Characterization, molecular modeling and antimicrobial activity of metal complexes of tridentate Schiff base derived from 5-acetyl-4-hydroxy-2H-1,3- thiazine-2,6(3H)-dione and 2-aminophenol

Article abstract of DOI:10.1016/j.saa.2012.04.030

Metal complexes of Ni(II), Co(II), Cd(II), VO(IV) and UO₂(VI) as well as several Cu(II) salts, including Cl^-,NO3-,AcO ^-,ClO4- and SO4-2 with a tridentate O₂N donor Schiff base ligand (H₂L), synthesized by condensation of 5-acetyl-4-hydroxy-2H-1, 3-thiazine-2,6(3H)-dione with 2-aminophenol, were prepared and characterized on the basis of elemental analyses, spectral, magnetic, molar conductance and thermal gravimetric analysis. Square planar, tetrahedral and octahedral geometries have been assigned to the prepared complexes. Molecular parameters of the ligand and its metal complexes have been calculated and correlated with the experimental data, and the changes of bond lengths are linearly correlated with IR data. The antimicrobial activities of the synthesized compounds were tested in vitro against the sensitive organisms Staphylococcus aureus as Gram positive bacteria, Proteus vulgaris as Gram negative bacteria and Candida albicans as fungus strain, and the results are discussed.

Full text of DOI:10.1016/j.saa.2012.04.030

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Characterization, molecular modeling and antimicrobial activity of metal
complexes of tridentate Schiff base derived from
5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione and 2-aminophenol
⇑
Omima M.I. Adly
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo 11711, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 23 April 2012
Metal complexes of Ni(II), Co(II), Cd(II), VO(IV) and UO2(VI) as well as several Cu(II) salts, including
Clꢀ; NOꢀ3 ; AcOꢀ; ClO4ꢀ and SOꢀ4 2 with a tridentate O2N donor Schiff base ligand (H2L), synthesized by con-
densation of 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione with 2-aminophenol, were prepared and
characterized on the basis of elemental analyses, spectral, magnetic, molar conductance and thermal
gravimetric analysis. Square planar, tetrahedral and octahedral geometries have been assigned to the pre-
pared complexes. Molecular parameters of the ligand and its metal complexes have been calculated and
correlated with the experimental data, and the changes of bond lengths are linearly correlated with IR
data. The antimicrobial activities of the synthesized compounds were tested in vitro against the sensitive
organisms Staphylococcus aureus as Gram positive bacteria, Proteus vulgaris as Gram negative bacteria and
Candida albicans as fungus strain, and the results are discussed.
Keywords:
Tridentate Schiff base
5-Acetyl-4-hydroxy-2H-1,3-thiazine-
2,6(3H)-dione
Molecular modeling
Antimicrobial activity
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
molar conductance and thermal gravimetric analysis. Molecular
modeling carried out for the free ligand and its complexes, and
Schiff bases are important class of ligands in coordination chem-
istry, which have extensive application in different fields of science
[1,2]. They possess significant interest in the field of chemistry and
biological activities such as antibacterial, antifungal, antitumor,
antimalarial, antineoplastic and antiviral activities [3–8]. Transition
metal complexes of asymmetrical Schiff base ligands have been at-
tracted enormous attentions due to their important properties such
as catalytic, magnetic, fluorescent and electrochemical properties
[9–16]. Tridentate Schiff bases with nitrogen and oxygen donors
set atoms provide various coordination mode for a wide variety of
metal ions [11,12,17–19]. Further, transition metal complexes of
heterocyclic Schiff bases have been the subject of extensive investi-
gation because of their wide use in biological field [20–24]. In
continuation to our interest in metal complexes of the ligands
derived from 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione
[25], the present study deals with the synthesis of a new Schiff base
ligand (H2L), by the condensation of 5-acetyl-4-hydroxy-2H-1,3-
thiazine-2,6(3H)-dione with 2-aminophenol, and its complexes
with Ni(II), Co(II), VO(IV), Cd(II), UO2(VI) ions as well as a variety
of Cu(II) salts ðClꢀ; NO3ꢀ; AcOꢀ; ClO4ꢀ and SOꢀ4 2Þ to investigate the
effect of anions on the complexation process. These compounds
have been characterized by elemental analyses, spectral, magnetic,
the theoretical results were correlated with the experimental data.
2. Experimental
2.1.Materials
Nickel(II), cobalt(II) and cadmium(II) were used as nitrate salts
and were Merck. Oxovanadium(IV) sulfate monohydrate and diox-
ouranium(VI) acetate dihydrate were BDH. Copper(II) salts were
used as nitrate, acetate, chloride, sulfate and perchlorate. Organic
solvents (ethanol, methanol, diethylether, dimethylformamide
(DMF) and dimethylsulfoxide (DMSO)) were reagent grade. The
antibiotic Doxymycin and Fluconazole were purchased from Egyp-
tian markets and used in concentrations 100
for antibacterial and antifungal activities.
l
g mLꢀ1 as references
2.2. Synthesis of 4-hydroxy-5-[N-(2-hydroxyphenyl)ethanimidoyl]-
2H-1,3-thiazine- 2,6(3H)-dione, H2L ligand
5-Acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione (AHTD) was
prepared as described elsewhere [26]. A mixture of AHTD (1.87 g,
10.0 mmol) and 2-aminophenol (1.09 g, 10.0 mmol), in absolute
ethanol (25 mL) containing few drops of acetic acid, was heated un-
der reflux for 1 h. Yellow crystals were obtained after cooling at
room temperature. The product was filtered off and recrystallized
⇑
Tel.: +20 1008693220.
