chapter v cu(ii), ni(ii) and co(ii) schiff bases complexes...

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- 5Y-

Salicylaldehyde 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

112

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

115

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.

116

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 4-

fluoroaniline (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).

C

HO

CN

HO

X

Y

Y

X

F

OH

+

H

F

MeOH

1 1:

X = H & Y = H ( Stirring, 2h )X = Cl & Y = Cl ( Stirring, 1h )X = Br & Y = Cl ( Reflux, 3h )

NH2

Scheme 5.1 Synthesis of multisubstituted Schiff base ligands.

118

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)°.

119

Figure 5.5 the ORTEP representation of the molecule with thermal ellipsoids at the 50% probability level

120

Figure 5.6 Packing of molecules in the unit cell (Intermolecular interactions are shown with dashed lines)

121

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°.

122

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.

123

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.

127

CN

CN

HO

Y

X

X

C

1 : 2

+

4 h

O

H

H

F

F

X

Y

X = H / Cl /BrY = H / Cl

X = H / Cl / BrY = H / Cl

N

F

Y

O

H

Reflux

Cu

Cu(ClO4)2 . 6H2O

(ClO4)2

MeOH : DMSO

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

128

separated on slow cooling, filtered, washed with MeOH and dried in vacuo over

anhydrous CaCl2.

CN

CN

HO

Y

X

X

C

1 : 2

+

5 h

O

H

H

F

F

X

Y

X = H / Cl /BrY = H / Cl

X = H / Cl / BrY = H / Cl

N

F

Y

O

H

Reflux

Ni(OAc)2 . 4H2O

Co(OAc)2 . H2O(or)

M

M = Ni / Co

MeOH

Scheme 5.3 Synthesis of Ni(II) / Co(II) complexes.

129

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.

130

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 1497-

1509 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

131

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

132

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 π-

electron 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.

133

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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140

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)

141

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)

142

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)

143

Figure 5.7 Electronic spectra of [Cu (2H-4H-FPIMP)2] (ClO4)2

Figure 5.8 Electronic spectra of [Co (2Cl-4Cl-FPIMP)2]

144

Figure 5.9 Electronic spectra of [Ni (2Cl-4Cl-FPIMP)2]

Figure 5.10 FT-IR Spectra of 2H-2H-FPIMP

145

Figure 5.11 FT-IR Spectra of 2Cl-2Cl-FPIMP

Figure 5.12 FTIR Spectra of [Cu (2H-4H-FPIMP)2] (ClO4)2

146

Figure 5.13 FTIR Spectra of [Co (2H-4H-FPIMP)2]

Figure 5.14 FTIR Spectra of [Ni (2H-4H-FPIMP)2]

147

Figure 5.15 EPR Spectra of [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2

148

Figure 5.16 Cyclic voltammogram of [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2

Figure 5.17 Cyclic voltammorgam of [Co (2Cl-4Cl-FPIMP)2]

149

Figure 5.18 Cyclic voltammogram of [Ni (2Cl-4Cl-FPIMP)2]

Figure 5.19 Cyclic voltammogram of [Ni (2Br-4Cl-FPIMP)2]

150

Figure 5.20 Zone of inhibition of Figure 5.21 Zone of inhibition of 2Br-4Cl-FPIMP against 2Br-4Cl-FPIMP against Staphylococcus aureus Proteus mirabilis

Figure 5.22 Zone of inhibition of Figure 5.23 Zone of inhibition of

[Cu (2Br-4Cl-FPIMP)2] (ClO4)2 [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2 against Staphylococcus aureus against Proteus mirabilis

151

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 )

152

Table 5.1 Electronic spectral data

Complex

λmax*

(nm)

(1) [Cu (2H-4H-FPIMP)2] (ClO4)2

(2) [Cu (2Cl-4Cl-FPIMP)2] (ClO4)2

(3) [Cu (2Br-4Cl-FPIMP)2] (ClO4)2

(4) [Co (2H-4H-FPIMP)2]

(5) [Co (2Cl-4Cl-FPIMP)2]

