Spectroscopic and biological studies of mono- or binuclear complexes derived from thio-Schiff bases of some transition metals

Article abstract of DOI:10.1080/17415993.2010.503774

Two novel Schiff base ligands, 4,6-bis((E)-1-(2-mercaptophenylimino)ethyl) benzene-1,3-diol, H4La, and 1,2-((E)-1-(6-((E)-1-(2-mercaptophenylimino)ethyl) pyridine-2-yl)ethylideneamino)benzenthiol, H2Lb, have been synthesized by the condensation of 4,6-diacetyl resorcinol (DAR) or 2,6-diacetyl pyridine (DAP) with 2-aminobenzenthiol (ABT), in the molar ratio 1:2 [1 (DAR or DAP):2 ABT]. The structures of ligands were elucidated by elemental analysis, infrared (IR), UV-VIS as well as 1H-NMR. Reaction of the Schiff base ligands with the transition metals Co(II), Ni(II), Cu(II), Zn(II), VO(IV) and Ru(III) afforded two series of the corresponding transition metal complexes in the molar ratio 1:2 or 1:1. The ligand, H4La, behaves as tetrabasic hexadentate, which hosts the two metal ions at the centers of two SNO sites, while H2Lb acts as a compartmental dibasic pentadentate ligand forming mono- or binuclear complexes through the coordinate sites N3S2. The structures of the newly prepared complexes were characterized on the basis of the elemental analysis, spectroscopic data (IR, UV-VIS, 1H-NMR and ESR spectra along with magnetic susceptibility measurements) besides the molar conductance measurements and thermal gravimetric analyses. The bonding sites are the azomethane, sulfur atoms and phenolic oxygen for H4La or pyridine nitrogen for H2Lb. The complexes exhibit mono- or binuclear structures, distorted octahedral, tetrahedral, square planar or square pyramid structure. Synthesized compounds have also been screened for their biological activity against species of pathogenic fungi and bacteria and were found to possess appreciable fungicidal and bactericidal properties.

Full text of DOI:10.1080/17415993.2010.503774

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Spectroscopic and biological studies
of mono- or binuclear complexes
derived from thio-Schiff bases of some
transition metals
a
Azza A.A. Abou-Hussein
a
Department of Chemistry, Women Faculty of Arts, Science and
Education , Ain Shams University , Cairo, Egypt
Published online: 28 Sep 2010.
To cite this article: Azza A.A. Abou-Hussein (2010) Spectroscopic and biological studies of mono-
or binuclear complexes derived from thio-Schiff bases of some transition metals, Journal of Sulfur
Chemistry, 31:5, 427-446, DOI: 10.1080/17415993.2010.503774
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Journal of Sulfur Chemistry
Vol. 31, No. 5, October 2010, 427–446
Spectroscopic and biological studies of mono- or binuclear
complexes derived from thio-Schiff bases of some transition
metals
Azza A.A. Abou-Hussein*
Department of Chemistry, Women Faculty of Arts, Science and Education, Ain Shams University,
Cairo, Egypt
(Received 25 February 2010; final version received 20 June 2010)
Two novel Schiff base ligands, 4,6-bis((E)-1-(2-mercaptophenylimino)ethyl)benzene-1,3-diol, H4La, and
1
,2-((E)-1-(6-((E)-1-(2-mercaptophenylimino)ethyl)pyridine-2-yl)ethylideneamino)benzenthiol, H2Lb,
have been synthesized by the condensation of 4,6-diacetyl resorcinol (DAR) or 2,6-diacetyl pyridine
DAP) with 2-aminobenzenthiol (ABT), in the molar ratio 1:2 [1 (DAR or DAP):2 ABT]. The structures of
(
1
ligands were elucidated by elemental analysis, infrared (IR), UV–VIS as well as H-NMR. Reaction of the
Schiff base ligands with the transition metals Co(II), Ni(II), Cu(II), Zn(II), VO(IV) and Ru(III) afforded
two series of the corresponding transition metal complexes in the molar ratio 1:2 or 1:1. The ligand, H4La,
behaves as tetrabasic hexadentate, which hosts the two metal ions at the centers of two SNO sites, while
H2Lb acts as a compartmental dibasic pentadentate ligand forming mono- or binuclear complexes through
the coordinate sites N3S2. The structures of the newly prepared complexes were characterized on the basis
1
of the elemental analysis, spectroscopic data (IR, UV–VIS, H-NMR and ESR spectra along with magnetic
susceptibility measurements) besides the molar conductance measurements and thermal gravimetric analy-
ses. The bonding sites are the azomethane, sulfur atoms and phenolic oxygen for H4La or pyridine nitrogen
for H2Lb. The complexes exhibit mono- or binuclear structures, distorted octahedral, tetrahedral, square
planar or square pyramid structure. Synthesized compounds have also been screened for their biological
activity against species of pathogenic fungi and bacteria and were found to possess appreciable fungicidal
and bactericidal properties.
Keywords: thio-Schiff base ligands; transition metal complexes; spectroscopy; biological activates
1
.
Introduction
Over the past few years, thio-Schiff bases and their metal complexes have received considerable
attention in the field of coordination chemistry (1–4). Molecules containing electron-acceptor
Schiff bases are of great interest because of their potential therapeutic and pharmacological prop-
erties (5–7) and because of their ability to serve as polymeric ultraviolet stabilizers (8). It has
been reported that some of these complexes have increased activity when administrated as metal
complexes (9) and their interactions with DNA have been reported (10, 11). Moreover, it is well
*
Email: azza_aly2000@yahoo.com
ISSN 1741-5993 print/ISSN 1741-6000 online
2010 Taylor & Francis
©
DOI: 10.1080/17415993.2010.503774
http://www.informaworld.com

