Synthesis, characterization, and biological properties of bivalent transition metal complexes of Co(II), Cu(II), Ni(II), and Zn(II) with some acylhydrazine derived furanyl and thienyl ONO and SNO donor Schiff base ligands

Article abstract of DOI:10.1081/SIM-100001928

Some acylhydrazine derived furanyl and thienyl ONO and SNO donor Schiff base ligands and their Co(II), Cu(II), Ni(II), and Zn(II) complexes have been prepared and characterized on the basis of elemental analyses, magnetic moments, molar conductances, and

Full text of DOI:10.1081/SIM-100001928

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SYNTHESIS, CHARACTERIZATION, AND BIOLOGICAL
PROPERTIES OF BIVALENT TRANSITION METAL
COMPLEXES OF Co(II), Cu(II), Ni(II), AND Zn(II) WITH
SOME ACYLHYDRAZINE DERIVED FURANYL AND
THIENYL ONO AND SNO DONOR SCHIFF BASE LIGANDS
Zahid H. Chohan a
a Department of Chemistry , Islamia University , Bahawalpur, Pakistan
Published online: 20 Aug 2006.
To cite this article: Zahid H. Chohan (2001) SYNTHESIS, CHARACTERIZATION, AND BIOLOGICAL PROPERTIES OF BIVALENT
TRANSITION METAL COMPLEXES OF Co(II), Cu(II), Ni(II), AND Zn(II) WITH SOME ACYLHYDRAZINE DERIVED FURANYL AND
THIENYL ONO AND SNO DONOR SCHIFF BASE LIGANDS, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry,
31:1, 1-16, DOI: 10.1081/SIM-100001928
To link to this article: http://dx.doi.org/10.1081/SIM-100001928
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(1), 1–16 (2001)
SYNTHESIS, CHARACTERIZATION, AND
BIOLOGICAL PROPERTIES OF BIVALENT
TRANSITION METAL COMPLEXES OF
Co(II), Cu(II), Ni(II), AND Zn(II) WITH
SOME ACYLHYDRAZINE DERIVED
FURANYL AND THIENYL ONO AND SNO
DONOR SCHIFF BASE LIGANDS
Zahid H. Chohan
Department of Chemistry, Islamia University,
Bahawalpur, Pakistan
ABSTRACT
Some acylhydrazine derived furanyl and thienyl ONO and
SNO donor Schiff base ligands and their Co(II), Cu(II), Ni(II), and
Zn(II) complexes have been prepared and characterized on the basis
ofelementalanalyses, magneticmoments, molarconductances, and
1
spectroscopic (electronic, IR, H NMR, and 13C NMR) data. All
of the ligands function as tridentates and the deprotonated enolic
form is preferred in the coordination.
E-mail: zchohan@pakview.com
1
Copyright ꢀ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

ORDER
REPRINTS
2
CHOHAN
OH
X
X
O
O
C
C
N N
H
C
N N
H
C
H
H
HL1: X = O
HL3: X = O
HL2: X = S
HL4: X = S
X
O
N
C
N N
H
C
H
HL5: X = O
HL6: X = S
Figure 1. Proposed structures of schiff bases.
INTRODUCTION
Hydrazine and hydrazones have been actively investigated (1–5) because of
their varied ligational behavior toward metal ions and their manifestation of novel
structural features in their coordination chemistry. Certain acylhydrazines and their
transition metal chemistry also have been a subject of many researchers (6–8) due
to their significant properties as antibacterial and antifungal agents. The present
investigation, therfore, was undertaken to better understand the ligational behavior
of some novel acylhydrazine derived Schiff bases towards bivalent transition metal
ions and their role in biological systems.
Accordingly, some novel benzoylhydrazine, salicyloylhydrazine, and nicoti-
noylhydrazine derived furanyl and thienyl Schiff bases (Fig. 1) and their Co(II),
Cu(II), Ni(II), and Zn(II) complexes have been successfully synthesized and their
characterization, ligational behavior, and biological properties are reported.
RESULTS AND DISCUSSION
Physical Properties
The Schiff bases (HL1–HL6) (Fig. 1) were prepared by reacting equimolar
amounts of 2-furanecarboxaldehyde or 2-thiophenecarboxaldehyde with the re-
spective benzoylhydrazine, salicyloylhydrazine, or nicotinoylhydrazine in ethanol.
The structures of these Schiff base ligands were established with the help of their
IR, 1H NMR, 13C NMR, and microanalytical data (Tables 1 and 4).

