Synthesis of 4-Dicyclohexylaminomethyl antipyrine and its metal complexes: Spectral characterization and evaluation of thermodynamic parameters

Article abstract of DOI:10.1023/B:RUCO.0000008396.57645.7d

Complexes of Fe(III), Co(II), Ni(II), and Cu(II) with 4- dicyclohexylaminomethyl antipyrine (DCHAMA, L) were prepared and characterized by elemental and chemical analyses, IR, electronic absorption, ¹H NMR and EPR spectroscopies, thermal analysis, and magnetic susceptibility measurements. The stoichiometry of the complexes was found to be MLX ₂, MLX₃, or MLX₂(H₂O)₂ where X = Cl or NO₃. The ligand exhibits a bidentate mode of coordination. Thermal analysis of the chloro complexes shows a three stage decomposition pattern for the Cu(II) complex and a two stage decomposition pattern for Fe(III) and Co(II) complexes to yield the respective metal oxides as the end product. Kinetic and thermodynamic parameters such as n, E_a, ΔH^#, ΔS^#, and ΔG^# were calculated using Coats-Redfern and Madhusudhanan-Krishnan-Ninan integral methods. The coordination number of the metal atom is found to influence the thermal stability of the complexes. The antimicrobial screening shows that the four-coordinated complexes are more active than the five- and six-coordinated ones and DCHAMA.

Full text of DOI:10.1023/B:RUCO.0000008396.57645.7d

Russian Journal of Coordination Chemistry, Vol. 29, No. 12, 2003, pp. 845–851. From Koordinatsionnaya Khimiya, Vol. 29, No. 12, 2003, pp. 909–915.
Original English Text Copyright © 2003 by Kalarani, Sangeetha, Kamalakannan, Venkappayya.
Synthesis of 4-Dicyclohexylaminomethyl Antipyrine
and Its Metal Complexes: Spectral Characterization
and Evaluation of Thermodynamic Parameters1
N. Kalarani, S. Sangeetha, P. Kamalakannan, and D. Venkappayya
Department of Chemistry, Regional Engineering College, Tiruchirappalli, 620015, Tamil Nadu, India
e-mail: dvenka@rect.ernet.in
Received November 11, 2002
Abstract—Complexes of Fe(III), Co(II), Ni(II), and Cu(II) with 4-dicyclohexylaminomethyl antipyrine
(DCHAMA, L) were prepared and characterized by elemental and chemical analyses, IR, electronic absorption,
1H NMR and EPR spectroscopies, thermal analysis, and magnetic susceptibility measurements. The stoichiom-
etry of the complexes was found to be MLX2, MLX3, or MLX2(H2O)2 where X = Cl or NO3. The ligand exhib-
its a bidentate mode of coordination. Thermal analysis of the chloro complexes shows a three stage decompo-
sition pattern for the Cu(II) complex and a two stage decomposition pattern for Fe(III) and Co(II) complexes
to yield the respective metal oxides as the end product. Kinetic and thermodynamic parameters such as n, Ea,
∆H#, ∆S#, and ∆G# were calculated using Coats–Redfern and Madhusudhanan–Krishnan–Ninan integral meth-
ods. The coordination number of the metal atom is found to influence the thermal stability of the complexes.
The antimicrobial screening shows that the four-coordinated complexes are more active than the five- and six-
coordinated ones and DCHAMA.
INTRODUCTION
hexylamine (0.1 mol) with catalytic amount (~1 ml) of
concentrated HCl at ice cold condition) to a mixture of
8.6 ml of formaldehyde (0.1 mol) and 18.8 g of antipy-
rine (0.1 mol) maintained at 0°C with constant stirring
and left at room temperature for about 24 h. Chloro-
form extract of the reaction mixture is evaporated on a
steam bath. Pale yellow colored waxy solid separates
out. The crude product is washed with ether and dried
in a desiccator and crystallized from ethanol. The
iron(III), cobalt(II), nickel(II), and copper(II) chloro
complexes and the nitrato complex of copper(II) are
prepared by refluxing the methanol solution of the
ligand with the metal salts in 1 : 1 molar ratio for about
3 h. The complexes obtained as insoluble precipitates
after reflux are washed with chloroform and dried in a
desiccator. The cobalt(II) nitrato complex is prepared
by mixing the salt solution in EtOH with the ligand in
CHCl3. The resulting mixture obtained is kept over-
night in a freezer. Pink colored product obtained is
washed with chloroform and dried in a vacuum oven.