4
28 A.A.A. Abou-Hussein
known that Schiff base complexes have the ability to bind reversibly O2 and CO2 (12). Their
potential catalytic behavior for electrochemical reduction of organic halides, hydrogenation in
metallo-enzyme (13, 14) and recovering of metals from an aqua phase by solvent extractions
have been reported (15, 16). In the present work, two series of mono- or binuclear complexes
have been synthesized and characterized from the newly synthesized thio-Schiff bases, H4La,
4
,6-bis((E)-1-(2-mercaptophenylimino)ethyl)benzene-1,3-diol and H2Lb (1,2-((E)-1-(6-((E)-1-
(2-mercaptophenylimino)ethyl)pyridine-2-yl)-ethylideneamino)benzenthiol. We report here the
preparation and magnetic, spectroscopic characterization of two series of transition metal com-
1
plexes of Co(II), Ni(II), Cu(II), Zn(II), VO(IV) and Ru(III). H-NMR spectra, various ligand field
parameters, (10 Dq, B and β were calculated) and ESR spectra as well as thermal gravimetric
analyses (TGAs) have also been studied for some selected metal complexes.
In vitro biological screening of the synthesized ligands and complexes were carried out against
the phytopathogenic bacteria (Azotobacter and Rhizobium) and fungi (Aspergillus niger and
Fusarium oxysporium). It has been observed that the antimicrobial activities of metal complexes
are higher than the free ligands.
2
. Results and discussion
Schiff bases H4La and H2Lb were synthesized by the condensation of the bicarboxyl compounds
,6-diacetyl resorcinol (DAR) or 2,6-diacetyl pyridine (DAP) with 2-aminobenzenthiol (ABT) in
4
the molar ratio 1:2 (1 DAR or DAP:2 ABT) (Schemes 1 and 2). The structures of the thio-Schiff
1
bases are identified by elemental analysis, infrared (IR), UV–VIS and H-NMR. The physical
and analytical data of the ligands and their corresponding transition metal complexes are listed in
Table 1. The mode of binding of both thio-Schiff base ligands to the metal ions was elucidated by
recording the IR spectra of the complexes and comparing it with the spectra of the free ligands.
The IR frequencies of the Schiff bases H4La and H2Lb and their assignments are listed in Table 2.
O
O
(
CH CO) O, ZnCl
3
2
2
,
HCl
HO
OH
HO
OH
Resorcinol
4,6-Diacetyl resorcinol, DAR
Scheme 1. Synthetic preparation of 2,6-diacetyl resorcinol, DAR.
2
.1. IR spectra
The IR spectra of the thio-Schiff bases H4La and H2Lb exhibited strong sharp bands at 3216
−
1
and 3244 cm , respectively, due to the stretching vibrations of the intermolecular hydrogen
bonded N · · · HS or OH · · · N · · · HS (17, 18). H4La spectra show a medium broad band in the
−
1
−1
region 3050–3300 cm and another weak band at 2560 cm , assigned to the −OH and −SH
groups, respectively (19). The disappearance of these two bands on complexation indicates the
deprotonation of the hydrogen of the phenolic oxygen and thiol groups upon coordination with
the metal ions (20). Similar behavior has been observed for the Schiff base H2Lb, where the
−
1
band assigned to the stretching vibration of the thiol group (ca. 2523 cm ) also disappeared

Journal of Sulfur Chemistry 429
O
O
NH2
HO
OH
+
4,6-Diacetyl resorcinol, DAR
2
SH
2
-Aminobenzenthiol, ABT
N
O
O
ABT : DAR
ABT : DAP
(2:1)
(2:1)
2
,6-Diacetyl pyridine, DAP
X
N
N
SH
SH
Y
Y
For H L , X=C and Y=OH, while H L X=N and Y=H
4
a
2 a
Scheme 2. Synthetic preparation of the Schiff base H4La and H2Lb ligands.
due to the fact that coordination takes place through sulfur atoms after deprotonation (21). One
of the most conceptual features of the IR spectra of the Schiff bases is the disappearance of the
characteristic carbonyl group ν(C=O) bands in both DAR and DAP as a result of the condensation
−
1
and the appearance of new intense bands at 1638 and 1642 cm for the H4La and H2Lb Schiff
bases, respectively, which are assigned to the mixed mode of vibration arising from azomethine
moiety, ν(C=N) and ν(C=C) vibration (22). On complexation, these bands were shifted to lower
−
1
frequencies around 1616–1578 cm , for all the complexes of thio-Schiff bases, indicating the
coordinationthroughthenitrogenatomsoftheazomethinegroups(23, 24). Conclusiveevidenceof
the bonding is also shown by the observation of new bands in the spectra of metal complexes which
−
1
appeared with a medium or weak intensity at the region 467–435 cm due to ν(M−N) stretching
−
1
vibrations (25). The bands at 1126 and 1145 cm , assigned to the ν(N−N) absorption, were
−
1
shifted to 1135 and 1157 cm for H4La and H2Lb, respectively, supporting the involvement of
nitrogen atom of the azomethine group via coordination (26). These observations are inconsistent
−
1
with the appearance of new weak to medium bands in the two regions 543–573 and 356–382 cm
,
whichcouldbeassignedtothestretchingfrequenciesof ν(M−O)and ν(M−S)bands, respectively,

4
30 A.A.A. Abou-Hussein
confirming that the chelation to the metal ions is achieved by phenolic oxygen and thiol-sulfur
−
1
atoms (27). It is worth mentioning that the vibration band at 990 cm , corresponding to the ring
breathing mode of pyridine nitrogen disappeared in all the complexes of thio-Schiff base H2Lb
−
1
and a new medium-intensity band is observed in the range 1008–1028 cm , as a result of the
contribution of the pyridine nitrogen to the metal ion (28). One of the most fundamental features
of the spectra of some complexes is the appearance of a broad band between the range 3300 and
−
1
3
500 cm , which could be assigned to the stretching frequencies of the hydroxyl group of either
the crystalline or the coordinated water molecules associated with the complex (29). This result
is also confirmed by the elemental analysis as well as by TGA for some selected complexes. It is
−
1
worth mentioning that the absorptions at 324 and 332 cm in the spectra of Ru(III) complexes (6)
and (12) were attributed to ν(Ru−Cl) vibrations (30). In addition, for green vanadyl complexes,
−
1
a strong band is observed at 970 and 990 cm , which is assigned to the stretching vibrations of
ν(V=O) band of (5) and (11) complexes, respectively.
−
The NO ions are coordinated to the metal center as unidentate ligands for both complexes
3
[
Co2(Lb)(H2O)5(NO3)2]·H2O (7) and [Ni2(Lb)(H2O)3(NO3)2]·2H2O (8) with a C2v symmetry.
Each unidentate nitrate group possesses three non-degenerated modes of vibrations (νs, νsꢀ and
−
1
νas), which appeared at 1374–1452, 1323–1376 and 778–823 cm , respectively, for the metal
−
−
−
complexes that contain the nitrate groups. The νs(NO ) of the unidentate NO is markedly shifted
to lower frequencies compared with that of the free nitrate (1700–1800 cm ). This could be a
3
3
1
factor measuring the covalent bond strength which is formed due to the transfer of electron density
−
from NO to the metal ion (27).
3
2
.2. Electronic spectra
The electronic spectra of the thio-Schiff base ligands H4La and H2Lb show mainly four absorption
bands at 228, 297, 322 and 372 nm for the former ligand and 251, 268, 323 and 356 nm for the
∗
latter one. The two bands at higher energy arises from π–π transitions of the phenyl rings
1
1
1
1
(
La → Lb) and ( Lb → A1). On the other hand, the bands appearing at the lower energy side
∗
is attributed to the π–π transition associated with the azomethine chromospheres. The last broad
∗
band at 410–412 nm is due to the n → π transition which is overlapping with the intermolecular
CT from the phenyl ring to the azomethine group (31). On complexation, the absorption bands
are shifted to lower wavenumbers compared with the free ligands as a result of coordination via
the nitrogen atoms of the azomethine groups. The d–d transitions of the metal complexes have
lower value than the transition bands of the ligands (Table 3). The bands located around 230–380
∗
and at 390 nm were assigned to π–π transitions within the aromatic rings in the ligands while
the absorption band in the range 325–345 nm could be assigned to C=N group, and on the other
hand, the bands observed at 400–465 nm could be assigned to the charge transfer transition (32).
The electronic spectra of [Co2(La)(H2O)2] complex (1) showed a broad band at 534 nm which
2
2
is consistent with A1g ← B2g corresponding to a square planar geometry. The magnetic moment
of the complex is in agreement with the presence of one unpaired electron (1.87 μB) in a square
planar structure (33). On the other hand, the electronic spectrum of [Co2(Lb)(H2O)5(NO3)2]·H2O
complex (7) showed that the complex may be proposed as distorted octahedral structures, based on
4
the appearance of absorption bands at 665 and 558 nm which are normally assigned to A2g(F) ←
4
4
4
T1g(F) and T1g(P) ← T1g(F) transitions. The spectra of Co(II) octahedral complexes usually
4
4
consist of three bands. The third expected band which is due to T2g(F) ← T1g(F) transition was
not observed due to the limitations in the scanning range of the instrument used. The measured
magnetic moment is 5.14 μB which provides complementary means with the formation of a high-
spin octahedral geometry and lies in the range reported for the octahedral structure (34). The
ꢀ
ligand field parameters such as Racah inter-electronic repulsion parameter (B ), covalency factor

