Synthesis and Structural Studies of Some New Cobalt (II) Complexes with Chloride and Heterocyclic Nitrogen Donor ligands
Manoranjan Kar, R. R. Guin and S.C. Nayak*
Department of Chemistry, B.N.M.A College, Paliabindha, Bhadrak, Odisha 756167
*Corresponding Author E-mail: saratnayak31@rediffmail.com
ABSTRACT:
A new series of cobalt complexes of type [Co(L)6]Cl2 (where L =imidazole, pyridine, piperidine, piperazine, indole, triazole, benzimidazole, benzotriazole, quinoline, iso-quinoline and carbazole) have been synthesized and are well characterized by elemental analysis, IR, UV, Mass spectra and magnetic measurements. The thermal studies of these complexes are also reported. All these complexes are soluble in ethanol and the conductance measurement shows that all the complexes are of 1:2 type electrolyte. The IR spectra show clear indication for coordination between central cobalt atom and nitrogen atom of the ligands. The mass spectra clearly show the molecular ion peak and base peak at appropriate place. On thermo gravimetric analysis, it is found that the metal atom and chlorine are strongly attached to each other. The ligands are loosely attached and are removed first on heating. Finally considering all the spectral analysis, conductance values, thermo gravimetric analysis, octahedral structure are proposed for these complexes
KEYWORDS: Cobalt, complexes. IR spectra, conductance, mass spectra.
INTRODUCTION:
Large number of cobalt complexes both in (II) and (III) have been found to possess a wide variety of biological1 activity against bacteria, fungi and certain types of tumors. Some of these compounds closely stimulate the reaction of vitamin B12 and are important in vitamin B12 model chemistry. The X-ray crystal structure of alkyl substituted cobalt complexes suggest that the cobalt atom in the complexes have slightly greater positive charge, causing relatively stronger attachment of base along the axial direction.2-5 Large number of work have been done on the transition metal complexes containing various biological active donor ligands. From our point of view it was challenging to study the interaction between cobalt (II) metal ion and heterocyclic nitrogen donor compounds that occur in our living system. Now a days it is accepted that the heterocyclic compounds play a significant role in many biological system.
At the same time six membered ring system being a component of several vitamins and drugs may possess some biological properties. Now a days it is clear that some drugs acts via chelation or via the inhabitation of metal enzymes. But little is known about the modification activity of most drugs when their legating potential is utilized. The function of cobalt (II) atom which plays a vital role in a number of quite different biological processes is a subject of considerable interest.We have tried to synthesize and characterize some new chloro –cobalt(II) metal complexes containing number of different heterocyclic nitrogen donor ligands
MATERIAL AND METHODS:
Cobaltous(II)chloride,CoCl2.6H2O,Cobaltous(II)nitrate, Co(NO3)2.6H2O, are from BDH Glaxo. Imidazole, pyridine, peperidine, piperazine, indole, benzimidazole, are from Loba chem. benzotriazole, triazole, quinoline, iso-qunoline, carbazole are from Merck Germany.
|
|
|
|
|
Pyridine |
Piperidine |
Piperazine |
Fig.--1
Fig--2 Ball stick model of piperazine
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 gallenkamp MBF-595 apparatus. The FT-IR Spectrum of these samples were incorporated in KBr discs ( 4000—400 cm-1) was recorded in perking 783 spectrophotometer. The mass spectra of these complexes were recorded by Q-TofmicroTM spectrometer. The thermo gravimetric analysis was performed on a Shimadzu 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]Cl2
An alcoholic solution containing cobaltous chloride hexahydrate (one m mole ) in 25 ml ethanol 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 hrs. Then cooled. Dark brown crystals comes out. These are collected by filtration, washed with cold water and finally dried in vacuum over anhydrous CaCl2. All other complexes are prepared by the identical procedure and the yield was varied from 60% to 75%.
