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Metal Complexes Derived from Mixed Azo-Linked Schiff-Base Ligandwith Dithiocarbamate Derivative: Formation, Spectral Characterization and Biological Study

Ahmed K. Hussien, Enaam I. Yousif, Hasan A. Hasan and Riyadh M. Ahmed

.Department of  Chemistry, College of  Education for Pure Science(Ibn Al-Haitham), University of Baghdad, P.O. Box 4150, Adhamiyah, Baghdad, Iraq

Correspoding Author E-mail: enaamismail@yahoo.com

DOI : http://dx.doi.org/10.13005/ojc/340340

Article Publishing History
Article Received on : December 07, 2017
Article Accepted on : June 06, 2018
Article Published : 22 Jun 2018
Article Metrics
ABSTRACT:

The study includes preparation and characterisation of mixed azo-linked Schiff-base and DTCs ligands and their complexes. The starting material was isolated from the mixing of naphthyl amine diazonium salt with 2-amino phenole in a 1:1 mole ratio in water. In this work, the formation of azo-linked Schiff-base and DTCs ligands are reported. Ligand of the azo-linked Schiff-base was achieved by the reaction of starting material with 4-(dimethylamino)benzaldehyde) (HL1). The DTCs was isolated by the reaction of (C6H5)2NH with carbon disulphide in potassium hydroxide (L2). The complexes were prepared by mixing the azo-linked Schiff-base ligand and DTC ligand with the metal salts; CoII, NiII, ZnIIand CdII in a 1:1:1 mole ratio. Ligands and complexes were characterised by analytical and spectroscopic analyses including; microanalysis, chloride content, thermal analysis, magnetic susceptibility for complexes, conductance, FTIR, UV-Vis and 1H-NMR spectroscopy. Physico-chemical techniques indicated complexes demonstrated four and six coordinate structures in the solid and solution sate. Biological activity of the ligands and their metal complexes were screened for their antimicrobial activity against four bacterial species (Escherichia coli and  Enterobacter (G-)), (Bacillus stubtilis and  Staphylococcus aureus (G+)).

KEYWORDS:

Biological Activity; Dithiocarbamates (DTCs); Metal complexes; Mixed ligands; Thermal Analysis

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Hussien A. K, Yousif E. I, Hasan H. A. Ahmed R. M. Metal Complexes Derived from Mixed Azo-Linked Schiff-Base Ligandwith Dithiocarbamate Derivative: Formation, Spectral Characterization and Biological Study. Orient J Chem 2018;34(3).


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Hussien A. K, Yousif E. I, Hasan H. A. Ahmed R. M. Metal Complexes Derived from Mixed Azo-Linked Schiff-Base Ligandwith Dithiocarbamate Derivative: Formation, Spectral Characterization and Biological Study. Orient J Chem 2018;34(3). Available from: http://www.orientjchem.org/?p=46856


Introduction

Azo compounds are an interesting materials that have shown a range of applications including; food technology, analytical chemistry, pharmaceutical application and dyeing or textile industry. Their role in coloring approach has been widely investigated and a range of compounds are fabricated.1 The biological activity of azo-compounds allowed them to be used in the treatment of textile materials, also azo-compounds are well known for their medicinal importance and have shown a variety of applications as antitumor, antibacterial, antiseptics and antineoplastics.2 Variety of ligands type Schiff-base and their metal complexes have been isolated, these compounds have very flexible and diverse structures, therefore their properties have been studied.3 Dithiocarbamates (DTCs) are class of organic compounds that are capable to chelate to metal ions.4,5 DTCs compounds have a significant role in coordination chemistry. This may due to the metal ion stabilizationability in many oxidation states, and permitting the metal ion to implement its desirable structure.6 DTCs have shown asignificant biological activity including their role as antibacterial, antitumor and antifungal agents. They have other potential applications in materials science and supramolecular chemistry.7,8 In our research, we report here the preparation of mixedazo-linked Schiff-base andDTCs ligands and their metal(II) dithiocarbamate complexes.

Experimental

All chemicals in this work are commercially available and used as received.Solvents were distilled using appropriate protocol before use.

