Synthesis and characterization of Mn(II), Au(III) and Zr(IV) hippurates complexes

Article abstract of DOI:10.1016/j.saa.2007.09.020

Mn(II), Au(III) and Zr(III) complexes with N-benzoylglycine (hippuric acid) (abbreviation hipH) were synthesized and characterized by elemental analysis, molar conductivity, magnetic measurements, spectral methods (mid-infrared, ¹H NMR, mass, X

Full text of DOI:10.1016/j.saa.2007.09.020

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 840–849
Synthesis and characterization of Mn(II), Au(III) and Zr(IV)
hippurates complexes
a,∗
b
a
Moamen S. Refat , Sabry A. El-Korashy , Ahmed S. Ahmed
a
Department of Chemistry, Faculty of Education, Port Said, Suez Canal University, Mohamed Ali Street, Port Said, Egypt
b
Department of Chemistry, Faculty of Science, Suez Canal University, Ismailia, Egypt
Received 18 July 2007; received in revised form 13 September 2007; accepted 20 September 2007
Abstract
Mn(II), Au(III)andZr(III)complexeswith N-benzoylglycine(hippuricacid)(abbreviationhipH)weresynthesizedandcharacterizedbyelemental
1
analysis, molarconductivity, magneticmeasurements, spectralmethods(mid-infrared, HNMR, mass, X-raypowderdiffractionandUV/visspectra)
and simultaneous thermal analysis (TG and DTG) techniques. The molar conductance measurements proved that all hippuric acid complexes are
non-electrolytes. The electronic spectra and magnetic susceptibility measurements were used to infer the structures. The IR spectra of the ligand
and its complexes are used to identify the type of bonding. The kinetic thermodynamic parameters such as: E*, ꢀH*, ꢀS* and ꢀG* are estimated
from the DTG curves. The free ligand and its complexes have been studied for their possible biological antifungal activity.
©
2007 Elsevier B.V. All rights reserved.
1
Keywords: Hippuric acid; Infrared spectra; Thermodynamic parameters; H NMR spectra; Microbiological screening
1
. Introduction
a remarkable importance [6], and when discussing the possi-
bility of introducing an amino acid into an anticancer drug, it
is very important to know whether the amino acid forms metal
complexes and in particular, any special metal complexes.
Hippuric acid is a monocarboxylic acid with three types of
donor site: the nitrogen and oxygen atoms of the amide group,
and the oxygen atom of the carboxylic acid group.
The literature reveals that the hippuric acid is potentially
capable of forming coordinate bonds with many metal ions
through acarboxylic oxygen atom as a monodentate or bound
through the carboxylic oxygen atoms as a bidentate [7–18].
The NH group of L coordinates to the central metal atom
only in some complexes [5,19]. Infrared spectroscopy has been
widely used as a powerful means for this purpose, a shift in
the carboxylic stretching vibrations to lower wave numbers is
usually taken to indicate a metal–oxygen bond [17]. X-ray crys-
tal structure determination for some metal hippuric complexes
[Cd(hip)2(cyt)(H2O)]2 [7] and [Cu2(OH)(H2O)-(bipy)2(Am-
hip)](NO3)2·4H2O [8] have been reported and indicated that
the hippurate anions coordinated to cadmium(II) and copper(II)
as a bidentate via the two oxygen atoms of carboxylic group
after being deprotonated.
Amino acids and their compounds with different metal ions
play an important role in biology, pharmacy and industry [1].
Hippuric acid, (hippH), N-benzoylglycine, benzoylaminoacetic
acid, one of the amino acids, present in the urine of herbivorous
animals; also in smaller amounts in human urine [2]. Liebig [3] is
the first who discover the compound named hippuric acid which
was isolated from equine urine and in contrast to benzoic acid,
it contains nitrogen. Hippuric acid is synthesized in the liver
as derivative of glycine as a metabolite of benzoic acid urinary
excretion [4].
Coordination chemists have been interested for many years in
the donor properties of amino acids as models for metal–protein
interaction and recent studies have also emphasized the reac-
tivity of coordinated amino acids in the hope of finding simple
and easily interpretable models of reactivity of some biological
system which contain metals [5].