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 and 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]Cl2
|
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 |
Chlorine |
||||||
|
1 |
[Co(py)6]Cl2 |
CoC30H30N6Cl2 |
604 |
9.77 (9.76) |
59.61 (59.60) |
4.97 (4.96) |
13.91 (13.90) |
11.77 (11.75) |
30 |
220 |
|
2 |
[Co(pi)6] Cl2 |
CoC30H66N6Cl2 |
640 |
9.24 (9.21) |
56.27 (56.25) |
10.32 (10.31) |
13.13 (13.12) |
11.10 (11.09) |
32 |
225 |
|
3 |
[Co(pip)6] Cl2 |
CoC24H60N12Cl2 |
646 |
9.14 (9.13) |
44.59 (44.58) |
9.29 (9.28) |
26.01 (26.00) |
10.99 (10.99) |
35 |
223 |
|
4 |
[Co(ind)6] Cl2 |
CoC48H42N6Cl2 |
832 |
7.10 (7.09) |
69.25 (69.23) |
5.06 (5.04) |
10.10 (10.09) |
8.55 (8.53) |
38 |
228 |
|
5 |
[Co(bmz)6] Cl2 |
CoC42H30N18Cl2 |
916 |
6.46 (6.44) |
55.03 (55.02) |
3.29 (3.27) |
27.53 (27.51) |
7.78 (7.75) |
34 |
226 |
|
6 |
[Co(btz)6] Cl2 |
CoC42H30N18Cl2 |
916 |
6.46 (6.44) |
55.03 (55.02) |
3.29 (3.27) |
27.53 (27.51) |
7.78 (7.75) |
39 |
229 |
|
7 |
[Co(triz)6] Cl2 |
CoC12H18N18Cl2 |
544 |
10.85 (10.84) |
26.48 (26.47) |
3.32 (3.30) |
46.34 (46.32) |
13.07 (13.05) |
32 |
230 |
|
8 |
[Co(qui)6] Cl2 |
CoC54H42N6Cl2 |
904 |
6.54 (6.52) |
71.69 (71.68) |
4.66 (4.64) |
9.30 (9.29) |
7.87 (7.85) |
35 |
221 |
|
9 |
[Co(iso-qui)6] Cl2 |
CoC54H42N6Cl2 |
904 |
6.54 (6.52) |
71.69 (71.68) |
4.66 (4.64) |
9.30 (9.29) |
7.87 (7.85) |
39 |
223 |
|
10 |
[Co(car)6] Cl2 |
CoC72H54N6Cl2 |
1132 |
5.22 (5.21) |
76.34 (76.32) |
4.79 (4.77) |
7.44 (7.42) |
6.28 (6.27) |
40 |
227 |
|
11 |
Co(Im)6 Cl2 |
CoC18H24N12Cl2 |
538 |
10.97 (10.96) |
40.15 (40.14) |
4.47 (4.46) |
31.23 (31.22) |
13.20 (13.19) |
39 |
228 |
Conductance values in ohm-1 cm2 mol-1 at room temperature, 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 stereo-chemistries 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 shows two spin allowed transitions at 445.4nm and at 543.35nm 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 349(3.28), 303(3.17), 275(3.60), 303(3.31), 274(3.79), 259(3.74), 220(4.05). These transitions are simply intra ligand transitions7-8.
Fig.—3 UV spectra of [Co(ind)6]Cl2, Ind = indole.
Table -2. Electronic absorption spectra in nm of [CoL6]Cl2 complexes
|
Sl. No. |
Name of the Compound |
4T1g—4A2g(P) |
4T1g(F)—4T1g(P) |
Intra Ligand Transition |
Solvent |
|
1 |
[Co(py)6]Cl2 |
441 |
541 |
222, 250 |
Ethanol |
|
2 |
[Co(pi)2] Cl2 |
442 |
540 |
224, 252 |
Ethanol |
|
3 |
[Co(pip)6] Cl2 |
443 |
542 |
226, 253 |
Ethanol |
|
4 |
[Co(ind)6] Cl2 |
444 |
539 |
225, 252 |
Ethanol |
|
5 |
[Co(bmz)6] Cl2 |
439 |
538 |
227, 254 |
Ethanol |
|
6 |
[Co(btz)6] Cl2 |
445 |
537 |
228, 256 |
Ethanol |
|
7 |
[Co(triz)6] Cl2 |
443 |
540 |
225, 251 |
Ethanol |
|
8 |
[Co(qui)6] Cl2 |
442 |
541 |
228, 254 |
Ethanol |
|
9 |
[Co(iso-qui)6] Cl2 |
441 |
540 |
229, 257 |
Ethanol |
|
10 |
[Co(car)6] Cl2 |
447 |
539 |
228, 257 |
Ethanol |
|
11 |
[Co(im)6] Cl2 |
443 |
538 |
226, 254 |
Ethanol |
im=imidazole,py=pyridine.pi=piperadine,pip=piperazine,ind=indole,bmz=benzimidazole, btz=benzotriazole, triz=triazole,qui=quinolline, iso-qui=isoquinoline , car= carbazole.