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
3
Table 1. Physical, Spectra, and Analytical Data of the Schiff Bases
Calc. (Found) (%)
Schiff Base
Ligand
M.p
(◦C)
Yield
(%)
a
IR (cm−1
)
C
H
N
HL1
C12H10N2O2
[214.0]
HL2
145 3240 (s, NH), 1700 (m, NH + CN), 67.3
4.7
13.1
78
–
=
1635 (s, CH N), 1020 (s, N N), (67.7) (4.5) (13.2)
C12H10N2OS 148 3245 (s, NH), 1705 (m, NH+CN),
62.6
4.3
12.2
82
80
–
=
[230.1]
1635 (s, CH N), 1020 (s, N N), (62.9) (4.7) (12.5)
HL3
3365 (br, OH), 3245 (s, NH),
62.6
4.3
12.2
C12H10N2O3
[230.0]
135
1705 (m, NH + CN), 1630
(62.5) (3.9) (12.5)
–
–
(s, CH N), 1025 (s, N N)
HL4
3365 (br, OH), 3240 (s, NH),
58.5
4.1
11.4
80
C12H10N2O2S 128
[246.1]
HL5
1705 (m, NH + CN), 1630
(58.8) (4.0) (11.3)
–
=
(s, CH N), 1025 (s, N N)
C11H9N3O2
[215.0]
HL6
C11H9N3OS
[231.1]
138 3245 (s, NH), 1705 (m, NH + CN), (61.4) (4.2) 19.5
75
81
–
=
1635 (s, CH N), 1025 (s, N N) (61.6) (4.5) (19.8)
122 3245 (s, NH), 1700 (m, NH + CN), 57.1
3.9
18.2
–
=
1635 (s, CH N), 1020 (s, N N) (57.5) (4.1) (18.5)
as: Sharp; m: Medium; br: Broad.
All of the metal complexes [(1)–(24)] (Table 2) of these Schiff bases were
prepared by the stoichiometric reaction of the respective metal chlorides and the
prepared Schiff base ligands in the molar ratio M:HL = 1:2. The proposed reaction
between the Schiff base ligands and the metal salts is represented by the following
equation:
MCl2 + 2HL −→ [M(L)2] + 2HCl
where M = Co(II), Cu(II), Ni(II), or Zn(II) and L = L1, L2, L3, L4, L5, or L6.
The complexes are intensely colored and stable solids, which decompose
above 200◦C without melting and are insoluble in common organic solvents like
ethanol, methanol, chloroform, or acetone. DMSO and DMF, however, dissolved
all of the complexes. Their elemental analyses data, solubility, and melting be-
havior suggest that they are monomers. Molar conductance values of the soluble
complexes in DMF show low values (28–41 ohm−1 cm2 mol−1) indicating (9) that
they are all nonelectrolytic in nature.

ORDER
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4
CHOHAN
Table 2. Physical and Analytical Data of the Metal(II) Complexes
Calc. (Found) (%)
M.p.
(◦C)
B.M. Yield
Complex
(µeff)
(%)
C
H
N
(1) [Co(L1)2]
222–224
238–240
231–233
228–230
225–227
230–232
228–230
235–237
232–234
226–228
225–227
235–237
229–231
4.85
60
59.4
3.7
11.5
C24H18CoN4O4
(59.7) (3.5) (11.6)
[484.9]
(2) [Cu(L1)2]
1.55
3.20
Dia
65
62
58
60
58
65
60
62
62
60
61
62
58.8
3.7
11.4
C24H18CuN4O4
(59.1) (3.6) (11.5)
[489.5]
(3) [Ni(L1)2]
59.4
3.7
11.5
C24H18NiN4O4
(59.0) (3.5) (11.8)
[484.7]
(4) [Zn(L1)2]
58.6
3.7
11.4
C24H18ZnN4O4
(58.9) (3.3) (11.6)
[491.4]
(5) [Co(L2)2]
4.93
1.78
3.70
Dia
55.7
3.5
10.8
C24H18CoN4O2S2
(55.9) (3.3) (10.5)
[517.0]
(6) [Cu(L2)2]
55.2
3.5
10.7
C24H18CuN4O2S2
(55.0) (3.6) (10.5)
[521.6]
(7) [Ni(L2)2
55.7
3.5
10.8
C24H18NiN4O2S2
(55.9) (3.1) (10.5)
[516.8]
(8) [ZN(L2)2]
55.0
3.4
10.7
C24H18ZnN4O2S2
(55.5) (3.1) (10.8)
[523.5]
(9) [Co(L3)2]
4.90
1.60
3.50
Dia
55.7
3.5
10.8
C24H18CoN4O4
(55.9) (3.6) (10.6)
[516.9]
(10) [Cu(L3)2]
55.2
3.5
10.7
C24H18CuN4O6
(55.5) (3.2) (10.5)
[521.5]
(11) [Ni(L3)2]
55.7
3.5
10.8
C24H18NiN4O6
(55.9) (3.3) (10.9)
[516.7]
(12) [Zn(L3)2]
55.0
3.4
10.7
C24H18ZnN4O6
(54.8) (3.6) (10.6)
[523.4]
(13) [Co(L4)2]
4.92
52.4
3.3
10.2
C24H18CoN4O4S2
[549.0]
(52.5) (3.0) (10.1)

