PREPARATION AND CHARACTERIZATION OF MIXED LIGAND COMPLEXES OF Co(II)

PREPARATION AND CHARACTERIZATION OF MIXED LIGAND

COMPLEXES OF Co(II)

P. R. Shirode*

Department of Chemistry, Pratap College, Amalner (India) Affiliated to North Maharashtra

University, Jalgaon.

ABSTRACT

There is great interest in the study of mixed ligand complexes of

transition metals with oxygen, nitrogen and sulphur donor ligands.

Coordination complexes of Co(II)) of the type Co(L1L2)Cl2 Where

L1=salicylaldehyde semicarbazone and L2=salicylaldehyde oxime,

ortho hydroxy acetophenone oxime, anthranilic acid, benzaldehyde

semicarbazone, acetophenone semicarbazone and acetone

semicarbazone have been prepared by the reaction of metal chloride

with two ligands L1 and L2 in the ratio 1:1:1 molar ratio. The resulting

complexes have been characterized on the basis of elemental analysis,

magnetic measurement, IR and UV spectral analysis, conductivity

measurement, thermal analysis, antimicrobial activities. Analysis of

results reviles that the complexes shows octahedral geometry, electrolytic nature and having

more antimicrobial activity than the ligands. The ligands are bonded through oxygen and

nitrogen.

KEYWORDS: Mixed ligand, salicylaldehyde semicarbazone, salicylaldehyde oxime,

anthranilic acid, transition metals.

INTRODUCTION

Transition metal complexes of oxime, semicarbazone and thiosemicarbazone shows

remarkable antitumor, antiviral, anticancer, anti-malarial, anti-fungal, anti-bacterial and

catalytic activities. By considering these applications, we have carried out synthesis and

characterization and biochemical study of mixed ligand complexes of Co(II) with

salicylaldehyde semicarbazone(L1) and salicylaldehyde oxime, ortho-hydroxyacetophenone

oxime, benzaldehyde semicarbazone, acetophenone semicarbazone and acetone

Volume 6, Issue 8, 1494-1504. Research Article ISSN 2277– 7105

*Corresponding Author Prof. P. R. Shirode

Department of Chemistry, Pratap College, Amalner (India) Affiliated to North Maharashtra University, Jalgaon.

Article Received on 10 June 2017,

Revised on 30 June 2017, Accepted on 21 July 2017

semicarbazone(L2). In this complexation reaction ortho-hydroxyacetophenone oxime,

benzaldehyde semicarbazone and anthranilic acid are acting as a bidentet while

salicylaldehyde semicarbazone and salicylaldehyde thio-semicarbazone are acting as a

tridentate ligand with oxygen, nitrogen and nitrogen as the donor species. Multidentate

organic ligands forming complexes with transition metal ions have been the subject of

intensive research because they not only have interesting spectral and magnetic properties,

but they also possess a diverse spectrum of biological activities.[1,6]

Depending on the widely diverse coordination environment of the transition metal complexes

and variation in the identities of the coordinating ligands, synthesis of such complexes with

desired molecular geometry can be determined.

MATERIALS AND METHODS

All the reagents /chemicals were of reagent grade. Solvents were dried and distilled before

use according to standard procedures.[8] The metal chlorides / salts used were in their

hydrated form.

The amount of metals are determined volumetrically by EDTA using double burette

technique for optimum utilization of reagents. Indicator xylenol orange is used for Co(II.

Carbon, hydrogen, nitrogen and sulphur analysis were carried from Central Instrumentation

Laboratory, Pratap College, Amalner. IR spectra and UV spectra of the complexes were

recorded on JASCO instrument in the region 250-4000 cm-1 and 200-1400nm respectively

from Central Instrumentation Laboratory, Pratap College, Amalner. Thermo gravimetric

analysis was carried out on Perkin Elmer STA 6000 at the rate of 100C per minute.

Antimicrobial activities are determined by using three microbial nutrients.

Ligands L1 and L2 were prepared and general methods of their preparation are given below.

Synthesis of Ligand (L1).

Salicylaldehyde semicarbazone

A mixture of semicarbazide hydrochloride and salicyladehyde in 1:1 molar proportions in

alcoholic medium containing small amount of sodium acetate, was refluxed for15-20minutes

in a water bath. The reaction mixture was cooled to room temperature, white solid product

+ H₂N HN C NH₂

N

H H

N C NH₂

O H

O

O

Salicylaldehyde semicarbazone OH

OH

Synthesis of Ligand (L2)

1. Salicylaldehyde oxime

Equimolar quantities of hydroxylamine hydrochloride and salicylaldehyde in alcoholic

medium containing small amount of pyridine was refluxed on water bath half an hour .White

solid product separates out from solution. On Cooling filter and wash with cold water and

recrystallized from ethyl alcohol and record the melting point.

