Synthesis and structure investigation of the antibiotic amoxicillin complexes of d-block elements

Article abstract of DOI:10.1016/j.saa.2004.08.022

The study of some transition metals (M) and amoxicillin trihydrate (ACT) ligand complexes (M-ACT) that formed in solution involved the spectrophotometric determination of stoichiometric ratios and their stability constants and these ratios were found to be M:ACT = 1:1, 1:2 and 2:1 in some instances. The calculated stability constants of these chelates, under selected optimum conditions, using molar ratio method have values ranging from K_f = 10⁷ to 10¹⁴. These data were confirmed by calculations of their free energy of formation ΔG, which corresponded to their high stabilities. The separated solid complexes were studied using elemental analyses, IR, reflectance spectra, magnetic measurements, mass spectra and thermal analyses (TGA and DTA). The proposed general formulae of these complexes were found to be ML(H2O)w(H2O)x(OH)y(Cl)z, where M = Fe(II), Co(III), w=0, x = 2, y = 1, z = 0; M = Co(II), w=0, x = 1, y = 0, z = 1; M = Fe(III), w=0, x = 1, y = 2, z = 0; M = Ni(II), Cu(II) and Zn(II), w=2, x = 0, y = 1, z = 0, where w = water of crystallization, x = coordinated water, y = coordinated OH^- and z = Cl^- in the outer sphere of the complex. The IR spectra show a shift of ν(NH) (2968 cm^-1) to 2984-2999 cm^-1of imino group of the ligand ACT and the absence of ν(CO) (β-lactame) band at 1774 cm^-1 and the appearance of the band at 1605-1523 cm^-1 in all complexes suggest that 6,7-enolization takes place before coordination of the ligand to the metal ions. The bands of MN (at 625-520 cm^-1) and of MO (at 889-7550 cm^-1) proved the bond of N (of amino and imino groups) and O of CO group of the ligand to the metal ions. The reflectance spectra and room temperature magnetic measurements refer to octahedral complexes of Fe(II) and Fe(III); square planner form of Co(II), reduced Co(III), Ni(II) and Cu(II)-ACT complexes but tetrahedral form of Zn-ACT complex. The thermal degradation of these complexes is confirmed by their mass spectral fragmentation. These data confirmed the proposed structural and general formulae of these complexes.

Full text of DOI:10.1016/j.saa.2004.08.022

Spectrochimica Acta Part A 61 (2005) 2231–2238
Synthesis and structure investigation of the antibiotic amoxicillin
complexes of d-block elements
M.A. Zayeda,∗, S.M. Abdallahb
a
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
b
El-gamma El-Omalia, Cairo, Egypt
Received 3 June 2004; accepted 31 August 2004
Abstract
The study of some transition metals (M) and amoxicillin trihydrate (ACT) ligand complexes (M–ACT) that formed in solution involved
the spectrophotometric determination of stoichiometric ratios and their stability constants and these ratios were found to be M:ACT = 1:1,
1:2 and 2:1 in some instances. The calculated stability constants of these chelates, under selected optimum conditions, using molar ratio
method have values ranging from Kf = 107 to 1014. These data were confirmed by calculations of their free energy of formation ꢀG, which
corresponded to their high stabilities. The separated solid complexes were studied using elemental analyses, IR, reflectance spectra, magnetic
measurements, mass spectra and thermal analyses (TGA and DTA). The proposed general formulae of these complexes were found to be
ML(H2O)w(H2O)x(OH)y(Cl)z, where M = Fe(II), Co(III), w = 0, x = 2, y = 1, z = 0; M = Co(II), w = 0, x = 1, y = 0, z = 1; M = Fe(III), w = 0,
x = 1, y = 2, z = 0; M = Ni(II), Cu(II) and Zn(II), w = 2, x = 0, y = 1, z = 0, where w = water of crystallization, x = coordinated water, y =
coordinated OH− and z = Cl− in the outer sphere of the complex. The IR spectra show a shift of ν(NH) (2968 cm−1) to 2984–2999 cm−1of imino
group of the ligand ACT and the absence of ν(CO) (␤-lactame) band at 1774 cm−1 and the appearance of the band at 1605–1523 cm−1 in all
complexes suggest that 6,7-enolization takes place before coordination of the ligand to the metal ions. The bands of M N (at 625–520 cm−1
)
and of M O (at 889–7550 cm−1) proved the bond of N (of amino and imino groups) and O of C O group of the ligand to the metal ions. The
reflectance spectra and room temperature magnetic measurements refer to octahedral complexes of Fe(II) and Fe(III); square planner form
of Co(II), reduced Co(III), Ni(II) and Cu(II)–ACT complexes but tetrahedral form of Zn–ACT complex. The thermal degradation of these
complexes is confirmed by their mass spectral fragmentation. These data confirmed the proposed structural and general formulae of these
complexes.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Synthesis; ACT–M complexes; Spectroscopic measurements; Thermal analyses
1. Introduction
salmonella. It is usually given by mouth, as the trihydrate.
