Mono- and poly-nuclear copper(II) carboxylates with flourous ligands: Synthesis, structure and improved properties

Article abstract of DOI:10.1016/j.ica.2019.119177

Polynuclear copper(II) complexes [Cu(para-fluorophenyl acetate)₂]_n (1) and [Cu(para-nitrophenyl acetate)₂]_n (2) were converted in-situ to mono-nuclear complexes [Cu(para-fluorophenyl acetate)₂(1,10-Ph

Full text of DOI:10.1016/j.ica.2019.119177

InorganicaChimicaActa498(2019)119177
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Inorganica Chimica Acta
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Research paper
Mono- and poly-nuclear copper(II) carboxylates with flourous ligands:
Synthesis, structure and improved properties
Muhammad Iqbala,⁎, Saqib Alib, Muhammad N. Tahirc, Arif Nawaza, Paul A. Andersond,
Wilayat Khane
a Department of Chemistry, Bacha Khan University, Charsadda 24420, KPK, Pakistan
b Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
c Department of Physics, University of Sargodha, Sargodha, Pakistan
d School of Chemistry, The University of Birmingham, Birmingham, UK
e Department of Physics, Bacha Khan University, Charsadda 24420, KPK, Pakistan
A R T I C L E I N F O
A B S T R A C T
Keywords:
Polynuclear copper(II) complexes [Cu(para-fluorophenyl acetate)2]n (1) and [Cu(para-nitrophenyl acetate)2]n
(2) were converted in-situ to mono-nuclear complexes [Cu(para-fluorophenyl acetate)2(1,10-Phenanthroline)
(H2O)] (3) and [Cu(para-nitrophenyl acetate)2(2,2-Bipyridine)(H2O)].3H2O (4). The complexes were isolated in
Flourous copper(II) complexes
Structural study
DFT
́
quantitative yield, purified and characterized using FT-IR, absorption, electrochemical, electron paramagnetic
resonance and powder XRD techniques yielding results in accordance with structural data. Structures of 1 and 2
consist of directly interlinked paddlewheel units with square pyramidal geometry while those of 3 and 4 are
mononuclear with octahedral and square pyramidal geometry around Cu. Fluorinated complexes 1 and 3 were
found to consist of extensive intermolecular interactions while 2 and 4 contained no such interactions. Their
optical band gap was around 1.4 eV which indicates semiconducting property of the complexes. Moreover, the
flourous complex 3 was found to possess significant activity against Bacillus subtilis and Escherichia coli and good
activity against Micrococcus luteus. A similar trend was observed in their DNA-binding potency studied through
absorption as well as electrochemical solution studies yielding Kb values 1.494 × 104, 1.342 × 104 and
1.411 × 104 M−1 and 7.547 × 104, 2.457 × 104 and 3.667 × 104 M−1 for 1–3, respectively. The electronic
structures of the complexes elucidated using density functional theory ab-initio calculations confirmed the
Intermediate states which play important role in the enhancement of the optoelectronic properties. The structure
and properties of the flourous complexes were found different than their non-flourous analogues which was
attributable to fluorine.
Biological importance
1. Introduction
is different at para-position (mostly de-activating) than at ortho- and
meta-positions (usually activating) [1]. It has been inferred from the
The properties of metal complexes are a function of metal as well as
the attached ligands. The ligand centered properties depend mostly on
the attached substitutes. Since there is lot of diversity in the functional
groups, these affect the properties to variable extent. Replacing fluorine
for other substituents usually brings striking variation in properties of
the resultant complexes. The special chemistry of fluorine originated
from its small size, low polarizability, nuclear spin = 1/2 and being the
strongest grabber of electron. Once, substituted in a molecule, it ex-
hibits its strong inductive effect via sigma bond. It also establishes
strong intermolecular interactions with the sideling molecules in the
lattice. The latter type of bonding arises from the ability of the fluorine
to act as π-donor. Moreover, as a substituent on aromatic ring, its effect
coupling constant values of NMR spectroscopy of the aromatic sub-
stituted compounds that fluorine acts as a π-donor at ortho-position
while σ-acceptor at meta- or para-positions [2].
A comprehensive study on the recent progress in fluorine chemistry
of the bio-active complexes has been carried out [3]. F is the favorite
heteroatom after nitrogen whose substitution enhances the desired
biological activity of the molecule such as its binding to the target
molecule and membrane permeability [4]. Importance of fluorine-
containing compounds in bio-medicinal chemistry can be judged form
the fact that several F-containing compounds are extensively used as
chemotherapeutic agents [5] and many more are in various stages of
clinical trials [6].
⁎ Corresponding author.
E-mail addresses: iqbalmo@yahoomail.com, iqbal@bkuc.edu.pk (M. Iqbal), saqibali@qau.edu.pk (S. Ali).
https://doi.org/10.1016/j.ica.2019.119177
Received 1 July 2019; Received in revised form 2 September 2019; Accepted 26 September 2019
Availableonline27September2019
0020-1693/©2019ElsevierB.V.Allrightsreserved.

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
40
20
0
20000
0
2000
0
-20000
-40000
-60000
-80000
-2000
-4000
-6000
g
-20
-40
g
= 2.13246
= 2.07085
1200
2400
3600
4800
1000 2000 3000 4000 5000 6000
1000 2000 3000 4000 5000
G
G
G
A
B
C
Fig. 1. X-Band ESR spectra of the complexes 2(A), 3(B) and 4(D).
