Synthesis, spectroscopic, thermal, and antimicrobial studies of tetradentate 12 and 14 member Schiff bases and their complexes with Fe(III), Co(II), and Cu(II)

Article abstract of DOI:10.1080/00958972.2010.526707

Two Schiff bases, L¹ (5,6;11,12-dibenzophenone-2,3,8,9- tetramethyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene) and L² (6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradeca- 1,4,8,11-tetraene), bearing functionalized pendant arms have been synthesized by cyclocondensation of 3,4-diaminobenzophenone with 2,3-butanedione and 2,4-pentanedione, respectively. Mononuclear macrocyclic complexes [FeL ¹Cl₂]Cl, [FeL²Cl₂]Cl, [ML ¹Cl₂], and [ML²Cl₂] (where M = Co(II) and Cu(II)) have been prepared by reacting iron(III), cobalt(II), and copper(II) with the preformed Schiff base. The ligands and their corresponding metal complexes were characterized by elemental analyses, ESI-mass spectra, conductivity, magnetic moments, UV-Vis, EPR, IR, ¹H-, and ¹³C-NMR spectral studies, and TGA-DTA/DSC data. The TGA profiles exhibit a two-step pyrolysis, although the iron complexes decompose in three steps, leaving behind metal oxides as the final product. The ligands and complexes were screened invitro against Gram-positive bacteria, Gram-negative bacteria, and fungi.

Full text of DOI:10.1080/00958972.2010.526707

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Synthesis, spectroscopic, thermal, and
antimicrobial studies of tetradentate
12 and 14 member Schiff bases and
their complexes with Fe(III), Co(II), and
Cu(II)
Farha Firdaus a , Kaneez Fatma a , Mohammad Azam a
Mohammad Shakir a
&
a Division of Inorganic Chemistry, Department of Chemistry ,
Aligarh Muslim University , Aligarh 202002, Uttar Pradesh, India
Published online: 29 Oct 2010.
To cite this article: Farha Firdaus , Kaneez Fatma , Mohammad Azam & Mohammad Shakir (2010)
Synthesis, spectroscopic, thermal, and antimicrobial studies of tetradentate 12 and 14 member
Schiff bases and their complexes with Fe(III), Co(II), and Cu(II), Journal of Coordination Chemistry,
63:22, 3956-3968, DOI: 10.1080/00958972.2010.526707
To link to this article: http://dx.doi.org/10.1080/00958972.2010.526707
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Journal of Coordination Chemistry
Vol. 63, No. 22, 20 November 2010, 3956–3968
Synthesis, spectroscopic, thermal, and antimicrobial studies of
tetradentate 12 and 14 member Schiff bases and their
complexes with Fe(III), Co(II), and Cu(II)
FARHA FIRDAUS*, KANEEZ FATMA, MOHAMMAD AZAM
and MOHAMMAD SHAKIR
Division of Inorganic Chemistry, Department of Chemistry,
Aligarh Muslim University, Aligarh 202002, Uttar Pradesh, India
(Received 8 December 2009; in final form 26 July 2010)
Two Schiff bases, L1 (5,6;11,12-dibenzophenone-2,3,8,9-tetramethyl-1,4,7,10-tetraazacyclodo-
deca-1,3,7,9-tetraene) and L2 (6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraa-
zacyclotetradeca-1,4,8,11-tetraene), bearing functionalized pendant arms have been synthesized
by cyclocondensation of 3,4-diaminobenzophenone with 2,3-butanedione and 2,4-pentane-
dione, respectively. Mononuclear macrocyclic complexes [FeL1Cl2]Cl, [FeL2Cl2]Cl,
[ML1Cl2], and [ML2Cl2] (where M ¼ Co(II) and Cu(II)) have been prepared by reacting
iron(III), cobalt(II), and copper(II) with the preformed Schiff base. The ligands and their
corresponding metal complexes were characterized by elemental analyses, ESI-mass spectra,
conductivity, magnetic moments, UV-Vis, EPR, IR, 1H-, and 13C-NMR spectral studies, and
TGA-DTA/DSC data. The TGA profiles exhibit a two-step pyrolysis, although the iron
complexes decompose in three steps, leaving behind metal oxides as the final product. The
ligands and complexes were screened in vitro against Gram-positive bacteria, Gram-negative
bacteria, and fungi.
Keywords: Antimicrobial studies; Pendant arm; Physico-chemical studies; Schiff-base ligands;
Thermal studies
1. Introduction
Macrocyclic ligands have received attention due to their ability to discriminate among
closely related metal ions based on metal ion radius (ring size effect) [1, 2] and
significant enhancement in complex stability constants (macrocyclic effect) [1–3].
Different types of macrocyclic ligands are particularly exciting because of their
importance in generating new areas of fundamental and applied chemistry [4]. The most
*Corresponding author. Email: farha_firdaus@yahoo.co.in
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.526707