The usual dose is 250–500 mg three times daily. It may be
given by injection for moderate infections but in severe ones,
1 g may be given every 6 h [1].
Amoxicillin trihydrate (Fig. 1) is a white odorless crys-
talline powder. It is the 4-hydroxy analogue of ampicillin and
used against a similar variety of infections although it should
not be used in shigellosis. It had been used as an alternative
to chloramphenicol in the treatment of infections caused by
The mechanism of the colour reaction between ACT and
Cu salts together with biuret reagent to form mixed-ligand
copper complexes, in the molar ratio 1:1 [2] had been studied.
Spectrometric studies of this reaction had been used to de-
termine ACT in pharmaceuticals at λ = 750, 650 and 640 nm
[3]. Several physico-chemical studies of the complexation re-
action of the sodium salt of amoxicillin and Cu(II) were per-
formed by spectrophotometeric analysis. The data obtained
demonstrated the formation of 1:1, 1:2 and 2:1 complexes
[4].
∗
Corresponding author. Present address: Chemistry Department, Fac-
ulty of Education for Girls, Elmontazah, Elgarbi, P.O. Box 1921, Borida,
ElQasseem 9114, Saudi Arabia. Tel.: +966 63850783; fax: +966 63850783.
E-mail addresses: mazayed429@hotmail.com,
mazayed429@yahoo.com (M.A. Zayed).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.08.022

2232
M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
to 25 mL of a 0.01 M ACT (4.19 g L−1, 10 mmol) solution
with continuous stirring at room temperature and at pH val-
ues 8.2–8.8 adjusted by solutions of 0.1 M NaOH or 0.1 M
Na2CO3 using a pH-meter. The mixtures were refluxed in
a 100 mL rounded-bottom flask for 1–2 h. The solid pre-
cipitates obtained were filtered in a Hirsch funnel, washed
with hot water and N-pentane several times and dried in an
oven at 80 ◦C. The solids obtained were crystallized from
an ethanol–water mixture (1:1), dried and analyzed by mi-
croanalyses at the Microanalytical Center of Cairo Univer-
sity. The complexes were investigated by the various physico-
chemical methods previously mentioned.
2.2. Solutions
Fig. 1. Amoxicillin trihydrate (ACT) 6,7-keto-enol forms.
A 10−3 M ACT solution was prepared by dissolving the
appropriate amount (0.419 g) of the ligand in 1 L bidistilled
water. A 10−3 M solutions of Fe(II), Fe(III), Co(II), Co(III),
Ni(II), Cu(II) and Zn(II) cations were prepared by dissolving
the appropriate weights of the metal salts mentioned previ-
ously in bidistilled water.
The dc and differential pulse polarographic measurements
were used to study the behavior of Ni(II)–ampecillin and
Ni(II)–ACT complexes at the dropping mercury electrode
[5,6]. The spectrophotometric method used for the study of
the formation of Ni(II)–ACT in capsules was used for the
microdetermination of this drug [7].
2.3. Instruments and apparatus
The effects of pH, temperature and ion concentrations
on the hydrolysis kinetics of amoxicillin (AC) catalyzed by
Cu(II), V(IV) and V(V) ions were studied via the formation
of the binary complexes of these metals [8].
The UV and visible spectra of the ligand and complexes
in solution were measured by a recording 240 Shimadzu
UV–vis or a manual Spectronic 601spectrophotometer at
room and various temperatures using 1 cm matched silica
cells. The pH-meters used for pH adjustment were a model 28
The present research work aims chiefly to shed more light
on the chemical behavior of some life-essential drugs such
as amoxicillin trihydrate (ACT). ACT has essential biologi-
cal roles in curing different kinds of diseases. It takes several
pathways in the human body and interacts in vivo systems in
aqueous media. Consequently, it is important to manipulate
its chemical interaction with some important transition metal
cations of vital biological roles in the human body. It involved
a study of ACT–3d-block elements complexes both in solu-
tion and in the solid state. The synthesized solid complexes
were subjected to very careful inspection by elemental, spec-
troscopic and thermal analyses.