Effect of fluorine and other substituted ligands on structure and
spectroscopic properties of the resulting complexes has been studied
[7–10]. There is a pronounced effect on the non-covalent interactions of
the molecules of the complexes on replacing F for other substituents.
The anion-π interactions arising from F are strongest of all halogens and
other substituents [11]. This type of interaction adds cumulatively
when a complex has aromatic π-π stacking interactions arising from the
phenyl rings and planar ligands such as 1,10-phenanthroline and 2,2′-
bipridine. Effect of substituent is so important that these secondary
interactions are absent altogether on changing the substituent [12].
Similar two pairs of copper(II) complexes having flouro- and nitro-
substituted phenyl rings along with other hetero-aromatic planar li-
gands have been synthesized. Interestingly, the non-flourous pair of the
complexes has no intermolecular non-covalent interactions and the
flourous pair has ample amount of these stacking interactions. More-
over, the difference has been reflected in DNA-binding as well as anti-
fungal properties as well. The electronic structures of the complexes
were also studied theoretically using DFT calculations to understand
the enhancement in the photocatalytic and optoelectronic properties.
atom were clearly indicated in the respective spectra of all the four
complexes.
2.2. Electron paramagnetic resonance
X-Band ESR spectra of powdered samples of 3 and 4 (Fig. 1B, C)
showed typical copper(II) spectra with g⊥ values = 2.13246 and
2.07085, respectively. These spectra clearly indicate that copper is in
2+ oxidation state in these complexes. These spectra are similar to the
X-band spectra observed for other mono-nuclear copper(II) complexes
́
with two carboxylate ligands and 1,10-phenanthroline and 2,2-bipyr-
idine [16,17]. The spectrum of 2 (Fig. 1A) has an observable curve
between G values 3000 and 4000. The signal of copper(II) is usually
observed in this region. Such diffused signal was observed for the other
structural analogue of 2 as well [18].
2.3. Powder XRD studies
Being NMR-silent, the single crystalline samples of copper(II)
complexes were subjected to powder XRD technique and the resulting
spectra of complexes 1, 3 and 4 are shown in Fig. 2A–C. These spectra
indicate several well defined peaks between 2 theta values 5 and 30
which show the homogenous crystalline nature of these complexes. The
theoretical spectra were obtained from the respective single crystal XRD
data which were superimposed on the experimental powder XRD
spectra. These spectra show the bulk purity of the synthesized com-
plexes.
2. Results and discussion
Four complexes have been synthesized and purified in quantitative
yield and characterized structurally.
2.1. FT-IR spectroscopy results
The most pronounced peaks in the spectra of all the four complexes
were near 1600 and 1400 cm−1 which were attributed to the stretching
vibrations of the carboxylate moieties attached to copper. The differ-
ence in the asymmetric and symmetric stretching vibrations were 195,
179, 136 and 252 cm−1, respectively for 1–4. These values indicate
bridging bidentate coordination mode of carboxylate ligand in 1 and 2,
chelating bidentate binding mode in 3 and mono-dentate coordination
mode in 4. These assignments were in accordance to the structural data
of the complexes 1–4. There was a peak of low intensity in spectra of
each complex between 400 and 420 cm−1 attributable to the Cu–O
bond stretch. Nitro-group in 2 and 4 was indicated by two intense bands
observed in the region 1341–1435 cm−1. The appearance of C]N
stretching band of the complexes 3 and 4 in a frequency range
1586–1600 cm−1 instead of its normally observed characteristic region
(1610–1625 cm−1) [13,14] indicated the involvement of the nitrogen
2.4. Electronic spectra, optical band gap and stability studies
Electronic spectra of complexes 1–4 indicated a broad absorption
band at λmax = 725, 744, 691 and 658 nm, respectively as shown in
Fig. 3A, indicating penta-coordinated square pyramidal geometry
around copper in 1 and 2 [18] and hexa-coordinated octahedral geo-
metry in 3 and 4 [19] as observed in similar regions for copper(II)
complexes of same geometry and neuclearity. The absorption behavior
of 1 and 2 indicate the stable nature of the paddlewheel subunits where
the maximum number of ligands attached with Cu can be five and the
inner site is always unoccupied. Absorption spectra of 3 and 4 are ty-
pical of the usual octahedral coordination around copper(II).
The broad absorption bands of the complexes indicate that these can
harvest a wide range of wavelengths in UV–Visible region of the elec-
tromagnetic spectrum. This property enables them to be used as pho-
tosensitizers in semiconductors when combined with nano-films of
crystalline oxides [20]. The optical band gaps of the complexes have
been calculated from the extrapolation of the plots (shown in Fig. 3B)
between (Ahc)2 and hc/λ where A is the absorbance and the rest of the
́
atom of 1,10-pnhenanthroline and 2,2-bipyridine in bonding with
copper(II) ion [15]. In support to this, Cu–N bonding was indicated by
bands at 468 and 481 cm−1 for 2 and 4 which indicated the attachment
of heteroaromatic ligands through N. All the rest of the functionalities
such as methylene-H, aromatic CeH and the absence of carboxylate-H
2

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
better than some previously reported Co, Ni, Cu and Zn-complexes [20].
The stability of the geometry of complexes in the solvent system has
been checked by taking spectra at various intervals as shown in Fig. S1.
These indicate that the complexes retain their geometry in solution.
9000
6000
3000
0
Theoretical
2.5. DFT Analysis: electronic structure
5
10
15
20
25
30
For better insight into the optoelectronic properties, the partial
density of states (PDoS) in both regions (valence and conduction
bands), especially in the conduction band region of the complexes has
been described as shown in Fig. 4. Considering different chemical
compositions of 1–4, figures describe different intermediate bands
around the Fermi level contributed by different electronic states of the
respective complexes. Where different transitions can take place and
exhibit different absorbing peaks in UV spectra (Fig. 3).
