New binary and ternary complexes of fluclaxocillin and amino acids with some transition metals. Synthesis, characterization, and cyclic voltammetric studies

Article abstract of DOI:10.1081/SIM-120014865

The new binary and ternary complexes of fluclaxocillin (HFluc) and amino acids (HAA) [glycine (HGly) and alanine (HAla)] with Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions were prepared and characterized using various spectroscopic methods. According to the elemental analyses, the binary complexes were found to have the general formulas [M(Fluc)(X)(H₂O)_x]·yH₂O and [Fe(Fluc)(Cl)₂(H₂O)₂]·4H₂O while the ternary complexes had the formulas [M(Fluc)-(AA)(H₂O)_x]·yH₂O and [Fe(Fluc)(AA)(Cl)(H₂O)_x]·yH₂O where M = Fe(II), Co(II), Ni(II) and Cu(II), X = OAc in the case of Cu(II) and Cl in the case of Fe(II), Co(II) and Ni(II), AA = Gly^- and Ala^-, x = 2-6 and y = 1-3. IR, magnetic and solid reflectance spectral studies were utilized to infer the structure of the complexes. Thermogravimetric analysis (TGA) was utilized to differentiate between coordinated and hydrated water molecules. The Fluc^-, Gly^- and Ala^- molecules are decomposed in a second and subsequent steps. Cyclic voltametric investigations of these complexes were also carried out.

Full text of DOI:10.1081/SIM-120014865

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NEW BINARY AND TERNARY COMPLEXES OF
FLUCLAXOCILLIN AND AMINO ACIDS WITH SOME
TRANSITION METALS. SYNTHESIS, CHARACTERIZATION,
AND CYCLIC VOLTAMMETRIC STUDIES
M. A. Abd El-Rahim a , Gehad G. Mohamed a & Wafaa M. Hosny a
a Chemistry Department, Cairo University, Giza, Egypt
Version of record first published: 02 Sep 2006.
To cite this article: M. A. Abd El-Rahim , Gehad G. Mohamed & Wafaa M. Hosny (2002): NEW BINARY AND TERNARY
COMPLEXES OF FLUCLAXOCILLIN AND AMINO ACIDS WITH SOME TRANSITION METALS. SYNTHESIS, CHARACTERIZATION, AND
CYCLIC VOLTAMMETRIC STUDIES, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 32:8, 1501-1519
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 32, No. 8, pp. 1501–1519, 2002
NEW BINARY AND TERNARY
COMPLEXES OF FLUCLAXOCILLIN
AND AMINO ACIDS WITH SOME
TRANSITION METALS. SYNTHESIS,
CHARACTERIZATION, AND CYCLIC
VOLTAMMETRIC STUDIES
Gehad G. Mohamed,* Wafaa M. Hosny,
and M. A. Abd El-Rahim
Chemistry Department, Faculty of Science,
Cairo University, Giza, Egypt
ABSTRACT
The new binary and ternary complexes of fluclaxocillin
(HFluc) and amino acids (HAA) [glycine (HGly) and alanine
(HAla)] with Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions
were prepared and characterized using various spectroscopic
methods. According to the elemental analyses, the binary
complexes were found to have the general formulas
[M(Fluc)(X)(H2O)x]ꢀyH2O and [Fe(Fluc)(Cl)2(H2O)2]ꢀ4H2O
while the ternary complexes had the formulas [M(Fluc)-
(AA)(H2O)x]ꢀyH2O and [Fe(Fluc)(AA)(Cl)(H2O)x]ꢀyH2O
*Corresponding author. E-mail: ggenidy@hotmail.com
1501
DOI: 10.1081=SIM-120014865
Copyright # 2002 by Marcel Dekker, Inc.
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com