Antipyrine and its metal complexes have been
reported to possess important medicinal properties.
They act as anti-inflammatory [1], antirheumatic [2],
antipyretic [3], and analgesic [4] drugs. The carbonyl
group in antipyrine is a potential donor due to the large
dipole moment and strong basic character [5]. In the
metal complexes of antipyrine, the ligand was found to
act as a monodentate ligand bonding through its carbo-
nyl oxygen atom [6–8]. Antipyrine can be converted
into an effective chelating ligand by substitution of
groups containing donor atoms. We have previously
reported some Mannich bases of antipyrine and their
metal complexes [9–12]. In view of the varying possi-
bilities of structural type and biological activity, an
attempt is made to synthesize and structurally charac-
terize a new Mannich base of antipyrine and its metal
chelates.
EXPERIMENTAL
Physical measurements. The elemental analyses
(C, H, and N) were carried out using LECO-CHN ana-
lyzer. Metal contents in the complexes were analyzed
using standard procedures. Conductance measurements
were made using 10–3 M solutions of the complexes in
DMF with the help of Systronic Direct Reading Con-
All the reagents used for synthesizing the ligand and
its metal chelates were of analytical or reagent grade
and the solvents were purified by the standard methods
of distillation.
Synthesis. 4-Dicyclohexylaminomethyl antipyrine ductivity Bridge. IR spectra of the compounds were
(DCHAMA) is synthesized by adding acidified dicy- recorded as KBr discs using Perkin Elmer-1430 ratio
clohexylamine (prepared by mixing 19.9 ml of dicyclo- recording spectrophotometer. The far-IR spectral mea-
surements of the compounds on a polyethylene support
were made using Bruker IFS 66V FT-IR spectropho-
1
This article was submitted by the auhors in English.
1070-3284/03/2912-0845$25.00 © 2003 åÄIä “Nauka /Interperiodica”

846
KALARANI et al.
Table 1. Analytical and conductance data of DCHAMA and its Fe(III), Co(II), Ni(II), and Cu(II) complexes
Content (found/calcd), %
ΛM ,
–1 cm2 mol–1*
Compound
Ω
C
H
N
A
M
DCHAMA
75.54/75.59 9.18/9.18
52.99/53.01 6.43/6.44
56.36/56.37 6.84/6.85
51.06/51.07 6.20/6.20
11.00/11.02
7.76/7.77
8.21/8.22
12.40/1241
7.67/7.68
7.60/7.61
[Fe(DCHAMA)Cl3]
[Co(DCHAMA)Cl2]
[Co(DCHAMA)(NO3)2]
19.59/19.0 10.28/10.28
13.88/13.9 11.52/11.53
68.0
67.0
76.0
42.0
20.0
81.0
21.97**/28
10.44/10.45
[Ni(DCHAMA)(H2O)2Cl2] 52.66/52.67 7.13/7.13
[Cu(DCHAMA)(H2O)2Cl2] 52.20/52.21 7.07/7.07
12.98/12.8 10.73/10.73
12.86/12.7 11.52/11.52
[Cu(DCHAMA)(NO3)2]
50.64/50.65 6.15/6.15
12.30/12.31 21.80**/21.1 11.17/11.17
–3
* For 10 M solution in DMP.
** Obtained from the difference between the mass of the complex and the mass of the other constituents excluding anion.
tometer. The electronic absorption spectra of the com- carefully carried out under aseptic conditions. The
plexes in the UV-Visible region were measured using assay tubes are incubated at 37 ± 1°C. The resultant tur-
JASCO UVIDEC-430B double beam spectrophotome- bidities at 24 and 48 h are measured in a nepheloturbid-
ter and Hitachi UV-VIS-NIR spectrophotometer. The ity meter. The minimum inhibitory concentration of the
room temperature (305 K) magnetic moment measure- test compound is the least concentration showing no
ments of the complexes were carried out using a Gouy visible turbidity. However, the percentage bacterial
magnetic balance. A Varian E4XE4 Band ESR spec- growth inhibition produced by a particular concentra-
trometer was used for recording the EPR spectra. The tion of the test compound is calculated from the mea-
mass spectral studies were carried out using Finningam sure of the turbidities of the control and the particular
MAT-8320 mass spectrometer. NMR spectra were treatment, provided the influence of the solvent and the
recorded using JEOL GSX 400NB, 400 MHz spec- metal ion on the growth of the organism is negligible.
trometer and TMS as internal standard and CDCl3 as The relation used is inhibition (%) = [(Tc – Tt)/Tc] ×
solvent at ambient temperature. TG/DTG measure- 100, where Tc is the turbidity of the control and Tt is the
ments of the complexes were recorded on Shimadzu turbidity of the specific treatment or the test compound.
