Synthesis, spectroscopic characterization, X-ray crystal structure, antimicrobial, DNA-binding, alkaline phosphatase and insulin-mimetic studies of oxidovanadium(IV) complexes of azomethine precursors

Article abstract of DOI:10.1080/00958972.2020.1813282

A series of novel azomethine precursors were synthesized by the condensation reactions of 3-(trifluoromethyl)benzenamine (tfmb) with 2-hydroxybenzaldehyde (HL¹) (tfmbs), 2,3-dihydroxybenzaldehyde (HL²) (tfmbdh), 2-hydroxy-1-naphthaldehyde (HL³) (tfmbnd) and 5-chloro-2-hydroxybenzaldehyde (HL⁴) (tfmbCl). The oxidovanadium(IV) complexes of the type [VO(tfmbs)₂] (1), [VO(tfmbdh)₂] (2), [VO(tfmbnd)₂] (3) and [VO(tfmbCl)₂] (4) were also prepared by the reaction of ligands HL¹–HL⁴ with vanadyl(V) isopropoxide [VO(OCHMe₂)₃]. The synthesized compounds were characterized by elemental analysis, FT-IR, multinuclear (¹H and ¹³C) NMR spectroscopies, magnetic susceptibility measurements and thermogravimetry. The studies revealed that binding of precursors with metal took place through azomethine nitrogen and phenolic oxygen. The single-crystal analysis of HL¹, HL⁴ and 3 has been carried out. The intercalation mode of interaction of the complexes with Salmon sperm DNA (SS-DNA) was established by the observed hypochromicity through UV–vis spectroscopic studies. The determined negative ΔG values confirmed the spontaneity of the binding process of complexes with SS-DNA. All the synthesized precursors and complexes were screened for their alkaline phosphatase inhibition, antimicrobial, hemolytic and insulin-mimetic properties, which exhibited significant activities with a few exceptions.

Full text of DOI:10.1080/00958972.2020.1813282

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis, spectroscopic characterization, X-ray
crystal structure, antimicrobial, DNA-binding,
alkaline phosphatase and insulin-mimetic studies
of oxidovanadium(IV) complexes of azomethine
precursors
Khurram Shahzad Munawar , Saqib Ali , Muhammad Nawaz Tahir , Nasir
Khalid , Qamar Abbas , Irfan Zia Qureshi , Shabbir Hussain & Muhammad
Ashfaq
To cite this article: Khurram Shahzad Munawar , Saqib Ali , Muhammad Nawaz Tahir , Nasir
Khalid , Qamar Abbas , Irfan Zia Qureshi , Shabbir Hussain & Muhammad Ashfaq (2020):
Synthesis, spectroscopic characterization, X-ray crystal structure, antimicrobial, DNA-binding,
alkaline phosphatase and insulin-mimetic studies of oxidovanadium(IV) complexes of azomethine
precursors, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2020.1813282
To link to this article: https://doi.org/10.1080/00958972.2020.1813282
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1813282
Synthesis, spectroscopic characterization, X-ray crystal
structure, antimicrobial, DNA-binding, alkaline
phosphatase and insulin-mimetic studies of
oxidovanadium(IV) complexes of azomethine precursors
Khurram Shahzad Munawara,b, Saqib Alic, Muhammad Nawaz Tahird, Nasir
Khalide, Qamar Abbasf, Irfan Zia Qureshig, Shabbir Hussainh and
Muhammad Ashfaqd
b
aDepartment of Chemistry, University of Sargodha, Sargodha, Pakistan; Department of Chemistry,
c
University of Mianwali, Mianwali, Pakistan; Department of Chemistry, Quaid-i-Azam University,
d
e
Islamabad, Pakistan; Department of Physics, University of Sargodha, Sargodha, Pakistan; Chemistry
f
Division, Pakistan Institute of Nuclear Science & Technology, Islamabad, Pakistan; Department of
Physiology, University of Sindh, Jamshroo, Pakistan; Department of Animal Sciences, Quaid-i-Azam
University, Islamabad, Pakistan; Department of Chemistry, Lahore Garrison University,
g
h
Lahore, Pakistan
ABSTRACT
ARTICLE HISTORY
Received 25 February 2020
Accepted 21 July 2020
A series of novel azomethine precursors were synthesized by the
condensation reactions of 3-(trifluoromethyl)benzenamine (tfmb)
with 2-hydroxybenzaldehyde (HL1) (tfmbs), 2,3-dihydroxybenzalde-
hyde (HL2) (tfmbdh), 2-hydroxy-1-naphthaldehyde (HL3) (tfmbnd)
and 5-chloro-2-hydroxybenzaldehyde (HL4) (tfmbCl). The
oxidovanadium(IV) complexes of the type [VO(tfmbs)2] (1),
[VO(tfmbdh)2] (2), [VO(tfmbnd)2] (3) and [VO(tfmbCl)2] (4) were
also prepared by the reaction of ligands HL1–HL4 with vanadyl(V)
isopropoxide [VO(OCHMe2)3]. The synthesized compounds were
characterized by elemental analysis, FT-IR, multinuclear (1H and
13C) NMR spectroscopies, magnetic susceptibility measurements
and thermogravimetry. The studies revealed that binding of pre-
cursors with metal took place through azomethine nitrogen and
phenolic oxygen. The single-crystal analysis of HL1, HL4 and 3 has
been carried out. The intercalation mode of interaction of the
complexes with Salmon sperm DNA (SS-DNA) was established by
the observed hypochromicity through UV–vis spectroscopic stud-
ies. The determined negative DG values confirmed the spontan-
eity of the binding process of complexes with SS-DNA. All the
synthesized precursors and complexes were screened for their
alkaline phosphatase inhibition, antimicrobial, hemolytic and insu-
lin-mimetic properties, which exhibited significant activities with a
few exceptions.
KEYWORDS
Oxidovanadium(IV) com-
plexes; crystal structure;
DNA-binding; insulin-
mimetic studies;
antimicrobial activity;
alkaline phosphat-
ase inhibition
CONTACT Khurram Shahzad Munawar
Sargodha, Sargodha, Pakistan; Saqib Ali
University, Islamabad, Pakistan
khurramchemist@gmail.com
drsa54@hotmail.com
Department of Chemistry, University of
Department of Chemistry, Quaid-i-Azam
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1813282.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
K. S. MUNAWAR ET AL.
1. Introduction
Recent advances in the coordination chemistry and catalytic properties of vanadium
has attracted increasing interest during the last few years due to the model character
of many of its complexes for the biological functions of vanadium [1–5], role of van-
adium complexes in oxidation and oxo-transfer catalysis [6, 7] and potential medicinal
application such as treatment of diabetes mellitus [8–10]. One likely mechanism for
the insulin-mimetic activity of vanadium compounds is related to their potent inhib-
ition of protein tyrosine phosphatases (PTPs) [11]. The reasons for the superior activity
of vanadium compounds are not clear but could be related to better bioavailability of
these compounds or more potent activity at the enzyme’s active site.
Vanadium complexes have multiple biological and pharmacological activities,
including antimicrobial [12], anti-leukemia [13], antitumor [14] and photodynamic ther-
apy [15]. Vanadium complexes are further explored in DNA-binding and cleavage
properties for their potential applications in the study of DNA structural probes and
DNA-dependent electron-transfer mechanism [16–18]. The oxidative DNA-cleavage
that involves the heterocyclic bases and/or sugar moiety finds application in foot-
printing and therapeutic studies [19]. Several Schiff bases of VO(IV) complexes, such
as [VO(satsc)(phen)] (where satsc is salicylaldehyde thiosemicarbazone) [20],
[VO(salmdtc)(B)] (where salmdtc is dianionic N-salicylidene-S-methyldithiocarbazate
and B is N,N-donor phenanthroline base) [21] have been synthesized and studied for
their DNA-binding and cleavage activities. However, the mechanisms by which they
interact with DNA have not yet been clearly elucidated [22].
Human alkaline phosphatase (ALP) can be classified into at least four tissue-specific
forms or isozyme mainly according to the specificity of the tissue to be expressed,
termed as placental alkaline phosphatase (PLALP or Regan isozyme), intestinal alkaline
phosphatase (IALP), liver/bone/kidney alkaline phosphatase (L/B/K ALP) and germ cell
ALP (GCALP or NAGAO isozyme).

