In vitro biological, catalytic, and DFT studies of some iron(III) N-ligated complexes

Article abstract of DOI:10.1007/s11696-019-01009-z

Fe(III) complexes, [Fe(CH₃CN)₆][X]₃ and [Fe(CH₃CH₂CN)₆][X]₃ (where X: counter anion = B{C₆H₃(m-CF₃)₂}₄)^? and B(C

Full text of DOI:10.1007/s11696-019-01009-z

Chemical Papers
https://doi.org/10.1007/s11696-019-01009-z
ORIGINAL PAPER
In vitro biological, catalytic, and DFT studies of some iron(III) N‑ligated
complexes
Ahmed K. Hijazi1 · Ziyad A. Taha1 · Taher S. Ababneh2 · Heba M. Alshare1 · Nezar Al‑Bataineh3 ·
Waleed M. Al‑Momani4 · Abdulaziz M. Ajlouni1
Received: 13 May 2019 / Accepted: 22 November 2019
© Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
Fe(III) complexes, [Fe(CH3CN)6][X]3 and [Fe(CH3CH2CN)6][X]3 (where X: counter anion= B{C6H3(m-CF3)2}4)− and
B(C6F5)−4 ) have been synthesized by the reaction of FeCl3 with Ag[B(X)4]. Full characterization for the complexes has been
done in solution and in the solid state. The complexes are obtained in good yields and are moderately sensitive to air. All
complexes have been used as catalysts for aniline oxidation with yields up to 62%, in which azobenzene is the only product.
Furthermore, they exhibit good antimicrobial properties. The Fe(III) complexes molecular geometries have been studied
using DFT calculations at the B3LYP/6-31G(d) and B3LYP/6-31+G(d, p) levels of theory and obtained results are in agree-
ment with the experimental data.
Keywords Catalysis · N-ligands · Aniline oxidation · Antimicrobial · Weakly coordinated anions · DFT
Introduction
considered as “naked metal cations” (Strauss 1993; Krossing
and Raabe 2004; Vierle et al. 2003, 2004). The anions infu-
ence cation stability and the metal accessibility for substrate
coordination in intermediate species.
First transition metal series complexes with a formula
of [MII(NCR)4–6][X]2 (M = first transition metal series;
R = C6H5, CH3CH2, CH3; X = counter anion) with their
dimeric congeners are long known by, Hathaway and Holah
(1964), Angerman and Jordan (1969), Johnson et al. (1978),
Thomas et al. (1986), Rapaport et al. (1988), Thomas and
Sen (1989), Henriques et al. (1998), Buschmann and Miller
(1998) and (2002), Cotton and Kühn (1996), Liang et al.
(2002), Rach and Kühn (2009). Their behavior originates
among other reasons, from the presence of weakly or non-
coordinating anions, since they have a crucial role in the
reactivity enhancement of the complexes, which might be
Introduction of weakly coordinating anions into a salt has
been done using several methods. Until now, the metathesis
of silver salt precursors is the most applied method (Mishra
et al. 2013; McCann et al. 1994; Kühn et al. 1999; Pillinger
et al. 2001; Rach et al. 2011).
Some of these complexes have been applied as initiators
or precursors, in synthesis and catalysis, e.g. in: cyclopro-
panations (Sakthivel et al. 2006; Syukri et al. 2007; Ajlouni
et al. 2019), aziridinations (Mohr et al. 2005; Sakthivel et al.
2005a, b; Li et al. 2008a, b), and polymerizations (Sakthivel
et al. 2005a, b; Hijazi et al. 2007a, b, 2008, 2014; Krishnan
et al. 2007; Li et al. 2008a, b, 2010; Diebl et al. 2011).
In medicine, several compounds have been activated
using the metabolism of metal ions (Mishra et al. 2013).