Thermal Analyzer DT-40 in an atmosphere of air at a The organisms selected are Staphylococcus (S.) aureus
heating rate of 10°C/min in the range from ambient to and Escherichia (E.) coli. The inhibition of the growth
1000°C. The TG curves were analyzed as percentage of the gram-positive and gram-negative organisms by
mass loss as a function of temperature. The number of the compounds is compared with that for streptomycin.
decomposition steps was identified from the TG curves.
From the TG/DTG pattern of the compounds, kinetic
RESULTS AND DISCUSSION
and thermodynamic parameters such as n, Ea, ∆S#, ∆H#,
and ∆G# were evaluated using Coats–Redfern (CR)
DCHAMA is a pale yellow colored waxy solid and
[13] and Madhusudhanan–Krishnan–Ninan (MKN) its melting point is 78°C.Yield of the product is 75%. It
[14] equations. The turbidity of the bacterial suspen- is readily soluble in chloroform and moderately soluble
sions was measured using Systronics Nephelo Turbid- in methanol, ethanol, 1-propanol, and 2-propanol and
ity Meter-131.
slightly soluble in acetone. The elemental analysis of
the crystallized product is given in Table 1. Comparison
of the IR spectrum of antipyrine with that of DCHAMA
indicates that new bands appear in the spectrum of
DCHAMA which are due to the substitution of an addi-
tional moiety on antipyrine. A new and sharp intense
absorption band at 1153 cm–1 is due to ν(C–N–C) of
dicyclohexylamino moiety. The effect of substitution
on the antipyrine was indicated by a negative shift of
about 40 and 12 cm–1 in the ν(C=O) and pyrazolone
ring bending modes, respectively. The important IR
absorption bands are listed in Table 2.
The serial tube dilution method [15] is employed for
the antimicrobial screening. A nutrient broth medium
containing 1% (w/v) sodium chloride is prepared in dis-
tilled water and sterilized by autoclaving at 100°C for
about 30 min. A standard volume (10 ml) of the nutrient
broth medium that would support the growth of the test
organism is added to several labeled sterile stoppered
identical assay tubes. A solution of each test compound
is prepared in DMF and a series of dilutions are pre-
pared. The concentrations tested are 25, 50, 75, 100,
125, and 150 µg/ml of the compound under investiga-
tion, a wide spectrum antibiotic, the respective metal
1
The H NMR spectrum of DCHAMA in CDCl3
salt and the blank (DMF). A control tube containing no exhibits a signal at δ = 2.22 ppm that is assigned to –N–
test compound is also included. All these operations are (C6H11)2 moiety. Protons of the benzene ring appear at
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 12 2003

SYNTHESIS OF 4-DICYCLOHEXYLAMINOMETHYL ANTIPYRINE
847
Table 2. IR data of (cm–1) DCHAMA and its Fe(III), Co(II), Ni(II), and Cu(II) complexes
Pyrazolo- Pyrazolo-
N–Phenyl
Compound
Antipyrine
ν(C=O)
ne ring
stretch
ne ring
bend
ν(C–N–C) ν(M*–O) ν(M=N) ν(M–Cl)
stretch
1668 s*
1649 s
1620 s
1600 s
1581 s
1602 s
1482 s
1490 s
1492 s
1491 s
1490 s
1492 s
1495 s
1492 s
1464 m* 1170 w*
DCHAMA
1452 m
1470 w
1449 w
1455 w
1456 m
1385 w
1389 w
1170 w
1178 w
1187 w
1188 w
1167 w
1198 w
1195 w
1153 s
1143 s
1099 s
1143 s
1076 s
1133 s
1099 s
[Fe(DCHAMA)Cl3]
[Co(DCHAMA)Cl2]
[Co(DCHAMA)(NO3)2]
[Ni(DCHAMA)(H2O)2Cl2]
380
390
380
380
500
428
316
330
320
300
430
390
277
290
260
300
[Cu(DCHAMA)(H2O)2Cl2] 1575 s
[Cu(DCHAMA(NO3)2] 1638 s
* s, strong; w, weak; m, medium; M, metal.
