Download CHAPTER V Cu(II), Ni(II) and Co(II) Schiff bases complexes derived

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CHAPTER V
Cu(II), Ni(II) and Co(II) Schiff bases complexes derived from
2-H/Cl/Br-4-H/Cl-6-(4-fluorophenlyiminomethyl)phenol: Synthesis,
spectral, electrochemical, antibacterial and DNA binding properties
Abstract
A new series of ligands 2X-4Y-FPIMP; where FPIMP = 6-(4-fluoro phenyl imino
methyl)phenol ; X = H, Cl or Br and Y = H or Cl have been prepared by reacting 3X- 5YSalicylaldehyde and 4-Fluro aniline in 1:1 molar ratio and are characterized by spectral
studies.
The
representative
Schiff
base
ligand
2-bromo-4-chloro-6-(4-
fluorophenlyiminomethyl)phenol have been characterized by X- ray crystallography and
crystallizes in triclinic system with space group P-1 with one molecule in the unit cell
showing the inter and intra molecular interactions. The packing is further stabilized
through vander Walls interaction. The dihedral angle between the salicylaldehyde and
aniline moieties is 8.79 (0.16)˚. With these ligands Cu(II), Co(II) and Ni(II) complexes of
the type [Cu(2X-4Y-FPIMP)2](ClO4)2 and [M(2X-4Y-FPIMP)2]; have been prepared and
characterized by spectral and cyclic voltammetric studies. All complexes show strong
metal to ligand charge transfer (MLCT) transition in the visible region. In the IR spectral
observations, the disappearance of υ(O–H), the downward shift of υ(C–O) to higher
frequency region and the lower frequency shift of υ(C=N) of the ligands on complexation
to ruthenium atom proves the bonding through imine nitrogen and deprotonated phenolic
oxygen. Cyclic voltammetry of these complexes show an irreversible/reversible metal
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based MII/MIII oxidation in the range 42-82/576-788 mV versus saturated calomel
electrode and quasireversible metal based MII/MI in the range 312 to 360 mV and some
complexes showed ligand based reduction MII/MI with cathodic peak potential -555 to
-665 mV. In addition, Nickel complexes and unsubstituted cobalt Schiff base complexes
showed quasireversible MIII/MIV oxidation. The representative Schiff bases and their
copper complexes were tested in vitro to their antibacterial activity against Gram-Positive
bacteria Staphylococcus aureus and Gram-negative bacteria Proteus mirabilis. All the
complexes showed activity against both the organisms and the activity increases with
increase in concentration of test solution containing the new complexes. Further more the
DNA binding experiment of the complex [Cu(2Br-4Cl-FPIMP)2](ClO4)2 (3) was carried
out by UV-Vis absorption spectral titration and the binding constant Kb = 1.06 ± 0.4 ×
104 M−1 have been found.
Introduction
During the past two decades, considerable attention has been paid to the
chemistry of the metal complexes of Schiff bases containing nitrogen and other donors
[1,2]. This may be attributed to their stability and applications in many fields such as
catalysis, biocidal activity, etc.
Figure 5.1 Structures of Co(salen) and Co(salophen).
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Cobalt Salen and Salophen complexes (figure 5.1) are employed as Oxygen
Reduction Catalysts [3].
Square planar nickel(II) complexes were studied owing to their known catalytic
activity towards olefin epoxidation.
Transition metal complexes capable of cleaving DNA and RNA under
physiological conditions via oxidative and hydrolytic mechanisms are of important.
Binding studies of transition metal complexes have become a very important field in the
development of DNA molecule probes and chemotherapeutics in recent years [4-11]. In
order to find anticarcinogens that can recognize and cleave DNA, people synthesized and
developed many kinds of complexes. Among these complexes, metals or ligands can be
varied in an easily controlled way to facilitate the individual applications [12-14]. Nickel
macrocyclic complexes that possess vacant or labile coordination sites may also ligate to
DNA bases, and effect site-specific reactions with DNA [15].
Copper is a bioessential element with relevant oxidation states. More than a dozen
of enzymes that depend on copper for their activity have been identified; the metabolic
conversions catalyzed by all of these enzymes are oxidative. Due to their importance in
biological processes, copper(II) complexes synthesis and activity studies have been the
focus from different perspectives.