Many metal complexes are used as inhibitors for a variety
of bacterial strains (Shelke et al. 2012; Gaballa et al. 2007;
Gudasi et al. 2007). Several types of complexes were studied
due to their anticancer, antifungal, and antibacterial applica-
tions (Ferrari et al. 1999; Canpolat and Kaya 2004; Kostova
et al. 2006; Solomon et al. 2007). Bonded metal ions are
known as enhancers of the activities of a biologically active
species (Ferrari et al. 1999; Kostova et al. 2006).
* Ahmed K. Hijazi
akhijazi@just.edu.jo
1
Department of Chemical Sciences, Faculty of Science
and Arts, Jordan University of Science and Technology, P.O.
Box 3030, Irbid 22110, Jordan
2
Department of Chemistry and Chemical Technology, Tafla
Technical University, Tafla, Jordan
3
College of Pharmacy, Al Ain University of Science
and Technology, Abu Dhabi, UAE
4
Department of Basic Medical Sciences, Faculty of Medicine,
Yarmouk University, Irbid, Jordan
Vol.:(0123456789)
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Chemical Papers
Anilines as major contaminants exist in industrial waste
water. The oxidation process of anilines to safe substances is
very important for many applications, especially industrial
ones. The formation of nitrobenzene (White and Emmons
1962), nitrosobenzene (Baumgarten et al. 1965), azoxyben-
zene (Nezhadali and Akbarpour 2010; Zhao et al. 2011), and
azobenzene (Wheeler and Gonzales 1964), using a variety
of organic and inorganic oxidants (Emmons 1957; Hijazi
et al. 2017; Lima et al. 2018; Meenakshi et al. 2017), is the
signifcant part of this process.
as a brown–orange solid. For C84H18B3F60FeN6 (2339.26):
Calcd. C 43.13, H 0.78, N 3.59. Found: C 43.25, H 0.75,
N 3.51. Selected IR (KBr, cm−1): ν(CN), 2311, 2289.
11B-NMR: δ = − 6.79. EPR: g value = 2007. Yield 0.81 g
(76.4%).
[Fe(CH3CH2CN)6][B(C6F5)4]3 synthesis
(0.426 mmol, 0.069 g) FeCl3 is added to a (1.27 mmol,
1.00 g) solution of Ag[B(C6F5)4] in (15 ml) dry propyl
nitrile. Stirring overnight in dark is made for the mixture.
The precipitate is separated from the supernatant, which is
concentrated in vacuo at 238 K. The product is obtained
as a brown–orange solid. For C108H54B3F72FeN6 (2891.79):
Calcd. C 44.86, H 1.88, N 2.91. Found: C 44.81, H 1.9,
N 2.85. Selected IR (KBr, cm−1): ν(CN), 2319, 2293.
11B-NMR: δ = − 6.99. EPR: g value = 2008. Yield 0.79 g
(75.9%).
In this work, the synthesis, characterization, as well as the
biological and catalytic activities of complexes of general
formula [FeIII(NCR)6][A]3 (R=CH3, C2H5; A=[B(C6F5)4]−,
[B(C6H3)(m-CF3)2)4]− are reported.
Experimental
All chemicals and solvents have been purchased from Merck
Chemical Company and used as is unless stated otherwise.
Ag[B(C6F5)4] and Ag[B(C6H3)(m-CF3)2)4] are prepared
according to the literature procedures by Buschmann and
Miller (1998) and Hijazi et al. (2008). All complex prepa-
rations are done using standard Schlenk techniques under
argon atmosphere. A 400 MHz Bruker Avance spectrometer
have been used to record the 11B NMR spectra. Chemical
shifts are measured in ppm in D2O with tetramethylsilane
(TMS) as an internal standard. Infrared spectra (IR) are
recorded with a Bruker Alpha spectrometer in the region of
4000–400 cm−1 using KBr pellets. The spectra are recorded
at room temperature with 2 cm−1 resolution. A JEOL JES-
FA 200 spectrometer has been used to record the EPR spec-
tra. The spectra are measured at 9.25 GHz microwave fre-
quency with 5 mW power, 0.4 mT modulation amplitude,
4 min sweep time, 0.1 s time constant, and 100 kHz modu-
lation frequency. Liquid N2 is used to cool measurements
at 113 K. The g values are determined using Mn(II) (spin
I=5/2) embedded in standard magnesium oxide; experimen-
tal errors: ∆g 0.001. Thermal studies are performed using
a PCT-2A thermo balance analyzer operating at a heating
rate of 10 °C/min in the range of 30 °C up to 900 °C under
inert atmosphere. GC-MS data are collected using Varian
Saturn 2000 ion trap spectrometer, interfaced with a Var-
ian GC CP-3800 apparatus. Analyses for C, H, and N are
determined with a Flash 2000 organic elemental analyzer.
