Hz, Py); 6.25 (t, 1H, JHH¼5.84 Hz, Ar); 6.13 (t, 1H, JHH¼5.84 Hz, Ar), 5.95 (m,
1H, Ar); 5.85 (m, 1H, Ar); 5.75 (m, 1H, Ar); 5.51 (d, 1H, Ar); 2.19 (s, 3H, CH3). 13C NMR
(400 MHz, DMSO-d6), d (ppm): 167.13 (CH ¼ N); 155.89 (py); 154.37 (py); 139.60 (py);
134.42 (py); 129.16 (Ar); 128.75 (Ar); 128.00 (Ar); 104.83 (Ar); 89.23 (Ar); 87.87 (Ar);
84.81 (Ar); 80.62 (CH3); 68.54 (CH3); 18.76 (CH3). IR (KBr), (cmꢀ1): ꢀ(C ¼ N) 1600.21; ꢀ(P-
F) 825.52. Anal. Calcd for C20H20N2ClRuPF6: C, 42.15; H, 3.54; N, 4.92. Found: C, 42.18;
H, 3.58; N, 4.96%. MS (ESI, m/z): 425.04 [C20H20N2ClRu]þ.
2.3.9. Complex 9
1
Orange powder, yield 85%, m.p. 180 ꢁC(decomp.). H NMR (400 MHz, DMSO-d6), d (ppm):
9.59 (d, 1H, JHH¼5.4 Hz, py); 8.88 (s, 1H, CH ¼ N); 7.89 (m, 1H, py); 7.39 (s, 2H, py); 7.21
(s, 1H, Ar); 6.13 (t, 1H, JHH¼5.88 Hz, Ar), 5.82 (m, 2H, Ar); 5.73 (t, 1H, JHH¼5.84 Hz, Ar);
5.54 (d, 1H, JHH¼6.00 Hz, Ar); 2.41 (s, 6H, 2CH3); 2.11 (s, 3H, CH3). 13C NMR (400 MHz,
DMSO-d6), d (ppm): 167.39 (CH ¼ N); 156.05 (py); 154.65 (py); 151.83 (py); 139.90 (py);
138.76 (py); 130.99 (Ar); 129.69 (Ar); 128.66 (Ar); 128.16 (Ar); 119.93 (Ar); 104.53 (Ar);
90.20 (Ar); 89.64 (Ar); 84.71 (Ar); 84.59 (Ar); 81.2 (Ar); 20.9 (CH3); 18.48 (CH3). IR (KBr),
(cmꢀ1): ꢀ(C ¼ N) 1610.0; ꢀ(P-F) 831.47. Anal. Calcd for C21H22N2ClRuPF6: C, 43.20; H,
3.80; N, 4.80. Found: C, 43.22; H, 3.84; N, 4.84%. MS (ESI, m/z): 439.05 [C21H22N2ClRu]þ.

JOURNAL OF COORDINATION CHEMISTRY
7
Table 1. Summary of the crystal data of 1, 7, and 8.
Compound
1
7
8
Formula
C21.5H23ClF6N2O0.5PRu
598.91
Triclinic
P-1
8.5582(7)
14.2464(13)
20.8982(18)
105.041(2)
101.478(2)
99.521(2)
2347.2(4)
4
C21H22ClF6N2OPRu
599.89
Monoclinic
P21/c
12.4466(9)
12.8499(9)
15.2776(11)
90
109.803(2)
90
2299.0(3)
4
1.733
173(2)
C20H20ClF6N2PRu
569.87
Monoclinic
P21/n
12.194(3)
13.266(3)
13.528(3)
90
96.377(5)
90
2175.0(8)
4
1.740
173(2)
0.978
0.71073
1136
Formula weight
Crystal system
Space group
a, Å
b, Å
c, Å
ꢁ
a,
ꢁ
b, ꢁ
V, Å3
c,
Z
Dcalcd, Mg/m3
T, K
1.695
173(2)
0.912
0.71073
m, mmꢀ1
k, Å
0.933
0.71073
1200
F(000)
1200
Crystal size, mm3
0.100 ꢂ 0.080 ꢂ 0.030
1.521 to 27.193
100
10,385/0/601
44,738
10,385 [Rint¼0.0696]
ꢀ10ꢃh ꢃ 10,
ꢀ18ꢃk ꢃ 18,
ꢀ26ꢃl ꢃ 26
Semi-empirical
from equivalents
1.019
0.0361, 0.0679
0.0613, 0.0765
0.545 and ꢀ0.616
0.200 ꢂ 0.190 ꢂ 0.180
1.739 to 28.388
100
5763/57/300
55,906
5763 [R(int)] ¼ 0.0591]
ꢀ16ꢃh ꢃ 16,
ꢀ17ꢃk ꢃ 17,
ꢀ20ꢃl ꢃ 20
Semi-empirical
from equivalents
1.023
0.0288, 0.0618
0.0386, 0.0662
0.380 and ꢀ0.507
0.150 ꢂ 0.140 ꢂ 0.130
2.836 to 28.358
99.8
5397/48/284
57,716
ꢁ
hmin, hmax
,
Completeness to theta ¼ 25.242ꢁ
Data/Restraints/Parameters
No. of reflections collected
No. of independent reflections
Index ranges
5397 [Rint¼0.0899]
ꢀ16ꢃh ꢃ 16,
ꢀ17ꢃk ꢃ 17,
ꢀ18ꢃl ꢃ 18
Absorbed correction
Semi-empirical
from equivalents
1.054
Goodness-of-fit on F2
Final R indices
0.0368, 0.0916
0.0515, 0.1003
1.497 and ꢀ0.636
R indices (all data)
Largest diff. peak and hole, e Åꢀ3
2.4. X-ray crystallography
Crystals of 1, 7, and 8 suitable for single-crystal X-ray diffraction studies were grown