Scope of the present work
Schiff bases and their first row transition metal complexes such as Co(II), Ni(II),
Cu(II), etc., were reported to exhibit fungicidal, bactericidal, antiviral and
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antitubarculoral activity [16-22]. In specially, Cu(II) complexes with diverse drugs have
been the subject of a large number of research studies [23,24], presumably due to the
biological role of Cu(II) and its synergetic activity with the drug [25]. The antifungal and
antibacterial properties of a range of Cu(II) complexes have been evaluated against
several pathogenic fungai and bacteria [26-28]. For many years it has been believed a
trace of Cu(II) destroys the microbe, however, recent mechanisms becomes activated
oxygen in the surface of metal Cu kills the microbe because Cu(II) activity is weak.
For the past two decades, there has been tremendous interest in studies pertaining
to interaction of transition metal complexes with nucleic acid [29-31]. These studies are
relevant for the development of new reagents for biotechnology and medicine.
Researchers have shown substantial interest in the rational design of novel transition
metal complexes, which bind and cleave duplex DNA with high sequence and structure
selectivity [32,33].
In developing new DNA-interacting transition metal based coordination
compounds, it has been realized that multi-mode binding would provide advantages in
terms of administration, lowering of toxicity etc. [34,35]. Among the two modes of
binding with DNA residues, i.e., intercalating and covalent binding, the former requires
planar type structures while the latter needs coordination complexes with potential
coordination sites [36].
Copper(II) complexes are also attractive since Cu(II) is known to play a
significant role in naturally occurring biological systems as well as a pharmacological
agent [37-39]. Copper is a biologically relevant element and many enzymes that depend
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on copper for their activity have been identified. The metabolic conversions catalysed by
most of these enzymes are oxidative. Because of their biological relevance a large
number of copper(II) complexes have been synthesized with different perspectives.
Recently, Tonde et al [40] reported self- activating nuclease activity (DNA
cleavage) of Copper(II) Schiff base complexes of the type [CuL]n ; L = Schiff base. With
the above view, we have synthesized Cu(II) and Co(II) / Ni(II) Schiff base complexes of
the type [CuL2] (ClO4)2 and [ML2] ; M = Co / Ni, to characterize spectrally &
electrochemically and to evaluate their DNA binding ability and antibacterial sceening
ability.
Experimental
The instruments employed for recording the UV-Vis, IR & NMR spectra and
XRD & Cyclic Votammetry are described in Chapter II. The structure of synthesized
Schiff bases have been witnessed by the NMR spectral data.
Synthesis of multisubstituted Schiff base ligands (Scheme 5.1)
2-[(4-Flurophenylimino)-methyl]-phenol (2H-4H-FPIMP) (Figure 5.2)
2-hydroxybenzaldehyde (10 mmol) was added to a solution of 4-fluoroaniline (10
mmol) in 1:1 molar ratio in MeOH (25 cm3). The solution was continuously stirred for 2h
using magnetic stirrer and then concentrated to 5 cm3. On cooling the yellowishorange
crystalline product was separated out washed with ice cold EtOH and dried. The product
was recrystallised from EtOH. The purity of the compound was checked with TLC.
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Yield: 80%. ; m.p: 80 °C. 1H NMR (CDCl3, 400 MHz): δ=13.100 (O–H, s, 1H);
8.596 (–CH=N, s, 1H); 7.136-7.094 (Ar, m, 4H); 7.037-6,951 (Ar, m, 4H).
2-[(4-Flurophenylimino)-methyl]-4,6-dichlorophenol (2Cl-4Cl-FPIMP) (Figure 5.3)
3,5-dichloro-2-hydroxybenzaldehyde (10 mmol) was added to a solution of 4fluoroaniline (10 mmol) in 1:1 molar ratio in MeOH (25 cm3). The solution was
continuously stirred for an hour using magnetic stirrer and then concentrated to 5 cm3. On
cooling the pale-orange crystalline product was separated out washed with ice cold EtOH
and dried. The product was recrystallised from EtOH. The purity of the compound was
checked with TLC.
Yield: 76% ; m.p: 98 °C. 1H NMR (CDCl3, 400 MHz): δ=14.079 (O–H, s, 1H);
8.543 (–CH=N, s, 1H); 7.48 (Ar, s, 1H); 7.262-7.323 (Ar, m, 4H); 7.15 (Ar, s, 1H).