Table 1. Physicochemical properties of the Schiff base ligands H4La and H2Lb and their transition metal complexes.
Elemental analyses, Calc./(Found) (%)
◦
Ligand/complex
MF
MWt.
Yield (%) Color
DP ( C)
%C
%H
%N
%M
I
II
H4La
H2Lb
[Co2(La)(H2O)2]
C22H20N2O2S2
C21H19N3S2
408.54
377.53
558.40
629.99
585.64
625.36
607.47
749.61
725.48
706.99
493.10
476.93
478.49
548.07
68.71
62.30
60.66
58.27
67.28
56.62
84.13
63.67
74.32
81.73
63.24
61.32
64.64
67.79
Cream
Yellow
Yellow
Green
Violet
White
Dark green
Black
Green
Green
Pale blue
White
182
164
64.68 (64.90) 4.93 (5.37)
66.81 (67.26) 5.07 (4.73) 11.13 (11.56)
6.86 (6.49)
– –
– –
(
(
(
(
(
(
(
(
(
(
(
(
1)
2)
3)
4)
5)
6)
7)
8)
C22H20N2O4S2Co2
C22H28N2O8S2Ni2
C22H22N2O5S2Cu2
C22H26N2O7S2Zn2
C23H25N2O7S2V2
C22H24N2O6S2Cl2Ru2
C21H29N5O12S2Co2
C21H27N5O11S2Ni2
C21H23N3O3S2Cu
C21H21N3O2S2Zn
C21H21N3O3S2V
C21H21ClN3O2RuS2
>250
>250
>250
>250
>250
>250
>250
>250
>250
>250
>250
>250
47.32 (47.79) 3.61 (4.02)
41.94 (42.84) 4.47 (4.68)
45.12 (44.67) 3.79 (3.46)
42.25 (42.51) 4.19 (3.74)
45.48 (45.27) 4.15 (4.63)
35.25 (34.75) 3.23 (2.78)
34.76 (34.75) 4.02 (4.75)
35.67 (35.18) 3.84 (3.46)
51.15 (50.67) 4.70 (4.36)
52.89 (52.47) 4.44 (4.91)
52.71 (53.08) 4.42 (4.16)
46.02 (45.58) 3.86 (4.35)
5.02 (4.56)
4.44 (4.53)
4.78 (5.26)
4.48 (4.97)
4.61 (4.17)
3.74 (3.97)
9.65 (9.26)
9.90 (10.33)
8.52 (8.98)
8.81 (8.38)
8.78 (9.23)
7.67 (7.83)
21.11 (20.83)
18.63 (18.18)
21.70 (22.34)
20.91 (21.37)
– –
[Ni2(La)(H2O)4]·2H2O
[Cu2(La)(H2O)2]·H2O
[Zn2(La)(H2O)2]·3H2O
[(VO)2(La)(H2O)2]·H2O
[Ru2(La)(Cl)2(H2O)4]
[Co2(Lb)(H2O)5(NO3)2]·H2O
[Ni2(Lb)(H2O)3(NO3)2]·2H2O
[Cu(Lb)]·3H2O
– (–)
16.17 (17.05)
16.60 (17.32)
12.89 (13.48)
13.71 (14.26)
– –
9)
10)
11)
12)
[Zn(Lb)(H2O)]·H2O
[(VO)(Lb)]·2H2O
Green
Black
[Ru(Lb)(Cl)]·2H2O
– –