Physical Measurements

Elemental micro-analyses (carbon, hydrogen, nitrogen and sulphur) for ligand and its metal complexes were conducted on a Euro EA 3000.Electrothermal Stuart SMP40 apparatus was used to record melting points. FT-IR spectra were recorded as potassium bromidediscs with a Shimadzu 8300s in the range 4000-400 cm-1 and as CsI discs in the range 400-200 cm-1. UV-Vis spectra were obtained with 10-3 M solutions between 200-1100 nm in dimethylsulfoxide (DMSO) spectroscopic grade solvent at 25°C using a Perkin-Elmer spectrophotometer Lambda. TGA was carried out using a STA PT-1000 Linseis. NMR spectra (1H-NMR) were acquired in DMSO-d6 and CDCl3 using aBrucker-400 MHz and a Brucker-300 with tetramethylsilane (TMS). A Shimadzu (A.A) 680 G atomic absorption spectrophotometer was implemented to determine metal content in complexes. Conductivity measurements were performed using a Jenway 4071 digital conductivity meter with DMSO solutions at room temperature. Chloride was determined using potentiometer titration method on a (686-Titro processor-665Dosimat-Metrohm Swiss). A magnetic susceptibility balance (Sherwood Scientific) was used to determine magnetic moments of complexes.

Synthesis

Preparation of the Precursor

The compound was prepared according to the literature9,10 1-naphthyl amine (1g, 6.98mmol) was dissolved in H2O(10ml) and Hydrochloric acid Conc. (2.14ml, 60.98mmol) mixture with stirring, a clear solution was obtained. Temperature of (0–5)°C have been kept, then aqueous solution of sodium nitrite (0.48g, 6.98mmol) dissolved in (5ml) water,was dropwise slowly added, keeping the temperature below 5°C, followed by mixture stirring for 1hr using ice bath, then little amount of urea was added, the pH was  adjusted to (6–7) using sodium acetate [solution(1)]. H2NC6H4OH (0.762g, 6.98mmol) was dissolved in (12ml) KOH(10mmol) aqueous solution, cooled by ice bathto (0–5)°C [solution(2)]. Gradually the last solution was mixed with cooling with (solution1), the mixture resulted was stirredat (0–5)°C continually for 2hrs, the precipitate resulted was then filtered using acidification, cold H2Oused to wash several times after drying, a brown solid precipitate was obtained, Yield:1.35g (73.7%), melting point132°C.

Synthesis of free ligands

Preparation of [HL1]

The compound was prepared according to the literature.12

A solution of the derivative[2-amino-6-(naphthalen-1-yldiazenyl)phenol] (1g, 3.798mmol) in 25ml ethanol was mixed with(0.566g, 3.798mmol) of (CH3)2NC6H4CHO dissolved in (10ml) ethanol. After adding glacial acetic acid (3-5) drops, the mixture resulted was refluxed for 2hrs., filtered off, and after washingby ethanol and drying; it was obtained alight brown product. The product solid was recrystallized using EtOH. Yield:1.23g, 82.5%, melting point(190192°C).

Preparation of [L2]

The compound was prepared according to the literature.13

Ethanolic solutionof KOH (1.32g, 23.6mmol, 4eq) was added to solution of diphenyl amine (1g, 5.90mmol) dissolved in(10mL) ethanol. The resulted mixture was stirredkeeping the temperature at (0-5), dropwise with stirring it was added carbon disulphide solution(1.34g, 17.7mmol, 3eq) keeping the temperatureat 0°C for 2 hrs. The solid DTCS yellow salt was obtained, Yield :1.48g, 88.6%. Melting point (238- 240°C).

Synthesis of complexes

A one pot approach reported in14 was used to prepare the mixed ligand metal complexes.

Preparation of [CoII(HL1)(L2)(H2O)2]

To a mixture of HL1 (0.2g, 0.506mmol) dissolved in (10 ml) was added (0.0568g, 1.0139mmol) of potassium hydroxide dissolved in 10 ml ethanol. While, the solution was allowed to stirring, a mixture of CoII salt (0.120g, 0.506mmol) in 10ml ethanol with (0.143g, 0.506mmol) of dithocarbamte ligand (L2) was added to the above solution. The reaction mixture was kept stirring for two hrs, during which time agreen product was filtered off. Washed with absolute ethanol and recrystallized from ethanolto give the pure product. Yield: 0.187g, 50.33%, (Dec.over 320).