Further, a great deal of attention has been paid recently to
the close relationships between metals, or their complexes, and
carcinogenesis and some metal complexes are used in anti-
cancer therapy. In cancer chemotherapy amino acids assume
The present investigation was undertaken to study the course
of the reaction of hippuric acid with Mn(II), Au(III) and Zr(IV)
and the products were characterized. The thermal stabilities and
thekineticparametersdatawerecalculatedaswellastheantibio-
∗
Corresponding author.
E-mail address: msrefat@yahoo.com (M.S. Refat).
1
386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.09.020

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
841
logical screening of these complexes and the free ligands against
different fungi species have been reported.
ide. The metal salts were dissolved in 20 ml of methanol and
then the prepared solutions were slowly added to the solution of
the ligand under magnetic stirring. After heating for about 1 h,
the pH of each solution was then adjusted to 7.0 again by addi-
tion of methanolic solution of sodium hydroxide. The obtained
precipitates were filtered off, wash with hot methanol and dried
2
. Experimental
2
.1. Materials and instrumentation
◦
at 60 C.
All chemicals were reagent grade and were used without
further purification. Hippuric acid was purchased from Fluka
Chemical Co., MnCl2·4H2O, KAuCl4 and ZrCl4 from (Merck
Co.).
Carbon and hydrogen contents were determined using a
Perkin-Elmer CHN 2400 in the Micro-analytical Unit at the Fac-
ulty of Science, Cairo University, Egypt. The metal content was
found gravimetrically by converting the compounds into their
corresponding oxides.
2.2.1. Synthesis of hippurate complexes
2.2.1.1. [Mn(hip)2(H2O)2]·2H2O (I, C18H24N2O10Mn) com-
plex. Hippuric acid (0.716 g, 4.0 mmol) was added to 30 ml
methanol and the pH of the solution was adjusted at 7.0,
then 10 ml methanolic solution of (0.396 g, 2.0 mmol) of
MnCl2·2H2O was added with continuously stirring, after heat-
ing the mixture was titrated with methanolic sodium hydroxide
(0.1 M) to adjust pH at 7.0. The precipitate was settle down and
filtered off, washed several times by minimum amounts of hot
methanol and dried under vacuo over anhydrous CaCl2.
IR spectra were recorded on Bruker FTIR spectropho-
−
1
tometer (4000–400 cm ) in KBr pellets. The UV–vis spectra
were determined in the DMSO solvent with concentration
−
3
(
1.0 × 10 M) for the free ligand and its complexes using
2.2.1.2. [Au(hip)3]·3H2O (II, C27H30N3O12Au) complex. A
similar procedure as that described for complex (I) was car-
ried out, by mixing (0.537 g, 3.00 mmol) of hippuric acid with
KAuCl4 (0.377 g, 1.0 mmol).
Jenway 6405 Spectrophotometer with 1 cm quartz cell, in the
range 200–800 nm. Molar conductivities of freshly prepared
−3
3
1
.0 × 10 mol dm DMSO solutions were measured using Jen-
way 4010 conductivity meter.
Magnetic measurements were carried out on a Sherwood
Scientific magnetic balance in the micro analytical laboratory,
faculty of science, Mansoura University, Egypt using Gouy
method.
Calibration: Two very good solid calibrants are used:
Hg[Co(CNS)4] and [Ni(en)3](S2O3). They are easily prepared
pure, do not decompose or absorb moisture and pack well. Their
2.2.1.3. [Zr(hip)2Cl2]·4H2O (III, C18H24N2O10Cl2Zr) com-
plex. A cream complex, [Zr(hip)2Cl2]·4H2O was prepared
during the reaction of (0.716 g, 4.0 mmol) hippuric acid with
(0.233 g, 1.0 mmol) of ZrCl4 by a method similar to that used
for the preparation of (I) complex.
2.3. Antifungal investigation
◦
−6
−6
susceptibilities at 20 C are 16.44 × 10 and 11.03 × 10
−
6
−6
c.g.s. Units, decreasing by 0.05 × 10 and 0.04 × 10 per
degree temperature raise respectively, near room temperature.
The cobalt compound, besides having the higher susceptibil-
ity, also packs rather densely and is suitable for calibrating
low fields, while the nickel compound with lower susceptibil-
ity and density is suitable for higher field [20]. Here we are
For these investigations the hole well method was applied.
The investigated isolates of fungi were seeded in tubes with
3
nutrient broth (NB). The seeded NB (1 cm ) was homogenized
3
◦
in the tubes with 9 cm of melted (45 C) nutrient agar (NA).