[Fe(CH3CN)6][B(C6H3(m‑CF3)2)4]3 synthesis
(0.343 mmol 0.055 g) FeCl3 is added to a (1.03 mmol,
1.00 g) solution of Ag[B(C6H3(m-CF3)2)4] in (15 ml) dry
ethyl nitrile. Stirring overnight in dark is made for the mix-
ture. The precipitate is separated from the supernatant,
which is concentrated in vacuo at 238 K. The product is
obtained as a brown–orange solid. For C92H35B3F60FeN6
(2452.48): Calcd. C 45.06, H 1.44, N 3.43. Found: C 44.94,
H 1.38, N 3.55. Selected IR (KBr, cm−1): ν(CN), 2318,
2281. 11B-NMR: δ = − 16.72. EPR: g value = 2006. Yield
0.72 g (76.9%).
[Fe(CH3CH2CN)6] [B(C6H3(m‑CF3)2)4]3 synthesis
(0.343 mmol 0.055 g) FeCl3 is added to a (1.03 mmol,
1.00 g) solution of Ag[B(C6H3(m-CF3)2)4] in (15 mL) dry
propyl nitrile. Stirring overnight in dark is made for the
mixture. The precipitate is separated from the supernatant,
which is concentrated in vacuo at 238 K. The product is
obtained as a brown–orange solid. For C114H66B3F72FeN6
(2975.95): Calcd. C 46.01, H 2.24, N 2.82. Found: C 45.81,
H 2.44, N 2.96. Selected IR (KBr, cm−1): ν(CN), 2325,
2287. 11B-NMR: δ = − 6.91. EPR: g value = 2007. Yield
0.70 g (76.3%).
DFT method
[Fe(CH3CN)6][B(C6F5)4]3 synthesis
The package of Spartan 14 was used to perform all elec-
tronic structure calculations. All geometries were optimized
in the gas phase at the B3LYP theory level, which employs
the Becke exchange functional parameter B3 (Becke 1993,
1996) and the Lee–Yang–Parr nonlocal correctional func-
tional parameter LYP by Lee et al. (1988), along with the
(0.426 mmol, 0.069 g) FeCl3 is added to a (1.27 mmol,
1.00 g) solution of Ag[B(C6F5)4] in (15 mL) dry ethyl
nitrile. Stirring overnight in dark is made for the mixture.
The precipitate is separated from the supernatant, which is
concentrated in vacuo at 238 K. The product is obtained
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Chemical Papers
polarized basis set, 6–31G(d), (Petersson et al. 1988, 1991).
To ensure the reliability of the selected basis set, the efect of
difuse and polarization functions was inspected by employ-
ing the 6–31+G(d,p) basis set at the B3LYP level of theory.
Such procedures involving the utilization of a variety of
computational methodologies are conducted to essentially
assess the validity of selected level of theory and ensure
that similar results in terms of structural features and rela-
tive energies are produced. Minimal energy structures are
indicated by the absence of imaginary frequencies in the
vibrational analysis.
Results and discussion
[Fe(CH3CN)6][B(C6F5)4]3 (1), [Fe(CH3CN)6][B(C6H3(m-
CF3)2)4]3 (2), [Fe(CH3CH2CN)6][B(C6F5)4]3 (3), and
[Fe(CH3CH2CN)6][B(C6H3(m-CF3)2)4]3 (4) were synthe-
sized by reacting FeCl3 with Ag[B(X)4]in ethyl nitrile and
propyl nitrile solvent, Scheme 1. The prepared complexes
can be handled in air for short periods of time, since they are
only moderately sensitive to air. To keep them catalytically
active, the complexes were stored at −40 °C under argon,
to prevent decomposition.