OH O H

+

OH N H

OH

EtOH

2. Ortho-hydroxyacetophenone oxime

Mixture of alcoholic solution of o-hydroxyacetophenone and aqueous solution

hydroxylamine hydrochloride in 1:1 molar proportions were mixed together. The reaction

mixture is acidified by 3-4 drops of glacial acetic acid and refluxed on water bath for two

hour. The precipitated compound was filtered, washed with cold water, dried and melting

point was recorded.

OH

O

CH₃

o-hydroxy

acetophenone oxime +H₂N OH

OH N

OH

3. Anthranilic acid

Anthranilic acid is used directly by recrystallisation.

4. Benzaldehyde semicarbazone

Aqueous solution of semicarbazide hydrochloride and sodium acetate was mixed with

alcoholic solution of benzaldehyde in 1:1 molar proportions. Heat the mixture on water bath

for 10 to 15 minutes. Shake well and allow standing for 10 minutes. The semicarbazone

derivative crystallizes from the cold solution on standing. Therefore cool the reaction mixture

ice water. Filter the crystal on buchner funnel; wash the precipitate with cold water. The solid

product was recrystallized from hot ethanol and record the melting point.

+ H2N

H

N C NH2

N

H H

N C NH2

O H

O

O

Benzaldehyde semicarbazone

5. Acetophenone semicarbazone( L2)

Dissolve one gram semicarbazide hydrochloride and 1.5 gram of crystallized sodium acetate

in 8-10 ml distilled water, Then add 0.5 gram of salicylaldehyde and shake well. If the

solution is turbid, add Alcohol or water until a clear solution is obtained .Heat the mixture on

water bath for 10 to 15 minutes. Shake well and allow to stand for 10 minutes. The

semicarbazone crystallizes from the cold solution on standing. Therefore cool the reaction

mixture ice water. Filter the crystal on Buchner funnel; wash the precipitate with cold water.

The solid product was recrystallized from hot ethanol and record the melting point.

OH O CH3

+

OH N CH3

H N

EtOH H2N

N

H NH2

O

6. Acetone semicarbazone (L2)

Equimolar quantities of aqueous solution semicarbazide hydrochloride and acetone are mixed

together in presence of sodium acetate. Then the reaction mixture was thoroughly cooled with

constant stirring. White solid product separate out from solution. The solid product was

filtered wash with ethyl alcohol and recrystallized from ethyl alcohol.

H₃C O CH₃

+

H₃C N CH₃

H N

EtOH H₂N

N

H NH2 O

O NH₂

Table 1: Physical properties of ligands.

Name of ligand Mol.wt Nature Method of

purification

Meltingpoint °C(observed)

Salicylaldehyde

Semicarbazone(SALSC) 179

Yellowish Shining Crystals

Recrystallized from aq. ethanol

228(228)

Salicylaldehyde oxime(SAOX) 137

White Shining Crystals

Recrystallized

from methanol 52(52)

Ortho-hydroxyacetophenone

oxime(OHACPHOX) 151

White solid

Recrystallized

from methanol 114(115)

Anthranilic acid (ANT) 137 Faint yellow

Recrystallized

from ethanol 145(145)

Benzaldehyde

semicarbazone(BZSC) 163

Yellowish Shining Crystals

Recrystallized

from ethanol 225(225)

Acetophenone

semicarbazoneACPHSC 177

White solid

Recrystallized

from ethanol 198(197)

Acetone semicarbazoneACSC 115 White solid

Recrystallized

from ethanol 188(188)

Synthesis of transition metal complexes of the type M(L1)2

Alcoholic solution of salicylaldehyde was added to methanolic solution of Co(II) chloride in

1:2 molar praporation with continuous stirring at room temp, till clear solution was obtained.

Then the solution was refluxed on a heating mental at about 60-700C for four hours. The

colored solid complex separates out from solution. The product was filtered on cooling,

washed with methanol, dried under inert atmosphere and practical yield of complex is

Synthesis of transition metal complexes of the type M(L2)2

This complex is prepared by mixing methanolic solution of metal chloride and alcoholic

solution of ligand L2 in the 1:2 molar preporation with continuous stirring at room

temperature., The clear shown was refluxed on a heating mental .Then the solution was

refluxed on a heating mental at about 60-700C for four hours. The colored solid complex

separates out from solution. The solid product is filtered on cooling, washed with methanol,

dried in inert atmosphere.

