Novel Nickel (II), Copper (II) and Cobalt (II) Complexes of Schiff Bases A, D and E: Preparation, Identification, Analytical and Electrochemical Survey

Introduction

Schiff base was invented by Hugo-Schiff which is named after line,¹ They are defining as condensation results of the reaction between aldehyde or ketone with primary amine and theses are including azomethine functional group (HC=N), which is reversible reaction and commonly carry out in acid or base medium, or with high temperature.² Synthesis of Schiff base depends on the dehydration of carbinolamine which considers as the rate determination step of the reaction and this is the reason of using acid as catalyst.³  They comports as a Flexi-dentate ligand and generally coordinates by the oxygen phenolic group and the nitrogen atom of azometheine group.⁴ In Schiff base, azomethine N-atom and other donor atom such as O-atom act a necessary role in coordination chemistry and easily coordinate to metal atoms to obtain various complexes.^5,6,7 The aromatic aldehyde Schiff bases having effective conjugation and are more stable.⁸ It should not use high acid concentration due to the basicity of amine compounds, so if the amine protonation happens and turns to non-neucleophilic, the equilibrium is drawn to the left and this will ban carbinolamine formation. Thus, different Schiff bases preparation are best accomplished at modestly acidic PH.⁹ Schiff bases are considered as useful chelates due to their differentspecification such as easy synthesis, precise steric, structural varieties and electronic control on their structure. Lately, worthy utility have progressed in the preparation and identification of the complexes including Schiff bases for using as catalysts.^{10,11,12,13,14} Schiff base compounds have been vastly studied for their antibacterial, antifungal, antitumor activities.^15,16,17 CV defines as a kind of potentiodynamic electrochemical study. In CV technique, the relation between the potential of working electrode and time is linear.^18,19 CV is drawn between the current of the working electrode and the applied voltage.²⁰ CV is usually employed to explore the electrochemical features of an analyte in solution or of the compound which is adsorbed on the electrode surface.²¹ The advantage of CV is quite based on the analyte under survey. The substance should be redox active with in the potential window to be scanned.²² In reversible couples, the substances frequently shows irreversible cyclic voltammetry wave, which is watched when foremost substance can be recovered after a forward and reverse scan in the same cycle. In the spite of reversible couples are easier to analyze, they provide less information than more complexes wave forms.²³ The wave form of reversible couple is complex due to the united effects of polarization and diffusion, this variation mainly result from this effect, of analyte diffusion rates, the wave form is influenced too by the electron transfer rate.²⁴

Because of broad area of applications of the metal complexes of Schiff bases, we now report this present investigation which deals with new octahedral Cobalt(II), Copper(II) and Nickel(II) complexes with Schiff bases A, D and E. We have synthesized, characterized these compounds using CHN, FT-Infrared, electronic spectroscopy, ¹H and C¹³ NMR and studied analytical and electrochemical features, which were achieved by CV technique of Schiff base ligands as co-ligands for their coordination behavior in their complexes using various techniques.

Experimental Materials

All reagents, starting materials as well as solvents are employed to prepare Schiff bases in addition to their metal complexes were obtained from Aldrich, BDH, Fluka and Merck and were used as received. Tetrabutyl ammonium tetrafluroborate (TBATFB) which act as supporting electrolyte was purchased from Aldrich Chemical Co.