Biological properties
Elemental analyses
The biological properties of all prepared complexes were
measured against Candida albicans, Gram positive and
Gram negative bacteria using micro-broth dilution minimum
inhibition concentration, MIC (Hijazi et al. 2017).
The elemental analyses and yields of complexes 1–4 are
listed in Table 1. Based on the proposed molecular formula,
an agreement between the calculated elemental contents and
the obtained ones are obvious, indicating the correctness of
the assumed composition of the prepared complexes.
Aniline oxidation
To a 30% H2O2 solution (10 mmol), 8 mmol of aniline, 7 mL
ethyl nitrile or propyl nitrile, and 0.015 mmol of the cata-
lyst are added. The mixture is stirred at ambient tempera-
ture overnight. The reaction is continuously followed and
GC-MS is used for products identifcation.
Infrared spectroscopy
Two sharp bands of medium intensity are observed for all
complexes at 2311 and 2289 cm−1, at 2319 and 2293 cm−1,
at 2318 and 2281 cm−1, and at 2325 and 2287 cm−1, respec-
tively. Fundamental stretching (ν2) and (ν3 + ν4) modes of
CN are responsible for these bands. Presence of the ligands
(ethyl nitrile and propyl nitrile) in the inner sphere of com-
plexes is confrmed by these results, see Table 2, Fig. 1.
Due to the σ-donation of electron density from the lone
pair on nitrogen, the observed vibrations have higher ener-
gies compared to the corresponding vibrations of free ace-
tonitrile (Buschmann and Miller 1998; Pratikha et al. 2013),
and propionitrile (Hijazi et al. 2016). The respective orbit-
als have some anti- bonding character (Pratikha et al. 2013;
Higa et al. 2010; Shriver et al. 1965).
Two peaks at 3045 and 891 cm−1, and 3040 and 895 cm−1
are observed for complex 2 and complex 4, respectively.
These peaks are attributed to the aromatic C–H of the coun-
ter anion. These peaks are not observed for complexes 1
and 3.
The aromatic C=C bonds of all complexes are identifed
with the peaks at 1620 and 1450 cm−1, 1602 and 1471 cm−1,
Scheme 1 Synthesis of complexes 1–4
Table 1 Analytical data for
Complexes
C (%) found (calc.)
H (%) found (calc.)
N (%) found (calc.)
Yields (%)
complexes 1–4
1
2
3
4
43.25 (43.13)
44.81 (44.86)
44.94 (45.06)
45.81 (46.01)
0.75 (0.78)
1.94 (1.88)
1.38 (1.44)
2.44(2.34)
3.51 (3.59)
2.85 (2.91)
3.55 (3.43)
2.96(2.89)
76.4
75.9
76.9
76.3
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Chemical Papers
Table 2 FT-IR spectral data for
Complexes
ν(CN)
ν[Ar-(C–H)]
ν[Ar-(C=C)]
ν[Ar-(C–F)]
complexes 1–4 (cm−1
)
1
2
3
4
2311
2319
2318
2325
2289
2293
2281
2287
–
–
891
–
1620
1602
1643
1601
1450
1381
1358
1382
1357
1273
1283
1276
1280
1091
1121
1088
1125
3045
–
1471
1445
1475
3040
895
Complex1
Complex 2
Complex 3
Complex 4
200
300
400
500
600
700
800
Bo[mT]
Fig. 2 EPR spectrum of complexes 1–4, Trec =−140 °C
complexes (S=5/2). A shift in the g value from one of the
free electrons is observed, as expected.