JOURNAL OF COORDINATION CHEMISTRY
3
ALP is important in recycling phosphate within living cells. It seems to be particu-
larly prevalent in tissues which are transporting nutrients, including intestine and kid-
ney. Inhibitors of ALP include vanadate, arsenate, L-phenylalanine and L-tryptophan.
These inhibitors have been used in studies geared towards better understanding of
the physiological role of ALP [23]. The rate of an enzyme-catalyzed reaction depends
partly on how well the enzyme and substrate fit together. Thus, environmental factors
(such as pH, temperature or presence of inhibitor) which might change the shape of
either enzyme or substrate could alter the rate of formation of product. Vanadate in
its monomeric form is a strong competitive inhibitor of wild-type ALP [24]. The inhibi-
tory effect of vanadate has been ascribed to its mimetic ability to the anionic charac-
ter of inorganic phosphate [25]. In fact, small-sized inorganic ions that include
inorganic phosphate (ꢀ10 mM), vanadate (2 mM) and periodate (0.05 mM) [26, 27] are
the most potent inhibitors of ALP.
Azomethine precursors are preferred over carboxylates and thiols in the present
study because they have versatile applications and the most interesting is that they
form the complex immediately just by stirring without the involvement of tedious
reaction conditions. One problem found for carboxylate complexes is that we have to
prepare its either sodium or potassium salt before complexation. Secondly, they have
limited solubility. While the thiols makes S–S bridge during complexation which are
sometime unavoidable. Another drawback is that, in some cases, SH at ortho-position
makes a five-membered ring with carbon of aldehyde during the synthesis of ligands.
The substitution of phenolic group at ortho-position of the ligands is necessary
from the coordination point of view that vanadium can chelate by using “O” of phen-
olic part and “N” of azomethine part to make a stable six-membered ring. The other
substitutions in the ligands are to make the diversity and to elaborate the effect/
change on the application/activity.
In the present work, azomethine precursors HL1–HL4 and their oxidovanadium com-
plexes 1–4 have been synthesized and characterized. The interactions of the synthe-
sized compounds with Salmon sperm DNA (SS-DNA) were investigated using UV–vis
absorption titration. All the compounds were checked for their inhibition against ALP.
The synthesized compounds were tested for their in vitro antibacterial, antifungal and
hemolytic activities. The insulin-enhancing properties were also elaborated by treating
the diabetic mice with these compounds and then monitoring their blood
plasma level.
2. Experimental
2.1. Materials
The reagents, vanadyl(V) isopropoxide, 3-(trifluoromethyl)benzenamine, 2-hydroxyben-
zaldehyde, 2,3-dihydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde, 5-chloro-2-
hydroxybenzaldehyde, p-nitrophenyl phosphate hexahydrate (p-NPP), diethanolamine,
Alloxan monohydrate and magnesium chloride were purchased from Sigma Aldrich
(USA) and used without further purification. Sodium salt of SS-DNA was obtained from
ACROS Organics and used as received. All the solvents like dimethylsulfoxide (DMSO),
acetonitrile, ethanol, etc. were purchased from E. Merck (Germany). Human serum,

4
K. S. MUNAWAR ET AL.
obtained from “Capital Development Authority” (CDA) hospital Islamabad, was used as
a source of ALP.
All procedures performed in studies involving human participants were in accord
with the ethical standards of the institutional and/or national research committee and
with the 1964 Helsinki declaration and its later amendments or comparable ethical
standards. All applicable institutional and/or national guidelines for the care and use
of animals were followed.
2.2. Characterization of synthesized products
Elemental analysis of the synthesized compounds was carried out on an Elemental
Vario EL elemental analyzer. FT-IR spectra in the range of 4000–400 cmꢁ1 were
obtained on a Thermo Nicolet-6700 FT-IR spectrophotometer. Multinuclear (1H and
13C) NMR spectra were recorded on a Bruker-400 MHz FT-NMR spectrometer using
1
DMSO-d6 as a solvent [d H (DMSO) ¼ 2.5 ppm and d 13C (DMSO) ¼ 39 ppm]. Chemical
shifts are given in ppm and coupling constants (J) values are reported in Hz. The
multiplicity of 1H NMR signals (s ¼ singlet, d ¼ doublet, dd ¼ doublets of doublet,
t ¼ triplet, dt ¼ doublets of triplet and m ¼ multiplet) are mentioned with chemical
shifts. The absorption spectra were measured on a Shimadzu 1800 UV–visible spectro-
photometer. The melting points were determined in capillary tubes using an electro-
thermal melting point apparatus (Gallenkamp). Magnetic moment was determined by
using Sherwood magnetic susceptibility balance at ambient temperature (25 2 ꢂC),
using Hg[Co(SCN)4] as calibrant. Thermogravimetric analysis was performed by
Universal V4.3A TA Instruments. The XRD data of the titled compounds were collected
using the diffractometer Bruker KAPPA Apex-II having monochromator made of graph-
ite providing finely focused Ka X-rays, a CCD detector for recording of diffraction
peaks. Apex-II (Bruker 2009), SHELXS97 and SHELXS2014/6 software were used for data
collection, solution of structure and structure refinement, respectively. Thermal ellips-
oid diagrams were drawn by ORTEP-3 software [28]. Packing of molecules for the com-
pounds were shown by PLATON software whereas Mercury 4.0 was used for graphical
representation of p–p stacking interaction.
2.3. SS-DNA binding studies by electronic absorption titration
SS-DNA (20 mg) was dissolved in doubly deionized water (pH ¼ 7.0), kept at 4 ꢂC and
used within 4 days. The SS-DNA solution gave a ratio of UV absorbance at 260 and
280 nm of 1.84:1, indicating that the DNA is sufficiently free from protein [29]. The
DNA concentration was determined by measuring absorption intensity at 260 nm with
the known molar absorption coefficient value of 6600 Mꢁ1 cmꢁ1 [30] and was found to
be 2.0 ꢃ 10ꢁ4 M. The compound was dissolved in 70% DMSO:H2O at a concentration
of 2 mM. For UV absorption studies, 10 mL solution of SS-DNA and compound was
prepared by varying the concentration of SS-DNA, while keeping the concentration of
compound fixed, along with
a reference solution without the compound.
Compound–SS-DNA solutions were endorsed to incubate for 30 min at room tempera-
ture (25 1 ꢂC) before the absorption measurements were made. The data were then

JOURNAL OF COORDINATION CHEMISTRY
5
fitted into the following Benesi–Hildebrand equation to obtain the intrinsic binding
constant, K [31]:
Ao
eG
eG
1
¼
þ
ꢃ
A ꢁ Ao eHꢁG ꢁ eG eHꢁG ꢁ eG K½DNAꢄ
where K ¼ binding constant, Ao ¼ absorbance of the compound, A ¼ absorbance of the
compound–SS-DNA adduct, eG ¼ absorption coefficient of the compound and
eHꢁG ¼ absorption coefficient of the compound–SS-DNA adduct. The binding constants
may be obtained from the intercept-to-slope ratios of Ao/(A ꢁ Ao) versus 1/[DNA] plots.
The change in Gibb’s free energy (DG) may be determined using the following equa-
tion:
DG ¼ ꢁRT lnK
where R ¼ general gas constant (8.314 J Kꢁ1 molꢁ1), T ¼ temperature (K) and
K ¼ binding constant.
2.4. ALP inhibition
For the preparation of assay, the method used was similar to the one as reported ear-
lier with certain modifications [32]. Working substrate was made by mixing four parts
of reagent A [diethanolamine (pH 9.8), 2 M and magnesium chloride 0.5 mM] and one
part of reagent B [p-nitrophenyl phosphate (p-NPP) (50 mM)]. Substrate was incubated
for 5 min at 25 ꢂC. In a cuvette, 2 mL of the substrate was taken and 40 mL of human
serum containing ALP having the activity of 165 IU Lꢁ1 was added. After incubation of
1 min, absorbance was measured to confirm the activity of enzyme which is termed as
blank. ALP hydrolyzed the p-NPP and to give p-nitrophenol which produces yellow p-
nitrophenolate ion under basic conditions according to the following reaction that
absorbs at 405 nm.
O-
O
O-
O
O-
O
N+
N+
N
O
P
ALP
-O
O-
+
Hydrolysis
O-
O
O-
O
O
P
O-
-O
For the purpose of inhibition studies of the synthesized compounds, the concentra-
tion of substrate and ALP was kept constant but the quantities of inhibitors, ligands,
complexes and vanadium control (vanadyl(V) isopropoxide [VO(OCHMe2)3]) were