The homogeneous suspensions were poured into Petri dishes.
The holes (diameter 4 mm) were done in the cool medium. After
1
−3
3
used Hg[Co(CNS)4] only as calibrant. H NMR spectrum of
cooling in these holes, 2 × 10 dm of the investigated com-
the free acids and Au3 complexes were recorded on Varian
+
pounds were applied using a micropipette. After incubation for
◦
Gemini 200 MHz spectrometer using DMSO-d as solvent and
7 days in a thermostat at 25–27 C, the inhibition (sterile) zone
6
TMS as an internal reference. The purity of the ligand and
diameters (including disc) were measured and expressed mm.
An inhibition zone diameter over 7 mm indicates that the tested
compound is active against the fungi under investigation.
The antifungal activities of the investigated compounds were
tested against Aspergillus flavus ps., Fusarium solani ps. and
Penicillium verrcosum ps. In the same time with the antifungal
investigations of the complexes, the free ligand was also tested,
as well as the pure solvent. The concentration of each solution
[
Zr(hip)2Cl2]·4H2O complexes were checked from mass spec-
tra at 70 eV by using AEI MS 30 mass spectrometer. The X-ray
powder diffraction analyses were carried out by using Philips Pw
1
370 X ray generator. Radiation was provided by copper target
(
Cu/Ni) high intensity X-ray tube operated at 40 kV and 20 MA.
Divergenceslitandthereceivingslitwere1and0.1, respectively.
Thermogravimetric analysis (TGA and DTG) were carried out in
−
1
−3
3
dynamic nitrogen atmosphere (30 ml min ) with a heating rate
was 1.0 × 10 mol dm . Commercial DMSO was employed to
◦
−1
of 10 C min using a Schimadzu TGA-50H thermal analyzer.
dissolve the tested samples.
2
.2. Synthesis of metal complexes
3. Results and discussion
A general method is: the desired weight of the free ligand
was dissolved in 30 ml methanol and the solution was adjusted
to pH 7.0 by addition of methanolic solution of sodium hydrox-
The complexes are air-stable, hygroscopic, with higher melt-
ing points, insoluble in H2O and most of organic solvents, but
partly soluble in DMSO and DMF.

8
42
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
The elemental analysis data f the complexes indicates a
:2 metal:ligand stoichiometry for [Mn(hip)2(H2O)2]·2H2O and
Zr(hip)2Cl2]·4H2O complex, 1:3 for [Au(hip)3]·3H2O com-
plex.
CHN data, but in the case of [Zr(hip)2Cl2]·4H2O complex, the
1
[
chloride ion can be detected inside the coordination sphere of
the complex by the degradation of the complex using nitric
acid.
3
.1. Molar conductivities of metal chelates
The molar conductivity values for the hippurate com-
3.2. Infrared spectra
The main IR data of hippuric acid (hipH) and its complexes
are summarized in Table 1 and IR spectra are shown in Fig. 1.
The infrared spectra of hippurate complexes are similar. The
presence of the broad water bands in the 3500–3400 cm zone
confirms the presence of water molecules in all complexes, how-
−
3
plexes in DMSO solvent (1.0 × 10 mol) were in the range
−1 −1 −1
(
20.00–31.10) ꢁ cm mol . The conductivity data in these
−
1
range pronounced that, all hippurate complexes resulted are non-
electrolytes nature. Conductivity measurements have frequently
been used in structural of metal chelates (mode of coordination)
within the limits of their solubility. They provide a method of
testing the degree of ionization of the complexes, the molecu-
lar ions that a complex liberates in solution (incase of presence
anions outside the coordination sphere), the higher will be its
molar conductivity and vice versa [21]. It is clear from the
conductivity data that the complexes present seem to be non-
electrolytes. Also the molar conductance values indicate that the
anions may be exhibits outside the coordination sphere or absent
or inside the coordination sphere as in [Zr(hip)2Cl2]·4H2O.