1502
MOHAMED, HOSNY, AND EL-RAHIM
where M ¼ Fe(II), Co(II), Ni(II) and Cu(II), X ¼ OAc in the
case of Cu(II) and Cl in the case of Fe(II), Co(II) and Ni(II),
AA ¼ Glyꢁ and Alaꢁ, x ¼ 2ꢁ6 and y ¼ 1ꢁ3. IR, magnetic and
solid reflectance spectral studies were utilized to infer the
structure of the complexes. Thermogravimetric analysis (TGA)
was utilized to differentiate between coordinated and hydrated
water molecules. The Flucꢁ, Glyꢁ and Alaꢁ molecules are
decomposed in a second and subsequent steps. Cyclic volta-
metric investigations of these complexes were also carried out.
INTRODUCTION
Much interest had been shown in the chemistry of b-lactam antibiotics
in relation to their useful biological activities.[174] b-Lactam antibiotics, such
as penicillins, cephalosporins, oxacephalosporins, represent the most
important class of drugs against diseases caused by bacteria. Following the
evidence of the important roles of calcium and magnesium in the transport of
these drugs in blood plasma,[5] it is suggested that copper can act as a cofactor
of their antibiotic activity: first, the structural flexibility of copper binary
complexes is expected to favor mixed-ligand coordination with bacterial
nucleic acids; second, through formation of such ternary complexes, copper
may induce the attack of free radicals known to damage these nucleic acids.[6]
In continuation of our previous studies of the metal complexes of
antibiotics,[7711] the present investigation reports studies of binary and
ternary complexes of some metal ions with HFluc, HGly and HAla. The
structures of these binary and ternary complexes are proposed based on
elemental analyses, IR, magnetic and solid reflectance measurements.
Thermal analyses were used to distinguish between the crystal and coordi-
nated water molecules. The fragmentation of the ligand molecules (HFluc
and AA) is also discussed. Various thermodynamic activation parameters
were calculated. Cyclic voltammetric studies were also carried out to con-
firm the proposed structures.
Scheme. Structure of fluclaxocillin.

COMPLEXES OF FLUCLAXOCILLIN
EXPERIMENTAL
Materials and Reagents
1503
Fluclaxocillin is (60R)-6-(3-2-chloro-6-flourophenyl)-5-methylisox-
azole-4-carboxamido)pencillanic acid. It was obtained from the Nile Co.,
Egypt. The metal chlorides of Fe(II), Fe(III), Co(II) and Ni(II) were sup-
plied from Aldrich. Copper acetate and the amino acids glycine and alanine
were obtained from Sigma Chemical Co.
Instruments
IR spectra were recorded on a model 8001 Perkin-Elmer FT-IR
spectrometer as KBr discs. Solid reflectance spectra were measured on a
Shimadzu 3101 PC spectrophotometer. The molar magnetic susceptibilities
were measured on powdered samples using the Faraday method. Diamag-
netic corrections were made using Pascal’s constants with Hg [Co(SCN)4] as
calibrant at room temperature. TGA was carried out in a dynamic nitrogen
ꢁ1
atmosphere (20 mL minꢁ1) with a heating rate of 10 C min using a Shi-
ꢂ
madzu TGA-50H thermal analyzer in the temperature range from room
ꢂ
temperature up to 1000 C. Metal contents were determined by titration
against standard EDTA solution after complete decomposition of the
complexes with aqua regia in a Kjeldahl flask several times. Cyclic volt-
ammetric polarization measurements were performed using a potentio-
metric Amel 5000 instrument which is a complete microprocessor-controlled
electrochemical measurement system capable of satisfying all needs for
simple or complex measurements. Amel Easyscan software was used in
connection with a PC to control the system. The controlled potential ranges
vary from þ8 V to ꢁ8 V and the current range is up to 1 A. The measure-
ments were carried out on solutions of the various complexes in 0.5 M HCl
as a supporting electrolyte and 1610ꢁ3 M concentrations were chosen for
this study. The solutions were prepared by dissolving the appropriate
weighed complex in 0.5 M HCl solution.
Preparation of Binary Metal Complexes
A solution of the metal chloride (Fe(II), Fe(III), Co(II) and Ni(II)) or
Cu(II) acetate (1 mmol) in an ethanol-water mixture (1:1) (25 mL) was
added to a solution of HFluc (1 mmol, 0.4525 g) in the same solvent (50 mL).
The resulting mixture was stirred under reflux for a half-hour whereupon the
complexes precipitated. They were removed by filtration, washed with a 1:1