4
32 A.A.A. Abou-Hussein
Table 2. Infrared frequencies of the characteristic bands of the Schiff base ligands H2La and H2Lb and their transition
metal complexes.
Ligand/
complex
ν(C=N) and
ν(C=C)
Other
assignments
ν(OH)
ν(NH) ν(SH)
Py-ring ν(M–O) ν(M–N) ν(M–S)
I
II
3050–3300 m 3216 m 2560 s
1638 s
1642 s
1619 s
1600 s
1608 s
1616 s
1594 s
–
–
–
–
–
–
–
–
–
–
3244 m 2523 s
995 m
1019 m 562 m
1013 m 582 m
1028 m
1014m
1025 m 568 m
1023 m 556 m
1011 m 563 m
(
(
(
(
(
1)
2)
3)
4)
5)
3467 s, br
3346 s, br
3483 s, br
3362 s, br
3494 s, br
–
–
–
–
–
–
–
–
–
–
447 m
456 m
467 m
438 m
460 m
371 m Neutral complex
356 w Neutral complex
375 m Neutral complex
369 m Neutral complex
380 m Neutral complex,
70 m, ν(VO)
361 m Neutral complex,
24 w, ν (Ru–Cl)
378 w 1374 s, 1323 s,
556 s
546 m
9
(
(
6)
7)
3396 s, br
3472 s, br
–
–
–
–
1614 s
1586 s
451 m
464 m
3
778 w unidentate
coordinated NO3
group
(
8)
3434 s, br
–
–
1569 s
1030 m 550 m
459 m
366 m 1452 s, 1376 s,
823 w unidentate
coordinated NO3
group
(
(
(
9)
10)
11)
3368 s, br
3490 s, br
3353 s, br
–
–
–
–
–
–
1596 s
1606 s
1578 s
1008 m
1017 m M 543
1021 m 571 m
–
446 m
440 m
435 m
369 m Neutral complex
372 m Neutral complex
374 m Neutral complex,
9
90 m, ν(VO)
382 m Neutral complex,
32 w, ν (Ru–C)
(
12)
3462 s, br
–
–
1594 s
1015 m
–
456 m
3
Notes: s, strong; m, medium; w, weak; br, broad; νs, a single degenerate state which is symmetrical about the principle axis; νas,
antisymmetrical state with respect to the three C2v axis; νsꢀ, a symmetrical state with respect to the three C2v axes.
ꢀ
(
β) and ligand field splitting energy (10 Dq) for complex (7) were calculated (35). The B value is
ꢀ
−1
lower than the free ion value (B = 971 cm ) which is an indication of orbital overlapping and
delocalization of d-orbital. The nephelauxetic parameter, β = Bcomplex/Bfree ion, value obtained is
less than unity, suggesting a considerable cobalt–ligand bond character (Table 3).
−
1
2
−1
,
The measured molar conductance of the [Co2(La)(H2O)2] complex (1) is 10 ꢀ cm mol
indicating the non-electronic nature of the complex. On the other hand, the molar conductance
−
1
2
−1
value for [Co2(Lb)(H2O)5(NO3)2]·H2O complex (7) is 157 ꢀ cm mol , which is higher than
the expected value, since the complex is neutral. The higher value may be due to the fact that the
−
DMF solvent replaced the NO anion in the complexes, which results in the 1:2 electrolytes due
3
to the uncoordinated nitrate ion (36).
The electronic spectra of the green [Ni2(La)(H2O)4]·2H2O complex (2) showed two bands at
6
72 and 532 nm with a magnetic moment at 3.25 μB corresponding to the octahedral configura-
3
tion. Usually, the spectra of octahedral Ni(II) consist of three transitions, assigned as T2rmg(F) ←
3
3
3
3
3
3
3
A2g(F), T1g(F) ← A2g(F) and T1g(P) ← A2g(F). The last transition T1g(P) ← A2g(F) was
not observed as its position should be near IR and is out of the instrument used. The ligand
field parameters (10 Dq, B and β) were calculated and found in the range reported for the pro-
posed structure. For [Ni2(Lb)(H2O)3(NO3)2]·2H2O (8), the absorption bands were observed at
3
3
3
3
7
30 and 396 nm, which are attributed to the T1g(F) ← A2g(F) and T1g(F) ← A2g(F) transi-
tions, respectively, in an octahedral geometry (37). An additional broad band is also observed
around 478 nm in the spectrum of the complex which may be due to the existence of the square
planar configuration around the other Ni(II) ion. The ligand field parameters were calculated.
The values are lower than that reported for a regular octahedral, proving the suggested distorted

Table 3. Electronic absorption bands (nm), their transition assignment, ligand field parameters, magnetic moments (B.M.) and molar conductivities of the Schiff base ligands (H4La and
H2Lb) and their transition metal complexes.
Ligand field parameters
Magnetic moment(μB)
d–d Transition, (nm) and their
assignments
−
1
−1
a
b
eff
(ꢁc)
Complex
B(cm
)
β
10 Dq(cm
)
μ
μ
complex
2
3
3
2
2
2
(
(
1)
2)
[Co2(La)(H2O)2]
[Ni2(La)(H2O)4]·2H2O
534 (0.43)
613 (0.67)
A1g ← B2g
–
683
–
–
2.17
4.68
1.87
3.25
–
13
3
T2g(F) ← A2g(F)
0.654
10.243
3
514 (0.38)
T1g(F) ← A2g(F)
2
(
3)
[Cu2(La)(H2O)2]·H2O
578(0.56)
B1g → Eg
–
–
–
1.73
1.38
16
2
695(0.27)
B1g → A1g
(
(
(
4)
5)
6)
[Zn2(La)(H2O)2]·3H2O
[(VO)2(La)(H2O)2]·H2O
[Ru2(La)(Cl)2(H2O)4]
–
–
–
–
–
–
–
–
–
–
–
–
1.83
–
–
1.83
–
21
13
–
2
2
2
4
4
3
3
2
2
775 (0.82)
690 (0.54)
B2g ← E2(υ2)
2
T2g → A2g
2
5
53 (0.65)
558 (0.21)
65 (0.54)
730 (0.52)
96 (0.34)
T2g → Eg
4
(
(
7)
8)
[Co2(Lb)(H2O)5(NO3)2]·H2O
[Ni2(Lb)(H2O)3(NO3)2]·2H2O
A2g(F) ← T1g(F)
863
658
0.780
0.647
4365
5.16
3.68
4.34
2.26
157
148
4
6
T1g(P) ← T1g(F)
3
T2g(F) ← A2g(F)
10.547
3
3
T1(F) ← A2g(F)
2
(
(
(
9)
10)
11)
[Cu(Lb)]·3H2O
625 (0.73)
–
835 (0.52)
A1g ← B1g
–
–
–
–
–
–
–
–
–
1.72
–
1.54
1.72
–
1.54
11
23
12
[Zn(Lb)(H2O)]·H2O
[(VO)(Lb)]·2H2O
–
2
2
2
2
2
B2 ← E(υ1)
2
6
26 (0.76)
654 (0.67)
10 (0.56)
B2 ← B2(υ2)
2
(
12)
[Ru(Lb)(Cl)]·2H2O
T2g → A2g
–
–
–
–
–
24
2
5
T2g → Eg
Notes: aμcomplex is the magnetic moment of all metals ions present in the complex. μeff is the magnetic moment of one cation in the complex. Molar conductivities were measured in DMF solvent with
b
−3
−1
2
−1
c
−4
−1
−1
concentration × 10 M. Values are in ꢀ cm mol . Values of εmax are in parentheses and multiplied by 10 (mol cm ).