2-[(4-Flurophenylimino)-methyl]-4-chloro-6-bromophenol (2Br-4Cl-FPIMP)
(Figure 5.4)
3-bromo-5-chloro-2-hydroxybenzaldehyde (10 mmol) was added to a solution of
4-fluoroaniline (10 mmol) in 1:1 molar ratio in MeOH (25 cm3). The solution was heated
under reflux for 3 h with continuous stirring and then concentrated to 5 cm3. On cooling
the yellowishorange crystalline product was separated out washed with ice cold EtOH
and dried. The product was recrystallised from EtOH. The purity of the compound was
checked with TLC.
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Yield: 72% ; m.p: 116 °C. 1H NMR (CDCl3, 500 MHz): δ=14.1982 (O–H, s, 1H);
8.5047 (–CH=N, s, 1H); 7.477 (Ar, s, 1H); 7.3034-7.2529 (Ar, m, 4H); 7.1337 (Ar, s,
2H).
X
NH2
HO
+
O
Y
C
H
F
:
1
1
MeOH
X
HO
N
Y
C
H
F
X = H & Y = H ( Stirring, 2h )
X = Cl & Y = Cl ( Stirring, 1h )
X = Br & Y = Cl ( Reflux, 3h )
Scheme 5.1 Synthesis of multisubstituted Schiff base ligands.
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Single-crystal X-ray structure determination
The
representative
ligand
2-Bromo-4-chloro-6-(4-fluorophenyliminomethyl)
phenol (C13H8BrClFNO) crystallizes from EtOH as pale orange crystals in the triclinic
system with space group P-1 with one molecule in the asymmetric unit. Figure 5.5 shows
the ortep representation of the molecule with 50% anisotropic ellipsoids at the 50%
probability level. The packing of the molecules in the unit cell showing the inter
molecular interactions is depicted in Figure 5.6. The molecule and its inversion analogue
are linked to each other by π–π interaction between the salicylaldehyde moiety and the
aniline moiety with the shortest interplanar distance of 3.317 (3) A˚ ( 1-x, 1-y, 1-z ). The
molecules are further connected by C11─H11 . . . F1 hydrogen bonds between ( 2.452 A˚,
161.89 ˚, symm: 1+x, -1+y, 1+z ) forming an one dimensional infinite chain. The packing
is further stabilized by VanderWaals interactions. In addition an intramolecular hydrogen
bonding O1 ─ H1
. . .
N1 ( 2.577 (3) A˚, 145.9˚ ) linking the OH group of the former
salicylaldehyde and the imine N atom of aniline. The dihedral angle between the
salicylaldehyde and aniline moieties is 8.8 (2)°.
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Figure 5.5 the ORTEP representation of the molecule with thermal
ellipsoids at the 50% probability level
121
Figure 5.6 Packing of molecules in the unit cell
(Intermolecular interactions are shown with dashed lines)
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Refinement
All the hydrogen atoms were located from the difference Fourier map. However,
the aromatic H atoms were geometrically constrained at idealized positions (C⎯H = 0.93
A°) and were refined using a riding model with Uiso equal to 1.2 times Ueq of the parent
carbon atom. The hydroxyl hydrogen was refined isotrophically with restraint: O⎯H =
0.820 (1) A°.
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Special details
Geometry: All e.s.d.’s (except the e.s.d. in the dihedral angle between two l.s.
planes) are estimated using the full covariance matrix. The cell e.s.d.’s are taken in to
account individually in the estimation of e.s.d.’s in distances, angles and torsion angles;
correlations between e.s.d.’s in cell parameters are not only used when they are defined
by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.’s is used for
estimating e.s.d.’s involving l.s. planes.
Refinement: Refinement of F2 against ALL reflections. The weighed R-factor wR
and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set
to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for
calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for
refinement. R-factors based on F2 are statistically about twice as large as those based on
F, and R-factors based on ALL data will be even larger.
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125
126
127
Synthesis of Copper(II) complexes (Scheme 5.2)
The complex was prepared in high yield from a reaction of Cu(ClO4)2 . 6H2O (0.1
mmol, 37 mg) in methanol-dimethyl sulphoxide (DMSO) (2:1) with FPIMP (0.2 mmol,
43-65.7 mg) under reflux for 4h. The solid complex that separated out upon slow cooling,
was filtered, washed with diethyl ether and dried in vacuo over CaCl2. The crude
precipitate of [Cu (2X-4X-FPIMP)2](ClO4)2 was recrystallised from acetonitrile-DMSO
mixture.
Caution:
Perchlorate salts of metal complexes are potentially explosive and should be
handled in small quantities with care.
