Chelation behaviour of aceturic acid with Co(II), Ni(II) and Cu(II)

Article abstract of DOI:10.14233/ajchem.2015.18542

Aceturic acid consists of two parts e.g., peptide part i.e., CH₃CONH and -COOH part. It may act as bidentate ligand coordinating through either peptide or carboxylic acid part or both peptide as well as carboxylic acid part simultaneously forming chelates with transition metal ions. Some complexes of Co(II), Ni(II) and Cu(II) with aceturic acid have been prepared. The microanalysis and electrical conductivity of complexes revealed the formulation of complexes as ML₂X₂ where 'L' is aceturic acid and X' stands for α-picoline or pyridine. The comparison of infrared spectra of complexes with that of free ligand confirms the ligation point of the ligand through carboxylic acid and nitrogen of peptide part. Thus a 5-membered chelates are formed with Co(II), Ni(II) and Cu(II). The magnetic moment values of Co(II) complexes were found in the range of 4.90-4.93 BM at room temperature while it was in the range of 3.32-3.39 BM for Ni(II) complexes. Cu(II) complexes recorded magnetic moment 1.98-2.10 BM. These values are informative of octahedral symmetry around the metal ion which was confirmed by the electronic spectra of complexes.

Full text of DOI:10.14233/ajchem.2015.18542

Asian Journal of Chemistry; Vol. 27, No. 5 (2015), 1919-1922
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.18542
Chelation Behaviour of Aceturic Acid with Co(II), Ni(II) and Cu(II)
*
UMESH KUMAR, PUJA SINGH and SHIVADHAR SHARMA
University Department of Chemistry, Magadh University, Bodhgaya-824 234, India
*Corresponding author: E-mail: sharma.shivadhar@gmail.com
Received: 31 July 2014; Accepted: 12 January 2015;
Published online: 20 February 2015;
AJC-16922
Aceturic acid consists of two parts e.g., peptide part i.e., CH3CONH and -COOH part. It may act as bidentate ligand coordinating through
either peptide or carboxylic acid part or both peptide as well as carboxylic acid part simultaneously forming chelates with transition metal
ions. Some complexes of Co(II), Ni(II) and Cu(II) with aceturic acid have been prepared. The microanalysis and electrical conductivity of
complexes revealed the formulation of complexes as ML2X2 where 'L' is aceturic acid and X' stands for α-picoline or pyridine. The
comparison of infrared spectra of complexes with that of free ligand confirms the ligation point of the ligand through carboxylic acid and
nitrogen of peptide part. Thus a 5-membered chelates are formed with Co(II), Ni(II) and Cu(II). The magnetic moment values of Co(II)
complexes were found in the range of 4.90-4.93 BM at room temperature while it was in the range of 3.32-3.39 BM for Ni(II) complexes.
Cu(II) complexes recorded magnetic moment 1.98-2.10 BM. These values are informative of octahedral symmetry around the metal ion
which was confirmed by the electronic spectra of complexes.
Keywords: Aceturic acid, 5-Membered chelate, Metal(II) complexes.
rally proceed too slowly to be useful in living system7. Keeping
INTRODUCTION
in view the potential chelating tendency of α-amino acids and
The interaction of metal ions with amino acids and small
their importance in biological and medicinal fields, we were
peptides in aqueous solvent provides simple models of metal
motivated to undertake the present investigation of chelating
protein interaction in enzymatic processes. Ambidentities in
behaviour of aceturic acid with Co(II), Ni(II) and Cu(II).
metal ion coordination with peptide bonds are well known1.
Metal complexes with amino acids play important role in
EXPERIMENTAL
various biological systems. Transition metal ion chelates are
exploited by industry in the large scale purification of α-amino
acids and a wide range of drug and drug precursors containing
an amino carboxylic acid moiety. Amino acids are important
ligands in humans and other biosystems2,3. Their involvement
in Cu(II) transport and metabolism is also well documented4.
The amino acids are also useful in the prevention of damage
to normal tissues including peripheral nerves during chemo-
therapy5. Amino acids like histadine has high degree of speci-
ficity for the H2 receptor which reduces the acid and pepsin
content as well as the volume of basal and stimulated gastric
secretion. α-Amino acids are fundamental structural units of
proteins which perform diverse biological functions such as
regulation of metabolic processes, transportation of oxygen
in body and catalyzing biological reactions6. Generally the
reactivity of amino acids is modified when they are coordinated
to metal ions and nature exploits this effect through the
contraction of metal ion binding cavities within the active sites
of many enzymes that serve to accelerate reactions which gene-
All the chemicals used were of Anal-R grade. Glycine
and acetic anhydride were procured from Aldrich and were
used without further purification. α-amino acid and acetic
anhydride were taken in equimolar ratio and mixed together.