E-mail address: omima_adly@yahoo.com
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.04.030

484
O.M.I. Adly / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
was performed on medium potato dextrose agars (PDA) that contain
infusion of 200 g potatoes, 6 g dextrose and 15 g agar [32]. Uniform
size filter paper disks (3 disks per compound) were impregnated by
equal volume (10 lL) from the specific concentration of dissolved
tested compounds and carefully placed on inoculated agar surface.
After incubation for 36 h at 27 °C in the case of bacteria and for
48 h at 24 °C in the case of fungi, inhibition of the organisms was
measured and used to calculate mean of inhibition zones.
Scheme 1. Formation of the Schiff base, H2L ligand.
from ethanol: yield, 1.95 g (70%); and m.p., 200 °C. Scheme 1 illus-
trates the formation of the H2L ligand.
3. Results and discussion
2.3. Synthesis of the metal complexes
The analytical data, percentage yields, colors and melting points
of the free ligand, 4-hydroxy-5-[N-(2-hydroxyphenyl)ethanimi-
doyl]-2H-1,3-thiazine-2,6(3H)-dione (H2L), and its complexes with
Cu(II), Ni(II), Co(II), VO(IV), Cd(II) and UO2(VI) ions are given in
Table 1.
The analytical data of the current Schiff base (H2L) suggest the
molecular formula C12H10N2O4S corresponding to the formula
mass (278.28 amu). This finding is in consistent with the molecular
ion peak at m/e = 278, as indicated in the mass spectrum of the
present free ligand. The fragmentation pattern of the mass spec-
trum is depicted in Supplementary Scheme 1.
The main characteristic IR absorption frequencies of the free li-
gand (H2L) and its metal complexes are given in Table 2. Compar-
ison of the IR spectrum of the current Schiff base ligand with that
of 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione (AHTD) and
2-aminophenol was important to assign the IR absorption bands.
The intense band at 1611 cmꢀ1 was assigned to the azomethine
Methanolic solution of the deprotonated Schiff ligand (0.83 g,
3 mmol, 20 mL) was added dropwise to a methanolic solution of
the appropriate metal salt (3 mmol, 20 mL) in the molar ratio
1:1. The ligand was firstly deprotonated by lithium hydroxide,
LiOHꢁH2O (0.246 g, 6 mmol), in the molar ratio 1:2. The reaction
mixture of the deprotonated ligand with metal salts was stirred
for 3 h at room temperature, except some cases in which Ni(II),
VO(IV) and UO2(VI) were heated to reflux for 3 h. The resulting pre-
cipitates were collected by filtration and washed with methanol
then diethyl ether.
Trials to prepare Fe(III) and Zn(II) complexes of the Schiff base,
H2L ligand were unsuccessful; it gave oily product and was too dif-
ficult to isolate in their pure forms.
2.4. Molecular modeling
m(C@N) mode. This assignment was further supported by the dis-
appearance of the absorption band that assigned to the acetyl
C@O of AHTD at 1659 cmꢀ1, which condensed with the NH2 group
of the 2-aminophenol as suggested in Scheme 1. The IR spectrum of
the free ligand also revealed a characteristic bands at 3175, 1702,
1611 and 1551 cmꢀ1 attributed to (2OH, NH), (2C@O), (C@N) and
(C@C), respectively, in light of the IR data of similar compounds
[33,34].
An attempt to gain a better insight into the molecular structure
of the ligand and its complexes, geometric optimization and con-
formation analysis has been made using PM3 forcefield as imple-
mented in hyperchem 7.5 [27].
2.5. Measurements
1H NMR spectrum of the H2L ligand (Supplementary Fig. 1)
showed characteristic singlet signal at 2.44 ppm, which might
attribute to the methyl protons, in addition to broad exchangeable
signals at 10.32 (NHthiazine), 11.69 (OHphenolic) and 13.91 ppm
(OHthiazine) as depicted in Table 3.
Elemental analyses of C, H, N and S were carried out at the
National Research Center, Dokki, Giza, Egypt. Analyses of the metal
ions were carried out complexometrically [28,29]. The FT-IR spectra
(4000–400 cmꢀ1) of the ligand and its complexes were recorded as
KBr disks using FT-IR-4000 (Shimadzu) spectrophotometer. 1H NMR
(300 MHz) and 13C NMR (75 MHz) spectra were recorded using a
Mercury-300BB. Dimethylsulfoxide, DMSO-d6, was used as a sol-
vent and tetramethylsilane (TMS) as an internal reference. The elec-
tronic spectra of the ligand and its metal complexes were measured
on a JASCO model V-550 UV–Visible spectrophotometer in the range
of 200–900 nm. ESR spectra were recorded on the Bruker, Model:
EMX, X-band spectrometer. Mass spectra were obtained using
GC-2010 Shimadzu Gas chromatography instrument mass spec-
trometer (70 eV).