6
K. S. MUNAWAR ET AL.
increased (10, 20, 30 and 40 mL) in each absorption studies periodically from 12.5 mM
stock solution. Each sample was incubated for 3 min and the decrease in absorbance
was recorded after every minute for at least 5 min. The average value of these was
used to calculate the percentage inhibition. All ALP studies were carried out
in triplicate.
2.5. Antimicrobial activities
The bacterial (Escherichia coli, Bacillus subtilis, Staphylococcus aureus and Pasturella mul-
tocida) and fungal (Alternaria alternata, Ganoderma lucidum, Aspergillus niger and
Penicillium notatum) strains were cultured and inoculated by a reported procedure
[33]. Antimicrobial potential of the ligands and their complexes was measured by disc
diffusion method [34] with some modifications. Each filter paper disc (size, 9 mm) was
soaked with 100 lL of a sample solution having concentration of 1 mg mLꢁ1 of com-
pound in DMSO and laid flat on growth medium. The petri plates were then incu-
bated for 24 h at 37 ꢂC for bacterial growth and 48 h at 28 ꢂC for the growth of fungi.
The biologically active samples form clear zones of inhibition around the discs which
were measured in millimeters using a zone reader [33, 35].
2.6. Hemolytic activities
The hemolytic activities of azomethine precursors and their respective oxidovanadium
complexes were carried out by an earlier reported procedure [33, 36]. The hemolysis
percentage was calculated by the following formula [36]:
Abs
Abs
ðsampleÞ
ðcontrolÞ
% Hemolysis ¼
ꢃ 100
2.7. Antidiabetic studies
2.7.1. Animals and maintenance
All animals were handled according to the guidelines provided by the local ethics
committee of the “Department of Animal Sciences”, on human use of animals for sci-
entific research. Healthy adult male BALB/c mice (n ¼ 50, average body weight ¼
35 5 g) were obtained from the National Institute of Health, Islamabad. Five animals
were housed per cage and were given free access to standard rodent diet and water
ad libitum. Photoperiod was maintained at 12:12 h light/dark cycle.
2.7.2. Induction of diabetes
Diabetes was induced by a single intraperitoneal injection (i.p.) of Alloxan monohy-
drate at the dose of 150 mg kgꢁ1 body weight. Mice with fasting plasma glucose levels
>200 mg dLꢁ1 were considered diabetic and used for the current study.
2.7.3. Experimental design
Animals were divided into 10 groups, each containing five animals and treated with
acute doses (35.9 mg kgꢁ1 body weight) of HL1–HL4 and 1–4. Positive control groups

JOURNAL OF COORDINATION CHEMISTRY
7
were treated with a known antidiabetic drug Glibenclamide (Euglucon, Roche Pharma)
in distilled water at the dose of 10 mg kgꢁ1 body weight. Following were the treat-
ment groups:
Control groups
Group 1: Negative control(diabetic, only Alloxan pretreated)
Group 2: Positive control(diabetic, Alloxan pretreated followed by
Glibenclamide treatment)
Experimental groups
Animals of this group were diabetic, Alloxan pretreated. Groups 3–6 were treated
with ligands HL1–HL4, while Groups 7–10 were treated with complexes 1–4.
2.7.4. Determination of plasma glucose concentration
Blood was collected through caudal venipuncture using a 26 gauge butterfly cannula.
Blood samples were drawn at 0 h (Pre-Alloxan), 1 h (Post-Alloxan) and then at 1, 2, 3,
4, 5, 6 and 7 h after dosing with the respective compounds. Plasma glucose levels
were determined with a dextrostix using glucometer (Accu-Check Active, Roche).
2.7.5. Determination of total serum cholesterol and triglycerides
Total serum cholesterol and triglyceride concentrations were determined with com-
mercially available kits obtained from Globe Diagnostics S.r.l (Italy) using Microlab
300 (Germany).
2.7.6. Statistical analysis
Data were analyzed through one-way analysis of variance (ANOVA) using the
Statistical Package for Social Sciences (SPSS version 16.0 Inc., Chicago, Illinois, USA)
Post-hoc Tukey-Kramer test. Where normality test failed, ANOVA on ranks was applied.
p < .05 was considered statistically significant difference. Data are presented as line or
bar diagrams constructed using the Graph Pad Prism 5 (Version 5.01 Graph Pad
Software Inc., USA).
2.8. Syntheses of azomethine precursors
The general method for the synthesis of azomethine precursors is shown in the follow-
ing generalized equation:
where “R” is 2-hydroxyphenyl (HL1), 2,3-dihydroxyphenyl (HL2), 2-hydroxynaphthyl
(HL3), 5-chloro-2-hydroxyphenyl (HL4).

8
K. S. MUNAWAR ET AL.
2.8.1. Synthesis of (E)-2-((3-(trifluoromethyl)phenylimino)methyl)phenol (HL1)
Stoichiometric amounts of 3-(trifluoromethyl)benzenamine and 2-hydroxybenzalde-
hyde (5 mmol of each) were added to 100 mL of dried ethanol. The mixture was
refluxed for 3–4 h. The volume of reaction mixture was reduced to one-third of its ori-
ginal and left for crystallization at room temperature. Light yellow crystals were
obtained after 2–3 days. Yield: 69%; m.p.: 85 ꢂC; IR (t/cmꢁ1): 3445 (–OH), 1609 (HC ¼ N),
1109 (C–F); 1H NMR (DMSO-d6, 400 MHz), d (ppm): 12.86 (s, –OH), 8.66 (s, HC ¼ N),
7.54–7.58 (m), 7.41–7.50 (m), 7.07 (dd, J [1H–1H] ¼ 5.7, 1.2 Hz), 6.70 (dt, J [1H–1H] ¼ 7.5,
1.2 Hz); 13C NMR (DMSO-d6, 101 MHz), d (ppm): 149.2, 119.3, 123.4 (q, C–CF3, 2J
[19F–13C] ¼ 3.75 Hz), 130.0, 132.1, 131.7, 118.0 (q, CF3, 1J [19F–13C] ¼ 3.75 Hz), 164.2
(HC ¼ N), 118.9, 161.1 (C–OH), 117.4, 133.8, 124.6, 132.1.
2.8.2. Synthesis of (E)-3-((3-(trifluoromethyl)phenylimino)methyl)benzene-1,2-
diol (HL2)
Similar procedure was adopted as described for HL1, but instead of using 2-hydroxy-
benzaldehyde, 2,3-dihydroxybenzaldehyde was used. Yellow crystals were collected
from the mother liquor after 24 h. Yield: 85%; m.p.: 116 ꢂC; IR (t/cmꢁ1): 3454 (–OH),
1
1616 (HC ¼ N), 1106 (C–F); H NMR (DMSO-d6, 400 MHz), d (ppm): 12.66 (s, –OH), 9.29
(s, –OH0), 9.00 (s, HC ¼ N), 7.79 (s), 7.72–7.66 (m), 6.98 (dd, J [1H–1H] ¼ 8.0, 1.2 Hz), 6.81
(t, J [1H–1H] ¼ 8.0 Hz), 7.24 (dd, J [1H–1H] ¼ 8.0, 1.2 Hz); 13C NMR (DMSO-d6, 101 MHz), d
2
(ppm): 149.6, 119.4, 135.6 (q, C–CF3, J [19F–13C] ¼ 3.75 Hz), 123.5, 131.1, 126.2, 125.8
1
(q, CF3, J [19F–13C] ¼ 3.75 Hz), 166.2 (HC ¼ N), 118.4, 149.5 (C–OH), 146.0 (C–OH0),
117.5, 119.8, 123.4.
2.8.3. Synthesis of (E)-1-((3-(trifluoromethyl)phenylimino)methyl)naphthalen-2-
ol (HL3)
For the preparation of HL3, same procedure was adopted as described for HL1, but
instead of using 2-hydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde was used.
Yellow crystals were collected from the mother liquor after one day. Yield: 84%; m.p.:
144 ꢂC; IR (t/cmꢁ1): 3449 (–OH), 1621 (HC ¼ N), 1115 (C–F); 1H NMR (DMSO-d6,
400 MHz), d (ppm): 12.10 (s, –OH), 9.76 (s, HC ¼ N), 8.07 (s), 7.83 (dd, J [1H–1H] ¼ 8,
1.2 Hz), 7.72 (t,
J
[1H–1H] ¼ 8.0 Hz), 7.65 (d,
J
[1H–1H] ¼ 8.0 Hz), 7.07 (d,
J
[1H–1H] ¼ 9.2 Hz), 7.98 (d, J [1H–1H] ¼ 9.2 Hz), 8.57 (dd, J [1H–1H] ¼ 8.0, 1.2 Hz), 7.39 (d, J
[1H–1H] ¼ 8.0, 1.2 Hz), 7.58 (dt, J [1H–1H] ¼ 8.0, 1.2 Hz), 7.90 (dd, J [1H–1H] ¼ 8, 1.2 Hz);
13C NMR (DMSO-d6, 101 MHz),
[19F–13C] ¼ 3.75 Hz), 121.1, 127.3, 123.0, 123.1 (q, CF3, 1J [19F–13C] ¼ 3.75 Hz), 169.4
(HC ¼ N), 109.3, 158.3 (C–OH), 117.7, 133.4, 127.3, 125.6, 121.2, 124.1, 121.1, 137.5.
d
(ppm): 146.1, 117.8, 117.7 (q, C–CF3, 2J
2.8.4. Synthesis of (E)-4-chloro-2-((3-(trifluoromethyl)phenylimino)methyl)phe-
nol (HL4)
Procedure adopted for the preparation of HL4 was similar as described for HL1, but
instead of using 2-hydroxybenzaldehyde, 5-chloro-2-hydroxybenzaldehyde was used.
Yellow crystals were collected from the mother liquor within 24 h. Yield: 84%; m.p.:
88 ꢂC; IR (t/cmꢁ1): 3452 (–OH), 1615 (HC ¼ N), 1109 (C–F); 1H NMR (DMSO-d6,
400 MHz), d (ppm): 12.50 (s, –OH), 8.99 (s, HC ¼ N), 7.78–7.79 (m), 7.68–7.71 (m), 7.03