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X
HO
Cu(ClO4)2 . 6H2O
N
+
1
Y
C
H
: 2
Reflux
4h
MeOH : DMSO
F
X = H / Cl /Br
Y = H / Cl
X
X
O
O
Cu
Y
C
N
Y
N
C
H
H
F
(ClO4)2
F
X = H / Cl / Br
Y = H / Cl
Scheme 5.2 Synthesis of Cu(II) complexes.
Synthesis of Cobalt (II) / Nickel (II) complexes (Scheme 5.3)
A solution of the ligand FPIMP (0.2 mmol, 43-65.7 mg) in MeOH (75 cm3) was
added to a hot solution of Co(II) acetate (0.1 mmol, 39 mg) or Ni(II) acetate (0.1 mmol,
47.5 mg) in MeOH and the mixture was boiled under reflux for 5h on a water bath. Just
sufficient AcONa in MeOH was added in order to maintain the pH. The complexes were
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separated on slow cooling, filtered, washed with MeOH and dried in vacuo over
anhydrous CaCl2.
X
HO
Ni(OAc)2 . 4H2O
(or)
N
Co(OAc)2 . H2O
Y
C
+
1
H
: 2
Reflux
5h
F
MeOH
X = H / Cl /Br
Y = H / Cl
X
X
O
O
M
Y
C
N
Y
N
C
H
H
F
F
X = H / Cl / Br
Y = H / Cl
M = Ni / Co
Scheme 5.3 Synthesis of Ni(II) / Co(II) complexes.
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Results and discussion
All the complexes are amorphous powder, insoluble in water and ether, sparingly
soluble in solvents such as CHCl3, CH2Cl2, MeCN but completely soluble in DMF and
DMSO.
Electronic spectra
The electronic absorption spectral bands of the complexes (Cu, Co and Ni) were
recorded over the range 200-800 nm in DMSO and their λmax values together with
tentative assignments [41] are summarized in Table 5.1 are discussed in detail.
The spectral profiles below 350 nm are similar and are ligand centered transitions
(intraligand (IL) π-π * and n-π *) of benzene and non-bonding electrons present on the
nitrogen of the azomethine group in the Schiff base complexes [42].
Cu(II) complexes (Figure 5.7-5.9) shows d-π * Metal-Ligand Charge Transfer
(MLCT) transitions in the region 400-448 nm which can be assigned to the combination
of 2B1g → 2Eg and 2B1g → 2B2g transitions [43] in a distorted square-planar environment
[44]. For Co(II) complexes (Figure 5.10-5.12) the assigned bands at about 390-448 nm to
d-π* Metal-Ligand Charge Transfer (MLCT) transitions [45] assignable to the
combination of 2B1g → 1A1g and 1B1g → 2Eg transitions which also supports square-planar
geometry [46,47]. The Ni(II) complexes (Figure 5.13-5.15) are diamagnetic and the
bands around 390-427 nm could be assigned to 1A1g → 1B1g transition [48] consistent
with low spin square-planar geometry.
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FT-IR spectra
The IR spectra of the free Schiff bases (Figure 5.10&5.11) and the respective
metal complexes (Figure 5.12-5.14) are tabulated (Table 5.2) in order to determine the
coordination mode of the ligands. In the IR spectra of the complexes, the stretching
vibration of the free ligands (ν(O-H), 3430-3464 cm–1) is not observed, suggesting
deprotonation of the hydroxyl group and formation of M–O bonds [49,50]. Bands
between 1617-1637 cm–1 in the free ligands are assigned to ν(C=N). These bands are
shifted to lower wave numbers 1607-1620 cm–1 in the complexes due to the coordination
of the nitrogen atom of the azomethine group to the metal ion [51,44]. The bands
assignable to ν(C–O) between 1427-1452 cm–1 are shifted to higher wave number 14971509 cm–1 in the complexes. The bands observed for the complexes between 521–559
and 464-495 cm–1 were metal sensitive and are assigned to ν(M–O) and ν(M–N) [52]
respectively.