Magnetic susceptibilities of the complexes were measured by
the Gouy’s method at room temperature using Johnson Matthey,
Alfa product, Model No. (MKI), and the diamagnetic corrections
were calculated from Pascal’s constants for all atoms in the com-
pounds [30]. Thermal gravimetric analysis (TGA) of the current
compounds was measured from room temperature up to 800 °C
13C NMR spectrum of the current ligand (Supplementary Fig. 2)
showed characteristic signals at 20.5 ppm assigned to the methyl
carbon and 163.1 ppm due to the azomethine carbon (C@N). Fur-
thermore, two downfield signals were observed at 173.5 and
180.5 ppm, which could be assigned to C-2 and C-6 of the carbonyl
groups in the vicinity of the heterocyclic ring of the current ligand
as depicted in Table 3.
Electronic spectral data of the free ligand in DMF solution
displayed two absorption bands at 273 and 350 nm like those
reported for similar Schiff base compounds. The first band could
be attributed to the
p ?
pꢂ transition of the azomethine group
(K-band), and the second band due to the n ? pꢂ transitions result-
ing from nitrogen, oxygen and sulfur atoms (R-band) [35].
3.1. Metal complexes of H2L ligand
(10 °C/min), using
a Shimadzu TGA-50H instrument. Melting
points were measured in open capillaries on a Stuart SMP3 melting
point apparatus.
The Schiff base ligand was allowed to react with Ni(II), Co(II),
Cd(II), VO(IV) and UO2(VI) ions as well as Cu(II) salts including
Clꢀ; NO3ꢀ; AcOꢀ; ClO4ꢀ and SOꢀ4 2 in the presence of lithium hydrox-
ide to yield the corresponding metal complexes. The isolated
complexes were characterized by elemental analysis, FT-IR, UV–
Visible, mass, ESR, 1H NMR spectroscopy and thermal gravimetric
analysis (TGA), as well as molar conductance and magnetic suscep-
tibility measurements.
The standardized disk agar diffusion method [31] was followed
to determine the activity of the synthesized compounds against
the sensitive organisms Staphylococcus aureus as Gram positive bac-
teria, Proteus vulgaris as Gram negative bacteria and Candida albicans
as fungus strain. The compounds were dissolved in DMSO which has
no inhibition activity to get concentration of 100 l
g mLꢀ1. The test

O.M.I. Adly / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
485
3.1.1. Infrared spectra
The main characteristic IR-vibrational frequencies and their
assignments for the current complexes are given in Table 2. The
sites of coordination were deduced from the comparison of the
IR data of the free ligand with its complexes. The shift of m(C@N)
of the free ligand to a lower frequencies by 7–56 cmꢀ1 in the com-
plexes indicates the coordination through the azomethine nitrogen
(C@N) [36]. The broad bands in the range of 3429–3408 cmꢀ1 could
be assigned to the stretching frequencies of m(OH) of the water or
methanol molecules, as confirmed by the elemental analysis and
thermal analysis.
The coordinating modes of anions have been implied from the
IR data. In the acetate and perchlorate copper(II) complexes (3
and 4), the absorption bands at 1547, 1423 and 856 cmꢀ1 suggest
the ionic character of the CH3COOꢀ group for complex (3) [37].
Similarly, the bands at 1086 and 629 cmꢀ1 are attributed to m3
and m4 vibrations of uncoordinated perchlorate Td symmetry (4)
[38]. These assignments are further supported by the conductance
measurements, 66.20 and 89.30 ohmꢀ1 cm2/mol (vide infra). How-
ever, in the sulfate complexes (2 and 8), the bands at (1270,1123)
and (1113,1064) cmꢀ1 are due to the
m3(S–O) vibrations of the
bidentate (c2v) and monodentate (c3v) coordination of SOꢀ2 group,
4
respectively [37]. Furthermore, the IR spectrum of VO(IV) complex
8 displayed absorption band at 942 cmꢀ1 due to the stretching
vibration of the m(V@O) band in hexa-coordinated structure [39].
Similarly, the strong band located at 900 cmꢀ1 for complex 10
was assigned to m3(asym) of the O@U@O group, indicating the six
coordinate for the dioxouranium complex [40,41].
The frequencies of the weak bands in the range of 496–471 cmꢀ1
and 566–501 cmꢀ1 are attributed to
m(M–O) and m(M–N), respec-
tively [37]. Consequently, the coordinating sites of the current
ligand to the metal ions might be achieved by the phenolate and
thiazinate oxygen and azomethine nitrogen atoms of neutral,
monobasic or dibasic tridentate (O2N).
3.1.2. Electronic spectra, magnetic moment and conductance
measurements
The electronic spectral bands of the current colored metal com-
plexes in DMF solution with their tentative assignments along with
magnetic moments and conductance data are presented in Table 4.
In the current metal complexes, both n ? pꢂ and
p ?
pꢂ bands are
found as red-shifted by 9–38 and 6–11 nm, respectively, as com-
pared to that of the free ligand.