Thermal gravimetric analysis
Fig. 1 FT-IR spectrum of complexes 1–4
Table 3 The EPR data for
Thermo gravimetric (TG) and diferential thermal analysis
(DTA) were done within a temperature interval, ranging
from 30 °C to 800 °C under N2 fow. Table 4 shows the
data of thermal analysis of all complexes. The TGA-DTG
curve of complex 1, shows the frst onset is at 51 °C, with
7.11 wt% mass loss. The loss of four ethyl nitrile ligands
is associated to this step (calc. 7.03 wt%). The second step
onset at 106 °C, with a mass loss of 4.94 wt%, shows the
loss of two acetonitrile ligands (calc. 3.52 wt%). A similar
behavior is also observed for complex 2, the frst decomposi-
tion onset being observed at 55 °C, with a loss of 4.35 wt%.
This corresponds to the loss of three ethyl nitrile ligands
(calc. 4.26 wt%). The second onset at 165 °C is with a mass
loss of 23.67 wt%. This mass loss corresponds to the loss of
three of the ethyl nitrile ligands and to anion fragmentation
[B{C6H3(m-CF3)2}4]. These ligands contribute 4.26 wt% of
the total mass complex 2. Complex 3 shows its 1st decom-
position step at 68 °C with 9.00 wt% loss corresponding to
four propionitrile ligands (calc. 8.44 wt%). The second step
Metal complex
g value
complexes 1–4
1
2
3
4
2007
2008
2006
2007
1643 and 1445 cm−1, and at 1601 and 1475 cm−1 for com-
plexes 1, 2, 3, and 4, respectively, Table 2, Fig. 1.
Electron paramagnetic resonance (EPR)
The spectra of [Fe(C2H5CN)6]3+ and[Fe(CH3CN)6]3+ with
varying counter ions, (Trec =−140 °C) have symmetric lines
(Bpp = 9 mT) at g = 2.006–2.008, Table 3, in frozen solu-
tion. This signal, Fig. 2, is consistent with iron(III) high-spin
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Chemical Papers
Table 4 TGA data for complexes 1–4
the lowest mass in the examined temperature interval, with
a total 80.90% weight loss, while complex 1 has the lowest
stability of all complexes. Complex 3 loses the highest rela-
tive mass, with a total weight loss of 86.45 wt%. The resid-
ual mass in all complexes indicates the presence of FeF3,
(for complex 1 5.09 wt% (calc. 4.8%), complex 2 4.0 wt%
(calc. 3.8%), complex 3 4.8 wt% (calc. 4.6%), and complex
4 3.9 wt% (calc. 3.6%) after decomposition. The DTA cor-
respondingly shows a strong endothermic signal through all
decomposition steps.
Complex
Stage
DTA/C
Mass loss %
Total mass loss %
83.65
1
1
2
3
4
5
1
2
3
4
1
2
3
4
1
2
3
4
5
51
106
194
315
446
55
165
368
502
81
239
362
435
90
180
309
401
565
7.11
4.94
28.42
35.00
8.18
2
3
4
4.35
81.63
86.45
80.90
23.67
50.07
3.54
9.00
67.74
5.38
4.78
2.07
5.53
29.67
38.1
Figure 4 shows the proposed or the expected structure of
complex 2, which applies to all prepared complexes.
11B‑NMR
The 11B-NMR spectra were recorded in deuterium oxide
(D2O), in the range of (−25 to 15) ppm. Singlet peaks at
δ = − 16.72 ppm and δ = − 6.79 ppm are assigned to the
B atom of the [B(C6F5)4] counter anion of complexes
3 and 1, respectively. A singlet peak at δ = − 6.99 ppm
and δ = − 6.91 ppm are assigned to the boron atom of the
[B{C6H3(m-CF3)2}4]3 counter anion of complex 2 and com-
plex 4, respectively, Fig. 5.
5.53
DFT calculations
The optimized structures of complexes 3 and 4 at the
B3LYP/6-31G(d) level of theory are shown in Figs. 6, 7.