¨
Radiometer pH-meter, a model 87 digital pH/mV-Messgerate
or a model 701A pH/mV-Ionanalyzer. The various tempera-
tures of reactions in the solution vessels were adjusted by us-
ingaHAAKFModelNB22ultrathermostat. TheIRspectraof
the solid ligand and complexes as KBr disks were measured
using a Perkin-Elmer 1430 spectrophotometer in the wave
number range 400–4000 cm−1. The UV–vis reflectance spec-
tra of the solids were measured using a model 3101 Shimadzu
PC spectrophotometer and BaSO4 background. The thermal
analyses (TG, DTG, and DTA) were carried out using TGA-
5OH and DTA-5OH Shimadzu thermal analyzers respec-
tively with a heating rate 10 min−1 in nitrogen atmosphere.
2. Experimental
2.4. Selected suitable conditions for complex formation
in solution
All chemicals used in this study were of analytical grade.
They included ACT of the formula C16H19N3O5S·3H2O, and
the metal salts FeSO4·6H2O, Fe2(SO4)3, Co(NO3)2·6H2O,
Na3[Co(NO2)6], NiSO4·7H2O, CuCl2 and ZnSO4·7H2O.
These chemicals were purchased from Merck or Aldrich. The
organic solvents, methanol (98%), ethanol (95%), N-pentane
(98%) and acetone (97%) were purchased from BDH and
used without further purification.
The reactions of the various metal ions such as Fe(II),
Fe(III), Co(II), Co(III), Ni(II), Cu(II) and Zn(II) ions with
ACT were studied spectrophotometrically under various ex-
perimental conditions to select the optimum ones. The effect
of pH on the spectra of the various complexes were studied
by placing of 1.0 mL of a 10−3 M ACT solution in a 5 mL
measuring flask and addition of a series of universal buffers
of pH 1.91–12.40 and measuring absorbency at λ ranging
between 330 and 390 nm. The effect of N-bromosucinimide
(NBS) as oxidant and the effect of temperature on the com-
plex formation of ACT–3d-block series were studied.
2.1. Preparation of solid complexes
The solid M–ACT complexes were prepared by dropwise
addition of 25 mL of a 0.01 M metal salt solution (10 mmol)

M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
2233
2.5. The stoichiometry of d-block element–ACT
complexes
used for the calculation of Kf and ꢀG of the M–ACT
chelates.
The stoichiometric ratio between 3d-block elements [M]
and the drug ligand (ACT) was studied by the molar ratio
method (mrm) in which [ACT] was varied from 0.1 × 10−3
to1.0×10−3 Minamixturewithconstant[M]=1 ×10−3 M,
NaNO2, N-bromosuccinimide (NBS) and a buffer of suitable
pH. The absorbency of solutions was measured at selected
λmax and plotting absorbency against [ACT]/[M], the inflec-
tion points gave ratio values of 1:1 and 1:2 (M:ACT).
3. Results and discussion
In view of the vital role of amoxicillin as drug (given
orally to humans or as injection) it is very important to study
its interaction with transition metals that normally are present
in vivo system. This study involves two stages, in solution and
in the solid state in order to explain their possible interactions
in vivo systems [9]. Applying the recommended molar ratio
method (mrm) [10], the study of the formation of M–ACT
complexes under selected optimum conditions in all cases, it
shows straight lines intersecting at [ACT]:[M] ratios of 1:1
and 1:2.
The extent, to which these complexes are formed, is usu-
ally expressed by the formation constant Kf (apparent condi-
tional stability constant) at particular pH, λmax and tempera-
ture. This pH is usually calculated from the expression Kf/α
where α is the fraction of ligand attached to the metal cation.