Table -3 Prominent IR bands (cm-1) of [CoL6]Cl2 complexes
|
SL NO |
Name of the Compound |
V(N-H) |
C=N-Co |
Co-N |
|
1 |
[Co(py)6] Cl2 |
3351 |
1620 |
502 |
|
2 |
[Co(pi)6] Cl2 |
3353 |
1619 |
503 |
|
3 |
[Co(pip)6] Cl2 |
3355 |
1622 |
505 |
|
4 |
[Co(ind)6] Cl2 |
3352 |
1621 |
501 |
|
5 |
[Co(bmz)6] Cl2 |
3354 |
1622 |
504 |
|
6 |
[Co(btz)6] Cl2 |
3357 |
1620 |
501 |
|
7 |
[Co(tria)6] Cl2 |
3352 |
1621 |
503 |
|
8 |
[Co(qui)6] Cl2 |
3351 |
1625 |
504 |
|
9 |
[Co(iso-qui)6] Cl2 |
3355 |
1624 |
502 |
|
10 |
[Co(car)6] Cl2 |
3352 |
1621 |
501 |
|
11 |
[Co(im)6] Cl2 |
3353 |
1622 |
503 |
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
The strong band in IR spectrum at 3350 cm-1 can be assigned to n(N-H) stretching vibration 9.The different peaks in free indole appears at 3100cm-1,3400cm-1, 750cm-1. These peaks are shifted to higher frequencies10 in the complexes. The stretching vibration of C=N in the indole appears at 1610cm-1.Upon complex formation the peak is shifted to higher frequencies11 which is confirmed by bond formation of the metal (cobalt) with nitrogen atom of the respective heterocyclic ligands. This peak12 appears at around 1618cm-1 in the cobalt complexes. A broad band appears at 3500cm-1 in free ligand is shifted to 3400cm-1 indicating the involvement of indole in the complex formation13 of the cobalt atom. The characteristic band of (Co-N) appears at 503 cm-1 in the complexes. The band involving metal14 and chlorine n(M-Cl) has been reported15 to 419cm-1.
Fig-4 IRSPECTRA OF[Co(Ind )6]Cl2, Ind = indole
Fig.--5 MASS SPECTRA OF[Co(ind)6]Cl2 ind = indole
Mass spectra:
The mass spectra of the compound [Co(ind)6]Cl2 is in good agreement of the calculated16 values. The molecular ion peak appears at m/z 832.0028 and the base peak appears at m/z 348.3621 is assigned for [Co (ind)(ind-C6H5-NH2)]Cl2 . The peak at m/z 833.9534 is assigned to the fragment M+1. The peak at m/z 715.0012 is for [Co(ind)5]Cl2fragment of parent 17molecule.
Thermogravimetricanalysis:
The TG and DTA Curves for the [Co(btz)6]Cl2 are recorded. The TG curve for this complex indicates that it is unstable from beginning18, then proceeds through slow decomposition to Co3O4 as final product which formed at 980Oc. The TG curve shows five bending at 90,180,230,420 and 680oC. They correspond to the presence of five intermediate decomposition19 products.The most probable thermal decomposition scheme is here .
[Co(bmz)6]Cl2–90—120 0c[Co(bmz)5]Cl+Cl+bmz
[Co(bmz)5]Cl ---180-220 oC [Co(bmz)4 ] +Cl+bmz
[Co(bmz)4 ]----220—350 oC [Co(bmz)3]+bmz
[Co(bmz)3 ]----450—650 0c [Co(bmz)]+2bmz
[Co(bmz) ]----680—760 oc Co3O4
The DTA curve for the above complex presents four endothermic peaks at 60, 240, 350 and 590oc, corresponding to the loss of chlorine atom and benzimidazole molecule, followed by the decomposition of the [Co(bmz)5]Cl and simultaneous formation20 of Co3O4. There is exothermic maximum weak centre at about 470oc corresponding to the decomposition of benzimidazole molecule.
[hexa imidazole Co(II)] Chloride [Co(imidazole)6]Cl2
Fig-5
ACKNOWLEDGEMENTS:
We are indebted to IIT, Madras for providing TG and DTA Data. Thanks are due to IACS, Kolkata for providing CHN analysis, UV, IR Spectra. Thanks are also due to IICB, Kolkata for providing mass spectra.
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Received on 01.02.2015 Modified on 23.02.2015
Accepted on 16.03.2015 © AJRC All right reserved
Asian J. Research Chem 8(4): April 2015; Page 262-266
DOI: 10.5958/0974-4150.2015.00045.0