Preparation of  NiII,  ZnII and CdII Complexes

An analogues method to that reported for the synthesis of CoII complex was implemented to prepare NiII, ZnII, and CdIImixed ligands complexes. Table 1 displays the physical properties of the complexes and their reactant amount.

Table 1: Melting points, yields, metal salts quantities and colours of ligands and  thiercomplexes

Compound Dec. (°C) Weight of metal salt(g) Weight of complex(g) Yield (%) Colour
[Co(L1)(L2)(H2O)2] Over 320* 0.123 0.188 51 Light green
[Ni(L1)(L2)] Over 320* 0.121 0.172 49 Green
[Zn(L1)(L2)(H2O)2] Over 320* 0.07 0.148 40 Dark brown
K2[Cd(L1)(L2) Cl2] Over 320* 0.103 0.185 41 light yellow

 

Results and Discussion

Synthesis

The precursor was obtained using a standard azo dye approach. The reaction of naphthyl amine diazonium salt with 2-amino-phenole in a 1:1 mole ratio in water solvent gave the required compound, see Scheme 1. Two sorts of ligands were prepared; (i) Azo-linked Schiff-base ligand, which isolated by reaction of the precursor with (CH3)2NC6H4CHO and (ii) DTCs ligand that obtained from the reaction of (C6H5)2NH with carbon disulphide using KOH base (Schemes 2 and 3). The complexes were prepared by mixing the ligands with the metal salts in a 1:1:1 mole ratio (Scheme 4).A range of analytical and spectroscopic techniques were used to confirm the entity of compounds including; CHNS, FT-IR, UV-Vis, magnetic susceptibility and 1H-NMR spectra. The infra-red spectrum of [HL1], Fig.(1), exhibited bands  at 3423 and 2978cm–1 attributed to the OH phenolic group15,16 and ν(C–H)aliphatic stretching, respectively. Bands related to ν(C=N) imine and ν(C–N) are observed at 1630 and 1257cm–1, respectively. The formation of Schiff-base ligand  can be indicated by the absence of amine (NH2) and aldehydic CHO bands and appearance of the new imine (C=N) band in the ligand spectrum.17-19 Band related to stretching u(N=N) azo group are detected at 1460 cm–1.16,20 The FT-IR spectrum of [L2] is displayed in Fig.(2). The ν(C-N) of (N-CS2) moiety shows a band at 1471 cm-1.21 The spectrum indicates a couple of new bands at (894) and (1047) cm-1, which designated to νs(CS2) and  νas(CS2) respectively.22 The characteristic bands are summarised in (Table 3). The 1H-NMR spectrum of [HL1], Fig.(7), displays peak related to the azomethine group at δ=10.1ppm (H,s,N=C–H).23 Chemical shift at δ= 10.809 ppm (OH, S, H) correlated to the phenolic proton. The spectrum indicated that the non-equivalent two CH3 groups appeared at δ= 2.2 and 3.3-3.4ppm (2CH3, S, 6H). That may probably resulted from the position alternation of the two CH3 groups in the proposed structure of the molecule. An averaged symmetrical spectrum may resulted from rapid rotation process. On the other hand, two non-equivalent conformations may resulted from the slow rotation. The 1H-NMR spectrum of [L2] is depicted in (Fig. 8). The spectrum shows peaks at δ= 5.561ppm (2H, m) (C1, 1`, 5, 5`-H),  δ= 6.789-6.805 ppm (2H, m) (C3, 3`-H) and δ= 7.685-7.694 ppm (2H, m) (C2, 2`, 4, 4`-H) attributed to the aromatic ring protons. The complexes are air stable solid. The entity of new complexes was confirmed by elemental analysis, FT-IR, electronic spectra and magnetic susceptibility. The analytical data (Table 2) support the proposed formulae. The molar conductance of the complexes in DMSO solvents is indicative of non-electrolyte and 1:2 electrolyte behaviour.24,25

Scheme 1: Preparation path for Precursor.

