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112 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 113 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). 114 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 115 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 116 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. 117 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. 118 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. 119 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)°. 120 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) 122 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°. 123 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. 124 125 126 127 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. 128 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 129 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. 130 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. 131 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 132 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 133 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. 134 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]. 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Biochem. 85 (2001) 291. 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%