δ = 7.26–7.45 ppm almost in the same position as in the coordinated water molecules. The bands at 1439, 1286,
and 1034 cm–1 for the nitrato complex of cobalt(II) can
be assigned to the ν1(A1) (ν(N=O)), ν5(B2)(νa(NO2)),
and (A1)(νs(NO2). These bands indicate a bidentate
behavior of the nitrato group. Similarly, the nitrato
complex of Ni(II) shows absorption bands at 1470,
1303, and 1021 cm–1, which can be assigned to ν(N=O)
(ν1), νa(NO2) (ν5), and νs(NO2) (ν2), respectively, of the
nitrato group. The ν5 and ν2 are the split bands of ν4 in
spectrum of antipyrine. The >N–CH3 and C–CH3 pro-
tons of antipyrine ring appear at δ = 3.07 and 3.05 ppm,
respectively. The signal at δ = 2.25 ppm is assigned to
–CH2– group that links dicyclohexylamino moiety and
antipyrine. The intensity for the signals correlates well
with the total number of protons under each type.
The mass spectrum of DCHAMA exhibits the
molecular ion peak at m/z = 381, which corresponds to
the proposed molecular weight of the compound. Upon
fragmentation, it exhibits a signal at m/z = 298, which
indicates the loss of –C6H11 fragment from DCHAMA.
the free NO–3 . A value of 167 cm–1 for ν5–ν1 indicates a
bidentate mode of coordination. In the IR spectrum of
copper(II) nitrato complex, three strong bands overlap-
ping with the ligand bands are observed at 1418, 1320,
and 1046 cm–1. These are assigned to ν4, ν1, and ν2
vibrations, respectively, of the nitrato group. The bands
at 1418 and 1320 cm–1 are the split bands of ν3 mode of
+
The intermediate species further loses N–C6H11 and
registers a peak at m/z = 201. Based on the above data,
the structure proposed for DCHAMA is the following.
free nitrate group and the difference is 98 cm–1, which
indicates that the nitrato groups are monodentate. Far
IR spectra of these complexes show absorption bands
corresponding to M–O, M–N, and M–Cl stretching fre-
quencies (Table 2).
H3C
CH
N
2
H3C N
N
O
Electronic absorption spectral and magnetic sus-
ceptibility measurements. The electronic absorption
spectrum of iron(III) chloro complex shows an intense
band at 31400 cm–1 and another weak band at 17600 cm–1
which are presumably due to the charge transfer (CT)
and spin forbidden transitions, respectively. The µeff
value for the complex is 5.35 µB. Based on the above, a
trigonal bipyramidal geometry is assigned to the
iron(III) chloro complex. The diffuse reflection spec-
trum of cobalt(II) chloro complex exhibits three
absorption bands at 16393, 9107, and 5464 cm–1. These
All the complexes synthesized are soluble in polar
solvents DMF and DMSO. ΛM values (Table 1) suggest
all the complexes to be nonelectrolytes. The analytical
data indicate a 1 : 1 stoichiometry for the metal and
ligand (Table 1).
Infrared spectra. The IR spectra of all the com-
plexes show perceptible shifts by about 75–25 and 55–
20 cm–1 (Table 2) in the stretching frequencies of C=O
and C–N–C relative to DCHAMA. This observation
suggests that in all the complexes the ligand is bonded
to the metal atom through the same atoms, i.e., the O
atom of C=O and the N of C–N–C moieties. In the
4
4
absorptions are due to A2(F)
4T1(F), and 4A2(F) 4T2(F) transitions. The magnetic
moment of the Co(II) chloro complex is 4.60 µB which
4T1(P), A2(F)
nickel(II) chloro complex, the absorption bands around is well within the range of 4.30–4.80 µB expected for
3551, 1640, 870, and 590 cm–1 indicate the presence of Co(II) in a tetrahedral environment [16]. The number
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 12 2003

848
KALARANI et al.