4
34 A.A.A. Abou-Hussein
structure. The magnetic moment value of the isolated complex (8) was measured and was found
to be 2.26 μB, which is a subnormal value compared with that which lies in the range reported
for different stereochemistries of Ni(II) and supporting the presence of mixed stereochemistry
around the Ni(II) atoms (38). The molar conductance values of Ni(II) complexes (2) and (8) in
−
1
2
−1
DMF solution were 13 and 148 ꢀ cm mol , respectively, indicating the neutral nature of the
complexes. The high measured value in complex (8) was observed as a result of the replacement
of DMF by the coordinated nitrate group and the complex solution becomes 1:2 electrolyte.
[
Cu2(La)(H2O)2]·H2O (3) is suggested to be square planar and shows two absorption bands at
2 2 2 2
5
78 and 695 nm which are assigned to B1g → Eg and B1g → A1g transitions. On the other
hand, the electronic spectrum of the complex (9) [Cu(Lb)]·3H2O exhibits a d–d transition band
at 625 nm and another strong band due to S → Cu(II) metal ion as charge transfer transition at
4
36 nm. The measured value of the magnetic susceptibility for Cu(II) complexes was 1.48 μB
for the former complex (3) and 1.72 μB for the latter (9). These values lie in the range reported
for the square planar and square pyramidal geometry for complexes (3) and (9), respectively
(
1
34, 39). The measured molar conductances of Cu(II) complexes in DMF solution were 16 and
1 ꢀ cm mol , indicating the non-electronic nature of complexes (3) and (9).
− −1
1
2
[
Zn2(La)(H2O)2]·3H2O (4) and [Zn(Lb)(H2O)]·H2O (10) complexes are of diamagnetic nature
and so there is no electronic d–d transition or significant magnetic moment. With the aid of the
elemental analysis and IR spectra, the proposed configuration is expected to be tetrahedral and
octahedral for complexes (4) and (10), respectively. Molar conductance values in DMF were 21
−
1
2
−1
and 23 ꢀ cm mol , indicating the neutral nature of these complexes.
The electronic spectra of the green vanadyl complex [(VO)2(La)(H2O)2]·H2O (6) exhibits one
2
2
band at 775 nm, which is due to B2g → E(ν2) transition characteristic of the square pyramidal
geometry. The measured effective magnetic moment of the complex is 1.83 μB, supporting the
geometry of the observed electronic spectra and excluding the metal–metal interaction even in
−
1
the presence of two nuclei atoms in the complex. Moreover, the band at 970 cm , in the IR
spectra of the vanadyl complexes, agrees well with the proposed structure (40). On the other
hand, the spectra of complex [(VO)(Lb)]·2H2O (12) shows three bands at 835, 626 and 374 nm
2
2
2
2
2
2
which are assigned to B2 → E(ν1), B2 → B1(ν2) and B2 → A1(ν3) electronic transitions,
respectively, characteristic of the distorted octahedral geometry around theVO(IV) ion. The value
of the magnetic moment is 1.86 μB, which is in good agreement with a d system and is consistent
1
with a mono-nuclear distorted octahedral geometry (37).
2
The ground state of Ru(III) is T2g, and the first excited doublet levels in the order of increasing
2
2
4
2
1
g
g
5
energy are A2g and A1g which arise from the t e configuration. In a d system, and especially
in Ru(III) which is a relatively strong oxidizing agent, charge transfer bands of the type Lπy → t2g
are prominent in the low-energy region and obscure the weaker bands due to the d–d transition.
The electronic spectra of Ru(III) complexes (3) and (6) exhibit mainly three bands at 690, 553
and 337 nm and 654, 510 and 395 nm, respectively. The first band is assigned to the d–d transition
2
2
2
2
(
T2g → A2g), while the second intense band is due to M–Lπ * transition ( T2g → Eg). The
2 2
last one is attributed to the inter-ligand transition or to MLCT bands ( T2g → A1rmg). The
positions of the absorption bands as well as magnetic susceptibility measurements (1.72 μB for
[
Ru2(La)(Cl)2(H2O)4] and 1.93 μB for [Ru(Lb)(Cl)]·2H2O) indicate the presence of one unpaired
electron, confirming a low-spin octahedral configuration (37).
2
.3. ESR spectra
The X-band ESR spectra of some selected complexes have been studied in order to provide
information about the hyperfine and superhyperfine structures to elucidate the geometry and the
degree of covalency of the metal–ligand bonds (Figure 1). The ESR spectrum of the complex

Journal of Sulfur Chemistry 435
(
5) [(VO) (L )(H O) ]·H O
2 a 2 2 2
5
4
3
2
1
000
000
000
000
000
0
–
–
–
–
–
–
–
–
–
1000
2000
3000
4000
5000
6000
7000
8000
9000
1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
Field (g-factor)
(
9) [Cu(L )]·3H O
b 2
5
4
3
2
1
000
000
000
000
000
0
–
–
–
–
–
–
–
–
–
1000
2000
3000
4000
5000
6000
7000
8000
9000
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0
Field (g-factor)
Figure 1. ESR spectra of the complexes, (5) [(VO)2(La)(H2O)2]·H2O and (9) [Cu(Lb)]·3H2O.
[
Cu(Lb)]·3H2O (9) at room temperature was recorded at a frequency of 9.7 GHz with a field
set of 3250 G. The spin Hamiltonian parameters for the Cu(II) complex can be used to derive
the ground state. In square planar or square pyramidal complexes, the unpaired electron lies in
the d
2
2
2
2
orbital giving B1g as the ground state with gꢁ > g⊥ > 2.0023, while giving A1g with
x −y
g⊥ > gꢁ > 2.0023, if the unpaired electron lies in the d
2
orbital (41). The observed measurements
z
gꢁ(2.35) > g⊥(2.03) > 2.0023 indicate that the complex is axially symmetric and occupies its
unpairedelectronind
(
2
2
orbitalcharacteristicofthesquare-planarorsquarepyramidalgeometry
x −y
42). Kilveson (43) has reported the gꢁ value as an important function for indicating the covalent
character of M–L bond. For ionic and covalent characters, gꢁ > 2.3 and gꢁ < 2.3, respectively.
In the present complex, the gꢁ is more than 2.3, indicating an appreciable covalent character for
the Cu–L bond. In addition, the exchange coupling interaction between two copper centers is
explained by the Hathaway (44) expression: if the value of G is greater than 4, the exchange
interaction in the solid state is negligible, whereas when it is less than 4, a considerable exchange
interaction is noticed in the solid complex. The calculated G-value of the complex suggests some
interaction between Cu(II) centers (45). The elemental analysis, the electronic spectra as well