by the liquid diffusion method in which the solutions of the compounds in acetone
were layered with hexane and left undisturbed for 2 days. Crystal evaluation and data
collection were performed on a Bruker Smart APEX II diffractometer with Mo Ka radi-
ation (0.71073 Å). The reflections were successfully indexed by an automated indexing
routine built in the APEXII program suite [18]. The final cell constants were calculated
from a set of 6460 strong reflections from the actual data collection. Data reduction
was carried out using the program SAINTþ [18]. The structure was solved by direct
methods using SHELXS [19] and refined. All structures were checked for solvent-access-
ible cavities using PLATON [19]. Non-H atoms were first refined isotropically and then
by anisotropic refinement with full-matrix least-squares calculations based on F2 using
SHELXS [19]. All H atoms were positioned geometrically and allowed to ride on their
respective parent atoms. The carboxyl H atoms were located from the difference map
and allowed to ride on their parent atoms. All H atoms were refined isotropically. The
absorption correction was based on fitting a function to the empirical transmission
surface as sampled by multiple equivalent measurements [19]. Crystal data and struc-
ture refinement information for 1, 7, and 8 are summarized in Table 1.

8
J. M. GICHUMBI ET AL.
2.5. Antibacterial activity of L1 and 1–9
The antibacterial activities of 1–9 and L1 as a representative were determined via disk
diffusion method [20]. Stock solutions of 20 mg of the complexes or L1 were made up
in 1 mL DMSO. Sterile blank disks (6 mm; MAST, UK) were impregnated with 10 lL
(0.2 mg), 20 lL (0.4 mg), and 40 lL (0.8 mg) of each compound stock solutions and left
to dry for 1 h. Five Gram-negative (antibiotic-sensitive Escherichia coli ATCC 25922,
TEM-b-lactamase producing E. coli ATCC 35218, extended-spectrum b-lactamase pro-
ducing Klebsiella pneumoniae ATCC 700603, multidrug-resistant Pseudomonas aerugi-
nosa ATCC 27853 and Chromobacterium violaceum ATCC 12472) and four Gram-
positive (Bacillus subtilis ATCC 6633, Mycobacterium smegmatis mc2 155, antibiotic-sen-
sitive Staphylococcus aureus ATCC 29213, and methicillin-resistant S. aureus
ATCC43300) bacterial strains were grown on Tryptic soy agar plates overnight, while
suspended in sterile distilled water. The turbidity of the cell suspensions was adjusted
to be equivalent to that of a 0.5 McFarland standard. Mueller-Hinton (MH) agar plate
surfaces were swabbed with these suspensions and compound-impregnated discs
were applied to the surface. The plates were incubated at 37 ꢁC for 18 h, with M. smeg-
matis mc2 155 plates being incubated at 37 ꢁC for 48 h and C. violaceum ATCC 12472
plates being incubated at 30 ꢁC. Tests were carried out in duplicate and the results
averaged. Tetracycline (TE30), Ampicillin (AMP 10), Rifampin (RD5), and streptomycin
(S10) disks (Oxoid, UK) were used as standard antibacterial agent controls, while disks
impregnated with DMSO were used as the negative controls.