2 mL of pyridine was added slowly to it and the whole solvent
was heated on water bath with an air condenser. Yellowish
solid of aceturic acid appeared which was filtered and washed
with acetone. Finally, it was recrystallized in ethanol. The yield
was about 77 % and m.p. was recorded 135 °C. This ligand
was used for complexation with Co(II), Ni(II) and Cu(II). The
complexes were prepared by the usual method of refluxing
the metal salts and the ligand taken in 1:2 molar ratio for 2-3 h.
The medium was made alkaline by the addition of a little of
sodium acetate.
The content of carbon, hydrogen and nitrogen in comp-
lexes were determined by microanalysis on Perkin-Elmer 240
°C, H, N elemental analyzer. The estimation of Co(II) and
Ni(II) in complexes was carried out in laboratory gravimet-
rically, while Cu(II) was estimated volumetrically using

1920 Kumar et al.
Asian J. Chem.
standard method. The IR spectra of the ligand and complexes
were recorded on Perkin-Elmer 783 spectrophotometer as KBr
pellets. Electrical conductivity of complexes were determined
on conductivity meter CG 857 Schoot-Grate GmbH in DMF
solvent of 10-3 M concentration with a deep type cell having
pt electrode. The magnetic susceptibility of complexes was
determined on Gouy-balance at room temperature using
mercury(II) tetrathiocyanocobaltate(II) as calibrant. The
electronic spectra of complexes were recorded on Perkin-Elmer
Lambada 950 spectrophotometer in DMF.
appearing at 1420 cm-1 are safely assigned to νasym(COO–). and
ν
sym(COO–), respectively of the free ligand. In the IR-spectra
of complexes, the νasym(COO–) gets decreased by 40-60 cm-1
and appears at 1620-1600 cm-1 in the IR spectra of complexes.
However, the νsym(COO–) absorption frequency undergoes
bathochromic shift by 10-20 cm-1 in complexes and appears
at 1440-1430 cm-1 in place of 1420 cm-1 in the free ligand spectra.
It shows that COO- group has taken part in coordination14.
The ∆ν(= νasym-νsym) value is found to be 170-180 cm-1 if the
difference in ∆ν > 200 cm-1, COO- group behaves as mono-
dentate ligand coordinating through either of the two oxygens.
Here, in the present case, the ∆ν value is 170-180 cm-1 which
confirms the monodentate nature of COO- of aceturic acid to
the metal ions15,16. The band appearing at 3550 cm-1 in the IR
spectra of free ligand due to νO-H group was found missing in
the IR spectra of complexes confirming the deprotonation of
-OH of COOH group and coordination through deprotonated
carboxylate anion17. The aforesaid mode of coordination of
the ligand to the metal ions was further substantiated and
confirmed by the appearance of two new bands in the far IR
spectra of complexes. The band appearing at 560-532 cm-1 is
fairly assigned to νM-N stretching vibration and the other
appearing at 470-450 cm-1 was assigned to νM-O stretching
vibration18.
Thus, the comparison of IR spectra of complexes of Co(II),
Ni(II) and Cu(II) with aceturic acid clearly indicates that the
aceturic acid behaves as bidentate monoanionic coordinating
through nitrogen of peptide part and oxygen of acid part. The
important IR bands of complexes with their assignment are
given in Table-2.
In addition to these bands, the IR spectra of complexes
display some new bands which are not observed in the IR
spectra of free ligand. A broad band appears at 3360-3350
cm-1 followed by a sharp band at 860-825 and 720-710 cm-1 in
the IR spectra of complexes no. 1, 4 and 7. These bands may
be assigned to stretching, rocking and wagging vibrations
respectively of -OH group of coordinated water19,20. In the IR
RESULTS AND DISCUSSION
The percentage composition of aceturic acid and its
complexes with Co(II), Ni(II) and Cu(II) with their molar
conductivity has been displayed in Table-1.
The low values of electrical conductivity of complexes
are indicative of their non-electrolytic nature8,9. The infrared
spectra of complexes are very clumsy. However some impor-
tant bands of interest are considered and explained here.