Synthesis of transition metal complexes of the type ML1L2

In a round bottom flask containing alcoholic solution of metal chloride, hot methanolic

solution of mixture of salicylaldehyde semicarbazone and salicylaldehyde oxime in the molar

preporation 1:1:1 was added with continuous stirring at room temp, till clear solution was

obtained. Then the solution was refluxed on a water bath for four hours. The colored solid

complex separates out from solution. The solid product is filtered on cooling, washed with

methanol, dried and weight of the complex obtained is taken to determine practical yield.

Similarly, complexes of salicylaldehyde semicarbazone with ortho-hydroxyacetophanone

oxime, anthranilic acid, benzaldehyde semicarbazone, acetophenone semicarbazone with

Co(II) chlorides were prepared by mixing equimolar quantities in 1:1:1 proportions.

RESULTS AND DISCUSSION

Analytical Properties

The mixed ligand complexes formed were having different colors as shown in the table 2.

These complexes were insoluble in chloroform, carbon tetrachloride, methanol, ethanol but

soluble in DMF. The properties of complexes were indicated in table 2. The TLC of the

mixed ligand complexes with M(L1)2 and M(L2)2 was taken. It exhibit single spot with Rf

values being intermediate of the two corresponding symmetrical bis-complexes. From the

magnetic moments these complexes shows octahedral geometry. The amount of metals

present in complexes were determined volumetrically by EDTA using double burette

technique for optimum utilization of reagents. Indicator xylenol orange for Co(II). Specific

conductance were measured at room temperature in DMF by a Systronics direct reading 304

conductivity meter using a glass conductivity cell having a cell constant L1 and L2.

Antimicrobial activities were determined in the PG department of Microbiology, Pratap

The elemental analysis shown in Table 2 indicates that, all the metal complexes have 1:1:1

stoichiometry and are, soluble only in DMF and DMSO. The molar conductance values

obtained for these complexes at the concentration of 10-3 M are in the range of 52-109 ohm-1

mol-1 cm2. The magnetic moments these mixed ligand complexes shows that these complexes

were having octahedral geometry.

Table 2: Physical, analytical, magnetic susceptibility and molar conductance data of the

mixed ligand complexes:

Name of Ligand /

Complex Empirical

Formula

Mol.

Wt. Colour

Percentage of

µef f B.M

Molar Conductance

^m Ohm-1 cm2 mol-1

Metal C N H

[Co(SALSC) (SAOX)(H2O)]Cl2

CoC15N4O5H18Cl2 460.93 Yellow

13.90 (13.83) 39.01 (30.03) 12.14 (12.10) 3.90

(3.88) 4.473 60.48 [Co(SALSC)

(OHACPHOX)(H2O)]Cl2

CoC16N4O5H20Cl2 477.93 Brown

12.33 (12.29) 40.17 (40.01) 11.73 (11.71) 4.18

(4.16) 4.390 108.37 [Co(SALSC)

(ANT)(H2O)]Cl

CoC15N4O5H17Cl 424.43 Yellow

12.70 (12.67) 42.40 (42.31) 13.19 (13.13) 4.00

(3.98) 4.690 51.32 [Co(SALSC)

(BZSC)(H2O)]Cl2

CoC16N6O4H20Cl2 489.93 Brown

13.07 (12.95) 39.18 (39.10) 17.14 (17.02) 4.01

(4.03) 4.890 71.24 [Co(SALSC)

(ACPHSC)(H2O)]Cl2

CoC17N6O4H22Cl2 503.93 Black

12.67 (12.63) 40.48 (40.39) 16.66 (16.61) 4.36

(4.32) 4.791 63.70 [Co(SALSC)

(ACSC)(H2O)]Cl2

CoC11N6O4H20Cl2 429.93 Orange

13.70 (13.71) 30.70 (30.63) 19.53 (19.48) 4.65

(4.60) 4.93 67.31

Magnetic susceptibility

The magnetic moment values for Co(II) complexes with SALSC as one of the ligand and

SAOX,OHACPHOX, ANT,BZSC, ACPHSC AND ACSC as one of the other ligand are

shown in Table2. The mixing of the singlet states lowers the magnetic moments of Co(II)

complexes are in the range of 4.390-4.93 BM indicating that the Co(II) complexes are

typically high spin complexes and having octahedral structure.[7]