Results confrm that both complexes exhibit six coordina-
tion number (Oh) with the Fe3+. Due to high symmetry, all
bonds and angles of the same type have the same or very
close structural parameters. Complex 3 has an identical
C–N bond distance for the six groups at 1.157 Å. The
average Fe–N bond distance is shown to be 1.940 Å with
average N–Fe–N angles of 90.00° and 179.95°. Consider-
ing the similarity in the coordination environment around
the iron ion in these complexes, complex 4 exhibits similar
structural features. For complex 4, the results show that
the average Fe–N bond distance is 1.938 Å and the average
N–Fe–N angles are 90.00° and 179.78°. The C–N bond is
at a calculated value of 1.158 Å. Selected bond lengths
(Å) and angles (°) of complexes 1 and 2 ground state opti-
mized geometries are listed in Table 5. As can be seen
from the table, the structural features emanating from both
the B3LYP/6-31G(d) and B3LLYP/6-31+G(d,p) levels
of theory are very comparable resulting in no more than
0.002 Å and 0.24° discrepancy in bond lengths and angles,
respectively. Vibrational analysis for complex 3 reveals a
strong absorption band compromising the wavenumbers
2299 and 2315 cm−1 and attributed to υ(CN) (exp. 2281
and 2318 cm−1). This characteristic band appears at 2276
and 2301 cm−1 in the calculated IR spectrum of complex
4 (exp. 2287 and 2325 cm−1). Furthermore, molecular
Fig. 3 TGA/TDA spectra of complex 4
is at 239 °C with loss of 64.2 wt%. This step shows the loss
of two propyl nitrile ligands (calc. 3.43 wt%) and for anion
fragmentation. The frst and second decomposition steps of
complex 4 have been detected at 90 °C and 180 °C with
a loss of 2.07 wt% and 5.53 wt%, respectively, as shown
in Fig. 3. These steps correspond to the loss of one pro-
pionitrile (calc. 1.71 wt%) and three propionitrile ligands
(calc. 5.14 wt%), respectively. The third step at 309 °C is
associated with a 29.67 wt% loss. It accounts for the loss
of two propionitrile ligands and for fragmentation of the
counter anion. Complex 4 has the highest stability and loses
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Chemical Papers
Fig. 4 Proposed structure of
complex 2
H
C
C
N
F
H
B
H
F
F
H
H
C
C
F
F
F
H
C
H
C
F
F
F
F
F
H
C
F
H
F
C
C
H
C
C
F
H
F
H
H
H
H
H
H
C
C
H
H
N
N
N
N
Fe
N
H
C
H
C
F
H
H
H
F
H
F
C
H
H
F
F
C
F
F
H
H
C
F
C
F
C
H
Complex 1
Complex 2
Complex 3
Complex 4
0
-5
-10
ppm
-15
-20
Fig. 6 The optimized geometry for complex 3 at the B3LYP/6-
31G(d) level of theory
Fig. 5 11B-NMR of complexes 1–4
consistent with the cationic nature of studied complexes,
all electrostatic potential values for complexes 3 and 4 are
found on the positive side of potential distribution ranging
from 785–930 and 645–894 kJ/mol, respectively. While
regions with most electropositive potential are located
around the central metal ion and the carbon atom of the
CN group (thus more prone to nucleophilic attack), termi-
nal methyl groups bare relatively the most electronegative
potentials.
electrostatic potential (MEP) maps were constructed for
both complexes. These surfaces illustrate the charge dis-
tributions of molecules by mapping the calculated value of
the electrostatic potential onto an electron density surface.
Such maps bear useful information on the shape, overall
size of molecules, and how they interact with other mol-
ecules. Figure 8 depicts the electrostatic potential maps for
complexes 3 (left) and 4 (right), along with a color scale
indicating the positive and negative electrostatic poten-
tials. By convention, red-colored regions correspond to
minimum negative electrostatic potential, while colors
toward blue represent maximum positive potential. In
The harmony between the experimental structure
parameters and the calculated structure parameters con-
frms the suitability of the experimental and calculation
structures (Erkan and Karakas 2019).