The electronic spectra of Cu(II) complexes 2, 3 and 5 showed one
broad band in the visible region at 692, 675 and 685 nm, respectively,
2
and might be assigned to ð Eg 2T2gÞ transition, suggesting an octa-
hedral geometry around the Cu(II) ions, while the electronic spectra
of Cu(II) complexes 1 and 4 showed one band at 554 and 562 nm,
2
respectively, which might be assigned to dxy ! dx2ꢀy2 ð B1 2B2Þ,
indicating a square planar geometry [42,43]. The magnetic moment
values for Cu(II) complexes 1–5 (Table 4) were found in the range re-
ported for d9 systems containing one unpaired electron [44]. The
mass spectrum of Cu(II) complex 5 (Supplementary Fig. 3) showed
the molecular ion peak as the base peak at m/e = 411 (M ꢀ 1), which
is consistent with the formula weight, predicted from elemental
analysis and supports the identity of structure.
The electronic spectrum of the cumin Ni(II) complex 6 showed
two absorption bands at 633 and 416 nm assigned to
3
3T1gðFÞ 3A2gðFÞ and T1gðPÞ 3A2gðFÞ, respectively, indicating
octahedral structure [45]. The spectral data give the ligand field
parameter B (451 cmꢀ1), 10Dq (1030 cmꢀ1) and b (0.42), and the
first transition band in the spectrum can also predicted at
913 nm that assigned to 3T2gðFÞ 3A2gðFÞ. This finding was further
emphasized by the measured magnetic moment at 3.26 B.M.,
which lies in the range (2.9–3.3 B.M) of the Ni(II) octahedral
complexes [35]. Moreover, the mass spectrum of Ni(II) complex 6

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O.M.I. Adly / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
Table 2
a
Characteristic infrared frequencies (cmꢀ1
)
of the H2L ligand and its metal complexes.
(OH, NH) (C@O) (C@N)
Ligand/ complex
H2L
m
m
m
m
(C@C)
m
(M–N)
m
(M–O)
Other band
3175 br
1702 s
1663 m
1664 s
1662 s
1663 s
1664 s
–
1611 s
1546 s
1547 s
1601 s
1545 s
1559 s
1556 s
1564 s
1604 s
1555 s
1580 s
1551 s
1510 s
1517 m
1510 m
1513 s
1504 m
1517 s
1518 s
1510 m
1522 m
1520 m
–
–
–
–
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
[CuL(H2O)]
3429 br, 3184 br
3420 br, 3183 br
3408 br, 3165 br
3433 s
508 w
550 w
501 w
502 w
546 w
566 w
510 w
507 w
561 w
514 w
473 w
473 w
476 w
475 w
474 w
496 w
486 w
473 w
471 w
476 w
[Cu(H2L)(H2O)2SO4]ꢁ0.5 H2O
1270, 1123 m3 SO4 (bidentate)
1547, 1423, 856 CH3COO (ionic)
1086, 629 ClO4 (ionic)
–
–
–
942 w (V@O) 1113, 1064 m3 SO4 (unidentate)
–
900 w (U@O)
[Cu(HL)(H2O)2] CH3COOꢁCH3OH
[CuL(H2O)]ꢁClO4ꢁ2H2O
[Cu(HL)(H2O)2Cl]
3422 br 3184 br
3415 br
[NiL(CH3OH)2(H2O)]ꢁ1.5H2O
[CoL(H2O)]ꢁH2O
3399 br
–
[VO(H2L)(SO4)(H2O)]
[CdL(H2O)3]ꢁH2O
3429 br
–
3420 br
–
[UO2L(H2O)3]ꢁ0.5H2O
3417 br
–
a
s = strong, m = medium, w = weak, br = broad.
Table 3
1H NMR and 13C NMR spectra of the H2L ligand in DMSO.
1H NMR
13C NMR
Chemical shifts in ppm
Assignment
(CH3) (s, 3H, CH3)
(t, 1H, Ar–H, J = 7.5 Hz)
(d, 1H, Ar–H, J = 7.5 Hz)
(m, 2H, 2Ar–H)
(bs, 1H, NHthiazine
Exchangeable with D2O)
(bs, 1H, OHphenolic
Chemical shifts in ppm
Assignment
2.44
6.90
7.03
7.19–7.25
10.32
20.5
97.6
(CH3)
(C-5)
116.5
119.3
122.9
126.8
129.5
151.5
163.1
168.3
173.5
180.5
(C-60)
(C-40)
(C-30)
(C-50)
11.69
13.91
(C-20)
Exchangeable with D2O)
(bs, 1H, OHthmzme
Exchangeable with D2O
(C-1)
(C@N)
(C-4)
(C-2 as C@O)
(C-6 as C@O).
showed the molecular ion peak at m/e = 444, which is consistent
with the formula weight and supports the identity of structure.
The electronic spectrum of the pink Co(II) complex 7 showed
one band in the visible region at 561 nm, which is attributed to
4T1gðFÞ 4A2gðFÞ transition of Co(II) tetrahedral geometry [46].
The calculated ligand field parameters of the complex are B
(862 cmꢀ1), 10Dq (3320 cmꢀ1) and b (0.88), indicating a more
covalent character for Co(II)-ligand bonds. The tetrahedral struc-
ture of Co(II) complex 7 was further confirmed by the magnetic
sitions, respectively, in the vicinity of the Schiff base ligand. The 1H
NMR spectrum of Cd(II) complex (Supplementary Fig. 4) showed
(in addition to the aromatic protons in the range 6.88–7.26 ppm)
a characteristic singlet signal at 2.39 ppm, which might attribute
to the methyl protons, and broad exchangeable signal at 10.05
ppm (NHthiazine). Disappearance of the phenolic protons that ap-
peared at 11.69 (OHphenolic) and 13.91 ppm (OHthiazine) in the 1H
NMR spectrum of the free ligand suggests that these protons were
deprotonated during the coordination of the Schiff base ligand
with the Cd(II) ion, supporting the dibasic tridentate behavior.