(6) [Co (2Br-4Cl-FPIMP)2]

(7) [Ni (2H-4H-FPIMP)2]

(8) [Ni (2Cl-4Cl-FPIMP)2]

(9) [Ni (2Br-4Cl-FPIMP)2]

265 a, 448 c

287 a, 408 c

289 a, 400 c

272 a, 390 c

269 a, 448 c

276 a, 411 c

284 a, 348 b, 390 c

276 a, 314 b, 426 c

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

153

Table 5.2 FT-IR spectral data (cm-1) of the ligands and CuII / CoII / NiII complexes

Compound

υ (C=N)

υ (C–O)

υ (O–H)

υ (M–O)

(M=Cu/Co/Ni) υ (M–N)

(M=Cu/Co/Ni)

2H-4H-FPIMP

2Cl-4Cl-FPIMP

2Br-4Cl-FPIMP

[Cu (2H-4H-FPIMP)2] (ClO4)2

[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2

[Cu (2Br-4Cl-FPIMP)2] (ClO4)2

[Co (2H-4H-FPIMP – 4H 6H)2]

[Co (2Cl-4Cl-FPIMP – 4Cl 6Cl)2]

[Co (2Br-4Cl-FPIMP - 4Cl 6Br)2]

[Ni (2H-4H-FPIMP – 4H 6H)2]

[Ni (2Cl-4Cl-FPIMP – 4Cl 6Cl)2]

[Ni (2Br-4Cl-FPIMP – 4Cl 6Br)2]

1617

1637

1637

1607

1614

1618

1610

1620

1616

1610

1618

1617

1452

1427

1435

1497

1504

1489

1500

1504

1502

1509

1502

1504

3464

3454

3430

–

–

–

–

–

–

–

–

–

–

–

–

541

542

559

519

528

521

517

540

547

–

–

–

495

464

490

494

465

487

476

488

487

154

Table 5.3 ESR spectral data of Copper(II) complexes

Complex

g║

g⊥

giso

A║×10-4(cm-1)

A⊥×10-4(cm-1)

[Cu (2Cl-4Cl-FPIMP)2] (ClO4)2 [Cu (2Br-4Cl-FPIMP)2] (ClO4)2

2.28

2.34

2.09

2.05

2.07

2.15

147

129

68

52

155

Table 5.4 Electrochemical redox data of CuII / CoII / NiII complexes *

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)

Complex

∆Ep

E1/2

∆Ep

E1/2

EPc

∆Ep

E1/2




[Co (2H-4H-FPIMP)2]

[Co (2Cl-4Cl-FPIMP)2]

[Co (2Br-4Cl-FPIMP)2]

[Ni (2H-4H-FPIMP)2]

[Ni (2Cl-4Cl-FPIMP)2]

[Ni (2Br-4Cl-FPIMP)2]

–

–

–

–

92

122

130

230

224

–

–

–

–

973

973

1000

1057

1051

768

760

788

42

634

636

82

596

576

493

486

471

875

495

509

289

484

513

–

–591

–659

–

–

–

–616

–555

–665

320

360

312

308

326

330

240

196

304

–694

–699

–707

–692

–739

–743

–622

–706

–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.

156

Table 5.5 Antibacterial activity data of Schiff base ligands and Copper(II) complexes

Diameter of inhibition zone (mm) Staphylococcus aureus Proteus mirabilis Compound

0.15% 0.2% 0.25%

0.15% 0.2% 0.25%

2H-4H-FPIMP

2Cl-4Cl-FPIMP

2Br-4Cl-FPIMP




Control ( Dimethyl sulphoxide )

Standard ( Ampicillin )

─ ─ ─ ─ ─ ─

─ ─ ─ 8 9 10

─ 9 10 9 10 10

9 10 11 10 11 12

15 17 20 15 15 18

15 16 19 15 16 17

─ ─ ─ ─ ─ ─

30 32 34 22 23 24

Symbol “─” denotes no activity.

157

chapter v cu(ii), ni(ii) and co(ii) schiff bases complexes...

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