EPR Spectra
The EPR spectrum of the complexes [Cu(2Cl-4Cl-FPIMP)2](ClO4)2 (2) (Figure
5.15) & [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2 (3) have been recorded in equimolar mixture of
CH3CN : DMSO solution at LNT (77K). The spin Hamiltonian parameters have been
calculated (Table 5.3) and the complex exhibit a typical four–line spectral pattern,
assignable to monomeric copper(II) complexes [53-55]. From the observed ‘g’ values,
g||>g⊥>2, it is apparent that the unpaired electron lies predominantly in dx2
–y2
orbital
giving 2B1g as the ground state [56] and also indicate ionic nature of the metal-ligand
bond in the complex and the higher g|| values indicate, a slight distortion from regular
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planarity [57,58]. The broadening of g⊥ is due to spin-lattice relaxation that results from
the interaction of the paramagnetic ions with the thermal vibrations of the lattice.
Cyclic Voltammetry
The cyclic voltammogram (Figure 5.16-5.19) of all these Cu(II), Co(II) and Ni(II)
complexes were recorded in DMSO with a BAS CV–50 instrument at room temperature
and purge of N2 gas. The electrochemical data are given in Table 5.3.
All copper complexes showed a metal based irreversible (∆Ep=760-788 mV ; E1/2
= +471 to +493 mV) oxidation (CuIII/CuII), a metal based irreversible (∆Ep=312-360 mV
; E1/2 = –694 to –707 mV) reduction (CuII/CuI) and a ligand based reduction with EPc –591
to –659 mV, but the ligand based peak is not found in (1), this may be due to the absence
of halo substitution on Schiff bases.
But nickel complexes exhibit a quasi reversible / irreversible (∆Ep=130-230 mV ;
E1/2 = +1000 to +1057 mV) metal based oxidation (NiIV/NiIII), a metal based reversible /
irreversible (∆Ep=82-596 mV ; E1/2 = +289 to +513 mV) oxidation (NiIII/NiII), a metal
based irreversible (∆Ep=296 to 304 mV ; E1/2 = –622 to –706 mV) reduction (NiII/NiI)
and a ligand based reduction with cathodic peak potential EPc –555 to –665 mV. The
presence of such redox waves seems to be typical for salicyliminato complexes [58-60].
Antibacterial investigation
The antibacterial activity of the Schiff base ligands (Figure 5.20&5.21) and its
soluble Cu(II) complexes (Figure 5.22&5.23) was performed by the well diffusion
technique. The zone of inhibition was measured against Staphylococcus aureus, and
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Proteus mirabilis. A clearing zone around the wells indicates the inhibitory activity of the
compound on the organism. Results are shown in Table 5.4, clearly indicate that the
inhibition are much larger by metal complexes as compare to the metal free ligand. The
increased activity of the metal chelates can be explained on the basis of chelation theory
[61]. Also activity increases with concentration of the metal complexes. The chelation
tends to make the ligands act as more powerful and potent bacterial agents, thus killing of
the more bacteria than the ligand. It is observed that in complexes the positive charge of
the metal partially shared with the donor atoms present in the ligand and there may be πelectron delocalization over the whole chelate ring.
DNA binding experiment
Absoption spectral titration
Absorption titration experiments were carried out by varying the DNA
concentration (0 — 60 µM) and maintaining the complex concentration constant (5 µM).
The binding of metal complexes to DNA helix has been characterized through absorption
spectral titrations, by following the changes in absorbance and shift in wavelength after
each successive addition of DNA solution and equilibration (ca. 10 min) [62]. A plot
(Figure 5.24) of [ DNA ] / ( εA − εf ) Vs [DNA] gives Kb as the ratio of the slope to
intercept. The copper(II) complex [Cu(2Br-4Cl-FPIMP)2](ClO4)2 (3) in acetonitrile:tris
buffer mixture exhibit sharp band of intraligand (IL) π-π* transition at 289 nm and
another band at about 400 nm which is due to d-π* Metal-Ligand Charge Transfer
(MLCT) transition. Among, π-π* intraligand transition is sharp and prominent and hence
binding experiment was followed by measuring its absorbance and shift in wavelength.
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On titration of herring sperm DNA with the complexes considerable decrease in the
absorptivity of this 289 nm band is observed with a tremendous red shift (longer
wavelength) (20-24 nm). The appreciable decrease in absorption intensity and
considerable shift towards longer wavelength in acetonitrile:Tris buffer (1:10) mixture
suggests that the Cu(II) complex interact with DNA externally, may be through the
formation of hydrogen bond between the phenolic hydroxyl groups of the Schiff base and
the nucleotides [63]. To know their affinity towards DNA their binding constants, Kb
were determined from the data obtained from their spectral titrations [64,65] using the
expression [ DNA ] / ( εA − εf ) = [ DNA ] / ( εb − εf ) + 1 / Kb ( εb − εf )
Where εA, εf and εb correspond to Aobsd / [Cu], the extinction coefficient for the free of the
slope to intercept and found to be1.06 ± 0.4 × 104 M−1 . These binding constant indicate
finite interaction nucleotides, but are lower compared to the typical intercalators like
ethidium bromide (7 × 107 M−1).