1504
MOHAMED, HOSNY, AND EL-RAHIM
ethanol-water mixture and dried in a vacuum desiccator over anhydrous
calcium chloride. The analytical data are collected in Table I.
Preparation of Ternary Metal Complexes
A metal chloride (Fe(II), Fe(III), Co(II) and Ni(II)) or acetate (Cu(II))
solution (1 mmol) in ethanol-water mixture (1:1) (25 mL) was added to a
solution of HFluc (1 mmol, 0.4525 g) and the amino acid (1 mmol, 0.075 g
HGly or 0.088 g HAla) in the same solvent (50 mL) in the mole ratio 1:1:1
(metal salt:HFluc:HAA). The work-up was the same as mentioned above.
The analytical data are collected in Table I.
RESULTS AND DISCUSSION
The main objective of this article is the preparation and chemical
characterization of new binary complexes with HFluc and ternary com-
plexes of HFluc and HGly or HAla with Fe(II), Fe(III), Co(II), Ni(II) and
Cu(II) ions. As seen from Table I, 1:1 (M:Fluc) binary and 1:1:1 (M:Fluc:
AA) ternary complexes were prepared with satisfactory elemental analyses
results. The results indicate that HFluc and the amino acids (HGly and
HAla) behave as uninegative, bidentate molecules. They lose the carboxylate
hydrogen atom on coordination to the metal ions.
The formation of these binary and ternary complexes may proceed as
follows:
MX2 þ HFluc ꢁꢁw ½MðFlucÞXꢃ þ HX ðBinary complexesÞ
M ¼ Fe(II), Co(II), Ni(II), Cu(II); X ¼ Cl in case of Fe(II), Co(II),
Ni(II) and X ¼ OAc in case of Cu(II).
FeCl3 þ HFluc ꢁꢁw ½FeðFlucÞCl2ꢃ þ HCl ðBinary complexesÞ
MX2 þHFlucþHAAꢁꢁw½MðFlucÞðAAÞꢃþ2HX ðTernarycomplexesÞ
M ¼ Fe(II), Co(II), Ni(II), Cu(II), X ¼ Cl in case of Fe(II), Co(II),
Ni(II) and X ¼ OAc in case of Cu(II).
FeCl3 þ HFluc þ HAA ꢁꢁw ½FeðFlucÞðAAÞClꢃ þ 2HCl
ðTernary complexesÞ

COMPLEXES OF FLUCLAXOCILLIN
1505

1506
MOHAMED, HOSNY, AND EL-RAHIM

COMPLEXES OF FLUCLAXOCILLIN
1507
The structures of the prepared complexes were confirmed by using
various tools of analyses, namely IR, magnetic, solid reflectance and ther-
mal analysis measurements.
IR Spectra and Mode of Bonding
HFluc has various potential donor sites. A comparison between the IR
spectra of HFluc and those of the transition metal complexes provides
evidence regarding the bonding sites in the HFluc complexes. The IR
spectra of all HFluc binary complexes show bands at 345073300 and
8707750 cmꢁ1 characteristic of water of crystallization and coordinated
H2O molecules, respectively.[12,13] The IR spectrum of HFluc reveals bands
at 1615 and 1430 cmꢁ1 due to nasymðCOOꢁÞ and nsymðCOOꢁÞ.[14,15] These
bands decrease in intensity and shift to lower frequency on complexion,
suggesting coordination via the carboxylate group.[7,16] The band due to
n(C7N) of the b-lactam ring (1355 cmꢁ1) in the free ligand is shifted to lower
frequency and decreases in intensity on complexation, indicating coordi-
nation through the b-lactam nitrogen. The IR spectra of HGly and HAla
exhibit a band at 2590 cmꢁ1 assigned to nðNHþ3 Þ. In the spectra of the
ternary complexes, the NHþ3 band has disappeared, a behavior which pro-
vides convincing evidence for coordination through the amino group.[17] In
addition, the ligand HFluc exhibits bands at 1760, 1645 and 1490 cmꢁ1 due
to n(C¼O) of b-lactam, amide, C¼O stretch and n(C¼N)cyclic, respectively,
and these remain unchanged on complexation. The spectra of the Cu
complexes displays two intense bands at 1575 and 1400 cmꢁ1 due to nðNH3þÞ
and nðNHþ3 Þ of the acetate group.[12]
In the far-IR spectra, the bonding of nitrogen and oxygen is indicated by
the presence of bands at 5707515 cmꢁ1 (M7N) and 4307375 cmꢁ1 (M7O).[18]
The metal complexes of HFluc contain chloride attached to the metal ions
which is supported by the presence of a n(M7Cl)[18] band at 3307290 cmꢁ1
.
The presence of acetate or chloride ions in the structural configuration
of the complexes suggests that HFluc acts as a uninegative bidentate
ligand on complexation with the metal ions. Also, it indicates that HFluc
ligates with the metal ions through carboxylate and nitrogen in the b-lactam.
Electronic Spectra and Magnetic Properties
The solid reflectance spectrum of the [Cu(Fluc)(OAc)(H2O)3]ꢀ2H2O
complex shows a broad band at ꢄ17,490 cmꢁ1, which is consistent with an
octahedral environment.[19] This band may be attributed to the Eg ! T2g
transition in an octahedral environment. While, the meff value of the
2
3