2 theta
160
120
80
40
0
Experimental
The Cu-d-orbitals have different intensities and divergence positions
around the Fermi level corresponding to their elemental composition in
complexes 2, 3 and 4, respectively. But in all cases the contribution of
Cu-d-orbitals is predominant to the intermediate bands in addition to
the minor contribution of O-p-orbitals (in case of 2 and 4) and of O-p/N-
p orbitals (in case of 3). Other orbitals from different elements of the
complexes have minor contributions shown in the inset of the Fig. 4A-
D. The O-p-orbitals and Cu-d-orbitals in case of 2 and 4 and O-p-orbi-
tals, Cu-d-orbitals and N-p-orbitals show interaction in the region
around Fermi level and from −2 to −4 eV. The position of np/ns or-
bitals of non-metals, transition metals and halogens is relatively con-
stant and they follow different trends in intensities (see insets of Fig. 4).
To compare the experimental spectra with the theoretically simulated
PDoS, our findings have nicely explained the peaks. The main peaks in
the UV spectra come from the transitions of electrons from the orbitals
lying in the main band gap between valence band and conduction band,
while the small peaks originated from the transition of electrons from
the orbitals lying in the intermediate band gap.
5
10
15
20
25
30
2 theta
A
B
C
2100
1400
700
Experimental
6
9
12
15
18
21
24
27
30
2 theta
9000
6000
3000
0
Theoretical
2.6. Electrochemical solution study
6
9
12
15
18
21
24
27
30
Oxidation and reduction behavior of the synthesized complexes was
checked by cyclic voltammetry which yielded cyclic voltammograms
shown in Fig. 5. Since the electrochemistry is metal centered, and every
complex has Cu2+ center, therefore, all the four complexes have given
similar voltamograms. The oxidation signals of the complexes were in
potential range 0–0.3 V while the reduction signals were in potential
ranging from −0.1 to − 0.3 V. the signals of polymeric complexes 1
and 2 were assigned to CuIICuII/CuIICuI process while those of the
mononuclear complexes 3 and 4 were ascribed to CuII/CuI process as
observed in structurally similar copper(II) carboxylate complexes
[18,19]. The peak separation values (ΔE = Epa – Epc) and peak current
ratios (Ipc/Ipa) of complexes 1–4 are 250, 350, 250 and 450 mV, and
0.758, 0.843, 1.3 and 3, respectively. These parameters as well as the
shifting of peak potential with scan rate indicate that the redox pro-
cesses can be safely termed as irreversible processes [21]. Owing to the
far lying substituents on the aromatic ring, their relative effect was not
obvious on the redox properties of central copper ion however, the
observed electrochemical behavior was typical of the copper(II) com-
plexes and helped to indicate stable Cu(II) center in solutions of the
complexes.
2 theta
9000
6000
3000
0
Theoretical
12
15
18
24
27
30
2 t2h1eta
300
200
100
Experimental
12
15
18
21
24
27
30
2 theta
2.7. Structural description
Fig. 2. experimental and simulated powder XRD spectra of the complexes 1(A),
3(B) and 4(C) showing coincidence of the peaks on 2 theta values.
Molecular structures of the complexes have been shown in Figs. 6–9
while their refinement parameters and selected bond lengths and angles
have been listed in Tables 1–3. 1 and 2 adopt polynuclear motifs where
the secondary paddlewheel (pw) units are interlinked with one another
directly through their Cu and O atoms. The inter-pw Cu – O distance is
2.21 and 2.195 Å for 1 and 2. There is a debate whether this is a gen-
uine covalent bond or a secondary interaction. It was pointed out that a
parameters have usual meanings. The extrapolation to the x-axis of the
plot showed the band gap values between 1.3 and 1.5 eV. These values
clearly indicate that these complexes can find potential applications in
photovoltaic materials. Moreover, the band gap values were found
3

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
1
1
1500000
1250000
1000000
750000
500000
250000
0
4
3
2
2
4
3
500
600
700
800
900
1000
1100
1.2
1.4
1.6
1.8
2.0
2.2
2.4
Wavelength (nm)
Energy (eV)
A
B
Fig. 3. A, Absorption peaks of the complexes showing broad bands. B, optical band gap of the complexes.
Fig. 4. A, B, Calculated partial density of states of Cu-d-orbitals, Cu/O/N/C np/ns orbitals and H 1s orbitals (complexes 2 (B) and 4 (D)) and C, calculated partial
density of states of Cu-d-orbitals, Cu/O/N/C/F np/ns orbitals and H 1s orbitals (complexes 1 (A) and 3 (C)).
distance of Cu – O/N/F up to 2.4 Å might be considered a definite
covalent bond; 2.4–2.8 Å indicates a weaker secondary Cu∙∙∙L bond
primarily electrostatic in nature; while > 2.8 Å is mere van der Waals
bond [22]. As per this criterion, the structure of 1 and 2 are definitely
polymeric. This pw-pw distance was found typical of other structural
analogue without a substituent on phenyl ring [18]. This shows that the
electronic effect of the substituents on aromatic ring have little effect on
electronic properties of central copper ion as observed in electro-
chemical behavior. However, the effect of substituent is observable in
the form of the small contraction in Cu⋯Cu distance within the pw
units of substituted (NO2 and F in 1 and 2) and non-substituted [15]
phenyl rings of the phenyl acetate ligands. The former pair has Cu⋯Cu
distance = 2.574 and 2.576 Å compared to 2.584 Å observed for the
later [18]. This contraction is in accordance to the slightly higher ico-
nicity of the substituted than the non-substituted phenyl acetate li-
gands. Cu∙∙∙Cu distance within pw is further increased if donating ability
of ligand is increased as observed in dinuclear pw complexes with soft
pyridine ligands [23]. The decrease in carboxylate donor strength of 1
4

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
0.06
0.04
0.02
0.00
-0.02
-0.04
-0.06
2
1
4
3
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
E / V
Fig. 5. Cyclic voltammograms of the complexes at 100 mV/s.