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
5
Table 2. Continued
Calc. (Found) (%)
M.p.
(◦C)
B.M. Yield
Complex
(µeff)
(%)
C
H
N
(14) [Cu(L4)2]
224–226
228–230
232–234
235–237
228–230
232–234
230–232
225–227
228–230
231–233
228–230
1.68
65
52.0
3.3
10.1
C24H18CuN4O4S2
(52.2) (3.4) (10.5)
[553.6]
(15) [Ni(L4)2]
3.30
Dia
63
58
62
60
60
60
65
62
60
62
52.5
3.3
10.1
C24H18NiN4O4S2
(52.3) (3.2) (10.3)
[548.8]
(16) [Zn(L4)2]
51.8
3.2
10.8
C24H18ZnN4O4S2
(51.9) (3.3) (10.6)
[555.5]
(17) [Co(L5)2]
4.88
1.70
3.50
Dia
54.2
3.3
17.3
C22H16CoN6O4
(54.5) (3.6) (17.1)
[486.9]
(18) [Cu(L5)2]
53.7
3.3
17.1
C22H16CuN6O4
(53.9) (3.5) (17.6)
[491.5]
(19) [Ni(L5)2]
54.2
3.3
17.3
C22H16NiN6O4
(54.1) (3.3) (17.1)
[486.7]
(20) [Zn(L5)2]
53.5
3.2
17.0
C22H16ZnN6O4
(53.7) (3.5) (16.8)
[493.4]
(21) [Co(L6)2]
4.91
1.75
3.60
Dia
50.9
3.1
16.2
C22H16CoN6O2
(51.2) (3.3) (16.0)
[519.0]
(22) [Cu(L6)2]
50.4
3.1
16.0
C22H16CuN6O2S2
(50.6) (3.0) (16.2)
[523.6]
(23) [Ni(L6)2]
50.9
3.1
16.2
C22H16NiN6O2S2
(50.8) (3.3) (16.0)
[518.8]
(24) [Zn(L6)2]
50.2
3.0
16.0
C22H16ZnN6O2S2
[525.5]
(50.5) (3.2) (16.4)
Model Studies
Examination of the physical molecular models of these Schiff base ligands,
illustrated in Figure 1, show that in no case can the ligands exhibit quadridentate
ONNO or ONNS and bidenate ON or SN behavior. It is capable of exhibiting either

ORDER
REPRINTS
6
CHOHAN
X
X
HO
N
O
R C
R C
N
C
N
H
N
C
H
H
[Keto]
[Enol]
R = Ph; X = O (L1), R = Ph; X = S (L2)
R = PhOH-o; X = O (L3), R = PhOH-o; X = S (L4)
R = Py; X = O (L5), R = Py; X = S (L6)
Figure 2. Possible flexidentate keto–enol forms of Schiff base ligands.
tridentate monobasic (flexidentate keto–enol form) (Fig. 2) or neutral tridentate
behavior.
In its enol form, the ligand can function like an enol with ONO or ONS
donor sites by either the deprotonated hydroxyl group of the enol, ν(OH), the
–
nitrogen of hydrazine, ν(N N), and the heteroatom (X) of the furanyl or thienyl
groups. The keto form however, acts as tridentate ONO or ONS donors showing
=
=
coordination through the keto oxygen (C O), azomethine nitrogen (HC N), and
the heteroatom (X).
The physical model studies further showed that the phenolic OH of the Schiff
base ligands HL3 and HL4 could not participate stereochemically in the coordi-
nation because of their planar structures in which all atoms are sp2-hybridized
(Fig. 1). Moreover, the presence of OH protons in the 1H NMR spectra of HL3 and
HL4 confirmed that the hydroxyl group is not involved in the coordination. Also,
the molecular model studies revealed that nitrogen of pyridine in ligands HL5 and
HL6 could not get involve in the coordination due to its stereochemically out of
plane geometry.
Infrared Spectra
The IR spectra of the Schiff bases and their metal(II) complexes were
recorded in KBr and are summerized in Tables 1 and 3 with some tentative as-
signments of important characteristic bands. All the Schiff bases showed the ab-
sence of bands at ∼1735 and 3420 cm−1 due to characteristic carbonyl ν(C O)
=
and ν(NH2) stretching vibrations of the respective aldehydes and amines (start-
ing materials). Instead, a new band at ∼3240 cm−1 and sharp bands at ∼3215,
1700, 1635, and 1020 cm−1 assigned (10,11) to amide-I [ν(CO NH)], amide-II
–
–
=
[ν(NH + CN)], azomethine [ν(HC N)] linkage, and ν(N N) modes appeared, re-
spectively. It suggested that hydrazino amine and aldehyde moieties of the starting

