FTIR, magnetic, 1H NMR spectral and thermal studies of some chelates of caproic acid: Inhibitory effect on different kinds of bacteria

Article abstract of DOI:10.1016/j.saa.2007.07.036

A convenient method for the preparation of complexes of the Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺, ZrO²⁺, UO₂²⁺, Zr⁴⁺ and Th⁴⁺ ions with caproic acid (Hcap) is reported and this has enabled 10 complexes of caproate anion to be formulated: [Cr(cap)₃]·5H₂O, [Mn(cap)₂(H₂O)₂], [Fe(cap)₃]·12H₂O, [Co(cap)₂(H₂O)₂]·4H₂O, [Ni(cap)₂(H₂O)₂]·3H₂O, [Zn(cap)₂], [ZrO(cap)₂]·3H₂O, [UO₂(cap)(NO₃)], [Zr(cap)₂(Cl)₂] and [Th(cap)₄]. These new complexes were synthesized and characterized by elemental analysis, molar conductivity, magnetic measurements, spectral methods (mid infrared, ¹H NMR and UV-vis spectra) and simultaneous thermal analysis (TG and DTG) techniques. It has been found from the elemental analysis as well as thermal studies that the caproate ligand behaves as bidentate ligand and forming chelates with 1:1 (metal:ligand) stoichiometry for UO₂²⁺, 1:2 for (Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, ZrO²⁺ and Zr⁴⁺), 1:3 stoichiometry for (Cr³⁺ and Fe³⁺) and 1:4 for Th⁴⁺ caproate complexes, respectively, as bidentate chelating. The molar conductance measurements proved that the caproate complexes are non-electrolytes. The kinetic thermodynamic parameters such as: E*, ΔH*, ΔS* and ΔG* are estimated from the DTG curves. The antibacterial activity of the caproic acid and their complexes was evaluated against some gram positive/negative bacteria.

Full text of DOI:10.1016/j.saa.2007.07.036

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 217–233
FTIR, magnetic, 1H NMR spectral and thermal studies of some chelates
of caproic acid: Inhibitory effect on different kinds of bacteria
Moamen S. Refata,∗, Sabry A. El-Korashyb, Deo Nandan Kumarc, Ahmed S. Ahmeda
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, Ismalia, Suez Canal University, Ismalia, Egypt
c Department of Chemistry, Deshbandhu College, University of Delhi, New Delhi 110019, India
Received 10 May 2007; received in revised form 24 June 2007; accepted 3 July 2007
Abstract
AconvenientmethodforthepreparationofcomplexesoftheCr3+, Mn2+, Fe3+, Co2+, Ni2+, Zn2+, ZrO2+, UO22+, Zr4+ andTh4+ ionswithcaproicacid
(Hcap) is reported and this has enabled 10 complexes of caproate anion to be formulated: [Cr(cap)3]·5H2O, [Mn(cap)2(H2O)2], [Fe(cap)3]·12H2O,
[Co(cap)2(H2O)2]·4H2O, [Ni(cap)2(H2O)2]·3H2O, [Zn(cap)2], [ZrO(cap)2]·3H2O, [UO2(cap)(NO3)], [Zr(cap)2(Cl)2] and [Th(cap)4]. These new
complexes were synthesized and characterized by elemental analysis, molar conductivity, magnetic measurements, spectral methods (mid infrared,
1H NMR and UV–vis spectra) and simultaneous thermal analysis (TG and DTG) techniques. It has been found from the elemental analysis as
2+
well as thermal studies that the caproate ligand behaves as bidentate ligand and forming chelates with 1:1 (metal:ligand) stoichiometry for UO2
,
1:2 for (Mn2+, Co2+, Ni2+, Zn2+, ZrO2+ and Zr4+), 1:3 stoichiometry for (Cr3+ and Fe3+) and 1:4 for Th4+ caproate complexes, respectively, as
bidentate chelating. The molar conductance measurements proved that the caproate complexes are non-electrolytes. The kinetic thermodynamic
parameters such as: E*, ꢀH*, ꢀS* and ꢀG* are estimated from the DTG curves. The antibacterial activity of the caproic acid and their complexes
was evaluated against some gram positive/negative bacteria.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Caproic acid; Infrared spectra; Thermodynamic paramenters; 1H NMR spectra; Antibacterial activity
1. Introduction
n-Caproic acid (n-hexanoic acid) (Scheme 1) C6H12O2,
occurs in milk fats (about 2%), and in coconut oil (<1%) and is
employed in the manufacture of pharmaceuticals, esters for arti-
ficial flavors and of hexyl derivatives especially hexylphenols,
hexylresorcinol [13]. It is slightly soluble in water and readily
soluble in ethanol and ether [14].
Caproic acid has been used as a good extracting agent [15–17]
for rare earths, zirconium, chromium, manganese, iron, gallium
as well as aluminum with catechol violet by a mixture contain-
ing CHCl3, caproic and propionic acids. Pietsch [18] extracted
caproates of thorium, lead and iron into CHCl3. Compounds
of transition and non-transition elements with caproic acid are
not so common. A literature survey reveals that there are some
papers on the preparation of caproates of rare earth elements
[19,20] and anhydrous copper(II) hexanoate from cuprous and
cupric oxides [21]. Also, Refat et al. [22] have synthesized and
characterized Cu(II), Cd(II), Pb(II) and Al(III) caproate com-
plexes.
The carboxylic acid complexes are very interesting [1]
because they can contain two or more anti-ferromagnetically
coupled metal centers [2–9]. Since each carboxylate oxygen
atom has two lone pairs, they can either have only one lone
pair involved in the coordination resulting in a dinuclear paddle-
wheel structure or has the second lone pair donated to a metal
ion of another paddle-wheel structure resulting in a polymeric
structure. Also the binding of metal ions to carboxylic acids
has been a subject of intense research with diverse applications,
including as model systems for metalloactive sites in bioinor-
ganic chemistry [10,11]. The structural diversity encountered in
metal–carboxylate complexes can be attributed to the versatile
bonding of the carboxylate group which can act as a bidentate
ligand or a bridging ligand [1,12].
∗
The present investigation was undertaken to study the course
of the reaction of caproic acid with Cr(III), Mn(II), Fe(III),
Corresponding author.
E-mail address: msrefat@yahoo.com (M.S. Refat).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.07.036