4
36 A.A.A. Abou-Hussein
as the positions of the bands and the shape of ESR spectra agree well with the formation of the
square pyramidal geometry for the Cu(II) complex.
The ESR spectra of [(VO)2(La)(H2O)2]·H2O (5) complex exhibit a single asymmetric line
centered at g = 1.97 without a resolved hyperfine structure. The absence of vanadium hyperfine
coupling is common in solid state samples (46). This behavior is attributed to the simultaneous
flipping of neighboring electron spins or due to strong exchange interactions. Upon the pairing of
two vanadyl ions, the two electrons’ spins may combine to a non-magnetic spin singlet (S = 0)
or to a paramagnetic spin triplet state (S = 1), only the latter is observed in the spectra. The super
exchange interaction between the two vanadium ions leads to a configuration in which the two
electron spins have a strong interaction.A square pyramidal geometry is proposed for the binuclear
complex (47).
2
.4. 1H-NMR spectra of Zn (II) complexes
1
The H-NMR spectra of thio-Schiff base ligands H4La and H2Lb in dimethyl-sulfoxide (DMSO-
d6), without and with D2O. Their chemical shifts (ppm) and assignments are listed in Table 4.
The signals at 2.48 and 2.32 ppm are assigned to the protons of the methyl groups for H4La
and H2Lb, respectively. On the other hand, a triplet single at 7.23 and a doublet at 8.10 ppm
correspond to the protons of pyridine moiety for the H2Lb ligand. The proton resonance of the
hydroxyl groups (10.21 ppm) as well as thiol groups (3.32 ppm) for H4La ligands and the signals
of the thiol groups for H2Lb (3.37 ppm) disappeared in the presence of D2O, which indicate
that these protons are acidic. The absence of resonances for OH/SH protons in the spectra of
[
Zn2(La)(H2O)2]·3H2O (4) and [Zn(Lb)(H2O)]·H2O (10) complexes indicates the deprotonation
of the phenolic/thiophenolic group of the Schiff bases and coordination of the oxygen and sulfur
atoms through the coordination to the metal atom. It is noticeable that the signals due to the
pyridine moiety protons show a remarkable shift in [Zn(Lb)(H2O)]·3H2O complex suggesting the
involvement of the pyridine nitrogen with the metal ion. Moreover, in the spectra of diamagnetic
Zn(II) complexes (4) and (10), the protons of the methyl group bonded to the azomethine groups
areshifteddownfieldcomparedwiththatofthefreeligandasaresultofchelationoftheazomethine
group through coordination via metal ion (Figure 2). The broad bands of the aromatic protons of
the Schiff bases moiety appeared at the same position on complexation (48).
2
.5. Thermal gravimetric analysis
TGA studies were carried out to illustrate the thermal stability of the complexes and to investigate
whether the water molecules are in the inner or outer coordination sphere of the central metal ion
(
Figure 3)(49).TGAcurveof[Cu2(La)(H2O)2]·H2O(3)showsthatthefirststageofdecomposition
◦
is at 56–127 C with the elimination of one crystalline water molecule of the total weight of the
complex (Calc./Found %: 3.07/3.34%). The second stage at the range 130–233 C corresponds
◦
to the removal of two coordinated water molecules (Calc./Found %: 6.15/5.87%). The last stage
◦
within the temperature range from 233 to 736 C can be assigned to the loss of 64.00% of the
total weight of the complex as a result of the removal of the fragment part of the ligand and the
formation of copper oxide (Calc./Found %: 27.17/26.79%). DrTGA curve of the complex shows
◦
two endothermic peaks. The first at 116 C is due to the removal of crystalline water molecule,
◦
while the peak at 215 C is due to the loss of coordinated water molecules. The last endothermic
peak at 687 C is ascribed to the decomposition of the anhydrous complex (Scheme 3), depicting
◦
the thermal degradation pattern of the complex as follows:
On the other hand, the TGA–DrDTA curve for complex (8), [Ni2(Lb)(H2O)3(NO3)2]·2H2O,
◦
displays four degradation steps of decomposition. The former stage in the range of 64–136 C is

Table 4. 1H-NMR chemical shifts (δ, ppm) of the Schiff base, H4La and H2Lb, ligands and their Zn(II) complexes (4) and (10) in DMSO-d6 after
the addition of D2O.
(i)
OH
(a)
(a)
(
a)
HO
N
(h)
(
h )
(
b)
(d)
(b)
(b)
(
b)
(c)
(
e)
N
N
(
j )
(
j)
(c)
(
c)
N
(c)
(f)
N
N
N
(f )
N
N
N
(d)
(e)
(d)
(e)
(
d)
Zn+2
Zn
+2
Zn+2
(
e)
S
O
O
S
SH
(I) H
HS
(g)
S
S
SH
HS
g)
(a)
(f)
(
(f)
(
II) H
4
L
a
(4)
2
L
b
(10)
Chemical shifts, δH
Complexes
Assignment
H4La
H4La (D2O)
H2Lb
H2Lb (D2O)
(4) [Zn2(La)(H2O)2]·3H2O
(10) [Zn(Lb)(H2O)]·H2O
a
(
(
(
(
(
(
(
(
(
(
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
H [t, 1H, Ar–H]
6.24
2.48
7.68
6.58
7.25
6.42
3.32
–
6.24
2.48
7.68
6.58
7.25
6.42
–
–
–
8.36
7.23
2.32
7.59
6.62
7.21
6.79
3.37
8.10
–
7.23
2.32
7.59
6.62
7.21
6.79
–
8.10
–
–
6.31
2.53
7.63
6.58
7.25
6.42
–
–
–
7.98
7.25
2.39
7.59
6.62
7.20
6.78
–
8.22
–
–
b
H [s, 6H, 2CH3]
c
H [d, 2H–Ar]
d
H
[t, 2H–Ar]
e
H [t, 2H–Ar]
f
H
[d, 2H–Ar]
g
H [s, 2H]
h
H [d, 2H–Ar]
i
H [s, br, 2H, 2–OH]
10.21
8.36
j
H [s, 1H, Ar–H]
–

4
38 A.A.A. Abou-Hussein
1
Figure 2. H-NMR spectra (δ, ppm) in DMSO-d6 solvent of the (a) Schiff base, ligand H4La (b) Schiff base, H4La,
1
ligand after the addition of D2O. (c) Expansion to the range, 5.5–8.5 ppm from the spectrum of H4La (d) H-NMR spectra
∗
(
δ, ppm) in DMSO-d6 solvent of the complex, [Zn2(La)(H2O)2] · 3H2O ( suppressed solvent).
due to the loss of the crystalline water molecules, (weight loss; Calc./Found %: 5.09/6.45%). The
◦
second stage at the range 140–232 C ascribed to the loss of three coordinated water molecules
of the total weight of the complex (weight loss; Calc./Found %: 7.64/6.37%). The third stage
◦
observedintherange243–387 CcorrespondstotheevolutionofN2O5 molecules, withweightloss
(
Calc./Found %: 15.27/14.31%). The removal of the fragment part of the ligand occurred in the
◦
temperature range at 387–738 C, accompanied by weight loss (Calc./Found %: 53.05/52.24%),
as a result of the complete decomposition and the formation of the nickel oxide as a residue

Journal of Sulfur Chemistry 439
Figure 3. TGA/DrTGA curve of complex (3) [Cu2(La)(H2O)2]·H2O and (8) [Ni2(Lb)(H2O)3(NO3)2]·2H2O.