This stability is also expressed by the free energy change
(ꢀG) of these complexes, applying the molar ratio method
2.6. Evaluation of the stability formation constant Kf
and free energy change (ꢀG) of the formed complexes
The extent to which complex formation occurs is usu-
ally expressed by a formation constant, Kf, of a complex at
particular conditions. These conditions are (pH = 7.71–8.80,
λmax = 325, 255, 320, 255, 260, and 265 nm for Fe(II)–ACT,
Fe(III)–ACT, Co(II)–ACT, Co(III)–ACT, Ni(II)–ACT, and
Cu(II)–ACT, respectively, at room temperature and devel-
oping time of 5–10 min). Spectrophotometric results ob-
tained under the practical selected optimum conditions were
Table 1
The apparent formation (conditional) constant (Kf), and free energy change (ꢀG) for ACT–transition metal complexes by using molar ratio method (mrm) at
pH = 7.71–8.80, at ambient temperature (25 ◦C), developing time = 5–10 min and corresponding λmax (nm)
Compound
λmax
Ratio
A
Am
A − Am
1 − (A/Am)
Kf
ꢀG (25 ◦C)
(kcal mol deg−1
)
[FeL(OH)(H2O)2] (formula weight = 475)
325
1:1
1:2
1:1
1:2
0.72
1.08
0.75
1.22
0.76
1.12
0.78
1.25
0.947
0.964
0.961
0.976
0.0526
0.0357
0.0348
0.0240
1 × 107
9.608
18.414
9.608
2.604 × 1013
1 × 107
6.23 × 1013
18.934
[Fe(OH)2L(H2O)] (formula weight = 474)
[CoL(H2O)]Cl (formula weight = 475.5)
[Co(OH)L(H2O)2] (formula weight = 477)
[NiL(OH)]·2H2O (formula weight = 477.5)
[CuL(OH)]·2H2O (formula weight = 482)
[ZnL(OH)]·2H2O (formula weight = 483)
255
350
1:1
1:2
1:1
1:2
2.42
2.58
0.80
1.18
2.45
2.60
0.82
1.22
0.987
0.992
0.975
0.967
0.0122
0.0076
0.0243
0.0327
4.083 × 107
17.187× 1014
1.796 × 107
2.604 × 1013
10.446
20.911
9.957
18.414
320
350
1:1
1:2
1:1
1:2
1.08
1.24
0.95
1.18
1.13
1.28
0.98
1.22
0.955
0.968
0.969
0.967
0.0442
0.0312
0.0306
0.0327
6.333 × 106
2.604 × 1013
1 × 107
9.335
18.414
9.608
2.604 × 1013
18.414
255
305
1:1
1:2
1:1
1:2
2.44
2.66
1.40
1.54
2.47
2.69
1.44
1.58
0.987
0.988
0.972
0.974
0.0121
0.0111
0.0277
0.0253
4.083 × 107
2.126 × 1014
1.79 × 107
10.446
19.665
9.995
6.237 × 1013
18.934
265
310
1:1
1:2
1:1
1:2
2.52
2.58
1.98
2.01
2.54
1.60
2.01
2.03
0.992
0.992
0.985
0.990
0.0078
0.0076
0.0149
0.0098
16.5 × 107
11.279
20.911
10.446
19.665
17.18 × 1014
4.083 × 107
2.126 × 1014
265
310
1:1
1:2
1:1
1:2
1.52
1.56
1.98
1.84
1.54
1.58
2.01
1.86
0.987
0.987
0.985
0.989
0.0129
0.0126
0.0149
0.0107
4.083 × 107
2.12 × 1014
4.083 × 107
2.120 × 1014
10.446
19.665
10.446
19.665
305
350
1:1
1:2
1:1
1:2
1.78
1.90
0.86
1.20
1.82
1.93
0.90
1.24
0.978
0.984
0.955
0.967
0.0219
0.0155
0.0444
0.0322
1.79 × 107
2.126 × 1014
6.33 × 106
2.604 × 1013
9.955
19.605
9.335
18.414

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M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
Table 2
Analytical and physical data of amoxicillin complexes
Compound
Colour (%
yield)
mp (◦C) Found (calcd.) (%)
Found molecular µeff
ion [m/z] (calcd.) (BM)
C
H
N
M
[FeL(OH)(H2O)2] (C16
H
24FeN3O8S)
Brown (70) >300
Brown (70) >300
Brown (60) >300
40.05 (40.50) 5.00 (5.06) 8.68 (8.01) 10.90 (11.60) 475 (474)
40.20 (40.50) 5.10 (5.06) 8.86 (8.40) 11.81 (12.00) 475 (473)
40.25 (40.42) 4.42 (4.40) 8.80 (8.81) 12.00 (12.31) 473 (477)
40.42 (40.25) 5.03 (5.07) 8.80 (8.88) 11.94 (12.33) 478 (477)
40.17 (40.25) 5.03 (5.02) 8.41 (8.78) 12.26 (12.28) 478 (477)
5.24
5.24
2.24
2.5
[Fe(OH)2L(H2O)] (C16H23FeN3O8S)
[CoL(H2O)]Cl (C16 21ClCoN3O6S)
[Co(OH)L(H2O)2] (C16
[NiL(OH)]·2H2O (C16
H
H
24CoN3O8S) Brown (75) >300
H
24NiN3O8S)
Yellowish
>300
Diamg.