This results were strongly supported with the chemical anal-
−
1
ever, theabsenceoftheabsorptionbandsat1760and1745 cm
,
arising from the carboxylic group (COOH) for under investiga-
tion complexes, states that the hydrogen ions in the hippuric acid
molecules are substituted by the metal ions and the hippurate
is the coordination ligand [22,23]. The stretching asymmet-
−
1
ric (νas) of carboxylate group between 1577 and 1539 cm
−
1
and of the symmetric vibrations (νs) at 1401–1397 cm con-
firm these hypotheses. The coordination of the metal ions via
oxygen carboxylate is confirmed by the ν(M–O) bands at 410,
−
1
476 and 490 cm for Mn(II), Au(III) and Zr(IV), respectively.
According to the above discussion the hippurate is coordi-
nated with the metal ions as a bidentate through the carboxylic
group.
−
ysis (elemental analysis data) where Cl ions are not detected
by addition of AgNO3 solution, this tested well matched with
Table 1
IR frequencies (cm 1) of the hippuric acid (hipH) and its metal complexes
−
Assignments
Compound
Hippuric acid
[Mn(hip)2(H2O)2]·2H2O
[Au(hip)3]·3H2O
[Zr(hip)2Cl2]·4H2O
νas(OH); H2O
ν(N–H)
–
3416
3366
3390
3342
3
3
087
075
–
–
–
ν(C–H)
ν(C O)
2940
1760
2925
–
2973
–
3062
–
1745
δb(N–H)
1621
1637
1602
1577
1539
1637
1603
1577
1542
1
602
1577
540
486
1607
−
νas(COO )
–
1
C–H deformation-
CH2–
1492
1448
–
1
1487
1397
1486
1401
−
νs(COO )
1400
δb(CH2)
1336
1
1
318
304
1296
1301
1297
ν(C–C)
δb(CH), in plane bend
δr(CH2)
1259
1185
1080
–
1161
1076
1028
1001
928
1256
1184
1078
1028
999
–
1162
1078
1029
1001
931
1
1
031
000
943
ν(C–C)
927
8
8
80
51
–
843
801
714
843
802
718
846
802
713
−
δb(COO )
ν(M–O) + ring deformation
696
694
693
695
6
6
6
90
61
32
619
534
410
617
564
476
590
490

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
843
3.3. Magnetic measurements
Magnetic measurements were carried out on a Sherwood Sci-
entific magnetic balance according to the Gauy method. The
calculationswereevaluatedbyapplyingthefollowingequations:
cl(R−R0)
χg =
9
1
0 M
χm = χgMWt
ꢀ
μ
eff
= 2.828 χmT
where χ is the mass susceptibility per g sample, c is the cali-
bration constant of the instrument and equal to 1.135, R is the
balance reading for the sample and tube, R0 is the balance read-
ing for the empty tube, M is the weight of the sample in g and T
is the absolute temperature.
The magnetic moments of the [Mn(hip)2(H2O)2]·2H2O com-
plexat T = 300 K andtheir corresponding hybridorbitalsare 4.33
3
2
and sp d , respectively.
The observed value of the effective magnetic moments μeff
operated for above complex is convenient with experimental
value 5.92 [24] obtained for high spin octahedral for the men-
tioned complex under investigation.
3.4. Electronic absorption spectra
The spectra of the barbituric acid complexes in DMSO are
shown in Fig. 2 and the spectral data are listed in Table 2. There
Table 2
The electronic spectral date of the hippuric acid (hipH) and its metal complexes
−
1
−1
Compound
hipH
λmax (nm)
ε (mol cm )
Assignment
215
402
306
1792
357
184
2802
422
2415
250
3015
2546
2647
886
␲–␲* trans.
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
n–␲* trans.
n–␲* trans.
␲–␲* trans.
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
n–␲* trans.
n–␲* trans.
␲–␲* trans.
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
n–␲* trans.
n–␲* trans.
␲–␲* trans.
␲–␲* trans.
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
n–␲* trans.
n–␲* trans.
n–␲* trans.
235
245
262
285
323
[
[
[
Mn(hip)2(H2O)2]·2H2O
210
235
247
256
275
306
Au(hip)3]·3H2O
228
240
250
260
298
316
641
1109
1197
490
2922
270
1321
2662
1442
1491
447
Fig. 1. The FT-IR spectra of hippuric and its complexes.
Zr(hip)2Cl2]·4H2O
211
The stretching vibration, ν(NH) and bending motion, δ (NH)
b
227
248
257
are observed in the spectra of free hippuric acid and its
complexes at almost the same region, around 3340 and
−1
1
600 cm , respectively. The infrared spectra of the prepared
266
281
complexes display changes in the aromatic ring vibrations in
comparison to the corresponding absorption bands free acid
2
3
96
27
1739
2983
(Table 1).