4
40 A.A.A. Abou-Hussein
–
H O
–2H O
( La)
2
2
[
Cu (L )(H O) ]·H O
[Cu (L )(H O) ]
2
a
2
2
[Cu
2
(L
a
)]
Copper oxide
2
a
2
2
2
1
30–233°C
233–736°C
56–127°C
Scheme 3. Thermal degradation pattern of [Cu2(La)(H2O)2]·H2O, complex (3).
◦
◦
(
20.63%). DrTGA curve of the complex shows endothermic peaks at 126 C and 187 C as a
result of the loss of crystalline and coordinated water molecules, respectively. On the other
◦
hand, an exothermic peak observed at 364 C which is due to the loss of N2O5 molecules
◦
and the last endothermic peak at 639 C which is ascribed to the complete decomposition of
the complex (Scheme 4) depict the thermal degradation pattern of the complex in the range
◦
5
0–800 C.
–
2H O
2
[
Ni (L )(H O) (NO ) ]·2H
2O
[Ni
2
(L
40–232°C –3H O
2
b 2 3 3 2
)(H O) (NO ) ]
2
b
2
3
3 2
6
4–136°C
1
–
Lb
–N O
2
5
[
Ni (L )]
[Ni (L )(NO ) ]
2 b 3 2
Nickel oxide
2
b
3
87–738
°
C
343–387°C
Scheme 4. Thermal degradation pattern of [Ni2(Lb)(H2O)3(NO3)2]·2H2O, complex (8).
2
.6. Antimicrobial activities
Schiffbasesandtheircorrespondingtransitionmetalswerefoundtopossessappreciablefungicidal
and bactericidal properties against bacteria such as Rhizobium and Azotobacter and fungi such as
Aspergillus niger and Fusarium oxysporium). The results are summarized in Table 5. The ligands
and the complexes showed varying degrees of inhibitory effect on the growth of the bacterial/or
fungal strains tested (50, 51). It was observed from the results that the activity of complexes is
muchhigher thanthat of the correspondingligands(Figure 4).This enhancement ofthe activity can
be rationalized on the basis of their structures possessing an additional C=N bond. Furthermore,
Table 5. Antibacterial activity and antifungal activity data of the ligand and its transition metal complexes.
%
Zone diameter showing complete growth inhibition
Antibacterial activity Antifungal activity
Rhizobium Azotobacter A. niger F. oxysporium
Item
Ligand/complex
I
II
H4La
H2Lb
[Co2(La)(H2O)2]
53
48
38
45
46
58
48
41
50
55
55
56
52
56
54
58
43
47
48
46
45
47
48
47
46
50
43
46
43
58
58
62
58
67
58
66
67
63
71
61
71
69
73
52
56
62
57
56
58
57
54
56
58
58
61
63
(
(
(
(
(
(
(
(
(
(
(
(
1)
2)
3)
4)
5)
6)
7)
8)
[Ni2(La)(H2O)4]·2H2O
[Cu2(La)(H2O)2]·H2O
[Zn2(La)(H2O)2]·3H2O
[(VO)2(La)(H2O)2]·H2O
[Ru2(La)(Cl)2(H2O)4]
[Co2(Lb)(H2O)5(NO3)2]·H2O
[Ni2(Lb)(H2O)3(NO3)2]·2H2O
[Cu(Lb)]·3H2O
9)
10)
11)
12)
[Zn(Lb)(H2O)]·H2O
[(VO)(Lb)]·2H2O
[Ru(Lb)(Cl)]·2H2O

Journal of Sulfur Chemistry 441
(
a) The ligand H L and their transiꢀon metal complexes
4 a
(
b) The ligand H L and their transiꢀon metal complexes
4 a
(
c) The ligand H L and their transiꢀon metal complexes
2 b
(
d) The ligand H L and their transiꢀon metal complexes
2 b
Figure 4. Biological activity data of Schiff base ligands, H4La and H2Lb and their transition metal complexes against
antibacterial and antifungal activity.
coordination reduces the polarity of the metal ion mainly because of the partial sharing of its
positive charge with these donor groups and possibly because of the π-electron delocalization
within the whole chelate ring system. Thus, the chelation increases the lipophilic nature of the
central metal atom, which in turn favors its permeation through the lipid layer of the membrane
of the microorganisms’ cell wall more effectively, thus raising the activity of the drug.
3
. Conclusion
The reaction of ABT with DAR or DAP in the molar ratio 2:1 forms two Schiff bases H4La and
H2Lb which reacted with the transition metal ions Co(II), Ni(II), Cu(II), Zn(II),VO(IV) and Ru(III)
to afford the corresponding complexes which exhibit mono- or binuclear structures of distorted
octahedral, tetrahedral, square planar or square pyramid structure where the H4La ligand behaves

4
42 A.A.A. Abou-Hussein
N
N
N
N
H O
2
H O
H O
H O
2
2
2
2
H O
2
+
Ni
2
+
Ni
2
Co+
2
+2
Co
S
S
S
O
O
S
O
O
H O
H
2
O
H
O
2
2
(1)
H O
(2)
2
N
N
Cu+2
N
N
Zn+2
H O
3H O
2
2
+
2
+
+2
Cu
Zn
S
S
S
O
O
S
H
O
O
H O
H O
2
O
H
O
2
2
2
(3)
(4)
N
V
N
H
2
O
H O
2
N
N
H
2
O
Cl
Cl
V
+
3
+
3
S
Ru
S
O
O
Ru
S
S
O
O
H
O
O
(5)
H
2
O
H O
2
O
H O
2
2
(6)
NO
3
NO3
2
H O
2
H O
S
S
+
2
Ni+2
Co
H O
2
2
H O
2
N
N
H
2
O
H
2
O
2
H O
N
N
N
S
N
S
+
2
Ni+2
Co
NO3
7)
NO
3
2
H O
2
H O
(
(8)
N
N
3
H O
H O
2
2
N
N
S
N
N
Zn+2
Cu+2
S
S
S
H O
2
(
9)
(
10)
N
N
2
H O
2
2 H O
2
N
N
S
N
N
V
Ru+3
S
S
S
O
Cl
(11)
(12)
Figure 5. Representative structures of the metal complexes of the Schiff bases H4La and H2Lb.
as a tetrabasic hexadendate ligand while H2Lb behaves as a dibasic pentadentate ligand. The
bonding sites are azomethane, sulfur atoms and phenolic oxygen for H4La or pyridine nitrogen
for H2Lb. Figure 5 depicts the representative structures of the metal complexes on the basis of
the elemental analysis, electronic spectral measurements and magnetic susceptibility data. TGA
suggests high stability for the complexes, showed thermal decomposition in different stages and
confirmed the presence of crystalline or coordinated water molecules.