JOURNAL OF COORDINATION CHEMISTRY
9
Scheme 1. Synthesis of oxidovanadium complexes 1–4.
(d, J [1H–1H] ¼ 8.8 Hz), 7.45 (dd, J [1H–1H] ¼ 8.8, 2.8 Hz); 13C NMR (DMSO-d6, 101 MHz),
1
d (ppm): 148.7, 123.7, 123.8 (q, C–CF3, J [19F–13C] ¼ 3.75 Hz), 134.5, 131.8, 130.1, 118.2
1
(q, CF3, J [19F–13C] ¼ 3.75 Hz), 162.9 (HC ¼ N), 119.6, 159.7 (C–OH), 119.0, 133.6, 131.5
(C–Cl), 132.3.
2.8.5. Syntheses of [VO(tfmbs)2] (1), [VO(tfmbdh)2] (2), [VO(tfmbnd)2] (3) and
[VO(tfmbCl)2] (4)
Oxidovanadium complexes 1–4 were synthesized by dropwise mixing of VO(OCHMe2)3
with ligands in 1:2 ratio using acetonitrile as a solvent (Scheme 1). The green products
of 1, 2 and 4 were precipitated out immediately, which were washed with acetonitrile
and then air dried. However, 3 was obtained by refluxing the mixture for 1 h. On cool-
ing, needle-shaped dark green crystals settled at the bottom. These crystals were fil-
tered, washed with acetonitrile and air dried.
Complex 1: Yield: 83%; m.p.: >300 ꢂC; IR (t/cmꢁ1): 1595 (HC ¼ N), 1118 (C–F), 969
(V ¼ O), 599 (V–O); Anal. Calcd for [C28H18F6N2O3V] (MW ¼ 595.4) (%): C, 56.48; H, 3.05;
N, 4.71; O, 8.06. Found: C, 56.32; H, 2.83; N, 4.82; O, 8.21. leff ¼ 1.84 BM.

10
K. S. MUNAWAR ET AL.
Complex 2: Yield: 84%; m.p.: >300 ꢂC; IR (t/cmꢁ1): 1601 (HC ¼ N), 1119 (C–F), 975
(V ¼ O), 540 (V–O); Anal. Calcd for [C28H18F6N2O5V] (MW ¼ 627.4) (%): C, 53.60; H, 2.89;
N, 4.47; O, 12.75. Found: C, 53.84; H, 2.75; N, 4.52; O, 12.84. leff ¼ 2.17 BM.
Complex 3: Yield: 88%; m.p.: >300 ꢂC; IR (t/cmꢁ1): 1620 (HC ¼ N), 1119 (C–F), 967
(V ¼ O), 563 (V–O); Anal. Calcd for [C36H22F6N2O3V] (MW ¼ 695.4) (%): C, 62.17; H, 3.19;
N, 4.03; O, 6.90. Found: C, 62.35; H, 3.11; N, 4.23; O, 6.70. leff ¼ 2.10 BM.
Complex 4: Yield: 82%; m.p.: >300 ꢂC; IR (t/cmꢁ1): 1605 (HC ¼ N), 1118 (C–F), 969
(V ¼ O), 565 (V–O); Anal. Calcd for [C28H16F6N2O3V] (MW ¼ 664.3) (%): C, 50.63; H, 2.43;
N, 4.22; O, 7.23. Found: C, 50.73; H, 2.35; N, 4.32; O, 7.15. leff ¼ 2.17 BM.
3. Results and discussion
The synthesis, spectroscopic and analytical data of prepared azomethine precursors
and their respective oxidovanadium complexes are presented in Section 2. All the syn-
thesized ligands HL1–HL4 and their complexes 1–4 are in solid state, stable at room
temperature. Ligands are soluble in organic solvents like DMSO, ethanol and chloro-
form, but complexes are only soluble in DMSO. The ligands and complexes were char-
acterized by elemental analysis, FT-IR, multinuclear (1H and 13C) NMR studies, single-
crystal X-ray crystallography and thermogravimetric analysis.
3.1. FT-IR studies
The FT-IR spectra of free HL1–HL4 showed bands of medium intensity in the range of
1609–1621 cmꢁ1 due to azomethine t(HC ¼ N) stretching. Coordination of the azome-
thine nitrogen with vanadium atom was expected to give a shift of t(HC ¼ N) to lower
wavenumber (1595–1605 cmꢁ1) as mentioned in Section 2; this effect is in fact
observed for 1, 2 and 4 while for 3 the t(HC ¼ N) was not shifted at all which could
probably be due to extra stability gained by the influence of the conjugated aromatic
ring system attached to the azomethine moiety. This observed shifting of t(HC ¼ N)
stretching band in complexes suggests the coordination of the azomethine nitrogen
to vanadium. The phenolic oxygen t(–OH) band appeared in the range of
3445–3454 cmꢁ1 for free Schiff base ligand was disappeared upon complexation, due
to the formation of the t(V–O)phenolic [37]. The metal-terminal oxygen stretching
t(V ¼ O) in the complexes appeared as a single sharp peak in the range of
967–975 cmꢁ1, indicating that the oxidovanadium(IV) complexes have no intermolecu-
lar interaction with other oxidovanadium moiety [38]. The appearance of new bands
in all FT-IR spectra of complexes in the range of 565–599 cmꢁ1 could be attributed to
the V–O bonds formed during the complexation. Thus, based on the infrared data, it
is concluded that the azomethine precursors behave as monobasic bidentate, coordi-
nating through azomethine N and phenolic O atoms.
3.2. NMR spectroscopy
Deuterated dimethylsulfoxide (DMSO-d6) was used to record the 1H and 13C NMR
spectra of the ligands. The detailed chemical shifts of the diverse kinds of protons and