Table 3. Ligand field parameters of Co(II) and Ni(II) complexes of DCHAMA*
Parameter
[Co(DCHAMA)Cl2]
16393
[Co(DCHAMA)(NO3)2]
19431
[Ni(DCHAMA)(H2O)2Cl2]
25000
ν3, cm–1
ν2, cm–1
ν1, cm–1
ν3/ν1
9107
5464
3.00
1.66
1.80
27.00
607
0.90
546.43
0.62
38
15151
7048
2.76
2.15
1.28
21.84
889
15873
10220
2.45
1.55
1.58
36.71
681
1.50
ν2/ν1
ν3/ν2
ν3/B
B, cm–1
Dq/B
Dq, cm–1
β
0.93
822.88
0.90
10
1021.00
0.98
β, %
2
LFSE, kcal/mol**
Color
µeff, µB
18.74
Bluish green
4.60
27.77
Pink
5.10
35.00
Green
2.89
–1
–1
* Free ion value for Co(II) is 971 cm and for Ni(II) is 1041 cm
** LFSE (Ligand Field Splitting Energy) = 12 Dq, kcal/mol = 350 cm
.
–1
.
and energy positions of the absorption bands suggest a The latter two absorption bands rule out tetrahedral
tetrahedral geometry around cobalt(II). The diffuse geometry for the complex since tetrahedral complex
reflection spectrum of Co(II) nitrato complex in MgCO3
usually shows no d–d bands in the range 10000–20000
2
cm–1. These transitions are assigned to B1g
2Eg,
medium registers absorption maximum at 7058 cm–1,
4
4T2g transition. The
2
2B1g
2B2g, and B1g
2A2g, respectively, which
which arises due to T1g(F)
next two bands at 15151 and 19431 cm–1 can be attrib-
arise due to the Cu2+ in a square planar crystal field. The
uted to 4T1g (F) 4A2g and 4T1g(F) 4T1g(P) tran-
magnetic moment value of this complex is 2.18 µB. Var-
sitions, respectively. The magnetic moment is 5.1 µB ious electronic spectral parameters calculated for some
of the complexes by taking recourse to Tanabe–Sugano
diagram are given in Table 3.
due to the spin orbit coupling in an octahedral environ-
ment. Diffuse reflection spectrum recorded for Ni(II)
chloro complex exhibits three intense absorption bands
at 25000, 15873, and 10220 cm–1 that are assigned to
Electron paramagnetic resonance spectra. In the
EPR spectrum of copper(II) chloro complex, g|| is less
than 2.3, which indicates a covalent environment. The
g|| and α2 values are 2.283 and 0.86, respectively, sug-
gest that the bond is sufficiently covalent in nature and
the unpaired electron spends 14% of its time on the
ligand donor atom. Inspection of the EPR data indicates
four hyperfine lines on the g|| feature due to the interac-
tion of the unpaired electron with nuclear spin of the
copper(II) nucleus (I = 3/2, 2I + 1 = 4). Super hyperfine
lines are seen on the g feature in some cases with a
very low resolution and a decrease in the number of
lines, which is expected if the N atom is the donor atom.
Based on the spectral data and magnetic moment val-
ues, distorted octahedral geometry is assigned to the
3A2g
3T2g(P)(ν3), 3A2g
3T1g(F)(ν2), and 3A2g
3T2g(ν1), respectively. These three bands are character-
istic of six-coordinated nickel(II) complex. The mag-
netic moment value is 2.89 µB, which does not differ
much from the only spin value. The µeff value supports
the octahedral geometry proposed for Ni(II) chloro
complex based on UV-VIS spectral studies. The elec-
tronic absorption spectrum of copper(II) chloro com-
plex exhibits a broad band at 13474 cm–1 which is
assigned to 2Eg
dral environment [17, 18] in this complex. Though
three transitions 2B1 2A1 (ν1), 2B1 2B2 (ν2), and
2B1 2E (ν3) are expected in copper(II) complexes of
2T2g suggesting a distorted octahe-
D2h symmetry due to Jahn–Teller distortion, they are copper(II) chloro complex. The EPR spectrum of cop-
per(II) nitrato complex exhibits four clear bands in the
g|| region and a clear g band with values of g|| = 2.182
and g = 2.097 expected for copper(II) complexes.