brown (66)
[CuL(OH)]·2H2O (C16H24CuN3O8S)
[ZnL(OH)]·2H2O (C16H24N3O8SZn)
Black (70) >300
Brown (65) 250
38.48 (38.48) 4.60 (4.60) 8.69 (8.42) 12.70 (12.71) 482 (484)
39.59 (39.97) 4.96 (4.97) 8.41 (8.87) 13.45 (13.48) 485 (483)
1.85
Diamg.
Diamag. = diamagnetic. The proposed general formulae of these complexes were found to be ML(H2O)w(H2O)x(OH)y(Cl)z, where M = Fe(II), Co(III), w = 0,
x = 2, y = 1, z = 0; M = Co(II), w = 0, x = 1, y = 0, z = 1; M = Fe(III), w = 0, x = 1, y = 2, z = 0; M = Ni(II), Cu(II) and Zn(II), w = 2, x = 0, y = 1, z = 0, where
also w = water of crystallization, x = coordinated water, y = coordinated OH− and z = Cl− in the outer sphere.
data obtained in the experimental part. The results obtained
are shown in Table 1. It is clear from the data that, Kf for the
Fe(II)–ACT system at λ = 325 nm, 1:1 (M:L) and 1:2 (M:L)
complexes, range from 107 to 1013; Kf of Fe(III)–ACT (1:1)
is 107 at 255 nm; Kf for the Co(II)–ACT (1:2) at λ = 320 nm
is 2.6 × 1013; Kf for the Co(III)–ACT (1:2) at 255 nm is 2.1
× 1014, etc. The high values of Kf ranging from 107 to 1014
for these complexes refer to their high stability in solution
at pH values very close to that of in vivo system. The calcu-
lated values of ꢀG range from 9.6 to 19.6 kcal mol deg−1 and
confirm the stability. Therefore, the use of a higher dose of
amoxicillin, than that recommended by the physician should
be avoid. The elemental microanalyses for the separated, pu-
rified and analyzed solid complexes together with other ana-
lytical and physical data are given in Table 2. Thus, it is very
interesting to prepare and to study such complexes in both
solution and in the solid state to shed more light on the na-
ture of bonding using IR spectra (Table 3) between 3d-block
metal cations and the amoxicillin drug.
signed to the asymmetric ν(NH) vibration of the amino group.
The other band at 3000 cm−1 may be due to the vibration of
the imino group. These two bands are shifted on complexa-
tions indicating the involvement of both NH2 and NH groups
in complex formation. The shift of ν(NH) to lower frequency
from 2968 to 2924–2927 cm−1 on complexation suggests co-
ordination via the NH of the amide group. The absence of a
C O (␤-lactame) ligand band at 1774 cm−1 and the appear-
anceofthebandat1603–1523 cm−1 inallcomplexes, suggest
that 6,7-enolization (Fig. 1) takes place before coordination
with metal ions. The occurrence of bands at 625–520 cm−1
(M N) and 420–455 cm−1 (M O) prove the bonding of ni-
trogenandoxygentothemetalions[11,12]. Thespectraofthe
solid complexes exhibited a broad band at 3630–3440 cm−1
;
which may be attributed to ν values of the water molecules
of crystallization, while the band observed at 889–750 cm−1
may be assigned to coordinated water molecules in the com-
plexes.
3.2. Electronic spectra and magnetic susceptibility
3.1. Infrared spectra of the solid complexes and mode of
chelation
The room temperature magnetic moment value of 5.7 BM
oftheFe(III)complexiswithintherangecorrespondingtothe
high-spin octahedral Fe(III) complexes. For the Fe(II)–ACT
complex, the obtained magnetic moment of 5.33 BM indi-
cates octahedral geometry of ligands around the metal cation.