The electronic spectrum of the orange red UO2(VI) complex 10
showed three absorption bands at 283, 379 and 500 nm, which
moment measurements, leff = 4.44 B.M. [25,47].
The electronic spectrum of the green oxovanadium(IV) complex
8 showed one band at 505 nm due to b1 b2 electronic transition,
suggesting hexa-coordinated structure, which would be an octahe-
dral structure [48]. This conclusion agrees well with the data ob-
tained from elemental analysis and IR spectrum of VO(IV) complex
might arise from the allowed electronic transitions of
p ? ,
p⁄
n ? p⁄ and metal ? ligand charge transfer (MLCT) and/or apical
oxygen ? F° (U) [50]. The magnetic moment measurement sug-
gested the diamagnetic geometry of the UO2(VI) complex as ex-
pected [51].
8 [49]. The magnetic moment measurements,
leff = 1.71 B.M., are
compatible with the presence of one unpaired electron.
The yellow Cd(II) complex 9 showed two absorption bands at
283 and 370 nm, which might attribute to
The molar conductance values at room temperature of the com-
p ?
pꢂ and n ? pꢂ tran-
plexes in DMF (10ꢀ3) solutions are shown in Table 4. The most
Table 4
Characteristic electronic transition bands, molar conductance and magnetic moments of the metal complexes of the H2L ligand.
f ꢃ 103
Ligand/complex
p–
pꢂ
n–pꢂ
d–d transition bands
K
Ohmꢀ1 cm2 molꢀ1
leff
H2L
[CuL(H2O)]
[Cu(H2L)(H2O)2SO4]ꢁ0.5 H2O
[Cu(HL)(H2O)2]ꢁCH3COOꢁCH3OH
[Cu(HL)(H2O)]ꢁClO4ꢁ2H2O
[Cu(HL)(H2O)2Cl]
273
284
283
280
284
279
280
279
282
283
283
350
360
375
383
380
380
362
389
375
370
379
–
554
692
675
562
–
–
–
26
14
20
22
14
–
18
–
–
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
20.80
10.70
66.20
89.30
7.34
36.2
18.5
34.2
9.15
1.80
1.70
1.65
1.82
1.68
3.26
4.44
1.71
–
685
[NiL(CH3OH)2(H2O)]ꢁ1.5HO
416, 633
561
[CoL(H2O)]ꢁH2O
[VO(H2L)(SO4)(H2O)]
[CdL(H2O)3].H2O
505
–
500
[UO2L(H2O)3].0.5H2O
32.5
–
–

O.M.I. Adly / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
487
Table 5
ESR spectral data of Cu(II) complexes 1–5 at room temperature.
Complex
g||
g\
A|| ꢃ 10ꢀ4 cmꢀ1
G
a2
b2
(1)
(2)
(3)
(4)
(5)
[CuL(H2O)]
–
2.087
2.10
2.069
2.085
2.076
–
–
–
–
[Cu(H2L)(H2O)2SO4]ꢁ0.5H2O
[Cu(HL)(H2O)2]ꢁCH3COOꢁCH3OH
[CuL(H2O)]ꢁClO4ꢁ2H2O
[Cu(HL)(H2O)2Cl]
2.27
2.40
–
182
182
–
2.7
5.8
–
0.86
0.98
–
0.66
0.90
–
2.29
200
3.8
0.91
0.69
complexes are neutral except 3 and 4 that exhibited 66.20 and
89.30 ohmꢀ1 cm2/mol, respectively, indicating 1:1 electrolytes, so
the CH3COOꢀ and ClOꢀ4 anions are in the outer sphere. These find-
ings agree well with the IR data that suggested ionic character of
CH3COOꢀ and ClOꢀ4 anions [52].
Table 4 shows the oscillator strength, f, values for some of
the current complexes in DMF solution [53]. These values
indicate dependence of d–d electronic transition probabilities
upon the geometry of the current Cu(II) complexes. Square
planer Cu(II) complexes 1 and 4 showed higher d–d electronic
transition probabilities than octahedral Cu(II) complexes 2,
3 and 5.
3.1.3.ESR spectra
The spin Hamiltonian parameters of the Cu(II) complexes 1–5
were computed from the spectra and given in Table 5. Supplemen-
tary Fig. 5 shows the X-band ESR spectra of Cu(II) complexes 1–3
and VO(IV) complex 8, in the solid state at 25 °C. The ESR spectra
of complexes 2, 3 and 5 are quite similar and display axially sym-
metric g-tensor parameters with g|| > g\ > 2.0023, indicating that
the unpaired electron of Cu(II) ion is localized in the dx2ꢀy2 orbital
[54]. Further, the shape of the ESR spectra of complexes 2, 3 and 5
is quite similar and indicates that the geometry around the Cu(II)
ions is elongated octahedron [55,56], whereas Cu(II) spectra for
complexes 1 and 4 exhibit one broad band with geff = 2.09 and
Table 6
Thermal gravimetric results of the H2L ligand and its metal complexes.