Instrumentation

All m.p. in degree Celsius were checked with a capillary devices and were recorded on electro thermal VeeGo Digital model VMP-D.Jenway. All the compounds were routinely characterized and checked by FT-IR, ¹H NMR and C¹³-NMR, CHN, electronic spectroscopies and CV. Infrared spectra were measured in KBr disc (400-4000 cm^-1) in Japan (a Shimadzu model 8400S FTIR spectrometer). ¹HNMR and C¹³-NMR were measured on Bruker 400 MHz spectrometer in Deuterochloro form and Deuterated dimethyl sulfoxide solvents. CHN analysis were recorded by Perkin CE-440 elemental analyzer. Electronic absorption spectra in aqueous solution were recorded by using UV-9200, Biotech Engineering Management Co.LTD (UK) Single beam in the region 230–1100 nm. Molar conductance was recorded on W.T.W conductivity Master LBR meter. Electrochemical properties of the synthesized metal complexes were examined by carried out the cyclic voltammetry (CV) experiments with CH Instruments, USA, Digi-Ivy (Model DY2300 Series-potenstiostate/ biopotensiostate, electrochemical analyzer), in absolute ethanol in the presence of tetrabutylammonium hexafluoroborate (TBATFB) (0.10 mol L⁻¹) as supporting electrolyte and about 10^-3 M complexes. All CV measurements were measured at r.t. (approximately 25^oC) with keeping N₂ atmosphere above the solution surface with coupling with Electrochemical System software (GPES version 4.7 for Windows). Typical model three electrodes array composed of Pt -wire working electrode, Pt counter electrode, and an Ag/AgNO₃ as reference electrode under nitrogen were utilized. Potentials were recorded against Ag/AgNO₃ and to eliminate interfering oxygen and purging the setup, before each experiment the solutions were bubbled with nitrogen gas. Before each measurement the working electrode was smoothed by sand paper to improve electrochemical sensitivity, providing active surface.

Synthesis of ligands (A, D and E)

The preparation method of ligands A, D, E was carried out according to method reported elsewhere by mixing equal amounts (1:1 mole ratio) each aldehyde or ketone with suitable amine.²⁵ They were synthesized in ethanol medium using glacial acetic acid as catalyst by the reaction from salicyladehyde, 2-bromo-4-phenol acetophenone or 1-([1,1′-biphenyl]-4-yl)-2-bromoethan-1-one as based ligands and two amines: 2,5-difluoro aniline or 1-amino-2,4-dibromo anthraquinone.

Synthesis of ligand A

(2.44 g, 20 mmol) salicylaldehyde in 10 ml warm ethanolic solution (40-50)^oC with (1-2) drops of glacial acetic acid were mixed with (4.64 g, 20 mmol) 2,5-difluoro aniline in ethanol solvent. Then the mixture was reflexed for 2 hours and cooled to r.t.. The mixture was filtered and the precipitate was washed and recrystallized with absolute ethanol and then dried to obtain yellow crystals. Yield: (4.59 g, 99%); m.p: 104-106^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3410, ѵ(C=N) 1604, ѵ(C=C) 1558, ѵ(C-N) 1371, ѵ(C-O) stretch 1281, ѵ(C-O) bending 1157; UV-Vis. spectrum, λ_max nm: π→π^* 266, n→π^* 320;  ¹H-NMR (400 MHz, DMSO-d⁶), δ(ppm): 12.74 (1H, s, O-H), 9.05 (1H, s, -CH=N-), 7.75 (1H, d, Ar J_HH =7.5 Hz ), 7.61 (1H, d, Ar J_HH =7.5 Hz), 7.50 (1H, t, Ar, J_HH =5 Hz), 7.33 (1H, t, Ar, J_HH =5 Hz), 7.17 (1H, s, Ar, J_HH =5 Hz), 6.88 (2 H, d, Ar, J_HH =5 H_z); ¹³C-NMR (100 MHz, DMSO-d⁶), δ(ppm): 166.25 (C-OH), 160.65 (-CH=N-), 159.70 (C-F), 157.66 (C-F), 152.80, 150.60, 133.75, 132.50, 118.80, 118.01, 117.50, 116.85, 114.35. Calculated for C₁₃H₉F₂NO: C, 66.95; H, 3.89; N, 6.01. Found: C, 67.00; H, 3961; N, 6.00.

Synthesis of ligand D

Same procedure as above is followed to synthesis ligand D by using the following weights: (1.22 g, 10 mmol) salicylaldehyde and (3.81 g, 10 mmol) 1-amino-2,4-dibromo anthraquinone). Red crystals; Yield: (1.69 g, 45%); M.p: 230-232^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3401, ѵ(C=O) 1683, ѵ(C=N) 1594, ѵ(C=C) 1488, ѵ(C-N) 1388, ѵ(C-O) stretch 1280, ѵ(C-O) bending 1194; UV-Vis. spectrum, λ_max nm: π→π^* 250, n→π^* 300; ¹H-NMR(400 MHz, DMSO-d⁶), δ(ppm): 9.75 (1H, s, O-H), 8.38 (1H, s,-CH=N-), 7.55 (1H, s, Ar), 7.44 (2H, t, Ar J_HH = 5Hz), 7.22 (2H, t, Ar J_HH = 5Hz), 7.01 (2H, d, Ar J_HH = 7.5 Hz), 6.89 (2H, d, Ar J_HH = 7.5 Hz), ¹³C-NMR (100 MHz, DMSO-d⁶), δ(ppm): 190.00 (C=O), 185.01 (C=O), 165.13 (C-OH), 163.01(-CH=N-), 145.51, 144.92, 130.32, 129.18, 127.54, 126.03, 126.30. Calculated for C₂₁H₁₁Br₂NO₃: C, 51.99; H, 2.29; N, 2.89. Found: C, 50.23; H, 2.433; N, 3.886.