In peptide group of the ligand, there is a secondary amide
group for which generally a strong band appears around 3300
cm-1 due to ν(N-H) stretching vibration with a band at 1655 cm-1
due to νC=O of the amide group. This is called amide-1 band10.
The other band appearing at 1550 cm-1 is mainly due to defor-
mation vibration of -NH, i.e., δ(N-H) mixed with ν(C-N) stretching
vibration. This is called amide-II band. The amide-III band
appears between 1360-1300 cm-1 mainly due to ν(C-N) mixed
with δ(N-H). In the IR-spectra of metal complexes, the strong
band appearing at 3300 cm-1 in the IR-spectra of free ligand
due to ν(N-H) shifts to lower frequencies and appears at 3270-
3260 cm-1. This is indicative of the coordination of nitrogen
of peptide part of amino acid i.e., aceturic acid to the metal
ions in complexes11,12. The νC=O stretching frequency appearing
at 1630 cm-1 undergoes bathochromic shift by about 20 cm-1
in the IR-spectra of complexes this confirms the coordination
of nitrogen of peptide group of amino acid to metal ions13.
The strong band appearing at 1660 cm-1 and a medium band
TABLE- 1
% COMPOSITION OF LIGAND AND COMPLEXES. CALCULATED/(FOUND)
λm (ohm-1 cm-1mol-1)
Compounds
Colour
M
-
C
H
N
Ligand (aceturic acid)
Yellowish
41.03
(42.50)
29.36
(29.58)
48.11
(48.72)
50.32
(50.58)
24.07
(24.62)
49.68
(49.89)
50.34
(50.88)
28.95
(27.00)
49.14
(50.00)
50.00
6.00
(5.88)
4.90
(4.44)
4.90
(4.51)
5.45
(5.22)
6.01
(15.96)
5.06
12.00
(11.90)
8.56
(8.320)
12.47
(12.41)
11.70
(11.61)
7.00
-
[Co(L)2(H2O)2]
[Co(L)2(Py)2]
Pinkish
Pink
18.01
(17.91)
13.12
(12.94)
12.35
(12.12)
14.72
(14.41)
13.50
(13.34)
12.31
(12.19)
19.16
(13.01)
14.46
(14.00)
8.00
7.72
Dull pink
Light green
Green
7.65
[Co(L)2(α-pic)2]
[Ni(L)2(H2O)2]
[Ni(L)2(Py)2]
9.34
(6.90)
9.66
10.52
10.34
12.56
11.34
12.00
(4.94)
5.45
(9.50)
11.75
(11.52)
08.00
(05.00)
9.55
(8.20)
11.06
(11.00)
Light green
Green
[Ni(L)2(α-pic)2]
[Cu(L)2(H2O)2]
[Cu(L)2(Py)2]
(5.31)
08.00
(11.50)
05.00
(06.00)
5.40
Green
Bluish green
13.00
(12.50)
[Cu(L)2(α-pic)2]
(49.80)
(4.50)
L = Aceturic acid (N-ethanoyl-2-aminoethanoic acid); Py = Pyridine, α-pic = α-picoline, (2-methyl pyridine)

Vol. 27, No. 5 (2015)
Chelation Behaviour of Aceturic Acid with Co(II), Ni(II) and Cu(II) 1921
TABLE-2
νasym
νsym
ν(
Sl. no.
Complexes
ν(
ν(
ν(
ν(
ν(
δ(
ν
aro.(C-H)
CH
)
(COO-)
(COO-)
1440
1438
1435
1433
1435
1430
1440
1438
1435
N-H)
C-O)
M-N)
M-O)
O-H)
O-H)
3
1
2
3
4
5
6
7
8
9
[Co(L)2(H2O)2]
[Co(L)2(Py)2]
[Co(L)2(α-pic)2]
[Ni(L)2(H2O)2]
[Ni(L)2(py)2]
[Ni(L)2(α-ico)]
[Cu(L)2(H2O)2]
[Cu(L)2(Py)2]
3270
3275
3275
3265
3270
3270
3275
3270
3275
1650
1650
1650
1648
1650
1645
1645
1650
1650
1620
1615
1610
1605
1605
1600
1618
1615
1615
560
560
560
545
540
540
530
535
535
470
470
470
465
460
460
450
450
455
3350
830
-
-
-
-
-
-
-
3070
320
-
3070
3020
-
2850
3355
825
-
-
-
-
-
2850
-
-
835
-
3360
-
-
3070
3020
-
-
2850
[Cu(L)2(α-pico)2]
spectra of complexes no. 2, 5 and 8, a medium band appears
at 3070 cm-1 and a weak band at 1560 cm-1 which clearly shows
the presence of the coordination of nitrogen of pyridine to
metal ion in these complexes21. In complexes no. 3, 6 and 9, a
sharp band appears 2850 cm-1 in addition to a sharp band at
3020 cm-1. The first is assigned to νaroC-H stretching and the
second to νC-H stretching of methyl group. They also display a
band at 765 cm-1 due to νC-N vibration. The appearance of these
bands is indicative of the presence of coordinated α-picoline
in the coordination sphere of these complexes22.