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
7

ORDER
REPRINTS
8
CHOHAN
reagents no longer exist and have been condensed and converted into their re-
spective Schiff bases. The physical molecular model studies and the comparison
of the IR spectra of the Schiff bases and their metal complexes indicated that
the Schiff bases are coordinated to the metal atom by three sites, thus suggesting
that the ligands act as tridentates. The band appearing at ∼3240 cm−1 due to the
amide-I band was substantially shifted to lower frequency (20–30 cm−1) relative
=
to the free ligand values, and the bands due to ν(C O) were completely missing
in the spectra of the complexes, suggesting (12) enolization of the Schiff bases
on complexation. This is also supported by the fact that no band for ν(OH) in
the spectra of the Schiff base ligands and also in the complexes is observed ex-
cept the phenolic ν(OH) at 3365 cm−1 in the Schiff base ligands HL3 and HL4
−1
–
and their complexes. Instead, a band due to ν(C O) at about ∼1245 cm was
observed for all the title complexes, which supports the observation of their eno-
lization during coordination. These facts suggest that the Schiff bases remain in
the keto form in the solid state but in solution, both the keto and enol forms
remain in equilibrium (13) (Fig. 2) and during complexation, deprotonation oc-
curs from the enol form. This coordination through the deprotonated enolized
oxygen results in a ν(NCO) band manifested in the region at ∼1245 cm−1. The
amide-II band was split, displaced to higher frequency and reduced in intensity.
A shift to higher frequency (5–10 cm−1) of the ν(N N) band at ∼1020 cm−1 and
–
its splitting indicated (14) coordination of the azomethine nitrogen. Moreover,
the shift to lower frequency (5–10 cm−1) of the band due to the azomethine
ν(CH H) linkage at ∼1635 cm−1 also indicated involvement of azomethine group
=
in coordination.
The new, weak, low-frequency bands at ∼360 and ∼455 cm−1 were assigned
–
–
(15) to metal-sulfur ν(M S) in the thienyl derived and metal-oxygen ν(M O) in
the furanyl derived ligands. These bands were only observable in the spectra of
the metal complexes and not in the spectra of their Schiff bases, which in turn
confirmed the participation of the heteroatoms (S and O) in the coordination.
NMR Spectra
The NMR spectra of the free ligands and some of their metal complexes
have been recorded in DMSO-d6. The features of the free ligands and some of
their complexes are shown in Table 4. NMR spectra of the free ligands support
the conclusions derived from the IR spectra. The ligands exhibit aromatic and
heteroaromatic proton signals at δ 4.5–7.9 ppm as expected. The signals for the
NH proton appeared at δ 11.4 ppm (s, br) in the spectra of the free Schiff base
ligands; these signals are absent in the spectra of their metal complexes. This
indicated (16) that the Schiff bases are coordinated to the metal ions in the enolic
form by deprotonation.