Compound
H2L
DTG peak (°C) Temperature range (°C) Decomposition product lost (formula weight) Weight loss (%) found (calculated)
205
306
570
251
532
38–226
226–345
474–625
113–311
311–800
Residue
40–98
–(2CO + S)
–C8H9O2N
–C2NH
–(H2O + 2CO + S)
–C10H7N
31.13(31.62)
54.62 (54.26)
14.25(14.01)
29.62 (29.62)
40.99 (39.40)
30.00(30.88)
1.77(1.94)
(1)
(2)
[CuL(H2O)]
–(CuO + NH + 0.5O2)
–0.5H2O
[Cu(H2L)(H2O)2SO4]ꢁ0.5H2O
80
146
384
536
96–191
193–346
348–508
Residue
35–80
–H2O
–(2CO + S + CH3CN)
–H2SO4
–(CuO + C8H5NO)
–CH3OH
3.87(3.87)
27.10(27.75)
21.93 (21.08)
45.33 (45.28)
6.40 (6.58)
(3)
(4)
[Cu(HL)(H2O)3]ꢁCH3COO
56
CH3OH
206
579
80–274
275–800
Residue
34–133
133–192
192–307
310–528
Residue
135–267
269–392
392–477
477–600
Residue
36–114
115–273
273–422
424–582
Residue
37–100
100–200
200–447
Residue
79–247
248–346
346–800
Residue
36–133
133–328
328–800
Residue
34–123
124–196
197–569
Residue
–(3H2O + 2CO + S)
–(CH3COOH + C6H4 + 2C)
–(CuO + 0.5O2 + NH + CH3CN)
–2H2O
–H2O
–C12H8NO3S
–HC1O4
–CuO
–2H2O
–HCl
–C4HO2NS
–C8H7ON
–CuO
–1.5H2O
–(H2O + 2CH3OH)
–(2CO + S)
–(C8H7N)
–(NiO + 0.5O2 + C2NH)
–H2O
29.43 (29.22)
33.75 (32.92)
30.40(31.18)
7.67 (7.28)
[CuL(H20)]ꢁC104ꢁ2H20
80
165
282
385
3.77 (3.64)
49.08 (49.79)
20.00 (20.34)
16.66(16.09)
8.54(8.73)
(5)
(6)
[Cu(HL)(H2O)2Cl]
217
317
426
500
8.58(8.85)
29.61 (30.80)
31.10(32.25)
18.54(19.28)
6.23 (6.07)
18.60(18.46)
20.00(19.82)
25.37 (26.34)
29.16(29.21)
4.85 (4.85)
[NiL(CH3OH)2(H2O)]ꢁ1.5H2O 79
226
343
481
(7)
(8)
(9)
[CoL(H2O)]ꢁH2O
80
150
376
–H2O
4.95 (4.85)
–C10H5NO2S
–(CoO + CH3CN + 0.5O2)
–(H2O + 2CO)
–S
–H2SO4
–(VO2 + C10H8N2O)
–H2O
–(3H2O + S)
–(2CO + C6H4)
–(C4H3ON2 + CdO)
–0.5H2O
–(3H2O + 2CO)
–(C8H7N + S)
–(C2NO2 + UO2)
53.63 (54.69)
36.58(35.53)
16.90(16.11)
7.00 (6.96)
22.00(21.33)
54.10(55.49)
3.42 (4.04)
19.30(19.33)
28.17(29.68)
50.00(50.14)
1.24(1.47)
18.60(18.05)
23.43 (24.45)
55.60(55.80)
[VO(H2L)(SO4)(H2O)]
[CdL(H2O)3]ꢁH2O
185
299
508
92
248
297
(10) [UO2L(H2O)3]ꢁ0.5H2O
95
167
315

488
O.M.I. Adly / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
2.08, indicating square planar geometry around Cu(II) ion in the
complex such as concluded from UV/Vis spectra [57].
ature than those in case of the lattice water molecules (Supplemen-
tary Fig. 6). There are two cases in the removal of the coordinated
water or methanol molecules of the complexes. The first case was
observed for complexes 2, 4, 5 and 7, which lose only all the coordi-
nated water molecules in the temperature range of 115–273 °C.
However, the second case elimination of the coordinated water
molecules was accompanied with the loss of a part of ligand in
complexes 1, 3, 6 and 8–10.
Complexes 2 and 8 are losing H2SO4 molecule at 536 °C and
508 °C, respectively, whereas decomposition of CH3COOH, HClO4
and HCl molecules from complexes 3, 4 and 5 occurs at 579, 385
and 317 °C, respectively.
In axial symmetry, the g-values are related to the G-factor by
the expression G = (g|| ꢀ 2)/(g\ ꢀ 2) = 4. According to Hathaway
and Billing [58], the calculated G-values of complexes 2 and 5 are
<4, indicating exchange interactions, while G-value of complex 3
is >4, suggesting that there is no copper–copper exchange interac-
tion. In the present Cu(II) complexes, g|| is >2.0023 indicating cova-
lent character for Cu–L bond such as reported by Kilveson [59].