218
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
heating rate of 10 C/min using a Schimadzu TGA-50H thermal
analyzer.
2.2. Synthesis of metal complexes
Scheme 1. Caproic acid.
2.2.1. [Cr(cap)3]·5H2O (I, C18H43O11Cr) complex
Caproic acid (3.0 mmol) was added to 30 ml methanol and
titrated against methanolic sodium hydroxide (0.1 M) to adjust
pH at 7.0, then 10 ml methanolic solution of (0.266 g, 1.0 mmol)
of CrCl3·6H2O was added with continuously stirring, after that
the mixture was warmed at about ∼60 ◦C and then neutralized.
Immediately, the black blue precipitate was settle down and fil-
tered off, washed several times by minimum amounts of hot
methanol and dried under vacuo over anhydrous CaCl2.
Co(II), Ni(II), Zn(II), ZrO(II), UO2(II), Zr(IV) and Th(IV) metal
ions and the products were characterized. The thermal stabilities
and the kinetic parameters data were calculated as well as the
antibacterial screening of these complexes and the free ligand
against different bacterial species has been reported.
2. Experimental
2.1. Materials and instrumentation
2.2.2. [Mn(cap)2(H2O)2] (II, C12H26O6Mn) complex
A similar procedure as that described for complex (I)
was carried out, by mixing (2.00 mmol) of caproic acid with
MnCl2·2H2O (0.198 g, 1.0 mmol).
All chemicals were reagent grade and were used without fur-
ther purification. Caproic acid was purchased from Fluka Chem-
ical Co., CrCl3·6H2O, MnCl2·4H2O, FeCl3, CoCl2·6H2O,
NiCl2·6H2O, ZnBr2, ZrOCl2·6H2O, UO2(NO3)2·6H2O, ZrCl4
and ThCl4 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.
2.2.3. [Fe(cap)3]·12H2O (III, C18H57O18Fe) complex
A brown complex, [Fe(cap)3]·12H2O was prepared during
the reaction of (3 mmol) caproic acid with (0.162 g, 1.0 mmol)
of FeCl3 by a method similar to that used for the preparation of
(I) complex.
IR spectra were recorded on Bruker FTIR Spectropho-
tometer (4000–400 cm−1) in KBr pellets. The UV–vis, spectra
were determined in the DMSO solvent with concentration
(1.0 × 10−3 M) for the caproic acid and their ten complexes
using Jenway 6405 Spectrophotometer with 1cm quartz cell,
in the range 800–200 nm. Molar conductivities of freshly pre-
pared 1.0 × 10−3 mol/dm−3 DMSO solutions were measured
using Jenway 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.
2.2.4. [Co(cap)2(H2O)2]·4H2O (IV, C12H34O10Co)
complex
Exactly, like the above procedure of the preparation of
Mn(II)caproatecomplex. AmethanolicsolutionofCoCl2·6H2O
(0.257 g, 1.0 mmol) was mixed with an equal volume of caproic
acid solution (2.0 mmol) in methanol. The mixture was allowed
to stays at room temperature for about 1 h with constant stirring
and then heated on a water bath at ∼60 ◦C for 30 min. The black
green complex was filtered off, washed several times with hot
methanol, dried under vacuo over anhydrous CaCl2.
2.2.5. [Ni(cap)2(H2O)2]·3H2O (V, C12H32O9Ni) complex
The nickel(II) caproate complex was prepared by the same
method which used for preparation of the Mn(II) and Co(II)
complexes. The weight of NiCl2·6H2O was (0.256 g, 1.0 mmol)
and mixing with caproic acid by (1:2) molar ratio in methanol
as solvent.
2.1.1. 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 suscepti-
bilities at 20 ◦C are 16.44 × 10−6 and 11.03 × 10−6 c.g.s. Units,
decreasing by 0.05 × 10−6 and 0.04 × 10−6 per degree tem-
perature raise respectively, near room temperature. The cobalt
compound, besides having the higher susceptibility, also packs
rather densely and is suitable for calibrating low fields, while
the nickel compound with lower susceptibility and density is
suitable for higher field [23]. Here we are used Hg[Co(CNS)4]
only as calibrant.
2.2.6. [Zn(cap)2] (VI, C12H22O4Zn) complex
The complex, [Zn(cap)2], was prepared by mixing equal vol-
umes (30 ml) of caproic acid (2.0 mmol) with ZnBr2 (0.224 g,
1.0 mmol). The mixture was neutralized by titrated with NaOH
to adjust pH at 7.0 and then heated on a water bath at 60 ◦C
with constant stirring for about 45 min. A white solid complex
was precipitated and its amount increasing with increasing the
time of heating. The obtained precipitate was separated, washed
several times with hot methanol and then dried in vacuo over
anhydrous CaCl2 and recrystalization occurs using a mixture of
water and methanol (1:1).
1H NMR spectrum of the free acid, Zn2+, Fe3+ and Th4+
complexes were recorded on Varian Gemini 200 MHz spec-
trometer using DMSO-d6 as solvent and TMS as an internal
reference. Thermogravimetric analysis (TGA and DTG) were
carried out in dynamic nitrogen atmosphere (30 ml/min) with a