Synthesis of ligand E

Same procedure as above is followed to synthesis ligand E by using the following weights: (2.75 g, 10 mmol) [1,1′-biphenyl]-4-carbonyl bromide and (3.81 g, 10 mmol) 1- amino-2,4-dibromo anthraquinone). White crystals; Yield: (3.24 g, 85%); m.p: 128-130^oC; FT-IR (cm^-1): ѵ(C=O) 1679, ѵ(C=N) 1590, ѵ(C=C) 1485, ѵ(C-O) 1284, ѵ(C-N) 1388; UV-Vis. spectrum, λ_max nm: π→π^* 230, n→π^* 319; ¹H-NMR(400 MHz, DMSO-d⁶), δ(ppm): 8.13 (2H, t, Ar J_HH = 5Hz), 8.00 (2H, d, Ar J_HH = 5Hz), 7.91 (2H, m, Ar),7.75 (4H, m, Ar), 7.47 (4H, m, Ar), 2.5 (2H, s, CH₂ group),¹³C-NMR (100 MHz, DMSO-d⁶), δ(ppm): 193.65(-C=N-), 191.04(C=O), 186.21(C=O), 144.88, 138.75, 138.11, 133.03, 132.45, 131.05, 130.31, 130.01, 129.40, 128.75, 128.10, 127.50, 127.33, 127.11, 126.70, 126.25, 65.00 (-CH₂-Br). Calculated for C₂₈H₁₆Br₃NO₂: C, 52.70; H, 2.53; N, 2.19 Found: C, 53.15; H, 2.952; N, 2.880.

Synthesis of Cobalt(II), Copper(II) and Nickel(II) complexes

Synthesis of the prepared metal complexes with ligands A, D and E were synthesized by the reaction between M(II) salt with the ligand under reflux.  

Synthesis of ACo complex. [Co(A)₂(CH₃COO)₂]

(5 ml) of the ligand A (0.232 g, 1 mmol) in ethanol is added  (5 ml) ethanolic solution of the (0.125g, 0.5 mmol) Co(CH₃COO)₂.4H₂O. The mixture was refluxed for 2 hours, then cooled. Brown precipitate was filtered and washed with absolute ethanol and then dried. Light brown precipitate; Yield: (0.172 g, 74%); D.p: 253^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3423, ѵ(C=N) 1604, ѵ(C=C) 1564, ѵ(C-N) 1415, ѵ(C-O) stretch 1240, ѵ(C-O) bending 1141, ѵ(Co-O) 525, ѵ(Co-N) 469; UV-Vis. spectrum, λ_max nm: π→π^* 286, n→π^* 310, LMCT 488, d-d 530. Calculated for C₃₀H₂₄F₄N₂O₆Co: C, 56.00; H, 3.76; N, 4.35 Found: C, 58.12; H, 3.532; N, 4.126.

Synthesis of ACu complex. [Cu(A)₂Cl₂]

The preparation method is similar to the above, using (0.085g, 0.5 mmol) CuCl₂.2H₂O instead of Co(CH₃COO)₂.4H₂O. Dark brown precipitate; Yield: (0.186 g, 80%); D.p: 288^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3435, ѵ(C=N) 1602, ѵ(C=C) 1552, ѵ(C-N) 1400, ѵ(C-O) stretch 1219, ѵ(C-O) bending 1135, ѵ(Cu-O) 541, ѵ(Cu-N) 473; UV-Vis. spectrum, λ_max nm: π→π^* 272, n→π^* 322, LMCT 475, d-d 967. Calculated for C₂₆H₁₈F₄N₂O₂CuCl₂: C, 51.97; H, 3.02; N, 4.66 Found: C, 52.415; H, 2.770; N, 4.842.