8
44
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
Fig. 2. The UV spectra of the hippuric acid and its complexes.
are six detected absorption bands at 215, 235, 245, 262, 285 and
23 nm in the spectrum of the free ligand, the first three were
and due to the OH (carboxylate group) proton at 12.50 ppm
disappears in the Au(III) complex indicating the coordination
of oxygen atom (carboxylate ion) with the metal ion [28,29].
The aromatic signals do not shift significantly, thus show-
ing that the magnetic environment of the aromatic ring has
not changed significantly with coordination. Also, according
3
assigned to ␲–␲* [25] and the second three were assigned to
n–␲* intraligand transitions [26,27], respectively, in the elec-
tronic spectrum of the ligand. These transitions also found in
the spectra of the complexes, but they are shifted and there
are evident that the increasing in the absorbance (hyperchromic
effect) clarified in all of the three mentioned hippuric acid com-
plexes attributed to the complexation behavior of hippuric acid
towards metal ions, confirming the coordination of the ligand to
the metallic ions.
1
to the H NMR data for Au(III), there is a peak appeared
at 4.86, which not found in the free hippuric acids, can be
attributed to the presence of water molecules in the com-
plex.
3.6. Mass spectra
3
.5. 1H NMR spectra
The corresponding mass fragmentation of the hippuric
The proton magnetic resonance spectra of the Au(III) com-
acid and [Zr(hip)2Cl2]·4H2O complex are presented in
Schemes 1 and 2, respectively. Mass spectrometry has been
applied in order to study the main fragmentation routes of hip-
puric acid and its Zr(IV) complex. Difference in fragmentation
was caused by the nature of the attached metal ions.
plex was analyzed in comparison of the spectra of the free
ligand (Table 3). The ligand structure is shown in Scheme 3.
The chemical shift (δ, ppm) of the different protons have been
recorded in Table 3. The brood signal exhibited by the free lig-
Table 3
1
a
b
The H NMR spectral data (δ, ppm) of the free ligand and its Au(III) complexes
Compound
H(1), COOH
H(2), CH2
H(3), NH
H(4), aromatic
H(5), aromatic
H(6), aromatic
H, H2O
Hippuric acid
12.50
–
3.99
3.72
8.63
8.11
7.91
7.92
7.53
7.52
7.40
7.48
–
4.86
[
Au(hip)3]·3H2O
a
Solvent DMSO-d6.
b
Relative to TMS.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
845
Scheme 1. Fragmentation pattern of hippuric acid.
Scheme 2. Fragmentation pattern of [Zr(hip)2Cl2]·4H2O.

8
46
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
3
.8.1. [Mn(hip)2(H2O)2]·2H2O
The thermal decomposition of this complex occurs at four
steps. The first degradation step take place in the range of
◦
3
0–150 C and it is corresponds to the eliminated of two water
molecules due to a weight loss of 7.52% in a good matching
with theoretical value 7.46%. The second step fall in the range
◦
of 150–250 C which is assigned to loss of two water molecules
and two C H (organic rest) with a weight loss 39.46% and the
6
5
calculated value is 39.22%. The third step fall in the range of
◦
2
50–350 C which is assigned to loss of C2H NO3 (organic rest)
5
with a weight loss 22.28% and the calculated value is 21.95%.
◦
The fourth step fall in the range of 350–500 C which is assigned
to loss of CO molecule with a weight loss 5.38% and the calcu-
lated value is 5.79%. This step can be interpreted according to
the transform of MnCO3 to MnO2. The MnO2 is the final product
◦
remains stable till 800 C. Reported data dealing in the thermal
analysis investigation within nitrogen atmosphere indicate that,
the Mn(II) complex decompose to give oxide contaminated with
few carbon atoms as final products, this reason, because of no
sufficiently of oxygen atoms help to evolved carbon as carbon
monoxide or dioxide).