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
219
2.2.7. [ZrO(cap)2]·3H2O (VII, C12H28O8Zr) and
3. Results and discussion
[UO2(cap)(NO3)] (VIII, C6H11NO7U) complexes
Preparation of these two complexes followed essentially
the same procedure as preparation of (I), but the weight of
ZrOCl2·6H2O and UO2(NO3)2·6H2O were (0.286 g, 1.0 mmol)
and (0.502 g, 1.0 mmol), respectively. The pH was adjusted at
7.0.
The results of the elemental analysis and some physical char-
acteristics of the obtained compounds are given in Table 1.
The complexes are air-stable, hygroscopic, with higher melt-
ing points, insoluble in H2O and most of organic solvents except
for DMSO and DMF.
The elemental analysis data (Table 1) of the complexes
indicates a 1:1 metal:ligand stoichiometry for [UO2(cap)
(NO3)] complexes, 1:2 for [Mn(cap)2(H2O)2], [Co(cap)2
(H2O)2]·4H2O, [Ni(cap)2(H2O)2]·3H2O, [Zn(cap)2], [ZrO
(cap)2]·3H2O, and [Zr(cap)2(Cl)2], 1:3 for [Cr(cap)3]·5H2O and
[Fe(cap)3]·12H2O and 1:4 for [Th(cap)4].
2.2.8. [Zr(cap)2(Cl)2] (IX, C12H22O4Cl2Zr) and
[Th(cap)4] (X, C24H44O8Th) complexes
These two complexes, [Zr(cap)2(Cl)2] and [Th(cap)4] were
prepared during the reaction of caproic acid with ZrCl4 and
ThCl4 at 60 ◦C, respectively, in (1:4) molar ratio (M4+: cap)
by a method similar to that used for the preparation of
[Cr(cap)3]·5H2O complex. These complexes were started to set-
tle down as a white precipitate after a 1 h of heating. Separately
by filtration, washed several times with hot methanol to remove
any residue of caproic acid and then dried in a vacuum dissector
over CaCl2 for about 4 days.
3.1. Molar conductivities of metal chelates
The molar conductivity values for the caproate com-
plexes in DMSO solvent (1.0 × 10−3 mol) were in the range
(9.64–31.80) ꢁ−1 cm−1 mol−1, suggesting them to be non-
electrolytes nature (Table 1). 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 molecular 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 [24]. 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 inside the coordination sphere as in
[UO2(cap)(NO3)]·H2Oand[Zr(cap)2(Cl)2]complexesorabsent
as found in the others. This results were strongly supported with
the chemical analysis (elemental analysis data) where Cl− ions
are not detected by addition of AgNO3 solution, this tested well
matched with CHN data, but in the case of [Zr(cap)2(Cl)2] com-
plex, the chloride ion can be detected inside the coordination
sphere of the complex by the degradation of the complex using
nitric acid.
2.3. Antibactrial investigation
For these investigations the hole well method was applied.
The investigated isolates of bacteria were seeded in tubes with
nutrient broth (NB). The seeded NB (1 cm3) was homogenized
in the tubes with 9 cm3 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 cooling in these holes, 2 × 10−3 dm3 of the investigated
compounds were applied using a micropipette. After incuba-
tion for 24 h in a thermostat at 25–27 ◦C, the inhibition (sterile)
zone diameters (including disc) were measured and expressed
mm. An inhibition zone diameter over 7 mm indicates that the
tested compound is active against the bacteria under investiga-
tion.
The antibacterial activities of the investigated compounds
were tested against Escherichia coli, Streptococcus penumo-
nia and Bacillus subtilis. The concentration of each solution
was 1.0 × 10−3 mol dm3. Commercial DMSO was employed to
dissolve the tested samples.
3.2. Infrared spectra
The main IR data are summarized in Table 2. Caproic acid
exhibits a strong absorption band at 1711 cm−1 due to the
Table 1
Elemental analyses and physical data of the caproate complexes
Compounds
Molecular mp (◦C) Color
weight
Content ((calculated) found)
% C % H
Black-blue (44.35) 43.09 (8.83) 8.63
ꢂm (ꢁ−1 cm−1
mol−1
)
% N
%M
[Cr(cap)3]·5H2O (I, C18H43O11Cr)
[Mn(cap)2(H2O)2] (II, C12H26O6Mn)
[Fe(cap)3]·12H2O (III, C18H57O18Fe)
486.99
320.94
616.85
>300
220
260
–
–
–
–
–
–
–
(10.67) 10.33 24.30
(17.12) 17.08 18.70
Brown
Brown
(44.87) 43.37 (8.10) 7.26
(35.01) 34.68 (9.24) 8.92
(9.05) 8.95
23.04
[Co(cap)2(H2O)2]·4H2O (IV, C12H34O10Co) 396.93
>300
>300
160
>300
>300
>300
>300
Black-green (36.27) 35.94 (8.56) 8.47
Pall-green
White
White
Yellow
White
(14.84) 14.77 31.80
(15.50) 13.79 30.10
(22.13) 21.98 9.80
(23.31) 23.24 23.80
[Ni(cap)2(H2O)2]·3H2O (V, C12H32O9Ni)
378.70
295.38
391.22
447.03
392.22
692.04
(38.02) 36.96 (8.44) 8.36
(48.75) 48.43 (7.44) 7.31
(36.80) 35.62 (7.15) 7.09
(16.11) 15.27 (2.46) 2.41 (3.13) 3.07 (53.24) 53.27 14.34
(36.71) 36.96 (5.61) 5.48
(41.62) 41.32 (6.36) 5.93
[Zn(cap)2] (VI, C12H22O4Zn)
[ZrO(cap)2]·3H2O (VII, C12H28O8Zr)
[UO2(cap)(NO3)] (VIII, C6H11NO7U)
[Zr(cap)2(Cl)2] (IX, C12H22O4Cl2Zr)
[Th(cap)4] (X, C24H44O8Th)
–
–
(23.26) 23.73 12.18
(33.53) 33.46 9.64
White

220
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
free carboxylic C O group. This group disappeared in the
spectra of their complexes. Interestingly, there are two bands
appeared at the range of 1515–1568 cm−1 which corresponding
to νas(COO−) and the other band is exhibited within the range
1313–1346 cm−1 assigned to νs(COO−).
Dependently, the antisymmetric and symmetric stretching
vibration modes (νas(COO−), and νs(COO−)) of the COO−
group, the structure of our complexes can be elucidated [25].
The direction of the frequency shift of the νas(COO−) and the
νs(COO−) bands with respect to those of the free ion depends
on the coordination mode of the COO− group with the metal
ion. There are three principle modes of coordination as shown
in Scheme 2.
Nakamoto and McCarthy [26] have established that if the
coordination is monodentate (structure a) the νas(COO−) and
νs(COO−) will be shifted to higher and lower frequencies,
respectively. Whereas, if the coordination is chelating bidentate
(structure b) or bridging bidentate (structure c) both νas(COO−)
and νs(COO−) frequencies will change in the same direction
because the bond orders of both C O bonds would change
by the same amount. Based on these facts and comparison
the νas(COO−) and νs(COO−) frequencies of our caproate
complexes by the νas(COO−) and νs(COO−) frequencies of
sodium carboxylate [27], as shown in Table 3, we can say
that: all of the resulted complexes are chelating bidentate struc-
ture.
The stretching broad band vibration of OH− group ν(O H)
is occurred as expected [28] at the range 3418–3445 cm−1. The
angular deformation motions of the coordinated water in the
hydrated caproate complexes can be classified into four types of
vibrations: δb(bend), δr(rock), δt(twist) and δw(wag).
The assignments of these motions in [Mn(cap)2(H2O)2],
[Co(cap)2(H2O)2]·4H2O and [Ni(cap)2(H2O)2]·3H2O com-
plexes., areasfollows. Thebendingmotion, δb(H2O), isassigned
to itscharacteristicband aroundat ∼1630 cm−1 (shoulderband).
The rocking motions, δr(H2O), is assigned at 730 cm−1 and
the wagging motion, δw(H2O), is observed at ∼600 cm−1. The
twisting motion, δt(H2O), is observed at above 620 cm−1. It
should be mentioned here that these assignments for both the
bond stretches and angular deformation of the coordinated water
molecules fall in the frequency regions reported for related com-
plexes [26].
The characteristic stretching vibrations of the bidentate
nitrato group, NO3−, in the [UO2(cap)(NO3)] complex is
observed at 1375 cm−1 (shoulder peak) attributed to ν(NO2)
[26]. The stretching motion of (ν(N O)) is observed at
1465 cm−1 as a very strong band combined with δ(CC) vibra-
tion motion in the same place, while the two bending motion
of the type δ(NO2) are well resolved and observed at 750
and 653 cm−1 as weak shoulder and weak bands, respec-
tively.
The ν(U O) vibration in the uranyl complex is observed as
expected as a strong band at 928 cm−1 is a good agreement
with those known for many dioxouranium(VI) complexes [26].
On the other hand concerning, the infrared spectra of [ZrO]2+
complex show a medium absorption band at 1109 cm−1 due to
ν(Zr O) as expected [26].