As λ is negative for Ni(II), d8 system, µeff becomes greater
than µs values, however the values are in good agreement for
the reported values for Oh Ni(II) complexes27. The electronic
spectra of Ni(II) complexes in the present study display three
bands whose assignments are given to the following transitions:
3
ν1 = 3T2g ← A2g = 9420-9200 cm-1
3
ν2 = 3T1g(F) ← A2g = 15610-15160 cm-1
3
ν3 = 3T1g(P) ← A2g = 27425-26240 cm-1
From these spectral data, the values of the different crystal
field parameters which have been shown in Table-3. The values
of various crystal field parameters are indicative of Oh geometry
of Ni(II) complexes in the present study28.
Magnetic and electronic spectra of complexes: The
magnetic moment of complexes has been determined by Guoy
balance method at room temperature. Cobalt(II) complexes
record magnetic moment 4.90-4.93 BM. These values are
higher than the values expected for 3 unpaired electrons (µs =
3.88 BM) in Co(II), a d7 system, in weak Oh crystal field. The
high values of µ of Co(II) Oh complexes may be attributed to
appreciable orbital contribution from orbitally triply degenerate
4T1g crystal field component in Oh crystal field for the ground
state term 4F of d7 system8,9,23. The electronic spectra of Co(II)
complexes display three bands which may be assigned to the
following transitions:-
The magnetic moment of Cu(II) complexes falls in the range
of 1.98-2.10 BM at room temperature which is in good agree-
ment with the reported values for mononuclear Oh complexes
of Cu(II)29. The electronic spectra of Cu(II) display one broad
band which is assigned to spin allowed transition:
2
ν1 = 2T2g ← Eg = 13250, 13320 and 13410 cm-1
The band is equivalent to 10Dq. So, the values of 10Dq
of Cu(II) complexes in the present study are 13320, 13250
and 13410 cm-1, respectively. The broadness of the band may
be attributed to the tetragonal distortion in their Oh geometry.
The values of ν1 and 10Dq are in good agreement with the
values reported for distorted Oh complexes of Cu(II)30.
The foregoing study of magnetic moment, electrical conduc-
tivity, IR spectra and electronic spectra of the complexes lead
to structure of complexes as given below:
4
ν1 = 4T2g ← T1g = 8200-8100 cm-1
4
ν2 = 4A2g ← T1g = 17990-17375 cm-1
4
ν3 = 4T1g(P) ← T1g = 29150-26310 cm-1
The values of different crystal field parameters were
calculated on the basis of three electronic spectral bands and
values have been tabulated in Table-3.
X
The values of various crystal field parameters are in good
agreement with the reported values for Oh complexes of
Co(II)24,25. The magnetic moment of Ni(II) complexes has been
found 3.32-3.39 BM at room temp. Here the magnetic moment
of Ni(II) complexes is greater that the spin only values
corresponding to 2 unpaired electrons of d8 system. Actually
for the system having ground termA2g there is no orbital contri-
bution but the magnetic moment due to first order Zeeman
effect26 is given by:-
O
H
C
:
N
H3C
O
C=O
CH2
M
H2C
O
C
O
:
N-H
C=O
CH3
X
where, M = Co(II), Ni(II) and Cu(II) and X = H2O, pyridine
µ
eff. = µs(1-4λ/10Dq)
and α-picoline.
TABLE-3
S no.
Complexes
[Co(L)2(H2O)2]
[Co(L)2(Py)2]
[Co(L)2(α-pic)2]
[Ni(L)2(H2O)2]
[Ni(L)2(Py)2]
10 Dq
9450
9270
9580
9350
9200
9420
B
ν2/ν1
2.142
2.145
2.142
1.667
1.647
1.657
β35
β (%)
7.31
4.53
5.90
5.40
11.53
5.28
1
2
3
4
5
6
900
927
913
984
920
985
0.926
0.954
0.940
0.946
0.880
0.940
[Ni(L)2(α-pic)2]

1922 Kumar et al.
ACKNOWLEDGEMENTS
Asian J. Chem.