Scheme 1: Preparation path for Precursor.

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Scheme 2: Preparation route for ligand [HL1]

Scheme 2: Preparation route for ligand [HL1]


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Scheme 3: Preparation route of ligand [L2]

Scheme 3: Preparation route of ligand [L2]



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Scheme 4: Preparation route of mixed ligand complexes.

Scheme 4: Structure of mixed ligand complexes



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Figure 1: FT-IR spectrum of ligand [HL1]

Figure 1: FT-IR spectrum of ligand [HL1]


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Figure 2: FT-IR spectrum of ligand [L2]

Figure 2: FT-IR spectrum of ligand [L2]


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Figure 3: FT-IR spectrum of [Co(L1)(L2) (H2O)2]complex

Figure 3: FT-IR spectrum of [Co(L1)(L2) (H2O)2]complex



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Figure 4: Electronic spectrum of [HL1]

Figure 4: Electronic spectrum of [HL1]


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Figure 5: Electronic spectrum of [L2]

Figure 5: Electronic spectrum of [L2]



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Table 2: Colours, Yields, (C, H, N, S) analysis and chloride content values for ligands and complexes.

Compound M.wt   colour Found (calc.) %
Yield % M% C H N S Cl
HL1 394.47 82.5 Light brown 75.74 5.38 14.04
-76.12 -5.62 -14.2
L2 283.46 88.6 yellow 53.38 3.38 4.65 22.34
-55.08 -3.56 -4.94 -22.63
[Co(L1)(L2) (H2O) 2] 732.78 51 Light green 7.12
(8.04.)
[Ni(L1)(L2)] 696.51 49 Light green 7.55
(8.42.)
[Zn(L1)(L2) (H2O) 2] 40 Dark brown 8
739.23 (8.84.)
K2 [Cd (L1)(L2)Cl2] 898.33 41 Light yellow 12.01 50 3.11 6.89 7.44 7
-12.51 -50.76 -3.45 -7.79 -7.21 -7.89

 

Table 3: FT-IR spectral data for ligands and complexes.

Compound ν(C-H)ar ν(C-H)ali ν(C=N)im ν(N-CS2)di ν(N=N)azo ν(CS2)as ν(M-N) ν(M -S) ν(M -Cl)
            ν(CS2)s ν(M-O)    
HL1 3097,3049, 2906 1642 1437
3008
L2 2968 1471 1,047,894
[Co(L1)(L2)(H2O)2] 2980 2927 1606 1500 1469 1,053,966 665,609 385,320
489,420
[Ni (L1)(L2) 3035 2983,2891 1639 1510 1462 1,051,993 673,619 387,302
[Zn(L1)(L2)(H2O)2] 2981 2895 1622 1506 1454 1,043,997 671 385,302
K2[Cd(L1)(L2)Cl2] 3035 2983,2889 1624 1504 1458 1,050,948 621 457416 393,304 298,268

 

FTIR and NMR Spectra for Complexes

The FTIR spectra of complexes show bands at rang (1606-1639) cm–1 were assigned to of imine v(C=N) group, with alower frequency shift. This may be related to the engagement of the nitrogen atom of the iminic moiety in the coordination reaction.26-28 The shift also may explained by delocalisation process of the d-10 (metal electron density) to the ligand (psystem).29,30 Spectra for complexes appeared bands at rang (1500-1510) cm–1 that attributed to v(N-CS2).21 This confirms that the v(N-C) double bond character may increase as a consequence of the moving of electrons to the metal centre as a result of coordination to the DTCs.22 Band located in the range (1454-1469) cm–1 is assigned to ѵ(N=N) azo. Finally, the spectra showed new bands in the range (609-673) and (416-489) cm–1 that attributed to v(M–N) and v(M–O), respectively. The appearance of these bands supported the involvement of the nitrogen of imin and oxygen phenolic atoms in the coordination of the ligand to the metal centre. These results are in accordance with that reported in literature.31,32 Bands detected at (1043-1053) and (948-997) cm-1are due to vas(CS2) asymmetric  and vs(CS2) symmetric mode of the DTCs moiety, respectively. This is in agreement with an anisobidentate chelation mode of the ligand to the metal ion.22 The anisobidentate mode of chelation of the ligand, may confirmed by the bands observed in the range (302-393) cm-1 which may attributed to v(M-S) bond.33 The spectra of Co, see Fig. (3), and Zn complexes exhibited a broad band that assigned to ѵ(OH) of the hydrated water molecule.16 Table (4) includes the prominent FTIR bands of complexes. The 1H-NMR spectrum of K2 [Cd(L1)(L2)Cl2], (Fig.9), displays peak at δ=10.9ppm related to the proton of the iminicmoiety (1H, s, N=C-H).23 The chemical shift at δ= 2.2 ppm that equivalent to six protons assigned to the methyl groups (2CH3,s, 6H ).