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
221
Scheme 2. Possible coordination features of the carboxylate group.
Table 3
Asymmetric and symmetric stretching vibrations of the carboxylate group
Compound
νas(COO−)
νs(COO−)
ꢀν = νas(COO−)–νs(COO−)
Bonding mode
Hacap
1565
1534
1555
1542
1554
1564
1533
1559
1532
1568
1515
1425
1319
1342
1316
1313
1342
1346
1318
1319
1344
1339
140
215
213
226
241
222
187
241
213
224
176
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
Bidentate
[Cr(cap)3]·5H2O
[Mn(cap)2(H2O)2]
[Fe(cap)3]·12H2O
[Co(cap)2(H2O)2] 4H2O
[Ni(cap)2(H2O)2] 3H2O
[Zn(cap)2]
[ZrO(cap)2]·3H2O
[UO2(cap)(NO3)]
[Zr(cap)2(Cl)2]
[Th(cap)4]
3.3. Magnetic measurements
under investigation except for Mn(II) and Fe(III) caproate com-
plexes which are low spin octahedral configuration.
Magnetic measurements were carried out on a Sherwood
Scientific magnetic balance according to the Gauy method.
The calculations were evaluated by applying the following
equations:
3.4. Electronic absorption spectra
The spectra of the caproic acid complexes in DMSO are
shown in Fig. 1 and the spectral data are listed in Table 5.
There are two detected absorption bands at around 225 and
265 nm assigned to ␲–␲* and n–␲* intraligand transitions,
respectively, in the electronic spectrum of the ligand. These tran-
sitions also found in the spectra of the complexes, but they are
shifted, confirming the coordination of the ligand to the metallic
ions. The first band around 225 nm is probably due to a ␲–␲*
of the alkyl group. However, the second band around 265 nm is
due to presence of COOH group [30]. In case of our complexes,
the carboxylic group is blue shifted. This result confirms the
complexation of metal ions via carboxylic group. Some com-
plexes have a band at range 270–415 nm may be assigned to the
ligand to metal charge-transfer [31,32]. The broad band which
appears at 575 in the spectrum of Cr(II) caproate complex can
be attributed to d–d transition.
√
cl(R−R )
0
χg =
,
χm = χgMWt,
μeff = 2.828 χmT
109M
where χ is mass susceptibility per g sample; c is the calibration
constant of the instrument and equal to 1.135; R is the balance
reading for the sample and tube; R0 is the balance reading for the
empty tube; M is the weight of the sample in g; T is the absolute
temperature.
The magnetic moments of the Cr(III), Mn(II), Fe(III), Co(II)
andNi(II)caproatecomplexesatT = 300 Kandtheircorrespond-
ing hybrid orbitals are given in Table 4.
From the data were represented in Table 4, the observed
values of the effective magnetic moments μeff operated for
above complexes are convenient with experimental values [29]
obtained for high spin octahedral for all mentioned complexes
Table 4
Magnetic moment of the Cr(III), Mn(II), Fe(III), Co(II) and Ni(II) complexes
Complex
μeff B.M. (found)
μeff B.M. (calc.)
Hybrid orbitals
Stereo-chemistry
[Cr(cap)3]·5H2O
3.35
1.76
2.20
1.74
2.82
3.77
2.18
2.25
1.88
3.89
d2sp3
d2sp3
d2sp3
d2sp3
sP3d2
Octahedral
Octahedral
Octahedral
Octahedral
Octahedral
[Mn(cap)2(H2O)2]
[Fe(cap)3]·12H2O
[Co(cap)2(H2O)2]·4H2O
[Ni(cap)2(H2O)2]·3H2O

222
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
Fig. 1. The UV spectra of caproic acid and their complexes.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
223
Fig. 1. ( Continued ).
3.5. 1H NMR spectra
Table 6 and their spectra are shown in Fig. 2. The Zn(II), Fe(III)
and Th(IV) complexes appear to binding to the caproic acid
through carboxylate group, the absence of proton of (COOH)
confirm the mode of coordination.
The 1H NMR spectral data of the Zn2+, Fe3+ and Th4+ com-
plexes and the free ligand (Hcap) caproic acid are collected in
Table 5
The electronic spectral date of the free ligand and its complexes
Compound
Hacap
λmax (nm)
ε (mol−1 cm−1
)
Assignment
225
265
3000
2784
␲–␲* trans.
n–␲* trans.
[Cr(cap)3]·5H2O
225
250
415
575
409
1203
70
␲–␲* trans.
n–␲* trans.
L → Cr C.T.
d–d trans.
69
[Mn(cap)2(H2O)2]
[Fe(cap)3]·12H2O
220
255
1225
1965
␲–␲* trans.
n–␲* trans.
230
255
371
1259
␲–␲* trans.
n–␲* trans.
[Co(cap)2(H2O)2]·4H2O
220
235
255
335
602
1594
662
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
L → Co C.T.
300
[Ni(cap)2(H2O)2]·3H2O
225
240
395
960
776
104
␲–␲* trans.
n–␲* trans.
L → Ni C.T.
[Zn(cap)2]
220
235
250
320
191
913
646
420
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
L → Zn C.T.
[ZrO(cap)2]·3H2O
220
240
270
480
482
677
␲–␲* trans.
n–␲* trans.
n–␲* trans.
[UO2(cap)(NO3)]
220
230
250
350
337
837
774
425
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
L → U C.T.
[Zr(cap)2(Cl)2]
[Th(cap)4]
230
240
250
365
310
740
218
40
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
L → Zr C.T.
␲–␲* trans.
␲–␲* trans.
n–␲* trans.
L → Th C.T.
220
230
250
322
726
814
396
257
Fig. 2. The 1H NMR spectra of caproic acid, Zn(II), Fe(III) and Th(IV) com-
plexes.