Fig. 9. Structure of complex 4 with atom numbering scheme.
copper(II) is 5-coordinated (CuO5) square pyramidal with elongated Cu
– O bond on the apical position. The longer Cu – O bond on the apical
position is weaker which is broken easily when a stronger Lewis base is
added to solution of the polymeric complex where the added ligand
competes successfully for this bond and the structure is converted to
binuclear pw complex [24]. The solubility of 1 and 2 in common sol-
vents contrasted to MOF type copper(II) complexes [25] also indicated
that the weaker bond is broken and the structure is discrete binuclear in
solution form rather than intact polymeric. The electrochemical solu-
tion and absorption spectroscopic studies yielded results which were
typical of binuclear pw–complexes [18,24].
Fig. 6. Structure of a paddlewheel unit of complex 1 with atom numbering
scheme.
Complexes 3 and 4 are the mono-nuclear structural analogues of the
1 and 2 with reference to the carboxylate functionality. These were
resulted owing to the relative preference of the intermediate hard Cu2+
ion for the N-donor ligands over the O-donor ones. Complete replace-
ment of the substituted carboxylate ligands by simple heterocyclic rings
was probably rendered difficult by the overriding solvation effect. Both
complexes contain two carboxylate ligands and a 1,10-phenanthroline
́
(3) and 2,2-bipyridine (4) moieties. Complex 3 has Jahn-Teller dis-
torted octahedral geometry with elongated Cu–O and Cu–N
bonds = 2.429 and 2.124 Å compared to the normal Cu–O and Cu–N
bonds = 2.147 and 2.006 Å. The trans O-Cu–N angle was found to be
156.14°. The striking angle deformation from 180° may be attributed to
the chelating carboxylate and phenanthroline moieties. One of the
carboxylate ligands is monodentate as compared to the para-methyl
analogue which has bidentate carboxylate ligands [19] and, probably
owing to this reason, the latter complex has more distortion from the
ideal octahedral geometry as far as angles and distances are concerned.
Complex 4 has both carboxylate ligands as mono-dentate and a water
molecule as fifth coordination member. Thus the geometry is distorted
square pyramidal. The octahedral analogue of this complex has both
carboxylate ligands acting in bidentate fashion [26] without water
molecule.
Fig. 7. Structure of a paddlewheel unit of complex 2 with atom numbering
scheme.
The packing interactions are quite different from one another owing
to variation in the structure and substituents. F atom of 1 is actively
involved in packing interactions and there are ample interlayer contacts
as compared to 2 which has no interlayer contacts as shown in
Figs. 10–13 similar picture is presented by 3 and 4 where the molecules
in 3 are held together by extensive OeH⋯C and CeH⋯C interactions
while no such inert-molecular contacts are found in 4 as shown in
Figs. 9–12. Moreover, owing to the small distance of 3.692 Å between
phenanthroline ligands, there are π–π interactions in 3 while no such
interactions are found in 4 because of the bipyridine rings are far apart
from each other. The 1D polymeric chain structures of 1 and 2 are
shown in Figs. S2 and S3.
Fig. 8. Structure of complex 3 with atom numbering scheme.
and 2 is also exhibited in slight shortening of Cu – O bond distances
(1.95 Å on the average for both) of the square base around Cu(II)
compared to the unsubstituted analogue (1.96 Å average) [18]. Within
the pw unit, Cu – O bond distances are shorter i.e., 1.95 Å on the
average compared to the pw-pw Cu – O bond. Overall, geometry around
5

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
Table 1
Structure refinement parameters of complexes 1–4.