The criteria for assigning Enterobacteriaceae susceptibility or resistance to AMP10
was as follows: (S)ꢄ17 mm, (I)¼14–16 mm, (R)ꢃ13 mm, while those for TE30 were:
(S)ꢄ15 mm, (I)¼12–14 mm, (R)ꢃ11 mm (CLSI, 2018). For staphylococci, the criteria for
susceptibility or resistance to TE30 were: (R)ꢃ14 mm, (I)¼15–18 mm, and (S)ꢄ19 mm
(CLSI, 2018). The zone diameter criteria used to assign resistance or susceptibility to
the tested compounds were: Resistant (R)ꢃ10 mm, Intermediate (I)¼11–14 mm and
Susceptible (S)ꢄ15 mm.
3. Results and discussion
3.1. Synthesis and characterization of cationic iminopyridyl Ru(II)-
arene complexes
The dimeric precursor [(g6-C6H5-CH3)Ru(m-Cl)Cl]2 was treated with N,N-bidentate
ligands in acetonitrile at room temperature to give the mononuclear complexes 1–9
(Scheme 1). The new complexes were obtained in good yields and characterized
1
using FTIR, H NMR, and 13C NMR spectroscopy, high resolution mass spectrometry,
and single-crystal X-ray diffraction.
The complexes were soluble in DMSO, acetonitrile, acetone, and methanol. They
were also slightly soluble in water. They were insoluble in ethanol, hexane, and diethyl
1
ether. The aqueous stability was followed using H NMR spectroscopy and the com-
plexes were0 stable with no change over 48 h. Complex formation was confirmed using
1H NMR and 13C NMR spectroscopy by following the behavior of the resonances for
the imine moiety in the spectra of the ligands and the complexes. A downfield shift of

JOURNAL OF COORDINATION CHEMISTRY
9
Scheme 1. Schematic representation of the synthetic procedure for 1–9.
the peaks assigned to the imine proton and carbon was observed, and is attributed to
the deshielding of the imine carbon upon coordination as a result of removal of elec-
tron density from carbon similar to those of related complexes from the literature [12,
13, 21–26]. On comparing the influence of the nature of the complexed ligand on the
imine proton shift it was observed that the presence of electron withdrawing or
donating groups played a role in the imine proton shift in the spectra of the com-
plexes. The spectra of 4 and 6 with the bromo-substituents and fluoro-substituents
displayed the highest shifts, with fluoro-complex 6 having a bigger effect than bromo-
complex 4 (9.05 and 8.92 ppm, respectively). The rest of the complexes all had elec-
tron donating substituents albeit in different positions. Complexes 3 that is ortho- and
para-substituted, 5 meta-substituted and para-substituted, and 7 which is ortho-
methoxy substituted, showed the smallest shift (8.82, 8.82, and 8.30 ppm, respectively)
in their proton NMR spectra. The rest of the compounds had very similar chemical
shifts for the imine proton in their spectra. The 1H NMR data for the complexes
showed resonances for the g6-toluene protons were influenced by the symmetry of
the Schiff base at the ruthenium center.
The FTIR spectra showed a downfield shift in the imine absorption bands of the
ligands as compared to those of the complexes. There is an increase in electron dens-
ity, which may be due to back-bonding from the metal centers to the imine bond on
coordination of the ligand to the complex [12, 13, 21–26]. The coordination of the lig-
and to the metal was further confirmed by mass spectrometry where in the spectra of
the complexes, mass-to-charge (m/z) signals corresponding to [Mþ] for the monomeric
complexes. The UV-vis spectra (Figure 1) of the complexes displayed absorption bands
ꢅ
ꢅ
between 230 and 380 nm, attributed to ligand-centered n-p and p-p transitions. The
spectra of the complexes also presented bands between 407 and 431 nm which could
ꢅ
be assigned to the metal-to-ligand (dp-p ) charge-transfer (MLCT) transition from the
ꢅ
filled 4d orbital to the empty p orbital [12, 13, 21–26].
3.2. Molecular and crystal structure analysis of 1, 7, and 8
Crystals suitable for X-ray diffraction analysis 1, 7, and 8 were grown by slow diffusion
of hexane into a solution of the complexes in acetone. ORTEP diagrams of 1, 7, and 8

10
J. M. GICHUMBI ET AL.
Figure 1. UV–vis absorption spectra of the mononuclear complexes 1–9 in acetonitrile at 298K.