3
.8.2. [Au(hip)3]·3H2O
The thermal decomposition of [Au(hip)3]·3H2O complex
completely in also four steps. The first degradation step take
place in the range of 30–175 C and it is corresponds to the
◦
eliminated of only one water molecule due to a weight loss of
2
.11% in a good matching with theoretical value 2.29%. The
◦
second step fall in the range of 175–300 C which is assigned to
loss of the other two water molecules with a weight loss 4.20%
and the calculated value is 4.58%. The third step fall in the
◦
range of 300–400 C which is assigned to loss of C19H24N3O
3
.5
(
organic rest) with a weight loss 44.70% and the calculated value
◦
is 44.59%. The fourth step fall in the range of 400–800 C which
is assigned to loss of two CO2 molecules with a weight loss
11.20% and the calculated value is 11.22%.
Fig. 3. The TG and DTG of the hippurate complexes.
3.8.3. [Zr(hip) Cl ]·4H O
2
2
2
The Zr(IV) hippurate complex decomposed unlike Mn(II)
and Au(III) complexes only in three steps. The first extended
3
.7. X-ray powder diffraction
X-ray powder diffraction patterns in the 6 < 2θ < 90 of
◦
from 30 to 225 C and can be assigned to the loss of four H2O
molecules, representing a weight loss of 12.36% and its calcu-
lated value is 12.20%. The second step occurring at 225–400 C
◦
◦
◦
Mn(II) hippurate complex was carried in order to obtain an
idea about the lattice dynamics of the compound. The X-ray
powder diffraction pattern throws light only on the fact that
each solid represents a definite compound of a definite struc-
ture which is not contaminated with starting materials. This
identification of the complex was done by the known method
corresponding to the loss of C7H8NO2 (organic moiety), rep-
resenting a weight loss of 23.88% and its calculated value is
◦
2
3.38%. The third step fall in the range of 400–500 C which is
assigned to loss of C7H8NO3 (organic rest) with a weight loss
2
5.18% and the calculated value is 26.09%. The final products
◦
resulted at 800 C contain ZrOCl2 polluted with carbon atoms.
[
30]. Such facts suggest that the Mn(II) hippurate complex
amorphous.
3.9. Kinetic studies
3
.8. Thermogravimetric analysis
In recent years there has been increasing interest in determin-
ing the rate-dependent parameters of solid-state non-isothermal
decomposition reactions by analysis of TG curves. Several equa-
tions [31–38] have been proposed as means of analyzing a TG
curve and obtaining values for kinetic parameters. Many authors
Thermal analysis curves (TG and DTG) of the studies com-
plexes are shown in Fig. 3. The thermoanalytical results are
summarized in Table 4.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
847
Table 4
Thermal data of the hippurate complexes (I–III)
◦
◦
Compound
Steps
Temperature range ( C)
DTG peak ( C)
TG Weight loss (%)
Assignments
2H2O
2H2O + 2C6H5 (organic moiety)
C2H6N2O3 (organic moiety)
CO
MnO2 + 3C (residue)
H2O
2H2O
C19H24N3O3.5 (organic moiety)
2CO2
1/2Au2O3 + 6C (residue)
4H2O
C7H8NO2 (organic moiety)
C7H8NO3 (organic moiety)
ZrOCl2 + 4C (residue)
Calc.
Found
[
[
[
Mn(hip)2(H2O)2]·2H2O
1st
30–150
150–250
250–350
350–500
100
226
293
400
7.46
39.34
21.95
5.79
7.52
39.22
22.28
5.38
2nd
3rd
4th
2
5.46
2.29
4.58
25.60
2.11
4.20
Au(hip)3]·3H2O
1st
30–175
175–300
300–400
400–800
71
2
3
4
nd
rd
th
267
341
622
44.59
11.22
44.70
11.20
37.79
12.36
23.88
25.18
38.58
37.32
Zr(hip)2Cl2]·4H2O
1st
30–225
225–400
400–500
75
293
454
12.20
23.38
26.09
2
3
nd
rd
38.33
[
31–36] have discussed the advantages of this method over the
are well agreement with each other. The following two methods
are discussed in brief.
conventional isothermal method. The rate of a decomposition
process can be described as the product of two separate functions
of temperature and conversion [32], using
3.9.1.1. Coats–Redfern equation
The Coats–Redfern equation, which is a typical integral
method, can be represented as:
da
=
k(T)f(α)
(1)
dt
ꢅ
α
ꢇ
ꢈ
ꢆ
∗
E
RT
dα
1−α)
A
T2
T1
where α is the fraction decomposed at time t, k(T) is the tem-
perature dependent function and f(α) is the conversion function
dependent on the mechanism of decomposition. It has been
established that the temperature dependent function k(T) is of
the Arrhenius type and can be considered as the rate constant k.