1508
MOHAMED, HOSNY, AND EL-RAHIM
[Fe(Fluc)(Cl)H2O)3]ꢀ3H2O binary complex (4.9 B.M.) is within the range of
values corresponding to high-spin complexes of Fe(II) ions. The solid
reflectance spectrum shows a doublet band at 10,30078,020 cmꢁ1 and a
shoulder at 20,550 cmꢁ1 assigned to T2gðDÞ ! Eg and t2g ! pꢅ, respec-
tively.[20] Cotton and Meyers[21] suggested that such doublet bands in six-
coordinated Fe(II) complexes could be due to Jahn-Teller distortion. The
solid reflectance spectrum of the [Co(Fluc)(Gly)(H2O)2]ꢀ5H2O complex
exhibits three bands at 8,250, 14,250 and 20,570 cmꢁ1, which are assigned to
5
5
4
4
4
4
4
4T1g ! T2gðFÞðn1Þ; T1g ! A2gðn2Þ and T1g ! T1gðPÞðn3Þ transitions,
indicating an octahedral[22] geometry of the Co(II) complex. This was fur-
ther confirmed by the value of the magnetic moment (5.2 B.M.) in Table I.
The solid reflectance spectrum of the [Ni(Fluc)(Gly)(H2O)2]ꢀ4H2O ternary
complex shows three bands at 8,060 (n1), 12,097 cmꢁ1(n2) and
22,946 cmꢁ1(n3), which are assigned to the following transitions,
3
3
3
3
3
3A2g ! T2gðn1Þ; A2g ! T1gðn2Þ and A2g ! T1gðPÞðn3Þ, respectively,
consistent with octahedral geometry[23] and is also confirmed by the mag-
netic moment value (3.75 B.M.) in Table I. The magnetic moment values of
the ternary Fe(III) complexes with HGly and HAla have been found to be
4.5 B.M. and 4.8 B.M, respectively, which is within the range of values
corresponding to high-spin octahedral complexes of Fe(III) ions. The meff
values of the [Fe(Fluc)(Gly)]ꢀH2O and [Fe(Fluc)(Ala)]ꢀH2O complexes are
4.5 B.M. and 4.32 B.M., respectively, which is in the range of values cor-
responding to tetrahedral complexes.
Redox Properties
When examined by cyclic voltammetry in HCl (Fig. 1a), it is observed
that HFluc itself exhibits redox peaks at about þ0.6 V (reduction) and
þ0.95 V vs. the normal hydrogen electrode (NHE). These peaks may be
explained as a result of reduction and oxidation of the carboxylate group in
the HFluc molecule. But on complexation with the various metal ions, these
redox peaks vanished, which proves that this carboxylate group is partici-
pating in complex formation. It is observed in the voltammogram of all
binary and ternary complexes for all metal ions except Cu(II), for which no
redox peaks are obtained, which proves the relatively high stability of these
complexes under the given experimental conditions.
In the case of the binary Cu(II) complexes, polarization usually started
at thye potential of hydrogen evolution. As a result, Cu(II) ions could be
chemically reduced by the evolved atomic hydrogen to Cu(I). In the positive
scan the reduced Cu(I) ions are electrochemically oxidized[24,25] to Cu(II), as
confirmed by the oxidation peak at 0.62 V vs. the NHE reference electrode
(Fig. 1b).