The µeff value of the Co(II)–ACT complex is found to be
2.24 BM, consistent with square–planar geometry [12]. This
The infrared spectra of the solid complexes and the ACT
ligand were recorded in the range 400–4000 cm−1. The IR
spectral data of ACT and its complexes and the assignment of
the vibrational frequencies are given in Table 3. The highest
frequency of the bands of the ligand at 3200 cm−1 can be as-
Table 3
Selected IR data (4000–200 cm−1) for amoxicillin and its complexes
Compound
ν(C N)
(cyclic)
ν(NH2)
ν(C=O)
ν(NH) (amide)
νasym− (COO−)
ν(M O)
(␤-lactame)
Coordinate
H2O
ν(M N)
(␤-lactame)
Amoxicillin
1379 s
1376 s
1379 s
1373 s
1380 s
1377 s
1384 s
1390 s
3200–3000 s
3251 b
3157 b
3276 b
3229 b
3278 b
3251 b
3258 b
1774 s
disap.
disap.
disap.
disap.
disap.
disap.
disap.
2968 s
2925 s
2924 s
2927 s
2926 s
2926 s
2924 s
2925 s
1582 s
1603 s
1601 s
1602 s
1602 s
1601 s
1599 s
1601 s
–
426 s
455 s
430 s
420 s
430 s
447 s
420 s
–
888, 796 s
889, 795 s
840, 750 s
841, 750 s
841, 750 s
841, 775 s
842, 780 s
–
615 s
540 s
586 s
535 s
519 s
625 s
599 s
[FeL(OH)(H2O)2]
[FeL(OH)2(H2O)]
[CoL(H2O)]Cl
[Co(OH)L(H2O)2]
[NiL(OH)]·2H2O
[CuL(OH)]·2H2O
[ZnL(OH)]2H2O
s = strong, b = broad and disap. = disappeared peak.

M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
2235
result may be due to the reduction of Co(III) to Co(II) dur-
ing complexation by the thiazol sulfur atom. The spectrum
of these complexes reveal bands at 424 and 416 mm suggest-
ing the presence of square–planar geometry around cobalt
ions. The room temperature magnetic susceptibility data of
the Ni(II)–ACT complex shows that, the complex is essen-
tially diamagnetic and of low-spin with 1A1g → A2g → Eg
transitions, respectively [12]. The complex is, therefore, of
square–planar geometry because it is a diamagnetic and there
is no band seen below 1000 nm.
The observed µeff = 1.85 BM of the Cu(II)–ACT complex
is very close to the spin-only value [11] of an unpaired elec-
tron (1.73 BM) which indicates that the orbital contribution is
almost quenched by the crystalline field. Electronic spectra of
1
1
Fig. 2. The proposed structural formulae of amoxicillin–d-block complexes,
where M = Fe(II), Co(III), w = 0, x = 2, y = 1, z = 0; M = Co(II), w = 0, x =
1, y = 2, z = 1; M = Fe(III), w = 0, x = 1, y = 2, z = 0; M = Ni(II), Cu(II) and
Zn(II), w = 2, x = 0, y = 1, z = 0, where also w = water of crystallization, x
= coordinated water, y = coordinated OH− and z = Cl− in outer sphere.
Fig. 3. Thermal analyses (TGA, Dr.TGA and DTA) of amoxicillin trihydrate (ACT) complexes of 3d-transition metals.

2236
M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
the complex show only three bands in the region 550–460 nm
tion of this complex. There is an exothermic broad peak at
200–456 ◦C; which may be attributed to the loss of some
ACT ligand parts that chemically recombined. This exother-
micprocessrequiredenergyof1.31 J g−1 at27–380 ◦Candits
maximum occurs at 315 ◦C. The complete process required
383 J g−1 of energy.
due to the transitions 2B1g → A1g → Eg and charge trans-
fer, respectively [12], which corresponds to square–planar
geometry [12]. The Zn(II)–ACT complex is diamagnetic and
has a tetrahedral structure as confirmed by its electronic tran-
sition spectra.
1
1
The structural formulae for all of the proposed complexes
of d-block element–ACT are illustrated in different shapes
varied between the square–planar and octahedral forms given
by Fig. 2.
The mass spectra of the Fe(II)–ACT complex of the mole
mass 475 show a molecular ion at m/z = 475 (RI = 4.72%).
This is followed by a molecular ion of m/z = 214 (RI = 25%)
of the residual oxide of mole mass 214 [12].