Synthesis of ANi complex. [Ni(A)₂(CH₃COO)₂]

The preparation method is similar to the ACo, using (0.124g, 0.5 mmol) Nickel acetate tetra hydrate instead of Cobalt acetate tetra hydrate. Green precipitate; Yield: (0.153 g, 66%); D.p: 130^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3438, ѵ(C=N) 1601, ѵ(C=C) 1587, ѵ(C-N) 1379, ѵ(C-O) stretch 1224, ѵ(C-O) bending 1142, ѵ(Cu-O) 534, ѵ(Cu-N) 464; UV-Vis. spectrum, λ_max nm: π→π^* 278, n→π^* 310, LMCT 434, d-d 731. Calculated for C₃₀H₂₄F₄N₂O₆Ni: C, 56.02; H, 3.76; N, 4.36 Found: C, 56.675; H, 3.556; N, 4.491.

Synthesis of DCo complex. [Co(D)

The preparation method is similar to the ACo, using ligand D (0.49 g, 1 mmol) instead of ligand A. Red precipitate; Yield: (0.358 g, 73%); D.p: 240^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3439, ѵ(C=N) 1564, ѵ(C=O) 1546, ѵ(C=C) 1417, ѵ(C-N) 1340, ѵ(C-O) stretch 1269, ѵ(C-O) bending 1131, ѵ(Cu-O) 533, ѵ(Cu-N) 477; UV-Vis. spectrum, λ_max nm: π→π^* 260, n→π^* 310, LMCT 488. Calculated for C₄₆H₂₈Br₄N₂O₁₀Co: C, 48.16; H, 2.46; N, 2.44 Found: C, 50.087; H, 2.774; N, 2.345.

Synthesis of DCu complex. [Cu(D)₂Cl₂]

The preparation method is similar to the ACu, using ligand D (0.49g, 1 mmol) instead of ligand A. Red precipitate; Yield: (0.421 g, 86%); D.p: 233^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3437, ѵ(C=O) 1633, ѵ(C=N) 1587,  ѵ(C=C) 1505, ѵ(C-N) 1383, ѵ(C-O) stretch 1265, ѵ(C-O) bending 1122, ѵ(Cu-O) 560, ѵ(Cu-N) 480; UV-Vis. spectrum, λ_max nm: π→π^* 260, n→π^* 320, LMCT 470, d-d 960. Calculated for C₄₂H₂₂Br₄N₂O₆CuCl₂: C, 45.66; H, 2.01; N, 2.54 Found: C, 46.078; H, 1.984; N, 2.621.

Synthesis of DNi complex. [Ni(D)₂(CH₃COO)₂]

The preparation method is similar to the ANi, using ligand D (0.49g, 1 mmol) instead of ligand A. Gray precipitate; Yield: (0.431 g, 88%); D.p: 124^oC; FT-IR (cm^-1): ѵ(O-H) stretch 3444, ѵ(C=N) 1541, ѵ(C=C) 1494, ѵ(C-N) 1421, ѵ(C-O) stretch 1262, ѵ(C-O) bending 1120, ѵ(Cu-O) 555, ѵ(Cu-N) 475; UV-Vis. spectrum, λ_max nm: π→π^* 230, n→π^* 320, LMCT 429, d-d 738. Calculated for C₄₆H₂₈Br₄N₂O₁₀Ni: C, 48.17; H, 2.46; N, 2.44 Found: C, 49.641; H, 2.567; N, 2.965.

Synthesis of ECo complex. [Co(E)₂(CH₃COO)₂]

The preparation method is similar to the ACu, using ligand E (0.64 g, 1 mmol) instead of ligand A. Pink precipitate; Yield: (0.346 g, 54%); D.p: 230^oC; FT-IR (cm^-1): ѵ(C=O) 1687, ѵ(C=N) 1599, ѵ(C=C) 1442, ѵ(C-N) 1336, ѵ(Co-O) 540, ѵ(Co-N) 471; UV-Vis. spectrum, λ_max nm: π→π^* 213, n→π^* 290, LMCT 478. Calculated for C₆₀H₃₈Br₆N₂O₈Co: C, 49.59; H, 2.64; N, 1.93 Found: C, 51.013; H, 2.687; N, 2.237.