Hyperfine splitting constant A|| of the complex is 175 G
often close in energy and give rise to a single broad
band. The intense band that appears near 38000 cm–1
might be of charge transfer origin. The room tempera-
ture magnetic moment of the complex is 1.83 µB. The
diffuse reflection spectrum of Cu(II) nitrato complex
exhibits a broad band centered at 16571 cm–1 along
which is typical of square planar complexes. The α2
value of 0.96 indicates that the bond is covalent in
with two less intense bands at 13774 and 10204 cm–1. nature and the unpaired electron spends 4% of its time
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 12 2003

SYNTHESIS OF 4-DICYCLOHEXYLAMINOMETHYL ANTIPYRINE
849
on the ligand donor atom. From the g|| > g trend, it is in Table 4. Based on the above discussion of the physi-
cal characteristics of the complexes, the tentative struc-
ture types are assigned as follows:
clear that unpaired electron lies predominantly on the
dx2 orbital. The EPR spectral parameters are given
– y2
H3C
H3C
H3C
H3C
CH
N
CH
N
H3C
H3C
CH
N
2
2
2
Cl
Cl
Cl
N
N
N
X
N
N
O
O
N
O
Co
Fe
M
Cl
Cl
Cl
Cl
X
M = Ni, Cu; X = H2O
H C
3
CH
N
H C
3
CH
N
2
2
H C N
3
H C N
3
O
Cu
N
Co
O
N
O
O
O
NO
N
2
O
O
O
O
N
O N
2
O
Thermal studies and evaluation of thermody- stage of the decomposition occurs in the 650–775°C
namic parameters. The TG/DTG of DCHAMA shows
a two-stage decomposition pattern. DCHAMA is stable
up to 150°C. A gradual mass loss is observed up to
400°C. The second stage decomposition temperature
range is 425–600°C. An exotherm at 525°C suggests an
oxidative degradation of the ligand. In the TG curve of
[Fe(DCHAMA)Cl3], the first stage of the decomposi-
tion starts at 300°C and mass loss occurs up to 400°C
which may be due to the loss of one of the cyclohexyl
moieties (calcd. 15.3%, obs. 15.0%). The second stage
of the decomposition starts at 400°C and ends at 675°C.
The mass of the final residue corresponds to the forma-
tion of Fe2O3 (calcd. 29.5%, obs. 29.0%). The TG curve
of the [Co(DCHAMA)Cl2] suggests two-stage decom-
position. The complex is thermally stable up to 325°C.
The first stage decomposition temperature range is
325–425°C. The second stage of the decomposition
starts at 500°C and ends at 675°C. The mass of the final
residue corresponds to the formation of Co2O3 (calcd.
32.47%, obs. 33.0%). The TG curve of the
[Cu(DCHAMA)(H2O)2Cl2] complex records a three-
stage decomposition pattern. It registers a mass loss at
120°C corresponding to the elimination of two coordi-
nated water molecules (calcd. 6.5%, obs. 7.0%). The
anhydrous complex is thermally stable up to 150°C as
indicated by a plateau in this region. The subsequent
mass loss corresponds to the removal of one of the
cyclohexyl moieties from the complex (calcd. 15.0%,
obs. 16.0%). The second stage of the decomposition
occurs in the temperature range 275–375°C. The third
range and the mass of the final residue does not corre-
spond to any definite product. The thermal stabilities of
the metal chloro complexes of DCHAMA are found to
be as follows:
[Co(DCHAMA)Cl2] > [Fe(DCHAMA)Cl3]
> DCHAMA > [Cu(DCHAMA)(H2O)2Cl2].
The bonding atoms being the same in all the com-
plexes, the thermal stability is influenced by the geom-
etry of the complexes. Among the complexes investi-
gated, it is found that the lower the coordination num-
ber the higher the thermal stability.
Table 4. EPR spectral parameters of Cu(II) complexes of
DCHAMA
Parameters [CuDCHAMA(H2O)2Cl2] [Cu(DCHAMA)(NO3)2]
g11
2.283
2.099
2.182
2.097
g
gav
2.160
2.182
G
2.91
3.69
A11, G
A11, cm–1
A , cm–1
Aav, cm–1
α2
150
175
159.89 × 10–4
5.88 × 10–3
9.25 × 10–3
0.86
192.22 × 10–4
7.34 × 10–3
11.30 × 10–3
0.96
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 12 2003

850
KALARANI et al.