3.3.2. Thermal analysis and mass spectra of the
Fe(III)–ACT complex
3.3. Thermal analyses and mass spectra of the solid
complexes M–ACT
The thermal decomposition process of the Fe(III)–ACT
complex occurs in five stages (Table 4) as a result of the de-
composition of ACT ligand together with the loss of water
molecules, total weight loss 36%, leaving Fe3O4·FeO as 64%
of a stable residue of mole mass 304. The DTA of this com-
plex shows a broad exothermic peak at a temperature range
219–470 ◦C; which may be attributed to the exothermic de-
composition of this complex and chemical recombination of
the fragments of the ligand obtained. This process required
3.3.1. Thermal analysis and mass spectra of the
Fe(II)–ACT complex
The thermal analyses of theses complexes are shown in
Fig. 3 and their mass spectra are shown in Fig. 4. Fig. 3 shows
the TG and DTA data of all studied complexes. The detailed
description and explanation of TA data of the prepared and
studied M–ACT complexes are given in Table 4. These data
reasonably account for the loss of water molecules [12] and
parts of the decomposed ligand during the heating processes
[13]. The Fe(II)–ACT complex is thermally decomposed at
several stages (Table 4) and the total weight loss is 55%,
leaving as residue a stable oxide Fe·F2O3 [12] of mole mass
214 and 45%. The DTA confirms the thermal decomposi-
an energy of 2.11 kJ g−1
.
The mass spectra of the Fe(III)–ACT complex show a
molecular ion of m/z = 474 (RI = 4.3%) of the main complex
(calcd. MW: 474), together with a residual oxide (calcd. MW:
304) appeared as a molecular ion of m/z = 304 (RI = 25.8%).
Fig. 4. Mass spectra of ACT–d-block elements complexes.

M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
2237
Table 4
Thermal decomposition data of amoxicillin (ACT) complexes
Complex
Temperature range
in TG (◦C)
Peak temperature
in TG (◦C)
Mass loss (%)
Assignment
Calcd. Found
[FeL(OH)(H2O)2]
23–140
143–306
306–412
425–565
68.58
241.24
366.15
471.47
3.79
17.9
15.6
3.45
17.64
16.68
17.69
Loss of H2O molecule (water of hydration)
Loss of CONH and CH3C CH3 molecules
Loss of C2S and H2O molecules (coordinated)
17.08
Loss of HC C CN, CHNH, C6H4OH, and Fe3O3 (45%)
[Fe(OH)2L(H2O)]
[CoL(H2O)]Cl
20–137
138–220
220–280
283–262
363–569
72.35
181.86
248.44
323.89
424.52
3.37
6.75
3.8
5.9
15.4
3.25
6.17
4.8
6.84
14.69
Loss of CH4 molecule
Loss of CH3OH molecule
Loss of H2O molecule (coordinated)
Loss of a CO molecule
Loss of NCH2CH2Oand leaving Fe3O4·FeO (64%) as residue
Loss of C2H6 molecule
Loss of C6H4OH molecule
Loss of CO2, 1/2 Cl and CH2CH2N molecule
Loss of C2S and H2NCH2(NH)CH and of Co2O3 (26%) as a residue
31–170
170–360
360–485
485–610
70.89
297.26
428.95
529.48
6.31
19.55
25.47
23.55
7.43
19.37
24.56
23.85
[Co(OH)L(H2O)2]
[NiL(OH)]·2H2O
[CuL(OH)]·2H2O
20–125
128–301
303–513
62.62
248.01
389.95
10.06
17.8
46.73
9.47
17.52
45.71
Loss of C2H6 and H2O molecules (coordinated)
Loss of CO2 and C2H2NH molecules
Loss of C6H4OH, H2NCHCONH and Co2O4 (38%) as a residue
20–170
170–440
440–600
172.91
357.15
458.53
10.06
50.31
23.29
9.59
51.75
24.8
Loss of C2H6 and H2O molecules (water of crystallization)
Loss of CH2COOH + H2N + N2NCHCONH and C6H4OH molecules
Loss of CO + C3S, H2O and NiO (15%) as a residue
24–128
131–450
451–780
790–996
83.13
262.67
624.11
882.28
3.6
21.8
27
3.33
21.86
26.11
23.26
Loss of H2O molecule (crystallization)
Loss of CO2 and C2H6 molecules
Loss of C6H4OH and CH2 CH2N molecules
Loss of L parts and CuO3 (24%)as a residue
22.4
[ZnL(OH)]·2H2O
31–158
160–406
409–525
529–718
70.22
289.21
471.87
581.27
6.21
34.78
22.53
20.91
5.95
34.51
22.03
23.46
Loss of C2H6 molecule
Loss of C6H4OH, H2O (of crystallization) and H2NCHO molecules
Loss of H2O (of crystallization), CO2, and CH2CHNH molecules
Loss of HO CH2CH2NCS and leaving ZnO (17%) as a residue
3.3.3. Thermal analysis and mass spectra of the
Co(II)–ACT complex
and 41.4%) and final molecular ion of m/z = 183 (RI = 13%)
of the residual oxide [12].