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141
Figure 5.2 NMR Spectra of {2-[(4-Flurophenylimino)-methyl]-phenol} (2H-4H-FPIMP)
Figure 5.2 NMR Spectra of {2-[(4-Flurophenylimino)-methyl]-phenol}
(2H-4H-FPIMP) (Expanded)
142
Figure 5.3 NMR Spectra of {2-[(4-Flurophenylimino)-methyl]-4,6-dichlorophenol}
(2Cl-4Cl-FPIMP)
Figure 5.3 NMR Spectra of {2-[(4-Flurophenylimino)-methyl]-4,6-dichlorophenol}
(2Cl-4Cl-FPIMP) (Expanded)
143
Figure 5.4 {2-[(4-Flurophenylimino)-methyl]-4-chloro-6-bromophenol} (2Br-4Cl-FPIMP)
Figure 5.4 {2-[(4-Flurophenylimino)-methyl]-4-chloro-6-bromophenol}
(2Br-4Cl-FPIMP) (Expanded)
144
Figure 5.7 Electronic spectra of [Cu (2H-4H-FPIMP)2] (ClO4)2
Figure 5.8 Electronic spectra of [Co (2Cl-4Cl-FPIMP)2]
145
Figure 5.9 Electronic spectra of [Ni (2Cl-4Cl-FPIMP)2]
Figure 5.10 FT-IR Spectra of 2H-2H-FPIMP
146
Figure 5.11 FT-IR Spectra of 2Cl-2Cl-FPIMP
Figure 5.12 FTIR Spectra of [Cu (2H-4H-FPIMP)2] (ClO4)2
147
Figure 5.13 FTIR Spectra of [Co (2H-4H-FPIMP)2]
Figure 5.14 FTIR Spectra of [Ni (2H-4H-FPIMP)2]
148
Figure 5.15 EPR Spectra of [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
149
Figure 5.16 Cyclic voltammogram of [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
Figure 5.17 Cyclic voltammorgam of [Co (2Cl-4Cl-FPIMP)2]
150
Figure 5.18 Cyclic voltammogram of [Ni (2Cl-4Cl-FPIMP)2]
Figure 5.19 Cyclic voltammogram of [Ni (2Br-4Cl-FPIMP)2]
151
Figure 5.20 Zone of inhibition of
2Br-4Cl-FPIMP against
Staphylococcus aureus
Figure 5.22 Zone of inhibition of
[Cu (2Br-4Cl-FPIMP)2] (ClO4)2
against Staphylococcus aureus
Figure 5.21 Zone of inhibition of
2Br-4Cl-FPIMP against
Proteus mirabilis
Figure 5.23 Zone of inhibition of
[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
against Proteus mirabilis
152
Figure 5.24 Plot of [DNA] / (εa-εf) vs [DNA] for the absorption spectral titration of
DNA ( 10, 20, 30, 40, 50 and 60 µM ) with [Cu(2Br-4Cl-FPIMP)2](ClO4)2 ( 5 µM )
153
Table 5.1 Electronic spectral data
Complex
λmax*
(nm)
(1) [Cu (2H-4H-FPIMP)2] (ClO4)2
265 a, 448 c
(2) [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
287 a, 408 c
(3) [Cu (2Br-4Cl-FPIMP)2] (ClO4)2
289 a, 400 c
(4) [Co (2H-4H-FPIMP)2]
272 a, 390 c
(5) [Co (2Cl-4Cl-FPIMP)2]
269 a, 448 c
(6) [Co (2Br-4Cl-FPIMP)2]
276 a, 411 c
(7) [Ni (2H-4H-FPIMP)2]
284 a, 348 b, 390 c
(8) [Ni (2Cl-4Cl-FPIMP)2]
276 a, 314 b, 426 c
(9) [Ni (2Br-4Cl-FPIMP)2]
275 a, 311 b, 427 c
* In dimethyl sulphoxide
a
π–π * transition
b
n–π * transition
c
d-π * Metal-Ligand Charge Transfer (MLCT) transition
154