JOURNAL OF COORDINATION CHEMISTRY
11
carbons have been reported in Section 2. The synthesis of HL1–HL4 was confirmed by
the appearance of peaks due to azomethine protons (HC ¼ N) in the range of
8.66–9.76 ppm. The hydrogen bonded phenolic proton (–OH) gave downfield signals
from 12.10 to 12.86 ppm whereas the second phenolic proton (–OH0) in HL2 has a
slightly upfield signal at 9.29 ppm. Aromatic protons gave signals in the range of
6.70–7.83 ppm. 13C NMR spectra further support the formation of HL1–HL4 by the sig-
nals of azomethine carbon (HC ¼ N) in the range of 162.9–169.4 ppm. Fluorine showed
coupling with the neighboring carbons by giving two quartets with the same coupling
1
constant of 3.75 Hz surprisingly. H NMR spectra of HL2 and HL4 are shown in Figures
S1 and S2.
3.3. Crystal structures of HL1, HL4 and 3
Crystal data and structure refinements of HL1, HL4 and 3 are reported in Table 1
whereas details of hydrogen bonding and geometrical parameters (Å) for p–p stacking
for 3 are listed in Tables 2 and 3. Figures 1–4 show the molecular structures along
with atomic numbering schemes. The observed bond lengths and angles in all the lig-
and precursors are similar to the reported values for similar compounds [39].
In HL1 (Figure 1, Table 1), the o-cresol moiety A (C1–C7/O1) and m-toluidine moiety
B (C8–C14/N1) is planar with r.m.s. deviation of 0.0344 and 0.0119 Å, respectively. The
dihedral angle A/B is 41.1(7)ꢂ. In (trifluoromethyl)benzene, the fluorine atoms are disor-
dered over three sets of sites with occupancy ratio 0.364(3):0.335(3):0.301(3). The dihe-
dral angles between major part of disordered fluorine moiety C (FIA–F3A), the
intermediate disordered fluorine moiety D (F1B–F3B) and the minor part of disordered
fluorine moiety E (F1C–F3C) C/D, D/E and C/E is 13.01(1)ꢂ, 4.97(2)ꢂ and 18.03(7)ꢂ,
respectively. The dihedral angles B/C and B/D are 78.16(4)ꢂ, 88.97(37)ꢂ and 84.08(49)ꢂ,
respectively; these dihedral angles show that the m-toluidine moiety B is nearly per-
pendicular to the disordered fluorine moieties D and E, respectively. The crystal exists
in tautomeric form, as the phenolic hydrogen is not transferred to nitrogen of amine.
Intramolecular hydrogen bonding exists, since the OH group of o-cresol moiety A
interacts with nitrogen of m-toluidine moiety B through O–H … N bonding to form
S(6) loop [40] (as shown in Figure S3 and given in Table 2). No intermolecular hydro-
gen bonding found in the crystal packing.
In HL4 (Figure 2, Table 1), the 4-chloro-2-methylphenol moiety A (C1–C7/O1/CL1) and
m-toluidine moiety B (C8–C14/N1) is planar with r.m.s deviation of 0.0110 and 0.0174 Å,
respectively. The dihedral angle A/B is 7.62(2)ꢂ, indicating that moieties A and B are
nearly parallel to each other. In (trifluoromethyl)benzene, the fluorine atoms are disor-
dered over three sets of sites with occupancy ratio 0.436(3):0.315(3):0.249(3). The dihe-
dral angles between the part-I of disordered fluorine moiety C (FIA–F3A), part-II of
disordered fluorine moiety D (F1B–F3B) and part-III of disordered fluorine moiety E
(F1C–F3C) C/D, D/E, E/C are 13.02(8)ꢂ, 5.38(1)ꢂ and 13.46(9)ꢂ, respectively. The dihedral
angles B/C, B/D and B/E are 84.48(37)ꢂ, 83.56(49)ꢂ and 86.28(52)ꢂ, respectively; these
dihedral angles show that the m-toluidine moiety B is nearly perpendicular to the disor-
dered fluorine moieties C, D and E, respectively. Strong intramolecular O–H … N hydro-
gen bonding exists between the OH group of o-cresol moiety A and the nitrogen atom

12
K. S. MUNAWAR ET AL.
Table 1. Crystallographic data of HL1, HL4 and 3.
Crystal data
HL1
HL4
3
CCDC
983946
1986011
983950
Chemical formula
Mr
C14H10F3NO
265.23
C14H9ClF3NO
299.68
C36H22F6N2O3V
695.49
Crystal system,
space group
Temperature (K)
a, b, c (Å)
Monoclinic, P21/c
Monoclinic, P 21/n
Orthorhombic, P 21 21 21
296
13.894(3),
11.509(2), 7.7124(10)
90, 101.590(2), 90
1208.1(3)
296
296
11.6947(10),
4.7795(13), 17.8542(13)
90, 90, 90
3086.0(4)
4
4.6497(5),
20.399(4), 13.792(3)
90, 94.633(4), 90
1303.9(4)
a, b, c (ꢂ)
V (Å3)
Z
4
4
Density (calculated)
1.458
1.771
1.497
(mg/m3)
F(0 0 0)
544
Mo Ka
0.71073
0.12
708
Mo Ka
0.71073
0.711
1412
Mo Ka
0.71073
0.398
Radiation type
Wavelength (k) (Å)
m (mmꢁ1
)
Crystal size (mm)
Data collection
Diffractometer
0.38 ꢃ 0.16 ꢃ 0.14
0.40 ꢃ 0.20 ꢃ 0.16
0.34 ꢃ 0.20 ꢃ 0.18
Bruker APEXII CCD
diffractometer
Bruker APEXII CCD
diffractometer
Bruker APEXII CCD
diffractometer
Absorption correction
Absorption correction:
multi-scan (SADABS;
Bruker, 2007)
Absorption correction:
multi-scan (SADABS;
Bruker, 2007)
Absorption correction:
multi-scan (SADABS;
Bruker, 2007)
No. of measured,
independent and
observed [I > 2s(I)]
reflections
9246, 2369, 1007
7995, 2563, 1233
25367, 6711, 3475
Rint
0.070
0.0607
0.0780
Theta range for data
1.496–25.997
2.486–25.999
1.789–26.997
collection (ꢂ)
Index ranges
ꢁ17 ꢆ h ꢆ 17,
ꢁ14 ꢆ k ꢆ 14,
ꢁ9 ꢆ l ꢆ 9
0.617
ꢁ5 ꢆ h ꢆ 5,
ꢁ24 ꢆ k ꢆ 25,
ꢁ16 ꢆ l ꢆ 16
0.611
ꢁ14 ꢆ h ꢆ 14,
ꢁ18 ꢆ k ꢆ 18,
ꢁ22 ꢆ l ꢆ 19
0.639
(sin h/k)max (Åꢁ1
)
Refinement
R[F2 > 2r(F2)], wR(F2), S
No. of reflections
No. of parameters
No. of restraints
0.059, 0.190, 0.98
2369
197
19
0.0732, 0.2052, 1.024
2563
203
19
0.0593, 0.1287, 0.987
6711
448
247
H-atom treatment
H atoms treated by a
mixture of independent
and
H-atom parameters
constrained
H-atom parameters
constrained
constrained refinement
0.24,ꢁ0.29
Dqmax, Dqmin (e Åꢁ3
)
0.32, ꢁ0.35
0.27, ꢁ0.31
of m-toluidine moiety B through N–Hꢅ ꢅ ꢅO bonding to form S(6) loop. The molecules are
connected with each other in the form of dimers through C–Hꢅ ꢅ ꢅF bonding to complete
2
R1 (4) loop. These loops are shown in Figure S4 and given in Table 2.
In 3 (Figure 3, Table 1), the coordination sphere around the vanadium atom consists
of three oxygen atoms and two nitrogen atoms. Both ligands are chelating the central
vanadium atom in trans-configuration with respect to each other. The vanadyl oxygen is
at distance of 1.597(5) Å while the chelating oxygen atoms (O1/O3) are at the distance of
1.8969(40) and 1.9080(41) Å, respectively, from central vanadium atom. The chelating
nitrogen atoms (N1/N2) are at the distances of 2.0904(49) and 2.0935(50) Å, respectively,
from central vanadium atom, the equatorial bond angles range from 114.6(2)ꢂ to
130.7(2)ꢂ while the axial angles range from 84.2(2)ꢂ to 102.5(2)ꢂ, thus forming a distorted