Synthesis of ECu complex. [Cu(E)₂Cl₂]

The preparation method is similar to the ACu, using ligand E (0.64g, 1 mmol) instead of ligand A. red precipitate; Yield: (0.454 g, 71%); D.p: 132^oC; FT-IR (cm^-1): ѵ(C=O) 1687, ѵ(C=N) 1599, ѵ(C=C) 1483, ѵ(C-N) 1383, ѵ(Cu-O) 562, ѵ(Co-N) 474; UV-Vis. spectrum, λ_max nm: π→π^* 240, n→π^* 330, LMCT 467, d-d 954. Calculated for C₅₆H₃₂Br₆N₂O₄CuCl₂: C, 47.68; H, 2.29; N, 1.99 Found: C, 48.932; H, 2.936; N, 2.168.

Synthesis of ENi complex. [Ni(E)₂(CH₃COO)₂]

The preparation method is similar to the ACu, using ligand E (0.64g, 1 mmol) instead of ligand A. red precipitate; Yield: (0.403 g, 63%); D.p: 130^oC; FT-IR (cm^-1): ѵ(C=O) 1665, ѵ(C=N) 1597, ѵ(C=C) 1412, ѵ(C-N) 1364, ѵ(Cu-O) 555, ѵ(Co-N) 470; UV-Vis. spectrum, λ_max nm: π→π^* 225, n→π^* 300, LMCT 426, d-d 744. Calculated for C₆₀H₃₈Br₆N₂O₈Ni: C, 49.60; H, 2.64; N, 1.93 Found: C, 50.489; H, 2.731; N, 1.964.

Results and Discussion

Synthesis and Characterization

New Schiff bases A, D, E were prepared by combination of aldehyde or ketone and suitable amine as described below in experimental procedures (Scheme 1). Their structures were confirmed by elemental analysis, solubility test, conductance measurements and spectral studies (H¹-NMR, C¹³-NMR,FT-IR and UV-Vis spectroscopy), determination of ligand-metal bonded ratio and cyclic voltammetry. Scheme 2 illustrates the reaction of Schiff base ligands A, D and E with Cobalt acetate tetra hydrate, Copper chloride di hydrate and Nickel acetate tetra hydrate which gave solids compounds [ACo, ACu and ANi], [DCo, DCu and DNi] and [ECo, ECu and ENi]. All these compounds were stable and they are isolated in good yields. Their analytical data are corresponding to their experimental and composition section.

Scheme 1: Synthetic of Schiff bases A, D, E (Scheme 2): Synthetic of Schiff bases A, D, E complexes. FT-IR spectral studies. Click here to View Scheme

Scheme 2: Synthetic of Schiff bases A, D, E complexes. Click here to View Scheme

 

The infrared data provide considerable sign of the formula of ligands A, D and E and their metal complexes. The FT-infrared spectra gives the worthy information relating to the behavior of functional groups coordinated to the M(II) ions. However, the existence of a strong and sharp peak at (1590-1604 cm^-1) which is related to C=N stretching frequency and sharp peak at (1371-1388 cm^-1) due to C-N stretching frequency in ligands confirm the formation of ligands. These results are in good agreement with another studies reported  elswhere.^26,27,28 As compared with the corresponding starting materials aldehyde or ketone with amines, the absence of peak around 1690 cm^-1 of C=O stretching band in ligands and their complexes consider as good indication to reaction and formation of Schiff bases. The downward shift of υ (C=N) band by (7-53 cm^-1), the downward shifts of υ (C-N) band by (9-48) cm^-1 in all prepared metal complexes suggested the coordination of nitrogen in (-CH=N-) group with metal ion center and formation of M-N band.^{29, 30} A medium peaks at 3410 and 3401 cm^-1 in  IR spectra of Schiff base A and D are due to υ (O-H) stretch. The same spectra showed strong bands in 1281 and (1157- 1194 cm^-1) is assigned to υ (C-O) stretch and υ (C-O) bending respectively. The change of the position of υ (O-H) and downward shift of υ (C-O) stretch and υ (C-O) bending by (13-43 cm^-1), (11-78 cm^-1), (15-74 cm^-1) respectively in the complexes suggested coordination of the (O-H) phenolic in Schiff base A and D with metal ion center and formation of M-O band.^{31, 32} A strong peak at 1679 cm^-1 in FT-infrared spectrum of ligand E was due to υ (C=O) stretching frequency. The change of the position of υ (C=O) in FT-IR spectra of metal complexes of Schiff base E as compared with free ligand is considered good indication to take part of O-atom in carbonyl group in the coordination sphere. Furthermore, the stretching of two new bands, M(II)-O and M(II)-N appeared in lower wavelength region ranging 525-562 and 464-480 cm^-1 respectively. Which also enhance the suggestion of the coordination through nitrogen atom from (-CH=N-) group from Schiff base ligands A, D and E in their complexes (ACo, ACu and ANi), (DCo, DCu and DNi) and (ECo, ECu and ENi). In the other side, the oxygen atom from (O-H) group from A and D ligands and oxygen atom from C=O group in ligand E, take part of the coordination sphere. The important FT-IR bands for Schiff bases A, D and E and their Cobalt(II), Copper(II) and Nickel(II) complexes are given in Table (1).