Complex
1
2
3
4
Empirical formula
Formula weight (g mol−1
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C32H24F4Cu2O8
739.59
296(2)
0.71073
Monoclinic
C 2/c
C16H12CuN2O8
423.82
296(2)
0.71073
Monoclinic
P 21/c
C28H22CuF2N2O5
568.01
296(2)
0.71073
Monoclinic
P 21/n
C26H24CuN4O10
616.03
296(2)
0.71073
triclinic
P-1
)
26.1472(19)
5.1647(3)
22.2109(14)
90.00
98.892(4)
90.00
2963.4(3)
4
1.658
5.1547(7)
16.031(3)
20.523(3)
90
92.427(4)
90
1694.5(4)
4
1.661
13.0522(10)
12.0762(11)
16.4526(13)
90
101.533(5)
90
2540.9(4)
4
1.485
6.9891(2)
14.2334(4)
15.3188(5)
65.5750(10)
82.9650(20)
79.2140(10)
1361.26(7)
2
1.503
0.866
634
0.38 × 0.30 × 0.30
2.56 to 25.25
−8 ≤ h ≤ 8
−17 ≤ k ≤ 16
−18 ≤ l ≤ 17
20,979
b (Å)
c (Å)
α (°)
β (°)
γ (°)
Volume (Å3)
Z
ρ (calculated) (Mg/m3)
Absorption coeff. (mm−1
F(0 0 0)
)
1.513
1496
1.339
860
0.916
1164
Crystal size (mm3)
θ range (°)
0.25 × 0.20 × 0.18
2.24 to 25.25
−30 ≤ h ≤ 30
−6 ≤ k ≤ 6
−26 ≤ l ≤ 26
10,610
0.30 × 0.25 × 0.18
2.358 to 27.735
−5 ≤ h ≤ 6
−20 ≤ k ≤ 20
−26 ≤ l ≤ 26
10,974
0.30 × 0.24 × 0.23
1.824 to 26.000
−16 ≤ h ≤ 16
−14 ≤ k ≤ 14
−6 ≤ l ≤ 20
19,689
Index ranges
Reflections collected
Independent reflections
Completeness to θ %
Refinement method
2673
99.9
3843
96.80
4985
99.90
4940
99.90
Full-matrix LS on F2
2673/24/242
0.981
Full-matrix LS on F2
3843/0/244
0.927
Full-matrix LS on F2
4985/0/350
1.016
Full-matrix LS on F2
4940/3/282
1.047
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ (I)]
R1 = 0.0957,
wR2 = 0.0502
R1 = 0.1170,
wR2 = 0.1039
R1 = 0.0544,
wR2 = 0.0966
R1 = 0.1299,
wR2 = 0.1240
R1 = 0.0422,
wR2 = 0.0859
R1 = 0.0745,
wR2 = 0.0985
R1 = 0.0294,
wR2 = 0.0744
R1 = 0.0345,
wR2 = 0.0798
R indices (all data)
Table 2
Table 3
Selected bond lengths and angles of complexes 1 and 2.
Selected bond lengths and angles of complexes 3 and 4.
Bond
Complex
1
Complex
2
3
4
Distances, Å
Bond
Distances, Å
Cu(1)-O(1)
Cu(1)-O(2)
Cu(1)-O(3)
Cu(1)-O(4)
Cu(1)-O(5)
Cu(1)-O(2)
Cu(1)-Cu(1)
Cu(1)-O(6)
1.957(3)
2.015(3)
1.935(4)
1.942(4)
—
2.211(3)
2.5743(10)
—
1.948(3)
2.011(3)
—
Cu(1)-O(1)
Cu(1)-O(2)
Cu(1)-O(3)
Cu(1)-O(5)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-O(9)
2.147(3)
2.429(3)
1.937(2)
2.085(3)
2.123(3)
2.006(2)
—
1.9383(14)
—
—
1.9443(16)
2.0000(17)
2.0094(16)
2.3149(15)
—
1.924(3)
2.195(3)
2.5760(10)
1.940(3)
Angles, °
93.40(9)
91.71(10)
87.64(10)
174.60(10)
101.38(10)
95.16(10)
79.74(10)
93.40(9)
94.11(10)
88.82(10)
103.61(10)
153.69(11)
97.93(10)
—
Angles, °
90.19(15)
91.81(15)
169.68(12)
88.21(16)
87.92(14)
169.51(15)
96.05(15)
94.26(14)
109.62(12)
80.64(13)
—
O(1)-Cu(1)-O(2)
O(1)-Cu(1)-O(3)
O(1)-Cu(1)-N(2)
O(3)-Cu(1)-N(2)
O(1)-Cu(1)-N(1)
O(3)-Cu(1)-N(1)
N(2)-Cu(1)-N(1)
O(2)-Cu(1)-O(3)
O(5)-Cu(1)-O(3)
O(5)-Cu(1)-N(2)
O(5)-Cu(1)-N(1)
O(5)-Cu(1)-O(1)
O(5)-Cu(1)-O(2)
O(1)-Cu(1)-O(9)
O(5)-Cu(1)-O(9)
O(9)-Cu(1)-N(1)
O(9)-Cu(1)-N(2)
O(2)-Cu(1)-N(1)
—
—
O(4)-Cu(1)-O(1)
O(2)-Cu(1)-O(3)
O(1)-Cu(1)-O(2)
O(1)-Cu(1)-O(3)
O(4)-Cu(1)-O(2)
O(3)-Cu(1)-O(4)
O(2)-Cu(1)-O(3)
O(4)-Cu(1)-O(2)
O(1)-Cu(1)-O(2)
O(2)-Cu(1)-O(2)
O(5)-Cu(1)-O(6)
O(5)-Cu(1)-O(1)
O(6)-Cu(1)-O(1)
O(5)-Cu(1)-O(2)
O(6)-Cu(1)-O(2)
—
—
170.81(6)
—
94.24(7)
—
80.77(7)
—
—
90.23(7)
165.53(6)
93.06(6)
—
89.78(6)
90.54(6)
101.95(6)
98.77(6)
—
169.84(11)
—
—
—
—
—
—
81.36(12)
169.74(12)
89.98(13)
88.67(13)
88.81(13)
90.72(13)
—
—
—
—
—
—
—
156.14(10)
6

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
Fig. 10. Packing diagram of the complex 1 where each molecule represents a
1D-layer as shown in Fig. S1. The layers are held together by C⋯HeC inter-
actions.
Fig. 13. packing diagram of complex 4 showing no intermolecular interactions.