14. M. Kaliva, T. Giannadaki, A. Salifoglou, C.P. Raptopoulou, A. Terzis
and V. Tangoulis, Inorg. Chem., 40, 3711 (2001).
15. A.K. De and D. Deb, J. Indian Chem. Soc., 86, 76 (2009).
16. A.K. Srivastava, J. Indian Chem. Soc., 86, 281 (2009).
17. P. Bhatnagar and N.K. Bhatnagar, J. Indian Chem. Soc., 89, 1273
(2012).
One of the authors, Puja Singh is thankful to UGC, New Delhi
for granting Research Fellowship in Sciences for Meritorious
Students (RFSMS) under BSR scheme.
18. S. Raju, K.B. Kumar Nayak, B.A. Kumar and G. Nageshwar Rao, J.
Indian Chem. Soc., 89, 5 (2012).
REFERENCES
19. R. Srinivasan, I. Sougandi, K. Velavan, R. Venkatesan, B. Verghese
and P. Sambasiva Rao, Polyhedron, 23, 1115 (2004).
20. B.H. Mehta and S.D. Disala, J. Indian Chem. Soc., 89, 315 (2012).
21. R. Rani, R. Ranjan, N.C. Bhattacharjee, S. Sharma and A. Suriya, J.
Indian Chem. Soc., 19, 331 (2013).
22. S. Chandra, D. Jain, A. Sarkar and Amipama, J. Indian Chem. Soc.,
86, 220 (2009).
23. B.K. Rai and R. Kumari, Asian J. Chem., 23, 4625 (2011).
24. A.P. Mishra and K. Kumar, J. Indian Chem. Soc., 86, 1150 (2009).
25. A.K. Singh, S.P. Sinha, V. Kumar, S.S. Roy and S. Sharma, Asian J.
Chem., 23, 4347 (2011).
26. B.N. Figgis, Introduction to Ligand Fields, Wiley Eastern Limited,
New Delhi, pp. 265 (1964).
27. H.R.M. Bhowmik, A.K. De and R.N.D. Purkayastha, J. Indian Chem.
Soc., 89, 177 (2012).
28. R.N. Prasad and P. Sharma, J. Indian Chem. Soc., 89, 865 (2012).
29. R.N. Patel, N. Chaudhary, K.K. Shukla, N. Singh and A. Singh, J.
Indian Chem. Soc., 88, 789 (2011).
30. D. Prakash, C. Kumar, A.K. Gupta and K.R.R.P. Singh, J. Indian Chem.
Soc., 86, 1257 (2009).
1. T.R. Burman and G.N. Mukherjee, J. Indian Chem. Soc., 86, 1018
(2009).
2. N. Fujii and T. Saito, Chem. Rec., 4, 267 (2004).
3. L.G. Korotchkina, E.M. Ciszak and M.S. Patel, Arch. Biochem.
Biophys., 429, 171 (2004).
4. B.V. Tiwary, Rev. Soc. Quin. Peru, 76, 293 (2010).
5. G.H. Bindu and G.N. Rao, J. Indian Chem. Soc., 89, 1175 (2012).
6. P. Bhatnagar and N.K. Bhatnagar, J. Indian Chem. Soc., 89, 1273
(2012).
7. P. Bhushanwati, B. Veeraswamy, U. Viplavaprasad and G.N. Rao, J.
Indian Chem. Soc., 90, 347 (2013).
8. K. Siddappa, P.C. Redd, M. Kote, T. Reddy, M. Lambe and M. Mitra,
Asian J. Chem., 23, 4511 (2011).
9. P. Kumari, S. Prakash and D. Prakash, J. Indian Chem. Soc., 89, 19
(2012).
10. N.J. Leonard and F.H. Owens, J. Am. Chem. Soc., 80, 6039 (1958).
11. D. Steele and P.F.M. Verhoeven, Vib. Spectrosc., 25, 29 (2001).
12. C.H. Bindu and G. Nageshwara Rao, J. Indian Chem. Soc., 89, 1175
(2012).
13. B.K. Bera, A. Mandal, P. Karmaleav, S. Mallik, S. Mandal and A.K.
Ghosh, J. Indian Chem. Soc., 90, 1919 (2013).