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
9
Table 4. NMR Spectral Data of the Schiff Base Ligands and Selected Complexes
No
1H NMR(DMSO-d6) (ppm)
13C NMR (DMSO-d6) (ppm)
1
HL1 4.5–4.7 (m, 1H, furanyl), 4.8 (dd, 1H, J( H 1H) = 1.8,
104.5, 112.6, 121.3, 123.2
(furanyl), 124.8, 126.7,
129.1, 137.3 (Ph), 152.4
–
J( H 1H) = 1.7 Hz, furanyl), 5.8 (m, 1H, furanyl), 7.2
1
–
=
(s, 1H, HC N) 7.5–7.7 (m, 2H, Ph), 7.8–7.9 (m, 3H,
=
=
Ph), 10.8 (s, 1H, NH).
(HC N), 187.4 (C O).
104.6, 112.5, 121.4, 123.2
(thienyl), 125.0, 126.5,
129.3, 137.4 (Ph), 152.4
1
HL2 4.6–4.7 (m, 1H, thienyl), 4.7 (dd, 1H, J( H 1H) = 2.1,
–
J( H 1H) = 2.0 Hz, thienyl), 5.8 (m, 1H, thienyl), 7.3
1
–
=
(s, 1H, HC N), 7.5–7.7 (m, 2H, Ph), 7.8–7.9 (m, 3H,
=
=
Ph), 10.9 (s, 1H, NH).
(HC N), 187.4 (C O).
104.5, 112.6, 121.3, 123.2
(furanyl), 124.8, 126.7,
130.3, 176.7 (Ph), 152.4
1
HL3 4.5–4.7 (m, 1H, furanyl), 4.8 (dd, 1H, J( H 1H) = 1.8,
–
J( H 1H) = 1.7 Hz, furanyl), 5.8 (m, 1H, furanyl), 7.2
1
–
=
(s, 1H, HC N), 7.4–7.5 (m, 1H, Ph), 7.6–7.8 (m, 2H,
=
=
Ph), 7.9–8.1 (m, 1H, Ph), 10.8 (s, 1H, NH), 12.4 (s,
(HC N), 187.4 (C O).
–
1H, OH Ph).
HL4 4.5–4.7, (m, 1H, thienyl), 4.9 (dd, 1H, J(1H–1H) = 2.1,
104.5, 112.8, 121.5, 123.3
(thienyl), 124.7, 126.9,
130.4, 176.6 (Ph), 152.4
J( H 1H) = 2.0 Hz, thienyl), 5.7 (m, 1H, thienyl), 7.4
1
–
=
(s, 1H, HC N), 7.4–7.5 (m, 1H, Ph), 7.6–7.8 (m, 2H,
=
=
Ph), 7.9–8.2 (m, 1H, Ph), 10.9 (s, 1H, NH), 12.3 (s,
(HC N), 187.5 (C O).
–
1H, OH Ph).
1
HL5 4.5–4.7 (m, 1H, furanyl), 4.7 (dd, 1H, J( H 1H) = 1.8,
104.4, 112.6, 121.4, 123.0
(furanyl), 126.8, 167.8
–
J( H 1H) = 1.7 Hz, furanyl), 5.9 (m, 1H, furanyl), 7.5
1
–
=
=
(s, 1H, HC N), 7.6–7.8 (m, 2H, Py), 8.3–8.5 (m, 2H,
(Py), 152.4 (HC N),
=
Py), 10.7 (s, 1H, NH).
187.4 (C O).
1
HL6 4.6–4.8 (m, 1H, thienyl), 4.9 (dd, 1H, J( H 1H) = 2.1,
104.5, 112.6, 121.3, 123.2
(thienyl), 126.7, 167.8
–
J( H 1H) = 2.0 Hz, thienyl), 5.8 (m, 1H, thienyl), 7.3
1
–
=
=
(s, 1H, HC N), 7.7–7.9 (m, 2H, Py), 8.4–8.6 (m, 2H,
(Py), 152.4 (HC N),
=
Py), 10.8 (s, 1H, NH).
187.5 (C O).
1
(1) 4.6–4.8 (m, 1H, furanyl), 4.9 (dd, 1H, J( H 1H) = 1.9,
104.6, 112.7, 121.5, 123.3
(furanyl), 124.9, 126.8,
129.2, 137.5 (Ph), 152.8
–
J( H 1H) = 1.8 Hz, furanyl), 5.9 (m, 1H, furanyl), 7.4
1
–
=
(s, 1H, HC N), 7.6–7.7 (m, 2H, Ph), 7.9–8.2 (m, 3H,
–
=
Ph).
(HC N), 190.1 (C O).
1
(5) 4.7–4.8 (m, 1H, thienyl), 4.9 (dd, 1H, J( H 1H) = 2.2,
104.8, 112.6, 121.6, 123.3
(thienyl), 125.2, 126.6,
129.3, 137.5 (Ph), 152.7
–
J( H 1H) = 2.1 Hz, thienyl), 6.1 (m, 1H, thienyl), 7.6
1
–
=
(s, 1H, HC N), 7.7–7.8 (m, 2H, Ph), 7.9–8.1 (m, 3H,
–
=
Ph).
(HC N), 190.3 (C O).
1
(9) 4.6–4.8 (m, 1H, furanyl), 4.9 (dd, 1H, J( H 1H) = 1.9,
104.6, 112.8, 121.5, 123.3
(furanyl), 124.9, 126.8,
130.5, 176.9 (Ph), 152.8
–
J( H 1H) = 1.8 Hz, furanyl), 5.9 (m, 1H, furanyl), 7.5
1
–
=
(s, 1H, HC N), 7.6–7.7 (m, 1H, Ph), 7.8–7.9 (m, 2H,
–
–
–
=
Ph), 8.1–8.3 (m, 1H, Ph), 12.6 (s, 1H, OH Ph).
(HC N), 190.2 (C O).
1
(13) 4.6–4.8 (m, 1H, thienyl), 5.1 (dd, 1H, J( H 1H) = 2.2,
104.7, 112.8, 121.6, 123.5
(thienyl), 124.8, 126.9,
130.5, 176.8 (Ph), 152.8
J( H 1H) = 2.1 Hz, thienyl), 5.8 (m, 1H, thienyl), 7.5
1
–
=
(s, 1H, HC N), 7.6–7.7 (m, 1H, Ph), 7.8–7.9 (m, 2H,
–
–
=
Ph), 8.1–8.3 (m, 1H, Ph), 12.2 (s, 1H, OH Ph).
(HC N), 190.3 (C O).
(continued)