Table 5. Thermodynamic parameters for DCHAMA and its metal complexes
M.K.N. equation
C.R. equation
Compound
Stage
Ea,
kJ/mol
∆S#,
J/(K mol)
∆H#,
∆G#,
Ea,
∆S#,
J/(K mol)
∆H#,
∆G#,
kJ/mol kJ/mol kJ/mol
kJ/mol kJ/mol
DCHAMA
I
36.17
113.89
112.41
82.27
–170.56
–86.36
–51.35
–141.69
–48.05
–36.21
–125.33
–132.23
–23.50
25.73 132.84 35.85
–171.56
–86.78
–51.64
–142.38
–48.34
–36.42
–126.04
–132.95
–23.66
25.41 133.15
100.24 169.49
101.40 134.71
66.96 194.24
105.20 134.87
157.62 190.36
II
I
100.62 169.53 113.51
101.69 134.81 112.12
[Fe(DCHAMA)Cl3]
II
I
67.40 194.07
81.83
[Co(DCHAMA)Cl2]
115.70
172.95
42.82
105.50 134.98 115.40
157.99 190.56 172.57
II
I
[Cu(DCHAMA)(H2O)2Cl2]
35.62
89.89
42.58
59.71
35.38
89.96
II
III
60.04
50.03 129.64
49.70 129.74
196.94 219.97
213.54
197.36 220.23 213.12
Table 6. Antibacterial activity of DCHAMA and its Fe(III), Co(II), and Ni(II) complexes
S. aureus
E. coli
concentration of compound, µg/ml
concentration of compound, µg/ml
Compound
25
50
75
100
125
150
25
50
75
100
125
150
% inhibition
% inhibition
Streptomycin
82
77
87
90
79
89
82
90
94
84
91
87
92
94
89
92
90
94
96
93
94
92
96
96
96
96
92
96
96
96
65
67
64
82
60
72
74
70
86
69
83
86
78
90
74
86
92
83
92
80
90
93
84
92
81
91
94
85
92
83
DCHAMA
[Fe(DCHAMA)Cl3]
[Co(DCHAMA)Cl2]
[Ni(DCHAMA)(H2O)2Cl2]
The kinetic and thermodynamic parameters of the percentage of inhibition of the bacterial growth are
DCHAMA and its metal complexes evaluated using CR presented in Table 6.
and MKN equations are given in Table 5. Plot of the
The order of activity of DCHAMA and its metal
left-hand side of the CR and MKN equations versus 1/T
complexes against E. coli is [Co(DCHAMA)Cl2] >
was linear and the correlation coefficient value r
DCHAMA > Streptomycin > [Fe(DCHAMA)Cl3] >
approached to unity. The order parameter n was found
[Ni(DCHAMA))(H2O)2Cl2]. Against S. aureus, the activ-
to be 1 for all the complexes. From the slope of the lin-
ity order is [Co(DCHAMA)Cl2] > [Fe(DCHAMA)Cl3] >
ear plot, Ea is evaluated. A closer view of the TG/DTG
Streptomycin
>
[Ni(DCHAMA)(H2O)2Cl2]
>
curves and their corresponding kinetic data indicates a
two/three stage degradation pattern for the ligand and
its metal chelates. The DTG curve records an intense
sharp peak for the last stage of the decomposition of the
complexes. In all the cases the initial stage of decompo-
sition corresponds to the loss of water/degradation of
organic moiety and the last stage involves the formation
of the metal oxides. Kinetic parameters calculated indi-
cate that the entropy of activation is negative and so
transformations take place to a more ordered form and
the reactions are slow as inferred from the TG curve.
DCHAMA. From the above observation it is clear that
coordinately unsaturated complexes are found to be
more active than the coordinately saturated ones. The
higher activity of the coordinately unsaturated complex
may be due to the fact that the metal atom in the com-
plex is more prone for further interaction with the ligat-
ing sites like the enzymatic functional groups in the
biological system in order to increase its coordination
number. The metabolism of the microbe is probably
inhibited as soon as the metal atom binds with enzy-
matic functional groups.
Biological studies. Concentrations of 100 and
50 µg/ml of the test compound exhibit maximum inhi-
bition against E. coli and S. aureus, respectively. Fur-
ther increase in concentration of the test compounds
shows no pronounced increase in activity. The results of
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