Figure 2. ORTEP view of 1, displacement ellipsoids are drawn at the 30% probability level, hydro-
gens are omitted for clarity.
are shown in Figures 2–4, while selected bond distances and angles are in Table 2.
The crystal structures confirm the formation of complex salts composed of a Ru(II) cat-
ionic species and a PF6ˉ counter anion. The asymmetric units are however slightly dif-
ferent and in that of 1, we have two molecules of the cation [(g6-p-CH3-
(C6H5))RuCl(C12H12N2)]þ, two PF6ˉ anions and an acetone solvent molecule. Complexes
7 and 8 each have the cation, [(g6-p-CH3-(C6H5))RuCl(C14H14N2O)]þ and [(g6-p-CH3-
(C6H5))RuCl(C13H12N2)]þ, respectively, and PF6ˉ in their asymmetric units. All three com-
plexes present the three-legged, piano-stool arrangement in which the arene ring
occupies the apex, while the N,N0-bidentate ligand and Cl atom are the legs of the
piano-stool, similar to those of structurally related N,N0-bidentate complexes [5,
12–14, 21–27].
The Ru–Npyr and Ru–Nimine bond distances range between 2.0754(18) Å and
2.093(2) Å and are comparable to those reported for related compounds [5, 9, 12–14,

JOURNAL OF COORDINATION CHEMISTRY
11
Figure 3. ORTEP view of 7, displacement ellipsoids are drawn at the 30% probability level, hydro-
gens are omitted for clarity.
Figure 4. ORTEP view of 8, displacement ellipsoids are drawn at the 40% probability level, hydro-
gens are omitted for clarity.
21–30]. Similarly, the bond angles Npyr–Ru–Nimine range between 76.48(10)ꢁ and
76.96(7)ꢁ, while N–Ru–Cl range from 83.60(7)ꢁ to 86.99(7)ꢁ and are comparable to
those of similar cationic complexes [5, 12–14, 21–33, 35].

12
J. M. GICHUMBI ET AL.
Table 2. Selected bond lengths (Å) and angles (ꢁ) for 1, 7, and 8.
1
7
8
Bond Distances
Ru–N
Ru–N
Ru–N
Ru–N
2.078(3)
2.093(2)
2.083(2)
2.089(2)
2.3879(9)
2.3940(9)
2.0754(18)
2.0831(16)
–
–
2.3862(6)
–
2.076(3)
2.083(3)
–
–
2.3973(9)
–
Ru–Cl
Ru–Cl
Bond Angles
N–Ru–N
N–Ru–N
N–Ru–Cl
N–Ru–Cl
N–Ru–Cl
N–Ru–Cl
76.77(9)
76.58(10)
83.60(7)
86.65(7)
86.99(7)
85.52(7)
76.96(7)
–
83.64(5)
83.93(5)
–
–
76.48(10)
84.13(7)
86.67(7)
Figure 5. Inhibitory activity of 1–9 and L1 along with Ampicillin, Tetracycline, Rifampin, and
streptomycin against Gram-positive bacteria at 400 mg concentration.
3.3. Antibacterial activity results
The activities of the complexes were tested against Gram-negative and Gram-positive
bacteria. The results showed that the compounds were more effective than L1 against
susceptible S. aureus ATCC 29213 and methicillin-resistant S. aureus ATCC 43300 as
well as M. smegmatis mc2 155, with inhibitory activity being observed from 200 to
800 mg (Figures 5 and 6 and S10a-c). L1 was chosen as a representative for the other
ligands. For S. aureus ATCC 29213, activity in descending order was 3, 8, 1, 2, 4, 9, 7,
5, and 6. For L1 minimal zones of inhibition (ꢃ10 mm) were observed at 800 mg. The
increase in activities of the complexes may arise from the coordination, which makes
the metal complexes act as more controlling and potent to microorganism, thus hin-
dering their growth [9].
