Synthesis and Physico Chemical Studies of Some Cobalt (II) Complexes with Bromide and Biologically Active Ligands

 

Manoranjan Kar, R. R. Guin, S.C. Nayak*

Department of Chemistry, B.N.M.A College, Paliabindha, Bhadrak, Odisha 756167

*CorrespondingAuthorE-mail:saratnayak31@rediffmail.com

 

ABSTRACT:

Eleven cobalt (11) complexes of type [Co(L)6]Br2 (where L=imidazole, pyridine, peperidine, piperazine, indole, benzimidazole, benzotriazole, triazole, quinoline, iso-qunoline, carbazole) have been synthesized and are well characterized by elemental analysis, IR. UV. Mass Spectra and magnetic measurement. All these complexes are soluble in ethanol and the conductance measurement shows that all these complexes are of 1: 2 type electrolyte. The IR spectra indicate the coordination between the central cobalt atom and nitrogen atom of the ligands. In the mass spectra molecular ion peak of these complexes appear at appropriate place. The thermo gravimetric analysis shows the strong bond between the central cobalt atom and bromine atom of the complexes. In the complexes the ligands are loosely attached to the central cobalt atom as these are removed first on heating. Finally considering all the spectral analysis conductance values, thermo gravimetric analysis, conductance values octahedral structure are proposes for these complexes

 

KEYWORDS: Cobalt, bromine atom, conductance, IR spectra, Mass spectra, Complexes, Ligands.

 

 

INTRODUCTION:

Transitional metal complexes particularly cobalt complexes have been extensively studied and reviewed in recent years due to their applications in bio inorganic chemistry1-6. So the synthesis, characterization and physicochemical studies of cobalt (II) complexes are the important processes. During last few years correlation analysis in the area of solvent effects are also interesting because it explain the effect of different solvents upon rates of chemical change in any considerable processes .It is very interesting to study the interaction between cobalt(II) metal ion and heterocyclic nitrogen donor compounds which occur in our living system. So we have tried to synthesize and characterize the Bromo-cobalt(II) metal complexes containing different heterocyclic nitrogen donor ligands.

 

MATERIAL AND METHODS:

Cobaltus Nitrate Co(NO3)2.6H2O, potassium Bromide (KBr) are from BDH Glaxo. The imidazole, pyridine, peperidine, piperazine, indole, benzimidazole, are from Lobachem India . The benzotriazole, triazole, quinoline, iso-qunoline, carbazole are from Merck Germany.

 

 

Proposed molecular structurer  of Carbazole

 

                             

      Imidazole                           Quinolone                          Piperazine

 

 

 

                            

       Carbaole                                              Indole             

 

 

Bezimidazole

 

 

Proposed molecular structure of peperidine

 

 

Force Field model of benzotriazole

 

Analytical Measurement:

Chemicals were obtained from commercial sources and used without further purification. Elemental analysis (C.H.N.) was performed with a FISONS EA -1108 micro analyzer. Melting points were taken in a Gallen Kamp MBF-595 apparatus. The FT-IR Spectrum of these samples in corporate in KBr discs (4000—400 cm-1) was recorded ion perking 783 spectrophotometer. The mass spectra of these complexes were recorded by Q-TOF micro TM mass spectrometer. The thermo gravimetric analysis was performed on a Shimdazu TGA-DGT-50H instrument. Magnetic susceptibility measurements were made at room temperature using a Johnson Matthey magnetic susceptibility balance.

 

EXPERIMENTAL:

Synthesis of metal complexes [Co(L)6]Br2:

An alcoholic solution containing cobaltus nitrate hexa hydrate (one m mole) in 25 ml ethanol was mixed with potassium bromide (one m mole) in 20 ml ethanol. The solution was stirred for ten minutes. The KNO3 was filtered off, the solution containing cobaltus bromide was mixed with the heterocyclic ligands (imidazole, pyridine, peperidine, peperazine, indole, benzimidazole, benzotriazole, triazolequinoline, iso-quinoline, carbazole) (6 m mole) in 10 ml ethanol. Then whole solution was stirred for 2 hr. Then cooled. Reddish brown crystals come out. These are collected by filtration, washed with cold water and finally dried in vacuum over CaCl2. All other complexes are prepared by the identical procedure and the yield was varied from 70% to 80%.

 

RESULT AND DISCUSSION:

These series of cobalt (II) complexes  in this work are presented in the table-1 along with other analytical data, i.e. melting point conductance values. The conductance measurement are taken in ethanol solution. The molar conductance values shows that all the cobalt complexes are 1:2 ionic in nature. The magnetic moments of the cobalt complexes are around 2.14 BM to 2.34 BM are slightly higher than those expected for d9- system. This may be attributed to the incomplete quenching of the orbital contribution to the magnetic moment or to spin –orbit coupling.

 

 

 

Table-1. Analytical data and other physical properties of[CoL6]Br2

Sl

No.

Name of the

Compound

Mol Formula

Mol Wt.