The Co(II)–ACT complex thermally decomposed in sev-
eral stages (Table 4) of a total weight loss of 74%, leaving a
stable Co2O3 of mole mass 127 and 26%. The mass spectra of
Co(II)–ACT (calcd. MW: 475.5) show a molecular ion of m/z
= 477 (RI = 5.91%) referring to the main complex, followed
by a molecular ion of m/z = 126 (RI = 13%) of the stable final
residue of Co2O3 (calcd. MW: 127). The gradual appearance
of molecular ions in mass spectra supports the gradual mass
losses given by TA.
3.3.5. Thermal analysis and mass spectra of the
Ni(II)–ACT complex
The TG of Ni(II)–ACT complex exhibits total mass losses
of 84% leaving a stable NiO (calcd. MW: 75.5 and 16%).
The mass spectra show a molecular ion of m/z = 478 (RI =
5.96%) referring to the main complex Ni(II)–ACT, together
with a final residue of NiO (calcd. MW: 75.5) appeared as a
molecular ion of m/z = 75 (RI = 18.81%).
3.3.4. Thermal analysis and mass spectra of the
Co(III)–ACT complex
3.3.6. Thermal analysis and mass spectra of the
Cu(II)–ACT complex
The TG of Co(III)–ACT complex, refers the total mass
loss of 62% due to the fragmentation of the complex in four
stages (Table 4), leaving Co2O4 as a sable residue (calcd.
MW: 184 and 38%). All of the above mass losses appear in
DTA of this complexes as a broad exothermic peak in the tem-
perature range 20–448 ◦C and these stages required energy
The Cu(II)–ACT complex thermally decomposed in sev-
eral stages (Table 4) of the total mass loss of 76% leaving a
stable CuO·2H2O as a residue of mole mass 115.5 and remain
percent 24%.
These mass losses appear in DTA as endothermic peaks
centered at 630 and 693 ◦C. The Cu(II)–ACT complex (mole
mass = 482) appears in mass spectra a molecular ion of m/z
= 481 (RI = 5.77%) together with another molecular ion of
m/z = 370.5 (RI = 10.77%) leaving a residue of CuO3 (calcd.
MW: 114.5) appears as molecular ion of m/z = 114 (RI =
93.08%).
values of −83.5, −278.0, −103.6 cal g−1 and 389.8 J g−1
,
respectively.
The mass spectra of the main complex (calcd. MW: 477)
give a molecular ion of m/z = 478 (RI = 6.06%) followed by
molecular ions, of m/z = 93 of phenol ion (calcd. MW: 94

2238
M.A. Zayed, S.M. Abdallah / Spectrochimica Acta Part A 61 (2005) 2231–2238
3.3.7. Thermal analysis and mass spectra of the
Zn(II)–ACT complex
these complexes, elucidated the proposed structures of these
complexes.
The TG of Zn(II)–ACT complex thermally decomposed
in several stages of total loss 84% leaving a stable ZnO of
mole mass 81 and remain percent 16% as a stable residue.
In mass spectra of Zn(II)–ACT complex (calcd. MW: 483)
it appears as a molecular ion of m/z = 484 (RI = 4.44%) fol-
lowed by the molecular ion of m/z = 453 (6.85%), a molec-
ular ion of m/z = 284 (RI = 19.76%), a molecular ion of
m/z = 182 (RI = 19.16%) and finally a residual molecular
ions of m/z = 81 (RI = 7.66%) referring to ZnO (calcd. MW:
81).
The detailed description of TA behavior of different
M–ACT complexes in comparison with their mass spectral
behavior; leads to the conclusion that most of the molecu-
lar ions appeared in mass pathways are those obtained as a
result of stepwise thermal degradation of these complexes.
This means that generally mass spectral passways are cor-
related to the obtained pathways in thermal analyses (TA)
[13,14]. The main difference is that TA detect remaining part
of the complex but mass detect most and/or the fragments as
molecular ions. Therefore, both mass and TG support each
otherandactascomplementarytoolsaspreviouslyconcluded
by several research papers done in this laboratory [12–16].
The TA and mass spectra of these complexes, in comparison
with, IR, magnetic and the reflectance spectral analyses of
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