For S. aureus ATCC 43300, activity was observed with 1–5 and 7–9 from 200 to
800 mg. Only the ligand showed no activity from 200 to 800 mg. Similarly with M. smeg-
matis, activity was observed with 200–800 mg of 1–4, 7, and 8. The ligand and 5, 6,
and 9 demonstrated no antimicrobial activity against M. smegmatis. Compounds 5, 6,

JOURNAL OF COORDINATION CHEMISTRY
13
Figure 6. Inhibitory activity of 1–9 and L1 along with Ampicillin and Tetracycline against
Gram-positive bacteria at 400mg concentration.
and 9 appear to have minimal activity against the Gram-positive bacteria in compari-
son to the other compounds. No Gram-negative bacteria inhibition was observed with
L1 or 1–9 (supporting information), although minimal inhibition zones were observed
with 800 mg. This can be attributed to Gram-positive bacteria lacking the outer mem-
brane of Gram-negative ones, which acts as a barrier for penetration of numerous
molecules [35]. The ligand and compounds were also tested for Gram-negative, anti-
quorum sensing activity using C. violaceum ATCC 12472. Although a minimal anti-
microbial effect was observed at 800 mg, none of the tested samples were able to
inhibit quorum sensing. No Gram-negative activity was found but compounds could
be used for Gram-negative pathogens after more testing is undertaken. There was no
clear trend observed in changing the substituents on the phenyl rings, on the anti-
microbial activity. However, it has been observed that similar complexes, in which the
ligands had sulfur atoms, were generally more active than those with other substitu-
ents. For example, better activity was observed for arene-ruthenium complexes con-
taining phenyl hydrazine Schiff base [34], pyridyl benzothiazole hydrazine ligands [35],
and pyridyl benzothiazole hydrazones ligands [36].
The synthesized complexes were also less active when compared to similar com-
plexes reported by our group previously with p-cymene arene [12, 13], but were better
than those reported for some osmium half-sandwich complexes [11]. The complexes
were also less active than those half-sandwich complexes with pyridyl azine Schiff
base complexes [9]. However, the complexes reported show better activity than those
ruthenium(II) complexes of thiosemicarbazone reported by Yildirim et al. [37] despite
the presence of the sulfur atom in the ligand.

14
J. M. GICHUMBI ET AL.
4. Conclusion
A new series of arene-ruthenium(II) complexes [(g6-C6H5-CH3)RuLCl](PF6) (where
L ¼ N,N0-bidentate ligand; (C5H4NCH ¼ N-Ar) where Ar ¼ 4-methylphenyl (1); 3,4-dime-
thylphenyl (2), 2,4,6-trimethylphenyl (3); 4-bromophenyl (4); 2,5-dimethylphenyl (5); 2-
flourophenyl (6), (4-methoxy phenyl)methylene (7); phenylmethylene (8); and 3,5-
1
dimethylphenyl (9)) were synthesized. The compounds were fully characterized via H
NMR, 13C NMR, IR, and UV-Vis spectroscopy and elemental analyses. The molecular
structures of representative complexes (1, 7, and 8) were established by single-crystal
X-ray diffraction studies. The ruthenium atom is coordinated to the arene group,
which occupies the apex, while the N,N0-bidentate ligand and a halide make up the
base of the stool. The compounds were evaluated for their in vitro antibacterial activity
by the disk diffusion method against a panel of Gram-negative and Gram-positive bac-
teria. The complexes showed promising bactericidal activity against methicillin-resist-
ant S. aureus ATCC 43300. However, the complexes showed less activity as compared
to similar complexes where the arene is p-cymene or benzene, thus there is need for
further studies in the relationship of antimicrobial activity to the hexahapto arene and
the type of substituents on the N,N0-donor ligand.
Acknowledgements
We wish to extend our sincere thanks to the NRF and UKZN (URF) for financial support. Joel M.
Gichumbi thanks Chuka University for the research visit leave.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
[1] K.D. Mjos, C. Orvig. Chem. Rev., 114, 4540 (2014).
[2] Y. Wang, H. Wang, H. Li, H. Sun. Dalton Trans., 44, 437 (2015).
[3] C. Orvig, M.J. Abrams. Chem. Rev., 99, 2201 (1999).
[4] N.J. Wheate, S. Walker, G.E. Craig, R. Oun. Dalton Trans., 39, 8113 (2010).
[5] J.V. Mehta, S.B. Gajera, M.N. Patel. J. Biomol. Struct. Dyn., 35, 1599 (2017).
[6] A. Bolhuis, L. Hand, J.E. Marshall, A.D. Richards, A. Rodger, J. Aldrich-Wright. Eur. J. Pharm.
Sci., 42, 313 (2011).
[7] F. Li, J.G. Collins, F.R. Keene. Chem. Soc. Rev., 44, 2529 (2015).
[8] J.M. Gichumbi, H.B. Friedrich. J. Organomet. Chem., 866, 123 (2018).
[9] A. Lapasam, V. Banothu, A. Uma, M.R. Kollipara. J. Mol. Struct., 1191, 314 (2019).