COMPLEXES OF FLUCLAXOCILLIN
1509
Figure 1. Cyclic voltammograms of Cu(II)-binary and ternary complexes (a) and
Cu(II)-binary complex with repeated cycles (b). Scan rate 50 mVsꢁ1
.
Thermal Analysis (TGA)
The TGA for the complexes was cꢂarried out within a temperature
range from room temperature up to 1000 C. The observed mass losses are
based on the TG results and the calculated mass losses are based on the
molecular weight of the proposed formulas. The observed temperature
ranges, percent losses in mass, and thermal effects accompanying the
changes in the solid complexes on heating are given in Table II, which
reveals the following findings.
The thermograms of [Fe(Fluc)(Cl(H2O)3]ꢀ3H2 (1), [Fe(Fluc)-
(Gly)]ꢀH2O (6) and [Fe(Fluc)(Ala)]ꢀH2O (11) complexes show three de-
ꢂ
composition steps within the temperature range from 257900 C. The first
step of decomposition within the temperature range 257130 ꢂC corresponds
to the loss of water molecules of hydration with a mass loss of 8.42% (calcd.
for 3H2O 8.28%), 2.83% (calcd. for H2O 3.0%) and 2.69% (calcd. for H2O
2.93%) for (1), (6) and (11), respectively. The energy of activation of this
dehydration step is 56.91, 59.40 and 44.10 KJ molꢁ1 forꢂ (1), (6) and (11),
respectively. The second and third steps (from 1307900 C) correspond to
the removal of coordinated water, HCl, Flucꢁ, Glyꢁ and Alaꢁ molecules
leaving metal oxide as residue. The overall weight loss amounts to 88.50%

1510
MOHAMED, HOSNY, AND EL-RAHIM

COMPLEXES OF FLUCLAXOCILLIN
1511

1512
MOHAMED, HOSNY, AND EL-RAHIM

COMPLEXES OF FLUCLAXOCILLIN
1513
(calcd. 88.95%), 88.10% (calcd. 87.94%) and 90.74% (calcd. 90.82%) for
(1), (6) and (11), respectively. According to the stereochemistry of these
complexes suggested from electronic spectra, magnetic susceptibility mea-
surements and from the mode of bonding based on the IR spectra, the
proposed structure of these complexes is shown in Fig. 2.
The Fe(III) complexes with HFluc (2), HFluc-HGly (7) and HFluc-
HAla (12) ligands give a three-stage decomposition pattern. The first stage
ꢂ
(307150 C) represents the loss of three water molecules of hydration; two
water molecules of hydration and HCl molecules; and CH4 molecule from
(2), (7) and (12), respectively, with mass losses being very close to the cal-
culated mass loss (for water molecules of hydration, HCl and CH4) as
shown in Table II. The loss of Flucꢁ and amino acid molecules take place
within the temperature range of 1057750 ꢂC leaving metal chloride [in
1
2
1
2
the case of (2)], Fe2O3 [in the case of (7)] and Fe2S3 [in the case of (12)].
The structure of the Fe(III) complexes is suggested to be as shown in Fig. 3.
Figure 2. Suggested structural formulas of binary and ternary Fe(II) complexes.
Figure 3. Suggested structural formula of binary and ternary Fe(III) complexes.

1514
MOHAMED, HOSNY, AND EL-RAHIM
The [Co(Fluc)(Cl)(H2O)3]ꢀ3H2O (3), [Co(Fluc)(Gly)(H2O)2]ꢀ5H2O (8)
and [Co(Fluc)(Ala)(H2O)2] (13) complexes exhibit three steps of decom-
position on TGA analysis. The first decomposition step within the tem-
ꢂ
perature range 257130 C corresponds to the loss of three water molecules
of hydration (mass loss 7.85%; calcd. 8.25%), three water molecules of
hydration (mass loss 7.67%; calcd. 7.60%), and one water molecule of
hydration (mass loss 2.97%; calcd. 2.83%) for (3), (8) and (13), respectively.
The energy of activation of this dehydration step is 44.65, 50.10 and
45.30 KJ molꢁ1 for (3), (8) and (13), respectively. The loss of hydrated and
coordinated water, Flucꢁ, Glyꢁ and Alaꢁ molecules takes place within the
ꢂ
temperature range 1307990 C with mass losses 72.51% (calcd. 72.06%),
75.80% (calcd. 75.74%) and 85.37% (calcd. 85.44%) for (3), (8) and (13),
respectively. According to the IR, solid reflectance spectra and magnetic
susceptibility measurements, the proposed structures of these complexes are
shown in Fig. 4.
The TG curves of the [Ni(Fluc)(Cl)(H2O)3]ꢀ3H2O (4), [Ni(Fluc)-
(Gly)(H2O)2]ꢀ4H2O (9) and [Ni(Fluc)(Ala)(H2O)2] (14) complexes show
ꢂ
three stages of decomposition within the temperature range of 207760 C.
ꢂ
The first stage at 207180 C corresponds to the loss of water molecules of
hydration, while the second and third stages involve the loss of Flucꢁ, Glyꢁ,
Alaꢁ and coordinated water molecules. The energy of activation of the
dehydration step is 41.46, 53.21 and 30.85 KJ molꢁ1 for (4), (9) and (14),
respectively. The overall weight loss amounts to 80.64% (calcd. 80.31%),
89.09% (calcd. 89.12%) and 88.88% (calcd. 88.13%) for (4), (9) and
(14), respectively. According to the elemental analyses and various spec-
troscopic methods, the proposed structures of these complexes are shown in
Fig. 4.
Figure 4. Suggested structural formula of binary and ternary Ni(II), Co(II), and
Cu(II) complexes.