224
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
Table 6
The 1H NMR spectral dataa (δ, ppm)b of the caproic acid and their complexes
Compound
CH2 (C2)
CH2 (C3)
CH2 and CH2 (C4 and C5)
1.33
CH3 (C6)
0.90
Proton of COOH
Hcap
2.35
1.64
11.20
[Zn(cap)2]
[Fe(cap)3]·12H2O
[Th(cap)4]
2.12
2.20
2.42
1.57
1.55
2.05
1.28
1.28
1.40
0.88
0.89
0.78
–
–
–
a
Solvent DMSO-d6.
Relative to TMS.
b
3.6. Thermogravimetric analysis
organic moiety) with a weight loss 34.78% and the calculated
value is 33.84%. The Cr2O3 is the final product remains stable
till 800 ◦C. Reported data dealing in the thermal analysis inves-
tigation within nitrogen atmosphere indicate that, the Cr(III)
complex decompose to give oxide contaminated with few carbon
atoms as final products, this reason, because of limited supply
of oxygen.
Thermal analysis curves (TG and DTG) of the studies com-
plexes are shown in Fig. 3. The thermoanalytical results are
summarized in Table 7.
3.6.1. [Cr(cap)3]·5H2O
The thermal decomposition of this complex occurs at two
steps. The first degradation step take place in the range of
30–450 ◦Canditiscorrespondstotheeliminatedofallfiveunco-
ordinated water molecules beside of organic moiety (C6H12)
due to a weight loss of 35.18% in a good matching with the-
oretical value 35.69%. The second step fall in the range of
450–800 ◦C which is assigned to loss of C6H21O4.5 (remaining
3.6.2. [Mn(cap)2(H2O)2]
The thermal decomposition of [Mn(cap)2(H2O)2] complex
completely in two steps. The first step ranged at 30–375 ◦C cor-
responding to the loss of 2H2O molecules and C8H22O organic
molecule, representing a weight loss of 53.23% and its calcu-
lated value is 52.97%. The second step occurring at 375–800 ◦C
Table 7
Thermal data of the caproate complexes
Compound
Steps
Temperature range (◦C)
DTG peak (◦C)
TG weight loss (%)
Assignments
Calc.
Found
[Cr(cap)3]·5H2O
1st
2nd
30–450
450–800
298
507
35.69
33.84
30.47
35.18
34.78
30.04
5H2O + C6H12 (organic moiety)
C6H21O4.5 (organic moiety)
1/2Cr2O3 + 6C (residue)
[Mn(cap)2(H2O)2]
1st
2nd
30–375
375–800
300
455
52.97
8.72
53.23
8.89
2H2O + C8H22O (organic moiety)
CO
38.31
37.88
MnO2 + 3C (residue)
[Fe(cap)3].12H2O
1st
30–500
262
52.04
47.96
51.76
48.24
16.5H2O + 12H2 (organic moiety)
1/2Fe2O3 + 18C (residue)
[Co(cap)2(H2O)2]·4H2O
1st
2nd
30–225
225–550
71
364
18.14
26.70
55.16
17.86
24.84
57.30
4H2O
2H2O + 11H2 + 3/2O2 (organic moiety)
CoO + 12C (residue)
[Ni(cap)2(H2O)2]·3H2O
[Zn(cap)2]
1st
1st
30–550
50–450
319
310
61.27
38.73
60.54
39.46
5H2O + C6H22O3 (organic moiety)
NiO + 6C (residue)
72.37
27.52
72.65
25.35
C12H22O3 (organic moiety)
ZnO (residue)
[ZrO(cap)2]·3H2O
1st
2nd
30–250
250–800
193
324
13.80
39.37
46.83
13.48
40.59
45.93
3H2O
C7H22O3 (organic moiety)
ZrO2 + 5C (residue)
[UO2(cap)(NO3)]
[Zr(cap)2(Cl)2]
1st
30–500
290
23.48
76.52
23.45
76.55
11/2H2 + 3/2O2 + NO2 (organic moiety)
UO2 + 6C (residue)
1st
2nd
30–225
225–600
174
346
14.79
38.49
46.72
15.50
38.95
45.55
C4H10 (organic moiety)
C3H12O2 + Cl2 (organic moiety)
ZrO2 + 5C (residue)
[Th(cap)4]
1st
30–450
271
61.85
38.15
63.13
36.87
C24H44O6 (organic moiety)
ThO2 (residue)

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
225
Fig. 3. The TG and DTG of the caproate complexes.
corresponding to the loss of CO molecule, representing a weight
3.6.3. [Fe(cap)3]·12H2O
loss of 8.89% and its calculated value is 8.72%. This step
can be interpreted according to the transform of MnCO3 to
MnO2.
Theferric(III)caproatecomplexdecomposedinonlyonestep
which extended from 30 to 500 ◦C and can be assigned to the
loss of 16.5H2O molecules and 12H2 molecules, representing a

226
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
Fig. 4. Horowitz–Metzger (HM), Coats–Redfern (CR) of the first step of the caproate complexes.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
227
Fig. 4. ( Continued ).