JOURNAL OF COORDINATION CHEMISTRY
13
1
4
ꢂ
Table 2. Hydrogen-bond geometry (Å, ) of HL , HL and 3.
Compounds
D—Hꢅ ꢅ ꢅA
D—H
Hꢅ ꢅ ꢅA
Dꢅ ꢅ ꢅA
D—Hꢅ ꢅ ꢅA
HL1
O1—H1ꢅꢅꢅN1
O(1)–H(1)ꢅ ꢅ ꢅN(1)
C(9)–H(4)ꢅ ꢅ ꢅF(2B)i
C(9)–H(4)ꢅ ꢅ ꢅF(2C)i
C(2)–H(2)ꢅ ꢅ ꢅF(3B)ii
C(35)–H(35)ꢅ ꢅ ꢅF(5A)iii
C(35)–H(35)ꢅ ꢅ ꢅF(4B)iii
C—Hꢅ ꢅ ꢅCg
0.83(1)
0.82
0.93
0.93
0.93
0.93
0.93
C—H
0.93
1.85(2)
1.88
2.625(3)
2.605(5)
3.339(14)
3.454(13)
3.298(14)
3.277(13)
3.137(13)
Cꢅ ꢅ ꢅCg
155(4)
146.9
HL4
2.50
2.53
2.56
2.54
150.0
173.3
136.8
136.9
3
2.57
119.8
Hꢅ ꢅ ꢅCg
C—HꢅꢅꢅCg
C34—H34ꢅ ꢅ ꢅCg3iii
2.84
3.383(8)
119
Symmetry transformations used to generate equivalent atoms: (i) ꢁx, ꢁy þ 1, ꢁz; (ii) ꢁx þ 1/2, ꢁy, z ꢁ 1/2, (iii)
x þ 1/2, ꢁy þ 1/2, ꢁz, where Cg3 is the centroid of one of the benzene rings of naphthalene (C1–C10) directly
attached to O-atom of (Z)-3-iminoprop-1-en-1-ol moiety A.
Table 3. Geometrical parameters (Å) for p–p stacking for 3.
Ring i–ja
Rc
R1vc
R2vd
ae
bf
cg
Slippage
b
Cg3ꢅ ꢅ ꢅCg6iv
Cg1ꢅ ꢅ ꢅCg7iv
Cg5ꢅ ꢅ ꢅCg6v
Cg7ꢅ ꢅ ꢅCg3vi
Cg4ꢅ ꢅ ꢅCg2vi
Cg2ꢅ ꢅ ꢅCg3vi
Cg1ꢅ ꢅ ꢅCg6iv
3.474(4)
3.989(3)
4.011(4)
4.124(4)
4.174(4)
4.187(3)
4.285(3)
ꢁ3.3536(13)
ꢁ3.497(2)
3.995(3)
ꢁ3.515(3)
ꢁ3.580(3)
ꢁ3.351(2)
ꢁ3.534(2)
ꢁ3.454(3)
ꢁ3.570(3)
ꢁ3.702(3)
ꢁ3.481(3)
ꢁ3.383(2)
ꢁ3.554(3)
ꢁ3.521(3)
2.2(3)
2.3(3)
26.0(3)
0.9(3)
5.8(3)
6.7(3)
2.3(3)
6.2
5.3
28.8
5.1
31.5
30.9
36.8
34.4
–
–
–
–
–
–
–
26.5
22.6
32.4
35.8
31.9
34.7
Symmetry codes: (iv) 1/2 ꢁ x, ꢁy, ꢁ1/2 þ z, (v) 1 ꢁ x, ꢁ1/2 þ y, 1/2 ꢁ z, (vi) 1/2 ꢁ x, ꢁy, 1/2 þ z.
aCg1, Cg2, Cg3, Cg4, Cg5, Cg6, Cg7 and Cg8 are the centroids of (C1/C10/C11/N1/O1/V1), (C19/C28/C29/N2/O2/V1),
(C1–C4/C9/C10), (C4–C9), (C12 C17), (C19–C22/C27/C28), (C22–C27) and (C30–C35) rings.
bCentroid–centroid distance between rings i and j.
cVertical distance from ring centroid i to ring j.
dVertical distance from ring centroid j to ring i.
eDihedral angle between the first ring mean plane and the second ring mean plane of the partner molecule.
fAngle between the centroid of the first ring and the second ring.
gAngle between the centroid of the first ring and the normal to the mean plane of the second ring of the part-
ner molecule.
Figure 1. ORTEP diagram of (E)-2-(((3-(trifluoromethyl)phenyl)imino)methyl)phenol (HL1) drawn at
50% probability level. The minor part of disordered trifluoro moiety is not shown for clarity and
the hydrogens are shown by small circles of arbitrary radii.

14
K. S. MUNAWAR ET AL.
Figure 2. ORTEP diagram of (E)-4-chloro-2-(((3-(trifluoromethyl)phenyl)imino)methyl)phenol (HL4)
drawn at 50% probability level. The minor parts of disordered trifluro moiety are not shown for
clarity and the hydrogens are shown by small circles of arbitrary radii.
square pyramidal geometry with the s value of 0.42 [41]. In both chelating ligands, the
trifluoro moiety is disordered over three sets of sites with occupancy ratio of
0.444(8):0.341(8):0.215(5) with all disordered atoms set at equal anisotropic displacement
parameters during refinement of structure. In the first chelating ligand (C1–C18/N1/O1/
F1–F3), the (Z)-3-iminoprop-1-en-1-ol moiety A (C1/C10/C11/N1/O1), the naphthalene
moiety B (C1–C10) and benzyl moiety C (C12–C18) are planar with r.m.s. deviation of
0.0224, 0.0142 and 0.0064 Å, respectively. The dihedral angles A/B and C/A are 0.62(3)ꢂ
and 57.7(2)ꢂ, respectively. The dihedral angle between the (Z)-3-iminoprop-1-en-1-ol
moiety A and the naphthalene moiety B indicates that these moieties are almost parallel
to each other. In the second chelating ligand (C19–C36/N2/O2/F4–F6), the (Z)-3-imino-
prop-1-en-1-ol moiety D (C19/C28/C29/N2/O2), the naphthalene moiety E (C19–C28) and
benzyl moiety F (C30-C36) are planar with r.m.s. deviation of 0.0175, 0.0142 and
0.0103 Å, respectively. The dihedral angles D/E and F/D are 2.02(3)ꢂ and 66.02(2)ꢂ,
respectively. The dihedral angle between the (Z)-3-iminoprop-1-en-1-ol moiety A and
the naphthalene moiety B indicates that these moieties are almost parallel to each other.
The molecules are connected with each other through C–H … F bonding (Figure S5 and
Table 2). Another type of non-covalent interaction known as p–p stacking interaction
exists with centroid–centroid distances ranges from 3.474(4) to 5.946(4) Å which helps in
further stabilization of crystal packing [42]. The strongest p–p stacking interaction exists
between the centroids of those rings of naphthalene that are directly attached with che-
lating oxygens with the distance of 3.474(4) Å having zero slippage as shown in Figure 4
and given in Table 3. In addition to non-classical H-bonding and p–p stacking interaction,
another weak interaction of type C–H–Cg is found that assists in further strengthening of
packing of molecules in crystal structure where Cg is the centroid of one of the benzene

JOURNAL OF COORDINATION CHEMISTRY
15
Figure 3. ORTEP diagram of 3 drawn at 20% probability level. The minor parts of disordered tri-
fluoro moiety are not shown for clarity and the hydrogens are shown by small circles of arbi-
trary radii.
rings of naphthalene (C1–C10) directly attached to O-atom of (Z)-3-iminoprop-1-en-1-ol
moiety A as given in Table 2.
In order to investigate the intermolecular interactions quantitatively, Hirshfeld surface
inspection is carried out on crystal Explorer version 3.1 [43]. Figure S6 shows 2D plots for
HL1, HL4 and 3. These plots give the % contribution of each interatomic contact with
respect to overall interactions [44a–c]. It is found that the most significant contribution for
crystal packing in HL1, HL4 and 3 is from F–H/H–F interatomic contact including reciprocal
contact with % contribution of 29.3%, 24.6% and 31.4%, respectively. The % contribution
of F–H interatomic contact in HL4 is less than in HL1 due to presence of electronegative Cl-
atom in HL4. The % contribution of F–H interatomic contact is largest in 3 as compared to
HL1 and HL4 because 3 has more fluorine and H-atoms compared to HL1 and HL4.
3.4. Thermogravimetric studies
Room temperature stability for 1 and 2 was revealed by its thermogravimetric analysis,
carried out from ambient temperature to 1000 ꢂC in nitrogen atmosphere. Complex 1

16
K. S. MUNAWAR ET AL.
Figure 4. Graphical representation of p–p stacking interaction for 3; only major parts of disordered
trifluoro moieties are shown also H-atoms are also omitted for clarity.
showed first decomposition stage in the range of 77–447 ꢂC. The mass loss at this
temperature range may be corresponds to elimination of organic moiety, that is,
C7H4F3 (found/calc.: 24.04/24.37%). The second decomposition step from 447 to 765 ꢂC
corresponds to CF3 (found/calc.: 11.41/11.59%). The third decomposition step occurred
in the temperature range of 765–952 ꢂC, which corresponds to the loss of another
organic species, CH–C–CH (found/calc.: 7.16/6.38%) leaving metal oxide and organic
moiety behind, that is, C17H12N2O3V (found/calc.: 57.40/57.66%).
In thermogram of 2, the first step is elimination of CF3 and two hydroxyl groups
(2OH) in the temperature range of 24–324 ꢂC (found/calc.: 16.30/16.41%), the second
decomposition step ranged from 324 to 741 ꢂC with the loss of two aromatic rings,
C7H5N and C7H4F3 (found/calc.: 39.32/39.52%), whereas the third step ranged from 741
to 951 ꢂC with the loss of one more aromatic ring C7H5N and C–CH (found/calc.:
19.83/20.26%) leaving metal oxide and organic moiety behind, that is, C4H2O3V
(found/calc.: 24.39/23.81%). These observations further support the composition of 1
and 2, which are in agreement with a result obtained by elemental studies and single-
crystal analysis. Thermograms of 1 and 2 are shown in Figures S7 and S8.
3.5. Magnetic moment studies
The effective magnetic moment per metal atom was calculated from the equation:
pffiffiffiffiffiffiffiffiffiffi
leff ¼ 797:5 vm:T
where vm is the molar susceptibility of the complex which is obtained after applying
diamagnetic corrections by the use of Pascal’s constant for other atoms and groups in
the complex. The calibrant used was Hg[Co(SCN)4]. The oxidovanadium(IV) complexes