COMPLEXES OF FLUCLAXOCILLIN
1515
Table III. Thermodynamic Data of the Thermal Decomposition of Binary and
Ternary Metal Ions Complexes
Decomposition
ꢂ
Eꢅ
KJ molꢁ1
A
Sꢁ1
DSꢅ
DHꢅ
DGꢅ
Complex
range, C
JKꢁ1 molꢁ1 KJ molꢁ1 KJ molꢁ1
(1)
357120
1257445
4457700
307100
1057485
4857665
257140
1407400
4007650
307180
1857445
4457690
307100
1007210
2107750
257130
1357420
4207900
307150
1507450
4507720
207125
1257490
4907745
257130
1307500
5057760
207195
1957410
41071000
257105
1107415
4207570
357120
1257425
4307650
257120
56.91 1.046104
82.78 2.016106
133.9
ꢁ23.45
ꢁ23.81
ꢁ23.07
ꢁ20.04
ꢁ27.17
ꢁ20.84
ꢁ19.29
ꢁ19.96
ꢁ32.81
ꢁ23.66
ꢁ21.47
ꢁ31.20
ꢁ24.33
ꢁ71.75
ꢁ79.30
ꢁ18.40
ꢁ12.40
ꢁ15.52
ꢁ11.98
ꢁ25.69
ꢁ19.75
ꢁ13.50
ꢁ11.65
ꢁ26.95
ꢁ10.68
ꢁ14.86
ꢁ22.79
ꢁ17.26
ꢁ17.12
ꢁ25.20
ꢁ13.90
ꢁ13.20
ꢁ29.04
ꢁ15.16
ꢁ18.88
ꢁ16.36
ꢁ14.12
ꢁ11.30
ꢁ20.30
56.28
81.03
129.3
29.75
24.21
97.26
44.14
55.93
175.6
40.93
52.35
178.7
58.89
246.0
246.0
58.90
77.90
172.8
66.32
50.75
112.3
49.37
80.60
178.1
46.53
81.76
166.9
77.09
65.52
64.93
43.61
75.86
369.0
44.14
88.92
247.0
44.50
83.76
115.8
58.05
86.02
142.1
31.01
31.50
109.5
45.31
61.95
190.5
42.44
59.17
194.7
60.59
257.0
286.8
59.40
80.60
175.6
75.56
89.46
143.0
50.38
83.10
182.2
46.46
85.37
189.4
77.62
69.83
83.50
44.40
78.56
355.7
45.41
90.75
243.7
45.40
86.32
132.5
1.116105
(2)
(3)
30.27 2.586108
26.44 8.966105
102.1
1.096105
44.65 5.376106
58.44 1.366105
179.4
5.416108
(4)
41.46 7.106105
54.99 3.166106
183.0
3.046109
(5)
59.48 3.976106
247.4
268.0
2.2061011
7.966104
(6)
59.40 3.126108
79.71 1.916107
177.0
4.3461010
(7)
65.73 3.426107
95.42 2.486105
167.3
5.456108
(8)
50.10 3.306106
82.40 3.946107
183.0
1.2461010
(9)
53.21 2.856104
81.63 3.446106
178.0
4.426109
4.96109
(10)
(11)
(12)
(13)
78.20
76.64 2.406105
71.10 1.966102
44.10 1.066106
77.60 1.106107
372.8
44.84 4.606105
3.7361025
90.63 6.216108
251.4
6.3161015
45.30 1.036106
85.65 5.916107
122.6
1257625
6257900
2.746104
(continued)