228
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
weight loss of 51.76% and its calculated value is 52.04%. The
final products resulted at 800 ◦C contain Fe2O3 polluted with
carbon atoms.
(DTG) was carried out for this complex under N2 flow. DTG
thermogram is shown in Fig. 3. The thermal decomposition of
the cobalt(II) complex proceeds approximately with main two
degradation steps. The first stage occurs at maximum tempera-
ture of 71 ◦C. The weight loss associated with this stage 17.86%
which is very close to the theoretical value of 18.14% corre-
sponding to the loss of 4H2O as will be described in Table 7.
The second step occurring at 225–550 ◦C is corresponding to
3.6.4. [Co(cap)2(H2O)2]·4H2O
To make sure about the proposed formula and structure for
the new cobalt(II) complex, [Co(cap)2(H2O)2]·4H2O, thermo
gravimetric (TG) and differential thermo gravimetric analysis
Table 8
Kinetic parameters using the Coats–Redfern (CR) and Horowitz–Metzger (HM) operated for the caproate complexes
Complex
I
Stage
Method
Parameter
r
E (J mol−1
)
A (s−1
)
ꢀS (J mol−1 K−1
)
ꢀH (J mol−1
)
ꢀG (J mol−1
)
CR
HM
Average
CR
HM
3.30 × 104
3.95 × 104
3.62 × 104
8.70 × 104
8.53 × 104
8.62 × 104
5.19 × 105
1.51 × 103
2.60 × 104
4.65 × 103
2.17 × 103
3.41 × 103
−1.41 × 102
−2.28 × 102
−1.84 × 102
−1.85 × 102
−1.89 × 102
−1.87 × 102
2.83 × 104
4.48 × 104
3.65 × 105
8.05 × 104
7.88 × 104
7.96 × 104
1.09 × 105
1.65 × 105
1.37 × 105
2.25 × 105
2.26 × 105
2.25 × 105
0.9997
0.9997
1st
2nd
0.9989
0.9988
Average
II
1st
CR
HM
Average
CR
HM
9.10 × 104
9.61 × 104
9.53 × 104
2.27 × 105
2.20 × 105
2.23 × 105
1.41 × 106
4.98 × 106
3.19 × 106
2.27 × 1014
4.55 × 1013
1.35 × 1014
−1.33 × 102
−1.22 × 102
−1.27 × 102
22.50
09.13
15.81
8.63 × 104
9.13 × 104
8.88 × 104
2.20 × 105
2.14 × 105
2.17 × 105
1.52 × 105
1.61 × 105
1.56 × 105
2.04 × 105
2.08 × 105
2.05 × 105
0.9892
0.9992
2nd
0.9973
0.9967
Average
III
IV
1st
CR
HM
Average
2.40 × 104
3.25 × 104
2.82 × 105
1.42 × 106
5.10 × 1010
2.55 × 1010
−1.32 × 102
−2.36 × 102
−1.84 × 102
−1.57 × 102
−1.24 × 102
−1.40 × 102
−1.78 × 102
−1.55 × 102
−1.66 × 102
−2.23 × 102
−2.23 × 102
−2.23 × 102
−1.80 × 102
−1.81 × 102
−1.80 × 102
−1.62 × 102
−2.02 × 102
−1.82 × 102
−1.83 × 102
−1.25 × 102
−1.54 × 102
−1.83 × 102
−1.68 × 102
−1.75 × 102
1.96 × 104
2.81 × 104
2.38 × 104
9.02 × 104
1.54 × 105
1.22 × 105
0.9986
0.9998
1st
CR
HM
Average
CR
HM
4.95 × 104
5.41 × 104
5.18 × 104
7.60 × 104
8.79 × 104
8.23 × 104
3.43 × 104
4.41 × 104
3.92 × 104
5.67 × 104
6.56 × 104
6.11 × 104
3.58 × 104
4.17 × 104
3.86 × 104
9.33 × 104
9.86 × 104
9.59 × 104
6.27 × 104
6.95 × 104
6.61 × 104
3.72 × 104
4.30 × 104
4.01 × 104
5.41 × 104
6.80 × 104
6.10 × 104
4.75 × 105
5.75 × 105
5.25 × 105
4.48 × 104
2.26 × 106
1.15 × 106
7.06 × 103
1.05 × 105
5.60 × 104
59.80
29.40
44.60
4.66 × 104
5.13 × 104
4.89 × 104
7.07 × 104
8.26 × 104
7.66 × 104
2.94 × 104
3.92 × 104
3.43 × 104
5.18 × 104
6.08 × 104
5.63 × 104
3.19 × 104
3.78 × 104
3.48 × 104
8.83 × 104
9.36 × 104
9.09 × 104
5.85 × 104
6.48 × 104
6.16 × 105
3.35 × 104
3.92 × 104
3.63 × 104
4.90 × 104
6.28 × 104
5.59 × 104
4.30 × 104
5.30 × 104
4.80 × 104
1.01 × 105
9.41 × 104
9.75 × 105
1.84 × 105
1.81 × 105
1.82 × 105
1.12 × 105
1.71 × 105
1.41 × 105
1.57 × 105
1.66 × 105
1.61 × 105
1.07 × 105
1.32 × 105
1.19 × 104
1.71 × 105
1.69 × 105
1.70 × 105
1.61 × 105
1.60 × 105
1.6 × 105
1.10 × 105
1.26 × 105
1.18 × 105
1.53 × 105
1.77 × 105
1.65 × 105
1.35 × 105
1.55 × 105
1.45 × 105
0.9838
0.9808
2nd
0.9949
0.9992
Average
V
1st
1st
CR
HM
Average
0.9993
0.9989
VI
VII
CR
HM
Average
4.58 × 103
4.39 × 103
4.48 × 103
0.9905
0.9999
1st
CR
HM
Average
CR
HM
3.32 × 104
2.71 × 102
1.67 × 104
8.05 × 105
3.50 × 106
2.15 × 106
0.9942
0.9993
2nd
0.9951
0.9975
Average
VIII
IX
1st
CR
HM
Average
3.09 × 103
1.85 × 104
1.07 × 104
0.9971
0.9986
1st
CR
HM
Average
CR
HM
1.23 × 104
6.73 × 102
6.48 × 103
2.29 × 104
2.89 × 103
1.28 × 104
−1.70 × 102
−1.94 × 102
−1.82 × 102
−1.68 × 102
−1.85 × 102
−1.76 × 102
−1.68 × 102
−1.87 × 102
−1.77 × 102
0.9960
0.9998
2nd
0.9915
0.9990
Average
X
1st
CR
HM
Average
1.84 × 104
1.93 × 104
1.88 × 104
0.9945
0.9984