ORDER
REPRINTS
10
CHOHAN
Table 4. Continued
1H NMR(DMSO-d6) (ppm)
No
13C NMR (DMSO-d6) (ppm)
1
(17) 4.6–4.8 (m, 1H, furanyl), 4.9 (dd, 1H, J( H 1H) = 1.9,
104.5, 112.8, 121.5, 123.3
(furanyl), 126.8, 167.9
–
J( H 1H) = 1.8 Hz, furanyl), 5.9 (m, 1H, furanyl), 7.7
1
–
=
=
(s, 1H, HC N), 7.9–8.1 (m, 2H, Py), 8.4–8.6 (m, 2H,
(Py), 152.8 (HC N),
–
Py).
190.2 (C O).
1
(21) 4.7–4.9 (m, 1H, thienyl), 5.1 (dd, 1H, J( H 1H) = 2.2,
104.6, 112.8, 121.5, 123.3
(thienyl), 126.9, 167.9,
–
J( H 1H) = 2.1 Hz, thienyl), 5.9 (m, 1H, thienyl),
1
–
=
=
7.4 (s, 1H, HC N), 7.8–8.1 (m, 2H, Py), 8.5–8.7 (m,
(Py) 152.8 (HC N), 190.3
–
2H, Py).
(C O).
In the complexes, the aromatic and heteroaromatic proton signals appeared
downfield, as expected, due to increased conjugation on coordination (17).
13C NMR spectra (Table 4), likewise, showed similar diagnostic features (18)
for the free ligands as well as their complexes as expected. Furanyl and thienyl
carbons were found in the range 104.5–123.2 ppm, aromatic carbons at 124.8–
137.3 ppm and the azomethine carbon signal was found at 152.4 ppm. Similarly,
=
the presence of the C O signal at ∼187.4 ppm in the spectra of the ligands and
the absence of this signal in the spectra of the complexes and appearance of a signal
at lower values supported the evidence that the ligands act in an enolized form.
However, due to solubility problems it was not possible to obtain NMR spectra of
all the complexes and only a representative spectrum of the cobalt(II) complex of
each ligands was taken and reported in Table 4.
Magnetic Moments and Electronic Spectra
UV–visspectralbandsofthecomplexesarerecordedinTable3. Thecobalt(II)
complexes show magnetic moment values of 4.85–4.93 B.M. at room temperature.
These high values of the magnetic moments and the stoichiometries suggest a co-
ordination number of six for the central cobalt(II) ion and an octahedral geometry.
The electronic spectra of these complexes are also consistent with their octahedral
environment around the cobalt(II) ion. The spectra display two bands at ∼20,920
4
4
and ∼28,570 cm−1 attributed to 4T1g → T1g and 4T1g → T2g transitions, respec-
tively, in a high-spin octahedral geometry (19,20).
The copper(II) complexes exhibit magnetic moments of 1.55–1.78 B.M.,
respectively, at room temperature. These values are quite close to the spin-allowed
values expected for a S =1/2 system and may be indicative of a distorted octa-
hedral geometry around copper(II) ions. These copper(II) complexes deisplay a
2
broad band at ∼14,920 cm−1 due to 2B1g → Eg and two bands at ∼16,390 and