Molecular orbital coefficients, a
2 (a measure of the covalency of
the in-plane r-bonding between a copper 3d orbital and the ligand
orbitals) and b2 (covalent in-plane
p-bonding), were calculated by
the following equations [60]:
The activation energy parameters of the decomposition of vari-
ous decomposition stages are calculated by Coats–Redfern equa-
tions [63]. The activation energy (Ea) values of the decomposition
of coordinated water molecules for Cu-square planar complexes
1 and 4 (63.68 and 78.48 KJ molꢀ1, respectively) are higher than
those for the octahedral complexes 2, 3 and 5 (31.76, 38.99 and
30.56 KJ molꢀ1, respectively). Similarly, the same trend values are
found for enthalpy changes (DH); these findings agree well with
their d–d transition frequencies of the square planar and octahe-
dral structures (Table 4).
a2 ¼ ðAk=0:036Þ þ ðgk ꢀ 2:0023Þ þ 3=7ðg ? ꢀ2:0023Þ þ 0:04
b2 ¼ ðgk ꢀ 2:0023ÞE= ꢀ 8ka2
where k = ꢀ828 cmꢀ1 for the free copper ion and E is the electronic
transition energy. Molecular orbital coefficients, a
2 and b2, were cal-
culated, and their values indicate appreciable covalent bonds. b2 is
lower than -bonding is more cova-
2, indicating that the in-plane
lent than the in-plane -bonding [61].
a
p
r
The ESR spectrum of the oxovanadium(IV) complex 8 exhibits
two bands at g\ = 2.05 and g1 = 2.16, g2 = 2.30 and g3 = 2.44, indi-
cating an octahedral geometry around VO(IV) ion confirming the
results obtained from the IR and UV/Vis spectra. The absence of
vanadium’s hyperfine coupling that is common in the solid state
might attribute to the strong exchange interactions, which average
out the interaction with the nuclei or due to simultaneous flipping
of neighboring electron spin [62].
4. Molecular orbital calculations
The experimental data were correlated with theoretical data ob-
tained from molecular orbital calculations on the basis of the semi-
empirical PM3 level provided by HyperChem 7.5 software;
calculations for vanadyl and uranyl-complexes are failed. The calcu-
lated heat of formation, dipole moment, HOMO and LUMO energies
and selected bond lengths of the free ligand and its complexes are
given in Table 7. The optimized geometrical structures of the metal
complexes are shown in Supplementary Figs. 7–10. A comparison
between the bond lengths of the ligand and its metal complexes
was demonstrated in Table 8. The theoretical data were correlated
with the experimental data. The calculated bond lengths of M–N
and M–O bonds of the current complexes are linearly correlated
with their measured IR frequencies: M–N bond length/A° = 1.87–
3.1.4. Thermal analysis
Table 6 shows the data of the thermal gravimetric analysis
(TGA) of the free ligand (H2L) and its metal complexes that were
carried out within the temperature range from room temperature
up to 800 °C.
Complexes 2, 4, 6, 7, 9 and 10 lost the lattice water molecules in
the temperature range (80–133 °C), whereas the coordinated water
molecules were eliminated from their complexes at higher temper-
Table 7
Molecular orbital parameters of the H2L ligand and its metal complexes.
Property
H2L
Complexes
1
2
3
4
5
6
7
9
Total energy (kcal/mol)
Binding energy (kcal/mol)
Electronic energy (kcal/mol)
Heat of formation (kcal/mol)
Dipole moment (D)
HOMO (eV)
LUMO (eV)
Polarizability
Hydration energy
ꢀ75184
ꢀ3198
ꢀ473,414
ꢀ96
ꢀ109326
ꢀ3459
ꢀ658,009
ꢀ217
ꢀ141099
ꢀ4010
ꢀ10,04,151
ꢀ411
ꢀ124682
ꢀ3963
ꢀ844,355
ꢀ341
ꢀ109694
ꢀ3527
ꢀ69,958
ꢀ232
ꢀ124489
ꢀ3777
ꢀ831,369
ꢀ290
ꢀꢀ128008
ꢀ4665
ꢀ942,212
ꢀ524
ꢀ115626
ꢀ4184
ꢀ826,373
ꢀ540
ꢀ97,428
ꢀ3701
ꢀ624,859
ꢀ185
5.68
7.69
9.56
13.15
9.89
5.90
5.62
ꢀ10.26
ꢀ8.38
9.06
ꢀ9.07
ꢀ1.16
27.21
ꢀ15.79
ꢀ4.24
ꢀ9.46
ꢀ7.85
ꢀ8.79
ꢀ0.56
27.07
ꢀ22.40
ꢀ4.21
ꢀ8.36
ꢀ7.95
ꢀ0.86
ꢀ1.49
ꢀ0.92
ꢀ1.18
ꢀ0.92
ꢀ0.55
ꢀ0.62
27.32
29.48
28.62
30.16
ꢀ32.53
ꢀ18.74
28.60
28.96
ꢀ23.98
ꢀ24.91
33.82
ꢀ24.60
ꢀ33.82
ꢀ71.31
Table 8
Theoretically calculated bond lengths (A°) of the H2L ligand and its metal complexes on the PM3 level.
Compound
C@N
OH
OHsolv
.