[10] M. Sayed, A.M. Kamal El-Dean, M. Ahmed, R. Hassanien. Synth. Commun., 48, 413 (2018).
[11] J.M. Gichumbi, H.B. Friedrich, B. Omondi, K. Naicker, M. Singh, H.Y. Chenia. J. Coord.
Chem., 71, 342 (2018).
[12] J.M. Gichumbi, H.B. Friedrich, B. Omondi. J. Organomet. Chem., 808, 87 (2016).
[13] J.M. Gichumbi, H.B. Friedrich, B. Omondi, M. Singh, K. Naicker, H.Y. Chenia. J. Coord.
Chem., 69, 3531 (2016).
[14] J.M. Gichumbi, B. Omondi, G. Lazarus, M. Singh, N. Shaikh, H.Y. Chenia, H.B. Friedrich.
Z Anorg. Allg. Chem., 643, 699 (2017).

JOURNAL OF COORDINATION CHEMISTRY
15
[15] J.M. Gichumbi, B. Friedrich Holger, B. Omondi, G. Lazarus Geraldine, M. Singh, Y. Chenia.
Z. Naturforsch. B, 73, 167 (2018).
[16] M.A. Bennett, A.K. Smith. J. Chem. Soc., Dalton Trans., 233 (1974).
[17] H. Hu, L. Zhang, H. Gao, F. Zhu, Q. Wu. Chemistry, 20, 3225 (2014).
[18] Bruker-AXS, Madison, Wisconsin, USA (2009).
[19] G. Sheldrick. Acta Crystallogr., A, Found. Crystallogr., 64, 112 (2008).
[20] (CLSI) Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial
Susceptibility Testing. CLSI supplement M100. 28th edn, Wayne, Pennsylvania, USA (2018).
€
[21] O. Dayan, S. Demirmen, N. Ozdemir. Polyhedron, 85, 926 (2015).
[22] J.M. Gichumbi, H.B. Friedrich, B. Omondi. J. Mol. Catal. A: Chem., 416, 29 (2016).
[23] J.M. Gichumbi, H.B. Friedrich, B. Omondi. J. Mol. Struct., 1113, 55 (2016).
[24] J.M. Gichumbi, H.B. Friedrich, B. Omondi. Transit. Met. Chem., 41, 867 (2016).
[25] J.M. Gichumbi, B. Omondi, B.F. Holger. Z. Kristallograph. New Cryst. Struct., 232, 301
(2017).
[26] J.M. Gichumbi, H.B. Friedrich, B. Omondi. J. Coord. Chem., 72, 135 (2019).
[27] J.M. Gichumbi, B.F. Holger, B. Omondi. Z. Kristallograph. New Cryst. Struct., 232, 285
(2017).
[28] I. Lyngdoh Mawnai, S. Adhikari, L. Dkhar, J. Lakshmi Tyagi, K. Mohan Poluri, M.R. Kollipara.
J. Coord. Chem., 72, 294 (2019).
[29] L.C. Matsinha, S.F. Mapolie, G.S. Smith. Polyhedron, 53, 56 (2013).
[30] S.K. Mandal, A.R. Chakravarty. Polyhedron, 11, 823 (1992).
[31] M.J. Chow, C. Licona, D. Yuan, G. Pastorin, C. Gaiddon, W.H. Ang. J. Med. Chem., 57, 6043
(2014).
[32] P. Govender, A.K. Renfrew, C.M. Clavel, P.J. Dyson, B. Therrien, G.S. Smith. Dalton Trans.,
40, 1158 (2011).
[33] G. Gupta, K.T. Prasad, B. Das, G.P.A. Yap, K.M. Rao. J. Organomet. Chem., 694, 2618 (2009).
[34] A. Lapasam, V. Banonthu, U. Adepaly, M.R. Kollipara. J. Chem. Sci., 132, 34 (2020).
[35] L. Shadap, J.L. Tyagi, K.M. Poluri, E. Pinder, R.M. Phillips, W. Kaminsky, M.R. Kollipara.
Polyhedron, 176, 114293 (2020).
[36] L. Dkhar, V. Banothu, W. Kaminsky, M.R. Kollipara. J. Organomet. Chem., 914, 121225
(2020).
[37] H. Yildirim, E. Guler, M. Yavuz, N. Ozturk, P. Kose Yaman, E. Subasi, E. Sahin, S. Timur.
Mater. Sci. Eng. C Mater. Biol. Appl., 44, 1(2014).