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Chemical Papers
Biological properties
Minimum inhibitory concentration determination
Minimum inhibitory concentration (MIC, µg/cm3) of all
complexes are listed in Table 6. The complexes have difer-
ent MIC degrees on the bacterial strain growth and Candida
albicans tested. The results show that complexes 1 and 3
exhibit a broad and promising spectrum of antibacterial and
antifungal profles against the tested organisms. Complex
2 shows moderate antibacterial activity against Klebsiella
pneumonia (Gram negative) and low antibacterial activity
against Bacillus cereus and Staphylococcus aureus (Gram
positive). Complex 4 shows moderate antibacterial activ-
ity against Streptococcus pyogenes (Gram positive) and low
antibacterial activity against Escherichia coli, Proteus mira-
bilis, Staphylococcus aureus, and Pseudomonas aeruginosa,
while it was not efective against Klebsiella pneumonia, Sal-
monella enteritidis, and Bacillus cereus. The activity against
C. albicans (fungal) has been detected for both complexes.
All complexes 1–4 have similar geometries, but the results
show that the nature of ligands afects their activity. Hydro-
gen bonding between the ligands is facilitated and chelating
character occurs. Types of anions and the lipophilic nature
might be responsible for some interactions with selected
microorganisms, which will increase the complexes’ pen-
etration of the lipid membrane of the cell wall of the micro-
organism, increasing the complex activity and restricting the
possible growth of the afected organism (Singh et al. 2012).
The activity against Gram (+) species can be explained by
taking into consideration the efect on lipopolysaccharides
(LPS) (Al Momani et al. 2013). LPS are crucial to determine
the virulence of the outer membrane barrier function and
Gram negative pathogens. The complexes described here can
penetrate the cell membrane by coordination of the metal
through nitrogen atoms to LPS, leading to the damage of the
outer cell membrane and consequently inhibiting the bacte-
rial growth (Priya et al. 2009).
Fig. 7 The optimized geometry for complex 4 at the B3LYP/6-
31G(d) level of theory
Table 5 Selected bond lengths (Å) and angles (°) of complexes 3 and
4 at the B3LYP/6-31G(d) and B3LYP/6-31+G(d, p) levels of theory
Complex 3
Complex 4
Bond/angle 6–31G(d) 6–31+G(d,p) 6–31G(d) 6–31+G(d,p)
Fe–N
C–N
NC–C
H2C–CH3
N–Fe–N
N–Fe–N
C–C–C
1.940
1.157
1.452
NA
179.95
90.00
NA
1.942
1.158
1.452
NA
179.96
90.00
NA
1.938
1.158
1.460
1.548
179.78
90.00
113.16
1.940
1.158
1.460
1.548
179.79
90.00
113.40
Fig. 8 Electrostatic potential
maps for complex 3 (left) and
4 (right)
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Chemical Papers
Table 6 MIC (µg/mL) of all
complexes against clinical
isolates of some bacterial spp.,
and Candida albicans
Tested compounds
Gram (−) bacteria
Gram (+) bacteria
Antifungal
Ca
Ec
Kp
Pm
Pa
Se
Sa
Sp
Bc
8
256
64
N
N
8
–
1
2
3
4
256
N
256
256
N
32
64
16
N
N
2
32
N
256
256
N
256
N
128
512
N
2
–
265
N
256
N
N
8
16
256
16
256
N
N
N
N
64
N
8
16
128
32
32
N
–
4
DMSO (−ve control)
Oxytetracycline (+ve control)
Fluconazole (+ve control)
4
8
8
–
–
–
–
–
–
Ec, Escherichia coli; Kp, Klebsiella pneumonia; Pm, Proteus mirabilis; Pa, Pseudomonas aeruginosa; Se,
Salmonella enteritidis; Sa, Staphylococcus aureus; Ca, Candida albicans; Bc Bacillus cereus; Sp, Strepto-
coccus pyogenes
Fluconazole: antifungal positive control for Candida albicans
aniline derivatives (see Table 7). A very good yield (62%)
Oxidation of aniline
was reported for 2-nitro-4-(trifuromethyl) aniline, other
derivatives range from low to moderate yields. The applied
derivatives of aniline display either electron withdrawing
or electron donating groups. The derivatives having elec-
tron donating groups are oxidized only in low yields, rang-
ing from 14 to 17%, while ones having electron withdraw-
ing groups display higher yields when oxidation, namely
23–62%. It is has to be noted that with increasing strength
of the electron withdrawing efect increases the %yield. In
all complexes, azobenzene is the only product with 100%
selectivity according to the GC-MS data.