Figure 6: Electronic spectrum of [Co(L1L2)(H2O)2]

Figure 6: Electronic spectrum of [Co(L1L2)(H2O)2]


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Figure 7:1H-NMR spectrum of ligand HL1 in CDCl3

Figure 7:1H-NMR spectrum of ligand HL1 in CDCl3



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Figure 8: 1H-NMR spectrum of ligand L2 in DMSO-d6

Figure 8: 1H-NMR spectrum of ligand L2 in DMSO-d6



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Table 4: Electronic spectral data of complexes in DMSO solutions

Compound Wave number Wave number emaxmolar1 cm1 Assignment Suggested structure
 λnm (cm-1)
[Co(L1) (L2) (H2O)2] 287 34843 828 n→π*, π→π* Distorted octahedral
348 28735 559 C.T
528 19047 107 4T1g(F)4T1g(P)
886 11286 16 4T1g(F)4T2g(F)
[Ni(L1) (L2)] 295 33898 351 n→π*, π→π* Square planar
348 28735 551 C.T
617 16207 26 1A1g(F)→ 1A2g(F)
[Zn(L1) (L2)(H2O)2] 262 38167 33 n→π*, π→π* Distorted octahedral
349 28653 124 C.T
K2 [Cd(L1) (L2) Cl2] 305 32786 811 n→π*, π→π* Distorted octahedral
346 28901 1113 C.T

 

UV-Vis Spectral Data and Magnetic Susceptibility for the Complexes

The electronic spectra of the complexes exhibited peaks in the range 262-305 nm attributed to π→π* transition of the aromatic rings.34 The spectra of complexes revealed peaks around 349 nm related to (n→π*) transition of azo moiety. The blue shift recorded may attribute to the energy change of the conjugated chromophore (n→π*) and (π→π*electronic transitions, due to the chelation between metal ions and azo ligand.35 The spectrum of CoII complex, see (Figure.6), reveals peaks at 886 and 528 nm assignable to4T1g(F)4T2g(F) 4T1g(F) 4T1g(P) , transitions respectively whichmay confirm a distorted octahedral structurefor CoIIcomplex,36-39 this result was confirmed by the magnetic moment value μeff of 5.07 B.M for the CoII-complex.40 The NiII complex shows a peak at 617 nm attributed to 1A1g(f)1A2g(F), revealing a distorted square planar arrangement about Ni atom. This result was confirmed by the diamagnetic moment behavior of the NiII-complex.40 The spectra of ZnII and CdII compounds revealed peaks attributed to ligand field π→π* and M→L charge transfer.41 These data along with other analytical results indicated that the ZnII and CdII complexes adopt octahedral arrangement about metal centre.42 The six-coordinate number for the ZnII and CdII compounds may be due to sort of ligands that surrounding metal centre and their steric and electronic interaction that   occurred upon complex formation.43 The electronic data of the complexes are tabulated in (Table 5).

Figure 9: 1H-NMR spectrum of K2[Cd(L1)(L2)Cl2] in CDCl3

Figure 9: 1H-NMR spectrum of K2[Cd(L1)(L2)Cl2] in CDCl3



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Figure 10: (TGA/ DTA and DSC) thermogram of [Co(L1) (L2) (H2O)2]in an argon atmosphere

Figure 10: (TGA/ DTA and DSC) thermogram of [Co(L1) (L2) (H2O)2]in an argon atmosphere



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Figure 11: The effect of L1 L2 and its complexes on Escherichia coli.