Table 5.2 FT-IR spectral data (cm-1) of the ligands and CuII / CoII / NiII complexes
υ (M–O)
υ (M–N)
υ (C=N)
υ (C–O)
υ (O–H)
(M=Cu/Co/Ni)
(M=Cu/Co/Ni)
2H-4H-FPIMP
1617
1452
3464
–
–
2Cl-4Cl-FPIMP
1637
1427
3454
–
–
2Br-4Cl-FPIMP
1637
1435
3430
–
–
[Cu (2H-4H-FPIMP)2] (ClO4)2
1607
1497
–
541
495
[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
1614
1504
–
542
464
[Cu (2Br-4Cl-FPIMP)2] (ClO4)2
1618
1489
–
559
490
[Co (2H-4H-FPIMP – 4H 6H)2]
1610
1500
–
519
494
[Co (2Cl-4Cl-FPIMP – 4Cl 6Cl)2]
1620
1504
–
528
465
[Co (2Br-4Cl-FPIMP - 4Cl 6Br)2]
1616
1502
–
521
487
[Ni (2H-4H-FPIMP – 4H 6H)2]
1610
1509
–
517
476
[Ni (2Cl-4Cl-FPIMP – 4Cl 6Cl)2]
1618
1502
–
540
488
[Ni (2Br-4Cl-FPIMP – 4Cl 6Br)2]
1617
1504
–
547
487
Compound
155
Table 5.3 ESR spectral data of Copper(II) complexes
A║×10-4(cm-1) A⊥×10-4(cm-1)
g║
g⊥
giso
[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
2.28
2.09
2.07
147
68
[Cu (2Br-4Cl-FPIMP)2] (ClO4)2
2.34
2.05
2.15
129
52
Complex
156
Table 5.4 Electrochemical redox data of CuII / CoII / NiII complexes *
Complex
Metal based
oxidation
(mV)
Metal based
Oxidation
(mV)
Ligand based
Reduction
(mV)
Metal based
Reduction
(mV)
MIV/MIII
(M=Cu/Co/Ni)
MIII/MII
(M=Cu/Co/Ni)
MII/MI
(M=Cu/Co/Ni)
MII/MI
(M=Cu/Co/Ni)
∆Ep
E1/2
∆Ep
E1/2
EPc
∆Ep
E1/2
[Cu (2H-4H-FPIMP)2] (ClO4)2
–
–
768
493
–
320
–694
[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
–
–
760
486
–591
360
–699
[Cu (2Br-4Cl-FPIMP)2] (ClO4)2
–
–
788
471
–659
312
–707
[Co (2H-4H-FPIMP)2]
–
–
42
875
–
308
–692
[Co (2Cl-4Cl-FPIMP)2]
92
973
634
495
–
326
–739
[Co (2Br-4Cl-FPIMP)2]
122
973
636
509
–
330
–743
[Ni (2H-4H-FPIMP)2]
130
1000
82
289
–616
240
–622
[Ni (2Cl-4Cl-FPIMP)2]
230
1057
596
484
–555
196
–706
[Ni (2Br-4Cl-FPIMP)2]
224
1051
576
513
–665
304
–683
*Solvent – Dimethyl sulphoxide ; supporting electrolyte – [Bu4N]ClO4 (TBAP) 0.1M ;
reference electrode – SCE ; E½ = 0.5(Epa + Epc) where Epa and Epc are anodic and cathodic
peak potential respectively ; ∆Ep = Epa – Epc ; scan rate = 100 mVs-1.
157
Table 5.5 Antibacterial activity data of Schiff base ligands and Copper(II) complexes
Diameter of inhibition zone (mm)
Compound
Staphylococcus aureus
0.15%
0.2%
0.25%
2H-4H-FPIMP
─
─
─
2Cl-4Cl-FPIMP
─
─
2Br-4Cl-FPIMP
─
[Cu (2H-4H-FPIMP)2] (ClO4)2
Proteus mirabilis
0.2%
0.25%
─
─
─
─
8
9
10
9
10
9
10
10
9
10
11
10
11
12
[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2
15
17
20
15
15
18
[Cu (2Br-4Cl-FPIMP)2] (ClO4)2
15
16
19
15
16
17
Control ( Dimethyl sulphoxide )
─
─
─
─
─
─
Standard ( Ampicillin )
30
32
34
22
23
24
Symbol “─” denotes no activity.
0.15%