JOURNAL OF COORDINATION CHEMISTRY
17
usually exhibit low magnetic moments due to the presence of only one unpaired elec-
tron in its outer shell. The magnetic moments obtained at 298 K for 1–4 under study
were found to be 1.84, 2.17, 2.10 and 2.00 BM, revealing distorted square pyramidal
geometry around the V(IV)O ion [45]. The values correspond to a system which has,
formally, a single unpaired electron that is assumed to be localized into an orbital of
primarily d-orbital character. The data demonstrate that the metal ion of these 3d1-
oxidovanadium(IV) complexes is not involved in magnetic exchange with the neigh-
boring metal ion or atoms [46].
3.6. Electronic absorption titration
A compound can bind to DNA through intercalation, groove binding or electrostatic
interactions. Intercalation usually results in hypochromism and bathochromism, due to
ꢇ
strong p–p stacking interaction between an aromatic chromophore and nitrogenous
base pairs of DNA. It is generally accepted that the extent of hypochromism in the UV
band is related with the extent of intercalative interaction [47]. On the other hand,
hyperchomism is because of electrostatic binding [31].
The UV–vis titrations of HL1–HL4 and 1–4 in the absence (a) and in presence (b–i)
of SS-DNA have been studied in Tris buffer medium with the wavelength range of
600–250 nm. Successive addition of DNA produces changes in electronic absorption
spectrum of the complex, indicating interaction of the complex with DNA [48]. The
absorption spectra are shown in Figures 5 and S9.
The determined values of absorption bands, their shifts, binding constants (K) and
Gibb’s free energy (DG) are summarized in Table 4. Negative values of DG showed
that the interaction of the synthesized compounds with DNA is a spontan-
eous process.
Incremental addition of DNA lowers the intensity of absorbance, that is, hypochro-
mic effect in all cases, except 1. The strong absorption of these complexes in the near
UV (280–360 nm) is attributed to the long-lived triplet excited state of the aromatic
moiety [49]. Complexes 3 and 4 obey the same behavior (hypochromism) as displayed
by their respective free ligands HL3 and HL4, respectively. However, 1 dramatically
changes its behavior to hyperchromism in contrast to its precursor ligand HL1 (hypo-
chromism). Moreover, it has shown surprisingly higher value of binding affinity as
reflected from its K value (1.81 3 104 Mꢁ1). Complex 2 had shown no interaction with
DNA. Hypochromism is due to contraction of DNA helix along with other conform-
ational changes. The hypsochromism and hypochromism are associated with double-
helical structure of DNA. The hypochromism with minor blue shift (1–3 nm) in HL1 and
HL3 suggests an intercalative mode as well as by outside binding (groove binding);
however, the dominant mode of interaction is groove binding because Dk ꢆ 8 nm [50].
Groove-binders induce little or no structural rearrangement in the DNA and show
binding propensity for the AT-rich DNA pockets. The AT-rich base pairs not only pos-
sess H-bond acceptors (N3 of adenine and O2 of thymine), but can also develop favor-
able hydrophobic interactions between the adenine C2 hydrogens and the aromatic
rings present in the DNA-binding complexes [45]. Complexes 1 and 4 show hyper-
chromism and hypochromism, respectively, with no blue or red shift, suggesting

18
K. S. MUNAWAR ET AL.
Figure 5. Absorption spectra of HL3 and 3 in the (a) absence and presence of (b) 10 mM,
(c) 19 mM, (d) 27 mM, (e) 35 mM, (f) 42 mM, (g) 48 mM, (h) 54 mM and (i) 59 mM of DNA. The arrow
direction indicates increasing concentrations of DNA.
intercalative mode of binding with DNA. After intercalating the base pairs of DNA the
ꢇ
p
orbital of the intercalated ligand could couple with p orbital of base pairs thus
ꢇ
decreasing the p–p transition energy. It also indicates some interaction with minor
grooves which may be due to hydrogen bonding with bases [51]. On the other hand,

JOURNAL OF COORDINATION CHEMISTRY
19
Table 4. Drug–DNA interaction data.
kmax Hypochromism Hyperchromism Bathochromism Hypsochromism K (Mꢁ1
)
DG
Compounds (nm)
(%)
(%)
(nm)
(nm)
1 ꢃ 104 (kJ molꢁ1
)
HL1
1
273
288
308
317
374
316
356
316
330
13.85
–
–
27.3
–
–
–
–
–
–
–
1
–
–
1
3
–
–
–
–
–
–
2
–
–
1
2
6
–
0.45
1.81
0.207
1.00
–
0.80
–
1.46
0.17
ꢁ20.89
ꢁ24.29
ꢁ18.91
ꢁ22.83
–
HL2
HL3
25.34
23.1
23.5
24.11
25.88
23.69
28.3
3
ꢁ22.28
–
HL4
4
ꢁ23.76
ꢁ18.50
Figure 6. Concentration dependent inhibition of alkaline phosphatase (ALP) by 1–4 and VO(OiPr)3.
the observed hypochromism with minor red shift for HL2, HL4 and 3 revealed that
drug–DNA interaction is of electrostatic interaction and groove binding type. Same
results were obtained by taking the spectrum after 24 h, which confirms the stability
of drug–DNA complex.
3.7. Enzyme inhibition studies
The ALP activity takes advantage of the fact that the enzyme is non-specific and uti-
lizes the colorless non-biological substrate p-NPP to give yellow p-nitrophenolate ion
upon hydrolysis which helps to monitor the reaction [52]. Free ligands HL1–HL4, their
respective oxidovanadium complexes 1–4 and [VO(OCHMe2)3] were screened for their
inhibition of ALP enzyme. All ligands failed to show any activity while vanadium con-
trol the metal products (1–4) rendered active against ALP. The inhibition of ALPs was
attributed to coordination of vanadium with enzyme to block the active sites of the
enzyme. The vanadium may displace zinc or calcium from the enzyme and hence the
enzyme fails to bind with the substrate. Another possibility is that the enzyme binds
with the vanadium complex or vanadium ion more efficiently than substrate. The
exact mechanism is still unknown [53].
The screening tests revealed that enzyme inhibition is concentration dependent.
Increasing concentration of vanadium complexes decreases the activity of the enzyme
as shown in Figure 6. This proportionate decrease in the activity of ALP with increase

20
K. S. MUNAWAR ET AL.
Table 5. Antifungal activities of HL1–HL4 and 1–4.
Average zone of inhibition (mm)
Compounds
A. alternate
G. lucidum
A. niger
P. notatum
Fluconazole
38ab 0.41
17c 0.12
22bc 0.15
25bc 0.19
33ab 0.26
30ab 0.23
39a 0.28
21bc 0.16
25bc 0.17
41ab 0.52
15c 0.09
18bc 0.14
21bc 0.13
24bc 0.16
40ab 0.30
58a 0.33
19bc 0.17
22bc 0.14
40ab 0.36
17c 0.16
23bc 0.19
20bc 0.08
23bc 0.16
31bc 0.23
47a 0.29
22bc 0.15
25bc 0.11
35bc 0.27
0
HL1
1
21c 0.13
22bc 0.12
35bc 0.24
56ab 0.31
65a 0.36
30bc 0.26
27bc 0.21
HL2
2
HL3
3
HL4
4
Concentration
¼
1 mg mLꢁ1 in DMSO. 0 ¼ no activity, 5–10 ¼ activity present, 11–25 ¼ moderate activity,
26–40 ¼ strong activity. Antifungal values are mean SD of samples analyzed individually in triplicate at p < .1.
Different letters in superscripts indicate significant differences. a ¼ maximum activity, b ¼ intermediate activity,
c ¼ minimum activity, ab ¼ activity between maximum and intermediate and bc ¼ activity between intermediate
and minimum.
Table 6. Antibacterial activities of HL1–HL4 and 1–4.
Average zone of inhibition (mm)
Compounds
E. coli
B. subtilis
S. aureus
P. multocida
Streptomycin
30ab 0.26
18bc 0.11
25ab 0.19
17c 0.14
30ab 0.21
17c 0.12
31a 0.23
26ab 0.19
28ab 0.19
30a 0.19
19bc 0.17
22bc 0.13
20bc 0.16
21bc 0.13
17c 0.10
25ab 0.18
17c 0.11
23bc 0.15
30a 0.23
18bc 0.13
24b 0.16
19bc 0.17
25ab 0.20
17c 0.15
22bc 0.19
24b 0.15
26ab 0.17
30a 0.29
18bc 0.16
25ab 0.22
20bc 0.14
24ab 0.19
16c 0.11
29ab 0.27
21bc 0.18
26ab 0.16
HL1
1
HL2
2
HL3
3
HL4
4
Concentration
¼
1 mg mLꢁ1 in DMSO. 0 ¼ no activity, 5–10 ¼ activity present, 11–25 ¼ moderate activity,
26–40 ¼ strong activity. Antibacterial values are mean SD of samples analyzed individually in triplicate at p < .1.
Different letters in superscripts indicate significant differences. a ¼ maximum activity, b ¼ intermediate activity,
c ¼ minimum activity, ab ¼ activity between maximum and intermediate and bc ¼ activity between intermediate
and minimum.
in the concentration of complexes indicates anti-enzymatic activity. Complex 2 was
observed as the most potent inhibitor against all the concentrations of ALP studied.
This could probably be due to the presence of an extra free (–OH0) which may result
in the development of stronger enzyme–complex interactions and consequent failure
of the ALP to bind with the target substrate. Hence, there is a less amount of product
formation resulting in a decrease in absorption.
3.8. Antimicrobial activities
The synthesized free ligands and their respective vanadium products were screened
for their in vitro response against various strains of fungi (A. alternata, G. lucidum, A.
niger and P. notatum) and bacteria (E. coli, B. subtilis, S. aureus and P. multocida) by a
modified [33] disc diffusion method [34]. Fluconazole and Streptomycin were used as
the positive controls for antifungal and antibacterial screening tests, respectively, while
DMSO was used as a negative control. The data are summarized in Tables 5 and 6.
The vanadium complexes exhibited significantly higher activities towards the tested