Figure 11: The effect of L1 L2 and its complexes on Escherichia coli.



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Figure 12: The effect ofL1 L2and its complexes on Enterobacter.

Figure 12: The effect ofL1 L2and its complexes on Enterobacter.



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Figure 13: The effect of L1L2andits complexes on Bacillus stubtilis.

Figure 13: The effect of L1L2andits complexes on Bacillus stubtilis.



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Table 5: Biological activity of  compounds

  Gram negative (G+)   Gram negative (G-)  
Compounds Bacillus stubtilis Staphylococcus aureus (G+) Escherichia coli(G−) Enterobacter(G−)
Control _ _ _ _
HL1 _ _ _
L2 22 12
[Co(L1)(L2)(H2O)2] 12 _ _
[Ni(L1)(L2)] _ _ _ _
[Zn(L1)(L2)(H2O)2] 13 _ _
K2[Cd(L1) (L2) Cl2] 14 _ _

 

Thermal Analysis

The thermogram chart indicated the stability of [Co(L2)(L4)(H2O)2] up to 97ºC, see(Figure 10). peak detected at 297ºC may due to the loss of (HCN, 2H2O, NO and CS2) moieties, (obs. = 4.86mg, 23.15 %; calc. = 4.85mg. 23.1%. While second step at (594)ºC may refers to the loss of (C6H6 and N2) fragment, (det.=3.06mg, 14.56%; calc.= 3.07mg.14.46%). The final residue from the compound which may assigned to the (Co, CH3NCH3, 2C6H4, C6H3, and C10H7), calc. =13.1 mg. 62.4%). The dithiocarbamates analysis thermogram showed peaks at 97, 310, 320, 398 and 594 may assigned to an exo and endo thermal decomposition process. The peak at 320 (exothermic) may due to combustion process of the organic ligand part(in an argon atmosphere). While metal-ligand bond breaking maysignified by endothermic peaks at 97, 310, 398 and 594ºC.44,45

Figure 14: The effect of L1 L2and its complexes on Staphylococcus aureus.

Figure 14: The effect of L1 L2and its complexes on Staphylococcus aureus.


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Biologicalactivity

The synthesized ligands and its complexes were screened for their biological activity against some bacterial strains (Escherichia coli and Enterobacter(G−) Bacillus stubtilis and Staphylococcus aureus (G+)).The involvement of dimethylsulphoxide in the bacterial test was confirmed by individual tests that conducted with the DMSO alone that indicated no activity towards any bacterial species.46 The measured size of inhibition zones against growth of different microorganisms are summarised in (Table 6) that displays the effect of the prepared compounds on bacterial species. From collected data, it is clear that, compared with the free ligands,the ligands (HL1 and L2) showed no antimicrobial activity against Escherichia coli and Enterobacter. Hence, formation of complexes enhances the antimicrobial activity. Such increased activity of complexes may be related to the chelation theory.33 Therefore, the chelation decreases the polarity of the metal atom that resulted in the partial sharing of its positive charge with donor group and possible π-electron delocalisation over the whole ring. Zinc and cadmium complexes showed almost the higher antibacterial activity, compared with other compounds. This due to to their molecular weight and their electronic configuration (d10 system), compared with other metal complexes (Figures.11-14,47, 48

Conclusion

The preparation and characterisation of mixed ligands and their complexes are described. This was based on the preparation of two sorts of ligands; (i) the azo-linked Schiff-base ligand that obtained by reaction of the precursor with (CH3)2NC6H4CHOand (ii) the DTCS ligand that fabricated by reaction of (C6H5)2NH with carbon disulphide. The mixed ligand complexes were achieved by adding the HL1and  L2 with the appropriate metal salt in a 1:1:1 mole ratio. Physico-chemical and spectroscopic methods were implemented to confirm mode of bonding and over all structure of the complexes. These results lead to the preparation of four and six coordinate complexes.

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