Electronic spectra

The electronic spectral data of The magnetic moment values for Co(II) complexes with

SALSC as one of the ligand and SAOX,OHACPHOX, ANT,BZSC, ACPHSC and ACSC as

one of the other ligand shown in Table 3. In the electronic spectra of Co(II) complex the three

absorption bands ARE observed in the range 8771-10745cm-1, 16778-16211 cm-1 and

23419-25488 cm-1, due to 4T2g (F) --> 4A2g (ν1) , 4T1g (F) --> 4A2g (F)(ν2) and 4T1g (F) --> 4T1g (P)

(ν3) transitions respectively. These transition suggest octahedral geometry for Co(II)

complex.[8-9] These assignments are in good agreement with the reported value.[10,11] The

ligand field parameters such as Dq, B' and β have been calculated by using band-fitting

were found to be in the range 800-857.3 cm-1. These values are well within the range reported

are most of the octahedral Co(II) complexes. The Co(II) complex under present investigation

process interelectronic repulsion parameter (B') is in the range 926-961cm-1. The Racha

parameter (B') is less than free ion value 971 suggesting a considerable orbital overlap and

delocalization of electrons on the metal ion. The nephelauxetic ratio (β) for the present Co(II)

complexes is 0.98 which is less than one, suggesting partial covalency in the metal ligand

bond. The values Dq, β, LFSE, ν2 / ν1 (Table 2) suggest the octahedral geometry for Co(II)

complex.[13]

Table 3: Electronic spectral data and ligand field parameters of Co(II) complexes.

Name of Complex ν1 ν2 ν3

Dq

cm-1 B β ν1/ ν2

LFSE in Kcal/mole

[Co(SALSC) (SAOX)(H2O)]Cl2 9015 17015 24341 800 954 0.982 1.887 9.60

[Co(SALSC)(OHACPHOX)(H2O)]Cl2 8787 17211 23419 842 951 0.972 1.958 10.10

[Co(SALSC) (ANT)(H2O)]Cl 8771 16985 23752 821 961 0.990 1.993 10.01

[Co(SALSC) (BZSC)(H2O)]Cl2 10845 16778 25188 850.4 950 0.979 1.547 10.20

[Co(SALSC) (ACPHSC)(H2O)]Cl2 10531 16806 22421 857.3 926 0.998 1.595 10.28

[Co(SALSC) (ACSC)(H2O)]Cl2 11286 16528 21929 841.1 940 0.968 1.464 10.09

Infrared spectra

The important infrared bands for the ligands and their complexes together with their

assignments are listed in (Table 4). The IR spectra of the ligands show characteristic bands at

1685–1669 and 1647–1629 cm−1 due to the ν (C=O), ν (C=N) functional groups, respectively.

The bands at 3478-3372, and 3275- 3241 cm−1assigned to the ν (O–H) and ν (N–H) stretching

group for ligands L1 and L2, respectively.[14-16] The IR spectra of the complexes exhibited

ligand bands with the appropriate shifts due to complex formation (Table 2). The ν (C=O)

and ν (C=N) stretching bands that appeared in the free ligands in the range 1685–1669 and

1647–1629 cm−11, respectively, are shifted to lower frequency in the complexes and observed

in the ranges 1657–1638 cm−1 and 1614–1625 cm−1 for ν (C=O) and ν (C=N), respectively.

These bands are assigned to a ν (C=O) and ν (C=N) stretches of reduced bond order. This can

be attributed to delocalisation of metal electron density (t2g) to the π-system of the

ligand.[14,15] indicating coordination of oxygen of C=O and nitrogen of the C=N moieties to

the metal atoms.[16] The bands of ν (C–O) at ca. 1271 cm−1 in the free ligands are shifted to

lower frequencies and appeared at 1215 cm−1 for the complexes. At lower frequency the

complexes exhibited bands around 615–640 and 561–579 cm−1 which could be assigned

to ν (M–O) and ν (M–N) vibration mode.[17,18] These bands indicated that the imine, nitrogens

and the oxygen of carbonyl group of the ligands are involved in coordination with metal ion.

3255 cm−1 assigned for the free O–H and N–H functional groups. A broad band appeared in

the region 3541-3591cm-1 in all complexes complexes indicates the presence of coordinated

water or lattice water.[19]

Table 4.Characteristic IR frequencies (cm-1) of the ligands and its complexes Ligand/

complex.