JOURNAL OF COORDINATION CHEMISTRY
21
Table 7. Hemolytic activities of HL1–HL4 and 1–4.
Compound
% of hemolysis
HL1
77.77 0.03
58.46 0.04
32.40 0.02
52.26 0.03
32.79 0.03
42.21 0.02
34.65 0.03
44.39 0.01
99.53 0.72
1
HL2
2
HL3
3
HL4
4
Triton-X 100
organisms than their respective free azomethine precursors, which indicate that metal-
lation has increased the antimicrobial potential in accord with earlier reports [54]. This
increased activity may be attributed to the chelation of the metal with the ligand as
the chelation reduces the polarity of the central metal atom because of partial sharing
of its positive charge with the ligand, which favors the permeation of the complex
through the lipid layer of the membrane [55].
There is a close relationship between structure and antimicrobial activities of the
investigated products [56]. Although the antimicrobial activities were appreciably
enhanced after metal coordination in all cases against both the bacterial and fungal
strains, the results observed for HL3 and its respective complex 3 were quite fascinat-
ing. The highest activity among all the ligands was observed for HL3 against all the
fungal species; its corresponding complex was also found to possess the highest anti-
fungal action than all the tested novel complexes. The activity was found even higher
than the standard control drug Fluconazole. The variations in antimicrobial potencies
of these compounds may be explained based on two possible factors, that is, lipo-
philic character and diffusion on the bacterial strain [57]. So the highest antifungal
activity of HL3 and 3 was rendered to their more bulky structures which resulted in
greater lipophilicity and hence their greater diffusion through the microbial cell mem-
brane, thus ultimately causing greater sensitivity of the microbes towards these two
drugs. The difference in the effectiveness of various biocidal agents against different
organisms depends upon the permeability through cell membranes [58].
3.9. Hemolytic activities
Hemolytic activity was studied because, even if a synthesized compound possesses
potent antimicrobial activities, its use in medicine will be impossible without their
hemolytic investigations. The in vitro hemolytic bioassays of the synthesized com-
plexes were performed with human red blood cells and the average lysis was reported
with respect to the Triton X-100 as positive control (100% lysis) and PBS as negative
control (0% lysis). The results obtained are summarized in Table 7. The data revealed
that all the synthesized complexes possessed significantly lower hemolytic activities as
compared to Triton X-100 and higher than PBS. The cytotoxicity was found to increase
in the investigated complexes 2–4 in relation to the respective ligands HL2–HL4, how-
ever it was decreased in the case of vanadated product 1 as compared to the non-
coordinated free ligand, HL1. Therefore, the compounds showing the highest activity
may be considered for the antitumor activity [59].

22
K. S. MUNAWAR ET AL.
Figure 7. Plasma glucose concentration of mice treated with the synthesized compounds. Negative
ꢇꢇ
control was Alloxan only treated, while positive control was treated with Glibenclamide. p < .001.
3.10. Antidiabetic studies
Antidiabetic potential of oxidovanadium complexes and their respective precursors were
tested on BALB/c albino mice [60]. In general, the animals remained healthy and active.
Deaths occurred in HL1 and 3. For obvious reasons, compounds that showed glucose low-
ering, their results were compared with Glibenclamide, while compounds that led to an
increase in plasma glucose, cholesterol and triglycerides, their results were compared with
only Alloxan treated negative control mice. The results are presented in Figures 7 and 8.
HL1 did not show any glucose lowering activity (Figure 7), it raised triglyceride con-
centration significantly (p < .001; Figure 8(A)) and reduced cholesterol concentration
(p < .001; Figure 8(B)). Injection of 1 led to a significant lowering of plasma glucose
(p < .001; Figure 7), triglyceride (p < .003; Figure 8(A)) and cholesterol concentrations
(p < .002; Figure 8(B)).
HL2 significantly reduced plasma glucose (p < .001; Figure 7) and serum cholesterol
concentrations (q ¼ 3.693; Figure 8(B)) but increased the serum triglyceride concentra-
tion (p < .002; Figure 8(A)). Complex 2 did not cause any significant change in plasma
glucose (Figure 7) and serum cholesterol (Figure 8(B)) concentrations, but increased in
serum triglyceride concentration significantly (Figure 8(A)).
No significant change was caused by HL3 in plasma glucose (Figure 7) or choles-
terol (Figure 8(B)) concentrations but caused significant elevation of serum triglyceride
concentration (Figure 8(A)). Similarly, no significant change was caused by 3 in either
glucose or cholesterol concentrations (Figures 7 and 8(B)) but caused significant
increase in triglyceride concentration (Figure 8(A)).
HL4 significantly lowered plasma glucose (p < .002; Figure 7) and serum cholesterol
concentrations (q ¼ 3.693; Figure 8(B)) but no variation was observed in triglyceride con-
centration (Figure 8(A)). Complex 4 led to a significant reduction in plasma glucose,
serum cholesterol and triglyceride concentrations (p < .001; Figures 7 and 8(B) and (A)).
The present study revealed that 1 and 4 possess exactly similar activity as they low-
ered the serum glucose, cholesterol and triglyceride concentrations simultaneously. 2,
HL3 and 3 appear to be exactly similar in their activity as they showed significant ele-
vation of serum triglyceride concentration but caused no change in glucose and chol-
esterol concentration.

JOURNAL OF COORDINATION CHEMISTRY
23
Figure 8. Serum triglyceride and cholesterol concentrations of mice treated with oxidovanadium
complexes and azomethine precursors. Results were compared against Alloxan and Glibenclamide
treated animals. p < .001 (showing significant increase); aap < .001 (showing significant decrease).
ꢇꢇ
1 and HL4 appeared to be similar in lowering glucose and cholesterol concentra-
tions but showed different behavior for triglyceride concentration. Complex 1
decreased triglyceride whereas HL4 did not cause any change. Lastly, HL1 appeared to
be totally different in its activity as it did not cause any change in glucose concentra-
tion, however, caused a decrease in cholesterol concentration and raised the triglycer-
ide concentration but, on the other hand, 1 has significant activity in all respects.
Among all the eight compounds tested, HL1 and 3 have proved to be relatively
highly toxic as their application led to mortalities of animals.
4. Conclusion
A series of new azomethine precursors and their oxidovanadium(IV) complexes were
synthesized and characterized by elemental analysis, FT-IR and NMR spectroscopies,

24
K. S. MUNAWAR ET AL.
thermogravimetry, magnetic moment and X-ray crystallography. FT-IR and single-crys-
tal X-ray crystallography studies revealed that during complexation of ligands with
metal ion, the binding occurred through azomethine nitrogen and phenolic oxygen of
the precursors. Therefore, the ligands behaved as monobasic, bidentate during forma-
tion of complexes. The paramagnetic properties of the vanadium complexes 1–4 con-
firmed the d1 electronic configuration of vanadium. The mode of binding of the
compounds and their complexes with SS-DNA was investigated by UV–Visible spec-
troscopy. The observed hypochromocity indicated the intercalation mode of binding
of compounds with SS-DNA. The improved biological activities of the azomethine link-
age or heteroaromatic nuclei during complexation may be responsible for the increase
in hydrophobic character and liposolubility of the molecules in crossing the cell mem-
brane of the microorganism and enhance biological utilization ratio and activity
of complexes.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
Higher Education Commission under IndigenousThis work was supported by the Higher
Education Commission under Indigenous 5000 Program [PIN NO. 106-1087-ps6-016].
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