% FOUND / CALCULATED

Ω

ohm-1 cm2 mol-1

Melting Point °C

Cobalt

Carbon

Hydrogen

Nitrogen

Bromine

1

[Co(im)6] Br2

CoC18H24N12Br2

627

9.41(9.40)

34.45 (34.44)

3.83(3.82)

26.79(26.79)

25.52(25.51)

32

235

2

[Co(py)6] Br2

CoC30H30N6Br2

693

8.53 (8.51)

51.95 (51.94)

4.32(4.32)

12.13 (12.12)

23.09(23.08)

35

236

3

[Co(pi)6] Br2

CoC30H66N6Br2

729

8.10(8.09)

49.40(49.38)

9.06(9.05)

11.53(11.52)

21.95(21.94)

36

233

4

[Co(pip)6] Br2

CoC24H60N12Br2

735

8.03(8.02)

39.19(39.18)

8.17(8.16)

22.86(22.85)

21.77(21.76)

31

231

5

[Co(ind)6] Br2

CoC48H42N6Br2

921

6.05(6.04)

62.55 (62.54)

4.57(4.56)

9.13(9.12)

17.38(17.37)

40

238

6

[Co(bmz)6] Br2

CoC42H36N18 Br2

1011

5.84(5.83)

49.86 (49.85)

3.57(3.56)

24.93(24.92)

15.83(15.82)

35

>240

7

[Co(btz)6] Br2

CoC42H30N18 Br2

1005

8.88(5.87)

50.15 (50.14)

2.99(2.98)

25.08(25.07)

15.93(15.92)

38

>240

8

[Co(triz)6] Br2

CoC12H18N18 Br2

633

9.33(9.32)

27.75 (27.74)

2.85(2.84)

39.82(39.81)

25.28(25.27)

39

239

9

[Co(qui)6] Br2

CoC54H42N6 Br2

993

5.95(5.94)

65.26 (65.25)

4.23(4.22)

8.46(8.45)

16.12(16.11)

31

236

10

[Co(iso-qui)6] Br2

CoC54H42N6 Br2

993

5.95(5.94)

65.26 (65.25)

4.23(4.22)

8.46(8.45)

16.12(16.11)

33

233

11

[Co(car)6] Br2

CoC72H54N6 Br2

1221

4.84(4.83)

70.77 (70.76)

6.88(6.87)

5.90(5.89)

13.11(13.10)

32

>240

 % Found /(Cal)

Conductance values in ohm-1 cm2 mol-1at room temperature, ala=alanine,

im=imidazole, py=pyridine. pi=piperadine, pip=piperazine, ind=indole, bmz=benzimidazole, btz=benzotriazole,

triz=triazole, qui=quinolline, iso-qui=isoquinoline, car = carbazole.ac=acetate

ELECTRONIC ABSORPTION SPECTRA:

The electronic absorption spectra are often very helpful in the evaluation of results furnished by other methods of structural investigation. The electronic spectral measurements were used for assigning the stereochemistries of metal ions in the complexes based on the positions and number of d–d transition peaks. The electronic absorption spectra of the Co (II) complexes were recorded at room temperature using ethanol as solvent. The electronic spectra of co (II) complexes showed two spin allowed transitions at 445.4mn and at 543.35 mn assignable to 4T1g—4A2g(P), and 4T1g(F)—4T1g(P) transition respectively and are in conformity with octahedral arrangement for co (II) ion6. UV/Visible spectral data of all eleven complexes are investigated and summarized with the help of literature data. It is found that peaks at 350(0.28), 303(0.4), 275(0.3), 274(0.31), 249(0.4), 220(3.2). These transitions are simply intra ligand transitions7-8.

 

UV spectra of [Co (pip)6]Br2                                             pip =piperazine

Fig VI-11

 

Table VI-2 Electronic absorption spectra in nm of [CoL6]Br2 complexes

Sl. No.

Name of the Compound

4T1g—4A2g(P)

4T1g(F)—4T1g(P)

Intra ligand transition

Solvent

1

[Co(im)6] Br2

350

303

249,220

Ethanol

2

[Co(py)6] Br2

352

301

250,225

Ethanol

3

[Co(pi)2] Br2

345

298

252,222

Ethanol

4

[Co(pip)6] Br2

347

297

254,224

Ethanol

5

[Co(ind)6] Br2

358

305

257,226

Ethanol

6

[Co(bmz)6] Br2

362

304

255,228

Ethanol

7

[Co(btz)6] Br2

348

305

256,227

Ethanol

8

[Co(triz)6] Br2

349

307

259,229

Ethanol

9

[Co(qui)6] Br2

356

309

248,221

Ethanol

10

[Co(iso-qui)6] Br2

359

301

247,220

Ethanol

11

[Co(car)6] Br2

360

302

259,229

Ethanol

im=imidazole,py=pyridine.pi=piperadine,pip=piperazine,ind=indole,bmz=benzimidazole,

btz=benzotriazole,

triz=triazole, qui=quinolline, iso-qui=isoquinoline ,car= carbazole.