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
11
R
R = Ph; X = O (L1)
R = Ph; X = S (L2)
C
N
O
X
R = PhOH-o; X = O (L3)
R = PhOH-o; X = S (L4)
R = Py; X = O (L5)
R = Py; X = S (L6)
N
HC
CH
M
O
N
X
N
M = Co(II), Cu(II), Ni(II) or Zn(II)
C
R
Figure 3. Proposed structure of the metal(II) complexes.
∼27,250 cm−1 assigned to d–d transitions and a charge transfer band, respectively,
of a distorted octahedral environment (21,22).
Theelectronicspectraofthenickel(II)complexesexhibitedabsorptionbands
3
3
3
at ∼16,670 and ∼27,780 cm−1, attributable to A2g → T1g (F) and A2g
→
3T1g (P), transitions, respectively, in an octahedral geometry (23,24). The calcu-
lated values of the ligand field parameters lie in the range reported for an octahedral
structure. Also, the values of the magnetic moment (3.2–3.7 B.M.) may be taken
as additional evidence for their octahedral structure.
The diamagnetic zinc(II) complexes did not show any d–d bands and their
spectra are dominated only by charge transfer bands. The charge transfer band at
2
27,550 cm−1 was assigned to the transition 2Eg → T2g, possibly in an octahedral
environment (20).
On the basis of the above observations, it is tentatively suggested that all
of the complexes show an octahedral geometry (Fig. 3) in which the two ligands
act as tridentates. These possibly accommodate themselves around the metal atom
in such a way that a stable chelate ring is formed giving, in turn, stability to the
formed metal complexes.
Antibacterial Properties
The title Schiff bases and their metal(II) chelates were evaluated for their
antibacterial activity against the standard bacterial strains of a) Escherichia coli,
b) Staphylococcus aureus, and c) Pseudomonas aeruginosa. The compunds were
tested at a concentration of 30 µg/0.01 mL in DMF solution, using the paper disc
diffusion method as earlier reported (25,26). The inhibition zones were measured
in mm and the results are reproduced in Table 5. The inhibition zones are the clear

ORDER
REPRINTS
12
CHOHAN
Table 5. Antibacterial Activity Data of the Schiff Bases and Its
Metal(II) Complexes
Microbial Speciesa
Schiff Base/
Complex
a
b
c
HL1
HL2
HL3
HL4
HL5
HL6
(1)
(2)
(3)
(4)
(5)
++
++
++
+
++
+
++
+
++
++
++
+
++
+
++
+
++
++
+++
+++
+++
+++
++++
+++
++++
++
++
+++
++
+++
++
++++
+++
+++
++
++
+++
+++
++
(6)
(7)
(8)
(9)
+++
++++
++
+++
+++
+++
+++
++++
++
+++
+++
+++
+++
++
(10)
(11)
(12)
(13)
(14)
(15)
(16)
(17)
(18)
(19)
(20)
(21)
(22)
(23)
(24)
+++
+++
++
+++
+++
++
+++
+++
++
+++
++++
+++
+++
+++
+++
+++
++++
+++
+++
+++
+++
++
++++
+++
+++
++
++
+++
++
+++
+++
++++
+++
+++
+++
++
+++
aa: E. coli; b: S. aureus; c: P. aeruginosa.
Inhibition zone diameter mm (% inhibition): +, 6–10 (27–45%);
++, 10–14 (45–64%); +++, 14–18 (64–82%); ++++, 18–22
(82–100%). Percent inhibition values are relative to the inhibition
zone (22 mm) with 100% inhibition.