Table 1: Selected FT-IR bands (cm^-1) for Schiff bases A, D and E and their Cobalt(II), Copper(II) and Nickel(II) complexes.

 

Electronic Spectral Studies

The UV-Vis spectra taken in range of (210-1100 nm) in ethanol solution of ligands A, D and E and their metal complexes and electronic data are presented in Table 2. Data of ligands A, D and E show the same behavior in 210-400 nm. They exhibit two intense absorption bands at short wavelengths, (230-266) and (300-320 nm) which are assigned to aryl (π→π^* transition),azomethine and carbonyl groups (n→π^* transition) respectively. ^33,34,35  The UV-Vis spectra of ligands A, D and E are prevailed by intra-ligand transitions related to aryl ring and azomethine group parts. UV-Vis data of the metal complexes show variation of theelectronictransitions in UV region to (213-286) and (290-330 nm) upon coordination which are corresponding to π→π^* and n→π^* respectively. This is due to the coordination of the Cobalt(II), Copper(II) and Nickel(II) ions with ligands A, D, E via azomethine and carbonyl groups. The new single charge transfer (LMCT) band is assigned in Copper(II) and Nickel(II) complexes at (426-475 nm). In accordance with previous articles of Copper(II) complexes, band centered in (476-434 nm) 21000–23000 cm^-1 is due to phenolate O→Cu(II) LMCT transition.³⁶ Further, after complexation new peaks (Two peaks of Cobalt(II) complexes, a single peak of Copper(II) complexes and  three bands for Ni(II) complexes) appear in UV-Visible region. UV-Vis of Cobalt(II) complexes, ACo, DCo and ECo show two peaks (915-933 nm), (474-488 nm) assigned to ⁴T_1g(F)→⁴T_2g(F) and ⁴T_1g(F)→⁴T_2g(P) transitions respectively. New peaks are attributed to high spin octahedral Cobalt(II) complexes. The ⁴T_1g(F)→⁴A_2g(F) is not observed in the spectra may be it has been shielded by the broad band of ⁴T_1g(F)→⁴T_2g(P) transition. This is similar to study reported elsewhere for Co(II) complex which exhibit two absorption bands fall of 917 nm and 435 nm attributed to ⁴T_1g(F)→⁴T_2g(F) and ⁴T_1g(F)→⁴T_2g(P).³⁷ A single band in ACu, DCu and ECu complexes at (954-967 nm) is assigned to T_2g→e_g transition supporting a regular six coordinate octahedral Cu(II) complexes.³⁸ While three spin allowed transitions in ANi, DNi and ENi are attributed to ³A_2g→³T_2g, ³A_2g→³T_1g(F) and ³A_2g→³T_1g(p) ranging (1060-1084 nm), (731-744 nm) and (475-491 nm) respectively which support six coordinate Oh Nickel(II) complexes, which is in usual scale of reported octahedral complexes.³⁷  Figures (1 and 2) show the electronic spectra of ACu and ENi respectively.

Table 2: Electronic data (nm) of ligands A, D, E and their Cobalt(II), Copper(II) and Nickel(II) complexes.       

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