IR SPECTRA:

C-H stretching – the hetero aromatic compounds and its derivatives are structurally very closed to benzene. The C-H stretching vibration of aromatic and hetero aromatic structures appears9 in the region 2800-3100cm-1. This permits the identification of structure. The secondary and tertiary amines with symmetrical CH2 stretching of CH2 group which is next to nitrogen atom, appears10 at 2800cm-1. It is reported that C-H vibration appears at 3111, 3051 and 3048 cm-1. The C-H vibration of piperazine normally appears at 3087, 2987, 2914, 2853 & 2750 cm-1. This bands slightly shifted to 3100, 3209 & 3263 cm-1 in complexes.

 

C-H stretching vibration appears at 1120, 1055 cm-1. These are symmetric mode. These peaks slightly shifted to 1120 & 1086 cm-1in the piperazine complex of cobalt.

 

N-H stretching vibrations of piperazine generally appears at 3500 &3220 cm-1. This absorption depends upon the degree of hydrogen bonding between the atoms of two molecules. The symmetric and asymmetric vibration11appears at 3207 cm-1& 3406 cm-1respectively. These vibrations are shifted in our complexes and appears at 3209 cm-1&3433 cm-1.

 

C-N stretching vibration generally appears in mixing with the bands of other groups. By minute observation C-N stretching12 vibration appears at 1266 -1342 cm-1. This band slightly shifted and appears13 in our complexes at 1286-1351 cm-1.

 

Table VI-3 Prominent IR Bands (cm-1) of [CoL6]Br2 complexes

SL. No.

Name of the Compound

C-H

N-H

C-N

1

[Co(im)6] Br2

2805

3492

1266

2

[Co(py)6] Br2

2808

3495

1268

3

[Co(pi)6] Br2

2807

3497

1267

4

[Co(pip)6] Br2

2809

3491

1265

5

[Co(ind)6] Br2

2804

3492

1264

6

[Co(bmz)6] Br2

2803

3498

1265

7

[Co(btz)6] Br2

2806

3496

1262

8

[Co(tria)6] Br2

2805

3499

1266

9

[Co(qui)6] Br2

2807

3494

1269

10

[Co(iso-qui)6] Br2

2810

3498

1264

11

[Co(car)6] Br2

2809

3491

1267

 

im=imidazole,py=pyridine.pi=piperadine,pip=piperazine,ind=indole,bmz=benzimidazole,btz=benzotriazole,triz=triazole,qui=quinolline, iso-qui=isoquinoline, car= carbazole.

 

 

 

 

 

 

 

IR SPECTRA OF [Co(pip)6]Br2 Pip = piperazine

 

MASS SPECTRA:

The mass spectra of the compound [Co(pip)6]Br2 is in good agreement of the calculated14 values. The molecular ion peak appears at m/z 735.4132 and M+1 peak appears at 736.4334. The base peak appears at m/z 173.2857 is assigned for [Co(pip)(-CH2-CH2-). The peak at m/z 236.3212 is assigned to the fragment [Co(pip)(C4N2H). The peak15 at m/z 255.2729 is for [Co(pip)2(-c-c-)]. The peak at 385.5094 is assigned to the fragment [Co(pip)3(C3N2H2).

 

 

MASS SPECTRAOF [Co(pip)6]Br2

Pip = piperazine

 

THERMO GRAVIMETRIC ANALYSIS:

The TG and DTA Curves for the [Co(pip)6]Br2 is shown in the figure below. The TG curve for this complex indicate that it is unstable from beginning16. Then proceeds through slow decomposition to Co3O4 as final product formed at 1000Oc. The TG curve showsfive bending at 100, 180, 350, 420 and 670oC. They correspond to the presence of five intermediate decomposition products.The most probable thermal decomposition scheme is here.

[Co(pip)6]Br2–100—120 0c[Co(pip)5]Br+Br+pip

 

[Co(pip)5]Br ---180-250oC  [Co(pip)4]+Br+pip

 

[Co(pip)4 ]----350—420oC  [Co(pip)3]+pip

 

[Co(pip)3]----670—800oc  [Co(pip)]+2pip

 

[Co(pip) ]----800—1000oc  Co3O4

 

The DTA curve for the above complex presents three endothermic peaks at 100, 180, and 4800c, corresponding to the loss of bromine atom and piperazine molecule followed by the decomposition of the [Co(pip)5]Br and simultaneous formation of Co3O4. There is exothermic maximum weak centre at about 280oc and 540 0c corresponding to the decomposition of piperazine molecule.

 

TGA& DTA Curve of[Co(pip)6]B12

pip = piperazine

 

Molecule[Co(im)6]Br2

Im = imidazole

 

Proposed molecular structure of [Co(im)6]Br2

 

Proposed Molecular structure  of [Co(car)6](Br)2

Car=Carbazole

 

 

ACKNOWLEDGEMENTS:

We are indebted to IIT Madras for providing TG and DTA Data. Thanks are due to AICS Kolkatta for providing CHN Analysis and UV, IR Spectra. Thanks are due to IICB Kolkatta for providing mass spectra. Authors are thankful to UGC New Delhi for financial support under minor research project.

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Received on 22.03.2019                    Modified on 04.04.2019

Accepted on 10.05.2019                   ©AJRC All right reserved

Asian J. Research Chem. 2019; 12(2):84-88.

DOI: 10.5958/0974-4150.2019.00019.1