Name of Ligand / Complex νH2O νOH ΝN-H νC=O νC=N Vc–O νM–O νM–N

SALSC(L1) - 3478 3275 1685 1647

SAOX 3372 3263 - 1639

OHACPHOX 3445 3206 - 1641

ANT 3245 1669 1637 1271

BZSC 3258 1674 1629

ACPHSC 3271 1678 1632

ACSC 3241 1679 1641

[Co(SALSC)(SAOX)(H2O)]Cl2 3541 3360 3255 1638 1623 640 579

[Co(SALSC)(OHACPHOX)(H2O)]Cl2 3586 3351 3191 1641 1619 604 567

[Co(SALSC) (ANT)(H2O)]Cl 3567 3346 3245 1614 1215 615 571

[Co(SALSC) (BZSC)(H2O)]Cl2 3581 3359 3237 1645 1625 621 561

[Co(SALSC) (ACPHSC)(H2O)]Cl2 3605 3350 3251 1651 1621 621 567

[Co(SALSC) (ACSC)(H2O)]Cl2 3591 3346 3242 1657 1617 624 569

Antimicrobial activity

The synthesized ligands and its complexes were screened for their antibacterial activity.[20]

against E. coli, Baciullus Sp., Staphylococcus Sp,. Pseudomonas Sp. and Proteus Sp.at 100

µg/0.1 cm3 concentration. The zones of inhibitions of the antimicrobial activity have been

presented in Table 5. The results of antibacterial activity shows that complexes with Co(II)

shows weak activity.

Table 5: The results of antibacterial activity of ligands and its complexes.

Name of Ligand / Complex

Antibacterial Activity of zone of inhibition (in mm)

E.coli Baciullus Sp.

Staphylococcus Sp.

Pseudomonas

Sp. ProtusSp

SALSC(L1) 11 13 10 - -

SAOX 11 - - 12 11

OHACPHOX 12 10 13 11 13

ANT 13 10 12 09 10

BZSC 13 12 11 10 09

ACPHSC 09 10 09 10 10

ACSC 10 11 10 09 11

[Co(SALSC) (SAOX)(H2O)]Cl2 12 16 15 13 14

[Co(SALSC) (OHACPHOX)(H2O)]Cl2 14 13 14 12 12

[Co(SALSC) (ANT)(H2O)]Cl 17 15 17 18 17

[Co(SALSC) (BZSC)(H2O)]Cl2 15 15 13 15 14

[Co(SALSC) (ACPHSC)(H2O)]Cl2 14 13 15 15 14

CONCLUSIONS

The ligand salicylaldehyde semicarbazone is tridentate coordinating through ‘N’ and ‘O’

while ligands ortho hydroxy acetophenone oxime, anthranilic acid, benzaldehyde

semicarbazone, acetophenone semicarbazone and acetone semicarbazone are bidentate

coordinating through ‘N’ and ‘O’. Analytical data, electronic spectra, magnetic susceptibility,

IR spectral data reveal octahedral geometry for all the complexes. The conductance values

show electrolytic behavior of the complexes. The ligands and its all complexes were tested

for antimicrobial activity. The complexes are shows moderate to good antibacterial and

antifungal activity compared to its ligand. On the basis of spectral evidence, the following

probable structures have been assigned for synthesized compounds.

Structure of complexes

1. [Co(SALSC) (SAOX)(H2O)]Cl2 2.[Co(SALSC)(OHACPHOX)(H2O)]Cl2 3. [Co(SALSC) (ATN)(H2O)]Cl

OH N HN O NH2 Co H 2 HO N H H2O

HO

2Cl- OH

N HN O NH2 Co H 2 HO N CH3

H2O

HO

2Cl

-N H3C _HN

O NH2

OH Co

O

O NH2

H2O

+

Cl

-4. [Co(SALSC)(BZSC)(H2O)]Cl2 5. [Co(SALSC)(ACPHSC)(H2O)]Cl26. [Co(SALSC) (ACSC)(H2O)]Cl2

N HN O NH2

Co

H2N

H

H₂O

2+

2Cl- H3C

N HN

O NH₂

Co

H₃C

HO

N NH O

H₂N H

H₂O

2+

2Cl

-H3C

N HN

O NH2

Co

HO

N NH O

H2N

H

H₂O

2+

2Cl

-ACKNOWLEDGEMENT

Auther is very thankful to Principal, Pratap college, Amalner for providing necessary

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