n
= ϕ
exp −
dt
(
0
For convenience of integration the lower limit T1 is usually taken
as zero. This equation on integration gives
ꢉ
ꢊ
ꢉ
ꢊ
∗
RT
ln(1−α)
E
AR
∗
ϕE
ln −
= −
+ ln
2
∗
T
k = A e−
E /RT
(2)
*
A plot of left-hand-side (LHS) against 1/T was drawn. E is the
where R is the gas constant in (J mol 1
−
−1
K ). Substituting Eq.
−1
energy of activation in J mol and calculated from the slop and
(
2) into Eq. (1), we get
−1
A in (s ) from the intercept value. The entropy of activation
ꢁ
ꢂ
S* in (J K mol ) was calculated by using the equation:
−1
−1
ꢀ
da
A
=
f(α)
ꢁ
ꢂ
∗
−
E /RT
dT
ϕ e
Ah
ꢀ
S∗ = R ln
(3)
kBTs
where ϕ is the linear heating rate dT/dt. On integration and
approximation, this equation can be obtained in the following
form:
where kB is the Boltzmann constant, h is the Plank’s constant
and Ts is the DTG peak temperature [39].
ꢃ
ꢄ
∗
E
AR
∗
ϕE
ln g(α) = −
+ ln
3.9.1.2. Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the
approximation methods. These authors derived the relation:
RT
where g(α) is a function of α dependent on the mechanism of
the reaction. The integral on the right-hand-side is known as
temperature integral and has no closed for solution. So several
techniques have been used for the evaluation of temperature
integral. Most commonly used methods for this purpose are
the differential method of Freeman and Carroll [31] integral
method of Coat and Redfern [33], the approximation method of
Horowitz and Metzger [36].
In the present investigation, the general thermal behaviors
of the hippurate complexes in terms of stability ranges, peak
temperatures and values of kinetic parameters, are shown in
Fig. 4. The kinetic parameters have been evaluated using the
following methods and the results obtained by these methods
ꢋ
−n}ꢌ
1
∗
{
1 − (1 − α)
E θ
log
=
for n
ꢀ
(4)
2.303RTs2
1
− n
when n = 1, the LHS of Eq. (4) would be log[−log(1 − α)]. For a
first-order kinetic process the Horowitz–Metzger equation may
be written in the form:
ꢃ
ꢁ
ꢂꢄ
∗
wα
wγ
E θ
log log
=
− log 2.303
2.303RT2
s
where θ = T − Ts, wγ = wα − w, wα = mass loss at the com-
pletion of the reaction; w = mass loss up to time t. The plot of

8
48
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
Fig. 4. Horowitz–Metzger (HM), Coats–Redfern (CR) of the first step of the hippurate complexes.
log[log(wα/wγ)] vs. θ was drawn and found to be linear from the
slope of which E was calculated. The pre-exponential factor,
A, was calculated from the equation:
on Aspergillus ps., Alternaria ps., and Penicillium ps., and the
effect of complexation on the ligand has no affect on the selected
fungi.
*
∗
E
A
=
3.11. Structure of the hippurate complexes
2
∗
RT
ϕ exp(−E /RTs)
s
*
The entropy of activation, ꢀS , was calculated from Eq. (3).
The enthalpy activation, ꢀH , and Gibbs free energy, ꢀG ,
Theinsolubilityofthecompoundsinbothpolarandnon-polar
solvents would suggest that they have polymeric structures [40].
The fact that these compounds were isolated as powders and not
as single crystals means that no complete structure determina-
tion can be made. Accordingly, the abovementioned discussions
*
*
*
*
*
*
*
were calculated from; ꢀH = E − RT and ꢀG = ꢀH − TꢀS ,
respectively.
using elemental analysis, magnetic studies, molar conductance,
3
.10. Antifungal investigation
1
(infrared, HNMRandmass)spectraaswellasthermogravimet-
ric analysis; the suggested structures of the hippurate complexes
can be represented in Scheme 3.
The results of antifungal actives in vitro of the ligand and
its complexes show that all the test compounds have no effect

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 840–849
849
Scheme 3. The structures of the hippuric acid and its complexes.
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