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
13
zones around the discs, which were measured in mm. All the Schiff bases were
found to be biologically active and their metal(II) complexes showed significantly
enhanced antibacterial activity against one or more bacterial species in comparison
to the free Schiff bases. It is, however, known (27–29) that chelation tends to make
the ligands act as more powerful and potent bactericidal agents, thus killing more
of the bacteria than the parent Schiff bases do. It is suspected that factors such as
solubility, conductivity, dipole moment, and cell permeability mechanisms (influ-
enced by the presence of metal ions) may be the possible reasons for increasing
this activity.
EXPERIMENTAL
Material and Methods
All chemicals and solvents used were of Analar grade. All metal(II) salts
used were the dichlorides. 2-Furanecarboxaldehyde, 2-thiophenecarboxaldehyde,
benzoylhydrazine, nicotinoylhydrazine, and salicyloylhydrazine were obtained
from Merck. IR spectra were obtained as KBr discs on a Philips Analytical PU
9800 FTIR spectrophotometer. 1H-NMR and 13C NMR spectra were recorded on
a Bruker 250-MHz spectrometer in DMSO-d6. UV-vis spectra were obtained in
DMF on a Hitachi U-2000 double-beam spectrophotometer. C, H, and N anal-
yses were carried out by Butterworth Laboratories Ltd. (U.K). Conductances of
the metal complexes were determined in DMF on a Hitachi YSI-32 model con-
ductometer. Magnetic measurements were doen on the solid complexes using the
Gouy method. Melting points were recorded on a Gallenkamp apparatus and are
uncorrected.
Preparation of Schiff Base Ligands
N-(2-Furanylmethylene)benzoylhydrazine (HL1). 2-Furanecarboxal-
dehyde (0.83 mL, 0.97 g, 0.01 mol) in absolute ethanol (20 mL) was added to a
stirred ethanol solution (20 mL) of benzoylhydrazine (1.4 g, 0.01 mol). Then 2–3
drops of conc. H2SO4 were added and the mixture was refluxed for 1 h. The reaction
mixture was then cooled and left for 24 h at room temperature. During this period,
a yellow solid was formed. It was recrystallized from hot ethanol; Yield, 1.1 g.
N-(2-Thienylmethylene)benzoylhydrazine (HL2). 2-Thiophenecarbox-
aldehyde (0.93 mL, 1.12 g, 0.01 mol) in absolute ethanol (20 mL) was added to
a stirred ethanol solution (20 mL) of benzoylhydrazine (1.4 g, 0.01 mol). Then

ORDER
REPRINTS
14
CHOHAN
2–3 drops of conc. H2SO4 were added and the mixture was refluxed for 1 h. The
reaction mixture was then cooled and left for 24 h at room temperature. During
this period, a light yellow solid was formed, which was recrystallized from hot
ethanol to give the desired product; Yield 1.3 g.
All other Schiff base ligands were prepared following the same above
method.
Preparation of Metal Complexes
An ethanol solution (20 mL) of the appropriate metal(II) chloride salt
(0.001 mol) was added to a magnetically stirred ethanol solution (15 mL) of the
respective Schiff base (0.002 M). The mixture was refluxed for 2 h, then coolded
to room temperature, filtered and reduced to nearly half of its volume. The concen-
trated solution was left standing overnight at room temperature, which resulted in
the formation of a solid product. The product thus obtained was filtered, washed
with ethanol, then the ether, and dried. Crystallization in aqueous ethanol (50%)
gave the desired metal complexes.
Antibacterial Studies
Preparation of discs. The ligand/complex (30 µg) in DMF (0.01 mL) was
applied to a paper disc, (prepared from blotting paper, (3-mm diameter) with the
help of a micropipette. The discs were left in an incubator for 48 h at 37◦C and
then applied to the bacteria grown on agar plates.
Preparation of agar plates. Minimal agar was used for the growth of specific
bacterial species. For the preparation of the agar plates for E. coli, MacConkey
agar (50 g) obtained from Merck Chemical Company, was suspended in freshly
distilled water (1 L). It was allowed to soak for 15 min and the boiled on a water
bath until the agar was completely dissolved. The mixture was autoclaved from
15 min at 120◦C and then poured into previously washed and sterilized Petri dishes
and stored at 40◦C for inoculation.
Procedure of inoculation. Inoculation was done with the help of a platinum
wire loop, which was made red hot in a flame, cooled and then used for the
application of bacterial strains.
Application of discs. Sterilized forceps were used for the application of the
paper disc on the earlier inoculated agar plates. When the discs were applied,
they were incubated at 37◦C for 24 h. The zone of inhibition was then measured
(diameter in mm) around the disc.

ORDER
REPRINTS
TRANSITION METAL COMPLEXES OF SCHIFF BASE LIGANDS
ACKNOWLEDGMENT
15
TheauthorgratefullyacknowledgesthehelpoftheDepartmentofMicrobiol-
ogy, Qaid-e-Azam Medical College, Bahawalpur, in undertaking the antibacterial
studies.
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Received January 5, 2000
Accepted September 2, 2000
Referee I: P. J. Toscano
Referee II: M. Lieberman

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