2.8. DNA-binding study
In order to explore the complexes for their biological relevance,
these were screened for their ability to interact with DNA. The decrease
in the active concentration of the complexes on interaction with added
amount of DNA was indicated by the absorption spectroscopy as well as
cyclic voltammetry. Complex 1 exhibited clear red shift of 29 nm with
DNA addition as shown in Fig. 14 A. This is indicative of predominantly
an intercalative mode of the interaction of the complex with DNA. The
intercalation would result from the aromatic rings being able to get
inserted between the DNA base pairs. Other complexes also exhibited
red shift which is indicative of the same intercalative mode of inter-
action with DNA but of smaller extent (Fig. 15A and B) while 2 ex-
hibited small blue shift (Fig. 14B). The latter is attributed to the con-
comitant electrostatic with groove binding mode of interaction along
with intercalative mode. This mode of binding might be due to the
suitably oriented nitro group giving rise to ionic interactions with polar
groups of DNA [27]. The quantitative binding abilities of the complexes
with DNA were determined from the slope to intercept ratio of the re-
spective plots between reciprocal molar concentration of DNA and the
relative absorbance values of the respective complexes as shown in Figs.
S4–S7. These values have been listed in Table 4 which are similar to
those calculated spectrophotometrically for some already reported
copper complexes with similar structures [18,19,26].
Fig. 11. Packing diagram of the complex 2 where each molecule represents a
1D-layer as shown in Fig. S2. The layers are held together by C⋯HeC inter-
actions.
Since the complexes are electroactive owing to the redox-active
metal center, the decrease in the concentrations of the complexes in
solution can be followed in cyclic voltammetry as well where the net
current decreases as a result of addition of DNA. The resulting vol-
tammograms before and after DNA addition have been shown in Figs.
S8–S11. Since there is a change in current as a function of concentration
of DNA, a plot of logarithmic values of the relative current vs reciprocal
molar concentration of DNA (shown in Figs. S12–S15) gives a constant
value of intercept. This value is called binding constant which are listed
in Table 4 which are higher than some other copper complexes de-
termined through the same technique [18,19,26]. Since there is re-
duction in concentration of the free electro-active complex moving to
the electrode surface, the value of diffusion co-efficient Do should suffer
diminution as a result of addition of DNA. This has been proved to be so
where Do values have been calculated for all the complexes before and
after DNA addition using Randles–Sevcik equation [28]. These values
have been listed in Table 4 which show a considerable loss in Do values
on addition of DNA indicating that the complexes have potent DNA
binding abilities.
Fig. 12. packing diagram of complex 3 showing intermolecular interactions.
7

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
Fig. 14. Absorption peaks of complexes 1(A) and 2(B) before (uppermost peak) and after DNA addition (lower peaks) whereby the significant reduction in ab-
sorbance as well as shift in λmax on addition of DNA indicate complex-DNA interaction.
Fig. 15. Absorption peaks of complexes 3(A) and 4(B) before (uppermost peak) and after DNA addition (lower peaks) whereby the significant reduction in ab-
sorbance as well as shift in λmax on addition of DNA indicate complex-DNA interaction.
It is evident that the fluorous complexes in both polymeric and
monomeric pairs of complexes give rise to higher DNA-binding con-
stants and thus exhibit better DNA binding activity. This might be due
to the small size and higher electrostatic influence of the fluorine re-
sponsible for the electrostatic groove binding interactions of the
fluorous complexes with DNA-helix. Such increased activity of the
floro-substituted copper complexes relative to the unsubstituted, me-
thyl- and methoxy-substituted copper complexes has been observed
already [24].
Table 4
Do and Kb values of complexes 1–4.
Complex Do before DNA
addition × 10−8
Do after DNA
Cyclic
Absorption
K
b × 104
addition × 10−8
voltammetry
K
b × 104
1
2
3
4
23.170
121.101
5.778
0.891
36.192
0.022
1.337
7.547
2.457
3.667
1.820
1.494
1.342
1.411
1.351
1.807
The mode of DNA-binding behavior was further supported from the
viscosity measurement of the complex-bound-DNA solution. The in-
crease observed in the relative viscosity of DNA solution with incre-
mental amounts of the complexes, indicated classical intercalation
mode of interaction of the complexes with DNA helix as shown in
Fig. 16. This results from the lengthening of the DNA-helix as a result of
insertion of the planar moieties of the complexes into the DNA-base
pairs.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
3
4
2
1
2.9. Anti-bacterial study
The complexes were screened for their anti-bacterial activity against
gram positive as well as gram negative bacterial strains. It was noticed
that only complex 3, the mononuclear fluorous complex showed ex-
cellent anti-bacterial activity as given in Table 5 This may be due to the
small size of 3 as well as the F-substituent which gives rise to optimum
penetrability to the molecule through the bacterial cell wall.
0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
[Complex] / [DNA]
Fig. 16. Plots of the [complex]/[DNA] vs. relative viscosity of complexes 1–4.
The increase in viscosity indicated intercalative mode of complexes.
3. Conclusions
Four new (two polynuclear and two mononuclear) complexes of
8

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
Table 5
Antibacterial data of complex 3: Average zone of inhibition (mm) and Minimum Inhibitory Concentration (mg/mL).