Prepared complexes were used as catalysts for aniline oxida-
tion and its derivatives using 30% H2O2 with 1:10 catalyst/
aniline weight ratio and ethyl nitrile or propyl nitrile as sol-
vents at room temperature, for 24 h. GC-MS have been used
to monitor the reaction. During the reaction, azobenzene is
identifed as a product (Scheme 2).
Complex 2 leads to higher yields (24%) than complex
1 (9%), and when acetonitrile is replaced by propionitrile
as a ligand, the yields become much higher as observed
for complex 3 (43%) and complex 4, which displays the
highest yields (61%). This could be attributed to the solu-
bility factor, which leads to a better iron exposition. Since
complex 4 produces the highest oxidation yield, it was
additionally applied as a catalyst for the oxidation of some
The same amount of H2O2 was used to examine the
oxidation of aniline absence of the metal complexes; this
led to very low yields only (ca. 1–2%). When the reaction
was done using only the catalyst in the absence of H2O2,
no product was obtained.
Scheme 2 Oxidation of aniline
to azobenzene
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Chemical Papers
Table 7 Oxidation of various aniline derivatives with complex 1 after 24 h
T=298 K, t=24 h, H2O2: aniline: cat. (10: 8: 0.015 mmol), solvent: CH3CN
a, bBased on GC-MS data
electron defcient aniline using complex 4. Azobenzene
have been determined as the only product depending on
GC-MS data with 100% selectivity. Antimicrobial efects
have been studied for all synthesized complexes. Complex
1 showed promising antimicrobial activities against Sa and
Bc (Gram-positive bacteria), Kp and Pm (Gram-negative
bacteria), and Ca (fungal). Complex 3 exhibited promising
activities against Kp (Gram-negative bacteria), Sa (Gram-
positive bacteria), and Ca (fungal).
Conclusion
Fe(III) complexes, [Fe(CH3CN)6][X]3 and
[Fe(CH3CH2CN)6][X]3 (where X: counter
anion = B{C6H3(m-CF3)2}4)− and B(C6F5)4−) have been
prepared with very good yields and characterized. DFT
calculations show that the structures, proposed on spec-
troscopic data agree with the calculated ones. All com-
plexes have been used as catalysts for aniline oxidation
and some derivatives. Complex 4 showed the highest yield
(61%) when aniline was oxidized to produce azobenzene.
Acknowledgements The Deanship of Research, Jordan University of
Science and Technology are acknowledged for the fnancial support
(Grant no. 360/2015).
A maximum yield of 62% could be obtained for the most
1 3

Chemical Papers
thiosemicarbazone. Inorg Chim Acta 286:134–141. https://doi.
org/10.1016/S0020-1693(98)00383-1
Compliance with ethical standards
Gaballa AS, Asker MS, Barakat AS, Teleb SM (2007) Synthesis,
characterization and biological activity of some platinum(II)
complexes with Schif bases derived from salicylaldehyde,
2-furaldehyde and phenylenediamine. Spectro Chim Acta A
67:114–121. https://doi.org/10.1016/j.saa.2006.06.031
Gudasi KB, Havanur VC, Patil SA, Patil BR (2007) Antimi-
crobial study of newly synthesized lanthanide(III) com-
plexes of 2-[2-hydroxy-3-methoxyphenyl]-3-[2-hydroxy-
3-methoxybenzylamino]-1,2-dihydroquinazolin-4(3H)-one.
Metal Based Drugs. https://doi.org/10.1155/2007/37348 (7
pages)
Conflict of interest The author declares that they have no competing
interests.
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