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
229
the loss of 11H2 + 3/2O2 representing a weight loss of 24.84%
and its calculated value is 26.70%. The final thermal products
obtained at 800 ◦C are CoO + 12C.
moiety) and chlorine molecule. The theoretical value of weight
loss of is 38.49%. The ZrO2 is the final product formed at 800 ◦C.
3.6.10. [Th(cap)4]
3.6.5. [Ni(cap)2(H2O)2]·3H2O
The [Th(cap)4] complex showed the absence of water
molecules and the total weight loss was 63.13% with only one
decomposition step. This step occurs in the range of 50–450 ◦C
corresponds to a weight loss of molecular weight of 428 units
(C24H44O6; organic moiety), implied in a 1:4 (metal-to-ligand)
complex in accordance with the analytical data. The theoretical
value of weight loss is 61.85%. The ThO2 is the final stable
residue.
The thermal degradation of the [Ni(cap)2(H2O)2]3H2O com-
plex take place in mainly one degradation stage. This stage
occurs at a maximum temperature of 319 ◦C and accompanied
by weight of loss 60.54% corresponding to the loss of five water
molecules(coordinatedanduncoordinatedwatermolecules)and
an organic part C6H22O3 (organic moiety). Theoretically, the
loss of these molecules corresponds to a weight loss of 61.27%.
3.6.6. [Zn(cap)2]
3.7. Kinetic studies
As mentioned above in the nickel(II) complex, the zinc(II)
caproate, [Zn(cap)2] complex, also has only one decomposition
step. This step located in the range between 50 and 450 ◦C at
maximum temperature DTGmax = 310 ◦C and the weight loss at
this step is 72.65% due to the loss of C12H22O3 organic moiety
in agreement with the theoretical weight loss value of 72.37%.
The final formed product at 800 ◦C is ZnO.
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 [33–40] have been proposed as means of analyzing a TG
curve and obtaining values for kinetic parameters. Many authors
[33–37] have discussed the advantages of this method over the
conventional isothermal method. The rate of a decomposition
process can be described as the product of two separate functions
of temperature and conversion [34], using
3.6.7. [ZrO(cap)2]·3H2O
The thermal decomposition of [ZrO(cap)2]·3H2O complex
proceeds with two main degradation steps. The first step of
the degradation occurs at maximum temperature of 193 ◦C in
the ranged of 30–250 ◦C is accompanied by the formation of
anhydrous zirconyl(II) caproate complex with weight loss of
13.48% correspond to the loss of the three uncoordinated water
molecules. Theoreticallythelossofthesemoleculescorresponds
to a weight loss of 13.80% which agree with the experimental
results. The second decomposition stage occurs at the maximum
temperature 324 ◦C. The weight loss at this step is 40.59% asso-
ciated with the loss of C7H22O3 organic part. The theoretical
weight loss value is 39.37%. The final residue at the end of this
stage is ZrO2.
dα
= k(T)f(α)
(1)
dt
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
∗
k = A e−E /RT
(2)
where R is the gas constant in (J mol−1 K−1). Substituting equa-
tion (2) into equation (1), we get
ꢀ
ꢁ
dα
dT
A
3.6.8. [UO2(cap)(NO3)]
=
f(α)
∗
ϕ e−E /RT
The degradation of the [UO2(cap)(NO3)] complex take place
in only one sharp decomposition step. The weight found for the
residue after decomposition is 76.55% giving an actual total
weight loss of 23.45% in agreement with our calculated total
weight loss value of 23.48%. The degradation patterns of this
complex are NO2 + 11/2H2 + 3/2O2.
Table 9
Antibacterial activity data of the caproic acid and their complexes
Compound
Escherichia
coli
Streptococcus
penumonia
Bacillus
subtilis
Hacap
++++
−
++++
++
−
+++
−
3.6.9. [Zr(cap)2(Cl)2]
[Cr(cap)3]·5H2O
[Mn(cap)2(H2O)2]
[Fe(cap)3]·12H2O
[Co(cap)2(H2O)2]·4H2O
[Ni(cap)2(H2O)2]·3H2O
[Zn(cap)2]
[ZrO(cap)2]·3H2O
[UO2(cap)(NO3)]
[Zr(cap)2(Cl)2]
[Th(cap)4]
The thermal decomposition data obtained support the pro-
posed structure and indicate that, the thermal decomposition of
this complex proceeds with two main degradation steps. The
first stage of decomposition occurs at a temperature maximum
of 174 ◦C. The found weight loss associated with this step is
15.50% and may be attributed to the loss of the organic moiety
(C4H10) which is in good agreement with the calculated value
of 14.79%. The second step of decomposition occurs at a tem-
perature maximum of 346 ◦C. The weight loss found at this step
equals to 38.95% corresponds to the loss of C3H12O2 (organic
−
−
++
−
−
−
−
+++
−
−
−
++
++
+++
++
−
−
+++
+++
+++
++
−
++
−
−
++
−: NO antibacterial activity, +: mild activity, ++: moderate activity, +++: marked
activity, ++++: strong marked activity.

230
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
Fig. 5. The inhabitation zone of the caproic acid and its metal complexes on some kinds of bacterial.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
231
Scheme 3. The structures of caproate complexes.

232
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
where ϕ is the linear heating rate dT/dt. On integration and
approximation, this equation can be obtained in the following
form
ꢂ
ꢃ
E∗
AR
ϕE∗
ln g(α) = −
+ ln
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 tempera-
tureintegral and has noclosed forsolution. So severaltechniques
have been used for the evaluation of temperature integral. Most
commonly used methods for this purpose are the differential
method of Freeman and Carroll [33] integral method of Coat
and Redfern [35], the approximation method of Horowitz and
Metzger [38].
In the present investigation, the general thermal behaviors of
the caproate complexes in terms of stability ranges, peak tem-
peratures and values of kinetic parameters, are shown in Fig. 4
and Table 8. The kinetic parameters have been evaluated using
the following methods and the results obtained by these methods
are well agreement with each other. The following two methods
are discussed in brief.
3.7.1. Coats–Redfern equation
The Coats–Redfern equation, which is a typical integral
method, can be represented as:
ꢀ
ꢁ
ꢄ
ꢄ
α
T
2
dα
(1 − α)n
A
ϕ
E∗
=
exp
−
dt
RT
0
T
1
For convenience of integration the lower limit T1 is usually
taken as zero. This equation on integration gives
ꢂ
ꢃ
ꢂ
ꢃ
ln(1 − α)
E∗
AR
ϕE∗
ln −
= −
+ ln
T2
RT
A plot of left-hand side (LHS) against 1/T was drawn. E* is
the energy of activation in J mol−1 and calculated from the slop
and A in (s−1) from the intercept value. The entropy of activation
ꢀS* in (J K−1 mol−1) was calculated by using the equation:
ꢀ
ꢁ
Ah
ꢀS∗ = R ln
(3)
kB Ts
where kB is the Boltzmann constant, h is the Plank’s constant
and Ts is the DTG peak temperature [41].
3.7.2. Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the
approximation methods. These authors derived the relation:
ꢅ
ꢆ
{1 − (1 − α)1−n
(1 − n)
}
E∗θ
2.303RTs2
log
=
for n = 1
(4)
when n = 1, the LHS of equation (4) would be log[−log(1 − α)].
For a first-order kinetic process the Horowitz-Metzger equation
may be written in the form:
ꢂ
ꢀ
ꢁꢃ
Scheme 4. The three dimensional of caproate complexes.
wα
wγ
E∗θ
2.303RTs2
log log
=
− log 2.303