Bacterial strain
Parameter
Micrococcus luteus
Bacillus subtilis
Escherichia coli
Staphylococcus aureus
Average zone of inhibition (mm)
Minimum Inhibitory Concentration (mg/mL)
Complex 3
Cefixime
Complex 3
Cefixime
18
33
0.25
0.05
23
29
0.25
NA
26
30
0.25
0.03
18
35
0.5
0.02
Maximum Concentration: 1 mg/mL in DMSO. Reference drug, Cefixime: 1 mg/mL.
copper(II) with para-floro- and nitro-substituted-2-phenyl acetates have
been synthesized, characterized and their properties explored. The
polynuclear complexes have been successful converted to the corre-
sponding mononuclear analogues on addition of N-donor bidentate li-
gand to the reaction mixture containing the polynuclear complex. Both
polynuclear complexes contained paddlewheel secondary building
units (with square pyramidal copper) linearly interlinked via Cu and O-
atoms without intervening moieties. However, the corresponding
mononuclear analogues contained octahedral copper(II) centers with
two carboxylates and an N-donor ligand. The powder XRD spectra in-
dicated the uniformity of the crystalline samples. While the +2 oxi-
dation state of the metal was confirmed from the ESR spectra of the
complexes. Each complex gave an optical band gape near 1.4 eV which
is a good indication that complexes can find applications in the field
catalysis as well. The complexes exhibited irreversible metal centered
electro-activity assignable to CuII/CuI processes. The complexes have
given rise to excellent DNA-binding activity checked by absorption
spectroscopy and cyclic voltammetry with DNA-binding constant values
1.494 × 104, 1.342 × 104 and 1.411 × 104 M−1 and 7.547 × 104,
2.457 × 104 and 3.667 × 104 M−1 for 1–3, respectively. Moreover, the
fluorous complex 3 was found to possess significant activity against
Bacillus subtilis and Escherichia coli and good activity against Micrococcus
luteus. The fluorine substituted analogues have marked difference in
their structures, supra-molecular synthons, DNA-binding ability and
biological activity. The ab-initio calculations of DFT to determine the
electronic structure revealed intermediate states around the Fermi
level, which endorses that these complexes can be efficiently used in
photocatalytic materials.
chloroform and methanol (1:1) yielding crystals of 1.
Complex 2: The same procedure was followed for 2 except replacing
4–nitrophenyl acetic acid (6 mmol, 0.90 g) for 4–florophenyl acetic acid
(6 mmol, 0.925 g).
Complex 3: 3 was prepared by adding 1,10-phenanthroline (0.540 g,
3 mmol) to the reaction mixture after 3 h stirring of the appearance of
precipitates of 1. the resulting precipitates were washed with distilled
water and air-dried.
́
Complex 4: 4 was prepared by adding 2,2-bipyridine (0.468 g,
3 mmol) to the reaction mixture after 3hstirring of the appearance of
precipitates of complex 2. The resulting precipitates were washed with
distilled water and air-dried. The dried product was purified and
crystallized from a mixture of chloroform and methanol (1:1).
Appendix A. Supplementary data
CCDC 934916, 1880883, 951572 and 937195 correspond to the
crystallographic data of complexes 1–4, respectively, reported in this
manuscript. For free acquisition of the data: Fax: +44-1223-336-033;
E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk.
Complex 1: Blue crystals; m.p. 218–220 °C; yield (60%). FT-IR
(cm−1): 1592 ν(OCO)asym, 1395 ν(OCO)sym, Δν = 197, 2948 νCH2,
3020 ν(Ar–H), 1505 νAr(C]C), 1211 ν(Ar–F), 420 ν(Cu–O).
Elemental analysis: Calculated (%): C, 51.89; and H, 3.24. Found
(%):C, 52.09; and H, 3.19.
Complex 2: Light blue crystals; m.p. 190–191 °C; yield (65%). FT–IR
(cm−1): 1615 ν(OCO)asym, 1436 ν(OCO)sym, Δν = 179, 2920 νCH2,
3052 ν(Ar–H), 1580, 1437 νAr(C]C), 1431, 1341 ν(NO2), 414
ν(Cu–O). Elemental analysis: Calculated (%): C, 45.30; H, 2.83; and N,
6.60. Found (%): C, 45.28; H, 2.79; and N, 6.55.
4. Experimental
Complex 3: Blue crystals; m.p. 178–180 °C; yield (65%). FT–IR
(cm−1): 1580 ν(OCO)asym, 1444 ν(OCO)sym, Δν = 136, 2962 νCH2,
3084 ν(Ar–H), 1595, 1473 νAr(C]C), 1206 ν(Ar–F), 414 ν(Cu–O), 468
ν(Cu–N). Elemental analysis: Calculated (%): C, 59.15; H, 3.87; and N,
4.93. Found (%): C, 59.08; H, 3.90; and N, 4.89.
Complex 4: Blue crystals; m.p. 169–170 °C; yield (65%). FT–IR
(cm−1): 1570 ν(OCO)asym, 1439 ν(OCO)sym, Δν = 131, 2950 νCH2,
3032 ν(Ar–H), 1595, 1447 νAr(C]C), 1435, 1340 ν(NO2), 420
ν(Cu–O), 481 ν(Cu–N). Elemental analysis: Calculated (%): C, 50.65; H,
3.89; and N, 9.09. Found (%): C, 50.68; H, 3.82; and N, 8.99.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2019.119177.
4.1. Chemicals and methods
Analytical grade materials, used in this work were purchased from
suppliers. Melting point was determined by an electrothermal appa-
ratus and FT-IR spectra recorded on a Nicolet-6700 spectrophotometer
fitted with ATR. Powder XRD data was acquired using a PANalytical,
́
XPert PRO diffractometer having Cu-Kα radiation (λ = 1.540598 Å) at
298 K. X-band electron spin resonance (ESR) spectra were obtained
using
(−9.5 GHz).
See supplementary materials section for experimental protocols of
a Bruker ESP-300 spectrometer having X-band frequency
single crystal XRD study, electrochemistry, absorption spectroscopy,
computational details and antibacterial studies.