1516
MOHAMED, HOSNY, AND EL-RAHIM
Table III. Continued
Decomposition
ꢂ
Eꢅ
KJ molꢁ1
A
Sꢁ1
DSꢅ
DHꢅ
DGꢅ
Complex
range, C
JKꢁ1 molꢁ1 KJ molꢁ1 KJ molꢁ1
(14)
207150
1557490
4907690
207125
1307490
4907820
30.85 5.246105
ꢁ14.90
ꢁ16.70
ꢁ14.95
ꢁ17.53
ꢁ10.43
ꢁ16.04
30.30
103.7
307.2
156.3
203.0
470.4
31.32
103.7
307.2
156.9
205.2
474.0
104.0
319.8
156.9
204.8
475.4
6.016109
3.3061019
7.906108
2.146108
3.1061010
(15)
On the other hand, the [Cu(Fluc)(OAc)(H2O)3]ꢀ2H2O (5),
[Cu(Fluc)(Gly)(H2O)2]ꢀ3H2O (10) and [Cu(Fluc)(Ala)(H2O)2]ꢀ4H2O (15)
complexes exhibit three disꢂtinct decomposition steps. The first step in the
temperature range 307100 C (mass loss 5.40%; calcd. for 2H2O: 5.27%),
207195 ꢂC (mass loss 16.54%; calcd. for 3H2O, 2H2O and HF: 16.8%), and
257125 ꢂC (mass loss 5.64%; calcd. for 2H2O: 5.05%) may be accounted for
the loss of two water molecules of hydration; four water molecules of
hydration, two coordinated water molecule and HF gas, and loss of two
water molecules of hydration for (5), (10) and (15), respectively, as shown in
Table II. The energy of activation of the thermal dehydration of the com-
plexes are 59.48, 78.20 and 156.90 KJ molꢁ1 for (5), (10) and (15), respec-
tively. The mass losses of the second and third steps amounted to 74.58%
(calcd. 74.02%), 66.37% (calcd. 65.49%) and 77.98% (calcd. 77.69%)
for (5), (10) and (15), respectively. They correspond to the removal of
coordinated water, Fluc, Gly and Ala molecules leaving CuNCS[11] as a
residue in the of (5), (10) and (15), respectively. The structures of these
complexes are given as shown in Fig. 4.
Kinetics of the Decomposition of the Complexes
Integral Method Using the Coats-Redfern Equation
For a first order process, the Coats-Redfern equation[26] may be
written in the following form:
ꢀ
ꢁ
ꢀ
ꢂ
ꢃꢁ
logfWf=ðWf ꢁ WÞg
AR
yEꢅ
2RT
Eꢅ
Eꢅ
log
¼ log
1 ꢁ
ꢁ
ð1Þ
T2
2:303 RT

COMPLEXES OF FLUCLAXOCILLIN
1517
where Wf is the mass loss at the completion of the reaction, W is the mass
loss up to temperature T; R is the gas constant, Eꢅ is the activation energy in
J. molꢁ1, y is the heating rate. Since, 1ꢁ(2RT=Eꢅ) ffi 1, a plot of the left-
hand side of Eq. (1) against 1=T was drawn for all complexes from which Eꢅ
was calculated from the slope and A (Arrhenius constant) was determined
from the intercept. The calculated values of Eꢅ, A, DSꢅ, DHꢅ and DGꢅ for
the decomposition steps are given in Table III. According to the kinetic data
obtained from DTG curves, all of the complexes have a negative entropy
which indicates that the activated complexes are in a more ordered states
than the reactants. Based on the activation energy values, the Co(II) and
Ni(II) complexes have nearly the same thermal stability since they are iso-
structural.
Further investigation to provide more convincing evidence for the
structure of these complexes requires further studies including, e.g., X-ray
diffraction studies and other structural investigations.
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Received May 8, 2001
Accepted June 11, 2002
Referee I: Y. Z. Hamada
Referee II: S. L. Phillips