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 217–233
[8] M. Kato, Y. Muto, Coord. Chem. Rev. 92 (1988) 45.
233
where θ = T − Ts, wγ = wα − w, wα = mass loss at the comple-
tion of the reaction; w = mass loss up to time t. The plot of
log[log(wα/wγ)] versus 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:
[9] F.P.W. Agterberg, H.A.J. Provo´ Kluit, W.L. Driessen, H. Oevering, W.
Buijs, M.T. Lakin, A.L. Spek, J. Reedijk, Inorg. Chem. 36 (1997) 4321.
[10] A. Zell, H. Einspahr, C.E. Bugg, Biochemistry 24 (1985) 533.
[11] V.L. Pecoraro, M.J. Baldwin, A. Gelasco, Chem. Rev. 94 (1994) 807.
[12] E.V. Brusau, J.C. Pedregosa, G.E. Narda, E.P. Ayala, E.A. Oliveira, J. Arg.
Chem. Soc. 92 (1/3) (2004) 43.
[13] S. Budavari (Ed.), The Merck Index Text Book, 12th ed., Rahway, NJ,
1998, p. 286.
[14] F. Beilstein, Handbuch der Organischem Chemie, Bd. IX, Springer Verlag,
Berlin, 1926.
E∗
RTs2
A
=
[ϕ exp(−E∗/RTs)]
The entropy of activation, ꢀS*, was calculated from equation
(3). The enthalpy activation, ꢀH*, and Gibbs free energy, ꢀG*,
were calculated from; ꢀH* = E* − RT and ꢀG* = ꢀH* − TꢀS*,
respectively.
[15] L.L. Kolomiets, O.V. Lysenko, I.V. Pyatnitskii, Z. Anal. Khim. 43 (10)
(1988) 1773.
[16] I.V. Pyatnitskii, L.L. Kolomeits, O.V. Lysenko, M.G. Sobko, Z. Anal. Khim.
45 (1) (1990) 56.
[17] S. Kopacz, J. Szantula, T. Pardela, Z. Prikladoni Khim. 62 (11) (1989)
2535.
3.8. Antibacterial investigation
[18] R. Pietsch, Anal. Chim. Acta 53 (2) (1971) 287.
[19] T.N. Gushchina, G.A. Kotenko, Koord. Khim. 12 (3) (1986) 325.
[20] W. Brzyska, B. Paszkowska, J. Therm. Anal. 51 (1998) 561.
[21] A. Doyle, J. Felcman, M. Gambardella, C.N. Verani, M.L.B. Tristao, Poly-
hedron 19 (26/27) (2000) 2621.
[22] M.S. Refat, D.N. Kumar, R.F. De Farias, J. Coord. Chem. 59 (16) (2006)
1857.
[23] K. Burger, Coordination Chemistry: Experimental Methods, Butterworth
Group, Britain, 1973.
The results of antibacterial activities in vitro of the ligand
and the complexes are shown in Table 9 and Fig. 5. The minimal
inhibitory concentration values listed in Table 9 show that all
the test complexes have been obstructed the activity of caproic
acid against the order of antibacterial.
3.9. Structure of the caproate complexes
[24] M.S. Refat, J. Mol. Struct., in press.
[25] M.A. Mesubi, J. Mol. Struct. 81 (1982) 61.
[26] K. Nakamato, P.J. Mc Carthy, Spectroscopy and Structure of Metal Chelate
Compounds, John Wiley, New York, 1968, p. 268.
[27] R. Goto, T. Takenaka, J. Chem. Soc. Jpn. 84 (1963) 392.
[28] L.S. Gelfand, F.J. Iaconianni, L.L. Pytlewski, A.N. Speca, C.M. Mikulski,
N.M. Karayannis, J. Inorg. Nucl. Chem. 42 (1980) 377.
[29] A. Earnshow, Introduction to Magneto Chemistry, Academic Press, New
York, 1968.
Accordingly, theabove-mentioneddiscussionsusingelemen-
tal analysis, magnetic studies, molar conductance, (infrared and
1HNMR)spectraas well asthermogravimetricanalysis; thesug-
gested structures of the caproate complexes can be represented
in Schemes 3 and 4.
[30] G.D. Fasman, Handbook of Biochemistry and Molecular Biology, Nucleic
acids, vol. I, CRC Press, pp. 65–215.
References
[31] R.H. Holm, F.A. Cotton, J. Am. Chem. Soc. 80 (1958) 5658.
[32] F.A. Cotton, C.W. Wilkinson, Advanced Inorganic Chemistry, 3rd ed.,
Interscience Publisher, New York, 1972.
[1] R.C. Mehrotra, R. Bohra, Metal Carboxylates, Academic Press, London,
1983.
[2] B.P. Baranwal, S.S. Das, P. Singh, Synth. React. Inorg. Met. Org. Chem.
28 (1998) 1689.
[3] E.J. Baran, S.B. Etcheverry, M.H. Torre, E. Kremer, Polyhedron 13 (12)
(1994) 1859.
[4] G.C. Campbell, J.F. Haw, Inorg. Chem. 27 (1988) 3706.
[5] G.C. Campbell, J.H. Reibenspies, J.F. Haw, Inorg. Chem. 30 (1991)
171.
[6] R.D. Harcourt, F.L. Skrezenek, R.G.A.R. Maclagan, J. Am. Chem. Soc.
108 (1986) 5403.
[33] E.S. Freeman, B. Carroll, J. Phys. Chem. 62 (1958) 394.
[34] J. Sestak, V. Satava, W.W. Wendlandt, Thermochim. Acta 7 (1973) 333.
[35] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68.
[36] T. Ozawa, Bull. Chem. Sot. Jpn. 38 (1965) 1881.
[37] W.W. Wendlandt, Thermal Methods of Analysis, Wiley, New York, 1974.
[38] H.W. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464.
[39] J.H. Flynn, L.A. Wall, Polym. Lett. 4 (1966) 323.
[40] P. Kofstad, Nature 179 (1957) 1362.
[41] J.H.F. Flynn, L.A. Wall, J. Res. Natl. Bur. Stand. A 70 (1996) 487.
[7] R.D. Harcout, G.E. Martin, J. Chem. Soc. Faraday Trans. II 73 (1977) 114.