M–OL
M–N
M–Osolv
H2L
[CuL(H2O)]
[Cu(H2L)(H2O)SO4]ꢁ0.5H2O
[Cu(HL)(H2O)2]ꢁCH3COOꢁCH3OH
[Cu(HL)(H2O)]ꢁClO4ꢁ2H2O
[Cu(HL)(H2O)2Cl]
1.31
1.37
1.33
1.33
1.39
1.33
1.32
1.36
1.32
0.97
–
–
–
–
–
1.91
2.6
2.04
1.94
1.99
1.92
1.91
4.30
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(9)
0.96
0.95
0.95
0.96
0.95
0.96
0.96
0.95
1.84
2.13
2.05
1.95
2.09
2.01
1.90
2.12
1.88
1.91
1.94
1.92
1.93
1.82
1.88
2.26
0.95
0.95
0.95
0.95
–
[NiL(CH3OH)2(H2O)]ꢁ1.5H2O
[CoL(H2O)]ꢁH2O
–
–
[CdL(H2O)3]ꢁH2O

O.M.I. Adly / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 95 (2012) 483–490
489
Table 9
The antimicrobial activity of the newly synthesized compounds.
Compound
Diameter of inhibition zone (mm)conc. (100 l )
g mLꢀ1
C. albicans (fungal strain)
P. vulgaris (Gram ꢀve)
S. aureus (Gram +ve)
H2L
–
–
–
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
[CuL(H2O)]
18
13
15
–
15
10
17
–
9
8
–
15
–
10
10
–
20
–
–
–
10
–
–
–
15
8
15
–
[Cu(H2L)(H2O)2SO4]ꢁ0.5H2O
[Cu(HL)(H2O)2]ꢁCH3COOꢁCH3OH
[Cu(HL)(H2O)]ꢁClO4ꢁ2H2O
[Cu(HL)(H2O)2Cl]
[NiL(CH3OH)2(H2O)]ꢁ1.5H2O
[CoL(H2O)]ꢁH2O
8
13
12
20
28
11
–
[VO(H2L)(SO4)(H2O)]
[CdL(H2O)3]ꢁH2O
[UO2L(H2O)3]ꢁ0.5H2O
Doxymycin
Fluconazole
16
0.014
A° = 4.13–0.0046
m
M–N cmꢀ1, r = 0.96 except complexes 6–8, M–O bond lengths/
M–O cmꢀ1, r = 0.96 except complexes 1 and 9. The
some of the current complexes show superior activity than the ref-
erence drugs.
m
negative slopes reveal decreases in the bond strength, with the
increasing calculated bond lengths of M–N and M–O. This finding
supports the tentative assignment of the IR-vibrational modes of
M–N and M–O bonds.
The calculated energies of the high occupied molecular orbital
(HOMO) and low unoccupied molecular orbital (LUMO) are linearly
correlated with the IR data of the corresponding complexes:
6. Conclusion
In conclusion, a novel tridentate O2N Schiff base ligand derived
from 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione and 2-
aminophenol has been synthesized. Metal complexes of Ni(II),
Co(II), Cd(II), VO(IV) and UO2(VI) as well as several Cu(II) salts,
including Clꢀ; NO3ꢀ; AcOꢀ; ClO4ꢀ and SOꢀ4 2, have been synthesized.
The structures of the complexes were proposed based on elemental
analyses, spectral data, magnetic moment, molar conductance and
thermal gravimetric analysis. Square planar, tetrahedral and octa-
hedral geometries have been assigned to the prepared complexes.
Molecular parameters of the ligand and its metal complexes have
been calculated and correlated with the experimental data; the
changes of bond lengths are linearly correlated with IR data. The
synthesized compounds were screened in vitro for their antimicro-
bial activities and showed variable activities.
ELUMO = ꢀ1.77 + 0.141
m
m
M–N, r = 0.93 except complexes 1 and 3,
M–O, r = 0.975 except complexes 2, 4 and 5,
ELUMO = ꢀ1.77 + 0.141
EHOMO = ꢀ9.741 + 0.206
m
M–N, r = 0.975 except complexes 1, 3 and
M–O, r = 0.975 except com-
4. However, EHOMO = ꢀ9.741 + 0.206
m
plexes 1, 3 and 5. The positive slopes indicate increased bond
strengths of M–N and M–O as LUMO and HOMO energies increase,
which might attribute to the weakness of the bonds neighbor
to the coordinated centers with the strengthening of the metal–
ligand bonds in parallel with the increase in ELUMO. However, the
increase in EHOMO is accompanied by weakness of metal–ligand
bonds, which leads to strengthening of the sites adjacent to
the metal ligand centers; this interpretation agrees well with the
Gutmann’s variation rules ‘‘the bond strength increases as the
adjacent bonds becomes weaker’’ [64].
Acknowledgment
The author would like to express her deep gratitude to prof. Dr.
Ali M. Taha for his guidance and encouragements throughout the
work.
5. Antimicrobial activity
The results depicted in Table 9 showed various activities against
all species of microorganisms, which suggest that the variations in
the structures affect the growth of the microorganisms. Thus, we
can conclude from these results that:
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.04.030.
(1) The investigation of antibacterial and antifungal screening
data in Table 9 revealed that most of the synthesized com-
plexes were found to possess various antimicrobial activities
toward all microorganisms, while the ligand did not show
any activity toward all types of microorganism, suggesting
greater lipophilic nature of the complexes than the free
ligand.
(2) Most of the synthesized complexes showed good to excel-
lent activity toward P. vulgaris as Gram negative bacteria
and C. albicans as fungal strain
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