References
[1] R.D. Chambers, P.A. Martin, G. Sandford, D.L.H. Williams, J. Fluor. Chem. 129
(2008) 998–1002.
4.2. Synthesis of the complex
[2] E. Leyva, K.M. Baines, C.G. Espinosa-González, D.A. Magaldi-Lara,
S.E. LoredoCarrillo, T.A. De Luna-Méndez, L.I. López, J. Fluor. Chem. 180 (2015)
152–160.
[3] K. Haranahalli, T. Honda, I. Ojima, J. Fluor. Chem. 217 (2018) 29–40.
[4] K.L. Kirk, J. Fluor. Chem. 127 (2006) 1013–1029.
[5] E. Rowinsky, Ann. Rev. Med. 48 (1997) 353–374.
[6] I. Ojima, B. Lichtenthal, S. Lee, C. Wang, X. Wang, Expert Opin. Ther. Patents 26
(2016) 1–20.
Complex 1: Sodium bicarbonate (0.504 g, 6 mmol) was reacted with
an equimolar quantity of 4–florophenyl acetic acid (6 mmol, 0.925 g) at
60 °C in distilled water. After complete neutralization of the acid with
base, the aqueous solution of copper sulphate (0.240 g, 3 mmol) was
added drop wise. The reaction mixture was stirred for 4 h at 60 °C and
the resulting precipitates were filtered, washed thoroughly with dis-
tilled water and air dried. The solid was recrystallized from a mixture of
[7] A.L.P. Jerez, N.L. Robles, J. Fluor. Chem. 213 (2018) 1–10.
9

M. Iqbal, et al.
InorganicaChimicaActa498(2019)119177
[8] C. Tolia, A.N. Papadopoulos, C.P. Raptopoulou, V. Psycharis, C. Garino, L. Salassa,
G. Psomas, J. Inorg. Biochem. 123 (2013) 53–65.
Trans. 40 (2011) 8555–8568.
[17] F. Dimiza, F. Perdih, V. Tangoulis, I. Turel, D.P. Kessissoglou, G. Psomas, J. Inorg,
[9] A. Tarushi, S. Perontsis, A.G. Hatzidimitriou, A.N. Papadopoulos, D.P. Kessissoglou,
G. Psomas, J. Inorg. Biochem. 149 (2015) 68–79.
[10] M. Simunkova, P. Lauro, K. Jomova, L. Hudecova, M. Danko, S. Alwasel,
I.M. Alhazza, S. Rajcaniova, Z. Kozovska, L. Kucerova, J. Moncol, L. Svorc,
M. Valko, J. Inorg. Biochem. 194 (2019) 97–113.
Biochem. 105 (2011) 476–489.
[18] M. Iqbal, S. Ali, M.N. Tahir, J. Inorg. Gen. Chem. 644 (2018) 172–179.
[19] M. Iqbal, S. Ali, M.N. Tahir, J. Coord. Chem. 71 (2018) 991–1002.
[20] M.A. Hussien, N. Nawar, F.M. Radwan, N.M. Hosny, J. Mol. Struct. 1080 (2015)
162–168.
[11] H.I. Althagbi, D.R. Bernstein, W.C. Crombie, J.R. Lane, D.K. McQuiston,
M.A. Oosterwijk, G.C. Saunders, W. Zou, J. Fluor. Chem. 206 (2018) 61–71.
[12] P. Manna, S.K. Seth, A. Bauzá, M. Mitra, S.R. Choudhury, A. Frontera,
S. Mukhopadhyay, Cryst. Grow. Des. 14 (2014) 747–755.
[21] M.S. Mohamed, A.A. Shoukry, A.G. Ali, Spectrochim. Acta A 86 (2012) 562–570.
[22] M.A. Halcrow, G. Christou, Chem. Rev. 94 (1994) 2421.
[23] M. Iqbal, S. Ali, N. Muhammad, M. Sohail, Polyhedron 57 (2013) 83–93.
[24] M. Iqbal, S. Ali, M.N. Tahir, Acta. Chim. Slov. 65 (2018) 131–137.
[25] H.E. Mkami, M.I.H. Mohideen, C. Pal, A. McKinlay, O. Scheimann, R.E. Morris,
Chem. Phys. Lett. 544 (2012) 17–21.
[13] K.V. Shuvaev, S. Sproules, J.M. Rautiainen, E.J.L. McInnes, D. Collison, C.E. Anson,
A.K. Powell, Dalton Trans. 42 (2013) 2371–2381.
[14] C. Jayabalakrishnan, K. Natarajan, Transit. Met. Chem. 27 (2002) 75–79.
[15] Z.H. Abd El-Wahab, M.M. Mashaly, A.A. Salman, B.A. El-Shetary, A.A. Faheim,
Spectrochim. Acta A 60 (2004) 2861–2873.
[16] F. Dimiza, S. Fountoulaki, A.N. Papadopoulos, C.A. Kontogiorgis, V. Tangoulis,
C.P. Raptopoulou, V. Psycharis, A. Terzis, D.P. Kessissoglou, G. Psomas, Dalton
[26] M. Iqbal, S. Ali, M. Sohail, M.N. Tahir, P.A. Anderson, J. Chin. Chem. Soc. 66
(2019) 1–9.
[27] M. Sirajuddin, S. Ali, A. Badshah, J. Photochem. Photobiol. B 124 (2013) 1–19.
[28] J. Wang, Analytical Electrochemistry, 1st ed., VCH Publishers, New York, 1994, pp.
165–166.
10