Journal of Sulfur Chemistry 443
4
4
.
Experimental
.1. Materials
The nitrate salts of Co(II), Ni(II), Cu(II) and Zn(II) were Merck or BDH·RuCl3·3H2O was pur-
chased from Labo Chemie France. VO(IV) acetate and DAP were from Aldrich. Resorcinol,
acetic anhydride, zinc chloride and 2-aminobenzothiazole were supplied from Merck Chemicals.
Organic solvents were reagent grade chemicals.
4
.2. Physical measurement
Microanalyses of carbon, hydrogen and nitrogen were carried out at the micro-analytical Cen-
ter, Cairo University, Egypt. Analyses of the metals in the solid complex have been carried
out by using EDTA (52). Electronic spectra of the metal complexes as solid reflecting were
measured on a Perkin-Elmer 2400 series II analyzer, and spectra of the compounds in KBr
pellets in the range 4000–400 range were obtained with a Perkin-Elmer, FTIR model 8101 spec-
trophotometer. The UV–VIS spectra of the complexes were obtained on a Jasco model v-550
1
spectrophotometer. H-NMR spectra were recorded using a Varian genini-300 MHz spectropho-
tometer 90 MHz. DMSO-d6 was added as a solvent and tetramethylsilane as an internal reference.
D2O was added to every sample to test for the deuteration of the complexes. Abbreviations are:
s = singlet, d = doublet, t = triplet and m = multiple. Magnetic susceptibilities of the complexes
were measured at room temperature using a Johnson Matthey, Alfa Products, model MKI mag-
netic susceptibility balance. The effective magnetic moments were calculated from the expression
1/2
μeff. = 2.828(χM · T) B.M., where χM is the molar susceptibility corrected using Pascal’s con-
stants for the diamagnetism of all atoms in the compounds (53). A TGA/DTA thermal analyzer
was manufactured by using NETZSCH-gerateban Bestell – Nr 348472c. The thermal analyzer
was equipped with a thermobalance. Samples (∼50 mg) were heated at a programmed rate of
◦ −1
0 C min in a dynamic N2 atmosphere. The sample was contained in a boat-shaped platinum
2
pan suspended in the center of a furnace. ESR spectra of the copper complexes were recorded
on a JEOL microwave unit, JES-FE2XG Spectrometer, at the National Research Centre, Giza,
−
3
Egypt. Molar conductances of 10 M solutions of the complexes in DMF were measured with
the Corning conductivity meter NY 14831 model 441 (USA).
4
.3. Synthesis of the Schiff base
4
.3.1. Schiff base, 4,6-bis((E)-1-(2-mercaptophenylimino)ethyl) benzene-1,3-diol, H4La
The Schiff base H4La was prepared in two steps. The first step is the preparation of DAR by acety-
lating resorcinol (5.00 g, 45.5 mmol) with acetic anhydride (9.28 g, 91.0 mmol) in the presence of
excess zinc chloride (10.0 g, 73.4 mmol) at 140˚C in a paraffin oil path. The hot mixture was cooled
to room temperature and poured onto 140 ml of 50% dilute hydrochloric acid. Orange precipitate
was formed and increased with standing until 1 h. The orange crude product was obtained by fil-
tration with suction and washed with distilled water till the color of the filtrate is nearly colorless.
Orange needle crystals were obtained by crystallization using either ethanol or acetic acid/water
mixture (54). The second step is the addition of a solution ofABT (2.25 g, 9.015 mmol) in ethanol
(30 ml) to ethanolic solution of DAR (1.75 g, 9.00 mmol, 40 ml ethyl alcohol), corresponding to
the molar ratio 2:1, respectively. The solutions were refluxed for 3 h. A yellow (H4La) ligand was
formed on cooling the solutions slowly to room temperature and the precipitates were collected
by filtration, washed with ethanol then diethyl ether and finally air-dried. The yield was 2.68 g
◦
(
68.71%) and the m.p. is 182 C for H4La.

4
44 A.A.A. Abou-Hussein
4
.3.2. Schiff base, 2-((E)-1-(6-((E)-1-(2-mercaptophenylimino) ethyl) pyridine-2-yl)
ethylideneamino) benzenthiol, H2Lb
A solution of ABT (2.68 g, 10.725 mmol) in ethanol (30 ml) was added to DAP (1.75 g,
0.725 mmol) in ethanol (40 ml) in the molar ratio 2:1 and the solutions was refluxed for 3 h.
1
Yellow (H2Lb) crystals were formed on cooling the solutions slowly to room temperature and the
precipitate was collected by filtration, washed with ethanol then diethyl ether and finally air-dried.
The yield was 2.76 g (62.30%) and the m.p. is 164˚C for H2Lb.
4
.4. Synthesis of the transition metal complexes of the Schiff base ligands H4La and H2Lb
Ethanolic solutions of H4La and H2Lb ligands were added gradually to ethanolic solutions of the
metal nitrates in the molar ratio 1:2. The reaction mixtures were stirred for 30 min and then they
were refluxed for 2 h. Most of the complexes were formed during the reflux. The products were
isolated by filtration and washed with several portions of ethanol, then ether and air-dried. The
complexes are insoluble in most common organic solvents, but soluble in DMF and/or DMSO.
In the preparation of VO(IV) complexes, 0.1 g of sodium acetate was added as a buffering agent
to raise the pH medium. The following detailed preparations are given as examples and the other
complexes were obtained similarly. Reaction of the H2Lb ligand with few metals in the molar
ratio 1:2 was not successful in most cases to afford the corresponding binuclear mole ratio where
Cu(II), Zn(II), Ru(III) andVO(IV) (9–12) complexes are monometallic, even by using the template
method, probably due to their low solubility so that they precipitate immediately in the reaction
medium.
Representative examples of the preparation of thio-Schiff bases H4La and H2Lb of complexes 1
and 12, respectively, are illustrated and the other complexes were synthesized in the same manner.
4
.4.1. Synthesis of complex [Co2(La)(H2O)4] (1)
A solution of 4,6-bis((E)-1-(2-mercaptophenylimino)ethyl)benzene-1,3-diol, H4La, ligand
(
0.45 g, 1.102 mmol) in ethanol (30 ml) was added gradually to a solution of Co(NO3)2·6H2O
(0.641 g, 1.101 mmol) in the same solvent (20 ml) in the molar ratio 1:2 (ligand:metal). The solu-
tions were stirred for 30 min and heated to reflux for 3 h. The solid complexes were precipitated
and filtered off, washed with ethanol then diethyl ether and finally air-dried. Yellow precipitate
is formed. The complex is air-stable in the solid state and soluble in DMF. The yield was 0.66 g,
◦
(
60.66%) and the melting point was higher than 250 C.
4
.4.2. Synthesis of complex [Ru(Lb)(Cl)]·2H2O (12)
A solution of 2-((E)-1-(6-((E)-1-(2-mercaptophenylimino)ethyl)pyridine-2-yl)ethylideneamino)
benzenthiol, H2Lb, ligand (0.45 g, 1.102 mmol) in ethanol (30 ml) was added gradually to a solu-
tion of the RuCl3·3H2O (0.621 g, 1.191 mmol) in the same solvent (30 ml) in the molar ratio 1:2,
(1 H2Lb:2 metal). The solutions were stirred for 30 min and heated to reflux for 3 h. The solid
complexes were precipitated and filtered off, washed with ethanol then diethyl ether and finally
air-dried. Black precipitate was formed, giving products of the formula [Ru(Lb)(Cl)]·2H2O (3).
The complex is air-stable in the solid state and soluble in DMF. The yield was 0.72 g, (67.79%)
◦
and the melting point was higher than 250 C. The template method failed in an attempt to afford
the expected molar ratio 1:2 (1 H2Lb:2 metal).

Journal of Sulfur Chemistry 445
4
.5. The antimicrobial experiment
In vitro biological screening of the synthesized ligands and complexes were carried out against the
phytopathagenicbacteria(AzotobacterandRhizobium)andfungi(Aspergillusniger andFusarium
oxysporium) by the well diffusion method (55). The antimicrobial studies have been carried out
at the Faculty of Agriculture, Department of Plant Pathology, Al-Azhar University.
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