12 and 14 member Schiff bases
3957
interesting aspect of macrocyclic ligands are nature, number, and arrangement of the
ligand donors as well as ligand conjugation, substitution, and flexibility [5, 6]. The
availability of a number of structural derivatives and the ability to complex a large
number of metal ions in differing oxidation states have made these ligands attractive for
further investigations. Interest in macrocycles with pendant arms is growing for their
unique coordination and structural properties, their utility in enzyme-mimicking studies
and catalysis and their rapidly growing applications as radiopharmaceuticals, magnetic
resonance imaging reagents, and fluorescent probes [7–11]. The chemistry of macro-
cyclic tetraaza ligands bearing pendant coordinating side arms is a fascinating area of
research [12], since such ligands show enhanced thermodynamic and kinetic stabilities
due to their modified complexation properties relative to simple macrocyclic precursors
[9–13]. Introduction of pendant arms into the macrocyclic framework can enhance the
selectivity of the ligand for a given ion and allow for fine-tuning of the properties of the
complexes [14]. Properties and coordinating geometries of the complexes of these
ligands are influenced by position and number of the functional groups [12]. For N- and
C-based macrocyclic ligands, the mode of metal incorporation is very similar to that
of metalloproteins in which the requisite metals is bound in a macrocyclic cavity or
cleft produced by the conformational arrangement of the protein [11, 15]. A variety
of Schiff-base macrocyclic ligands and their complexes have been synthesized
[16], prompting us to prepare functionalized macrocyclic ligands, (L1): 5,6;11,12-
dibenzophenone-2,3,8,9-tetramethyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene and
(L2): 6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradeca-
1,4,8,11-tetraene by condensation of 3,4-diaminobenzophenone with 2,3-butanedione
and 2,4-pentanedione, respectively.
2. Experimental
Anhydrous FeCl3, CoCl2 Á 6H2O and CuCl2 Á 2H2O (E. Merck) were commercially
available as pure samples. The chemicals 2,3-butanedione, 2,4-pentanedione and 3,4-
diaminobenzophenone (Fluka) were used as received. Methanol (AR grade) was used as
solvent without purification.
2.1. Synthesis of 5,6;11,12-dibenzophenone-2,3,8,9-tetramethyl-1,4,7,10-tetraazacy-
clododeca-1,3,7,9-tetraene (L1)/6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-
1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene (L2)
To a stirring methanol solution (25 mL) of 3,4-diaminobenzophenone (3 mmol, 0.636 g),
2,3-butanedione (3 mmol, 0.27 mL)/2,4-pentanedione (3 mmol, 0.31 mL) was added
dropwise with constant stirring. The mixture was later refluxed for 12 h. The reaction
mixture was allowed to evaporate resulting in isolation of a dark yellow solid on
standing for 50 h. The product was filtered off, washed with methanol, and dried
in vacuum.

3958
F. Firdaus et al.
2.2. Synthesis of complexes, ([FeL1Cl2]Cl and [ML1Cl2])/([FeL2Cl2]Cl and
[ML2Cl2]) Dichloro[5,6;11,12-dibenzophenone-2,3,8,9-tetramethyl-1,4,7,
10-tetraazacyclododeca-1,3,7,9-tetraene]iron(III) chloride and metal chloride/
dichloro[6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclo-
tetradeca-1,4,8,11-tetraene]iron(III) chloride and metal chloride [M ¼ Co(II)
and Cu(II)]
A methanol solution (25 mL) of L1 or L2 (1 mmol) and equimolar amount of metal salt
(1 mmol) in methanol (25 mL) were reacted under reflux with constant stirring for 15 h.
The reaction mixture thus obtained was continually evaporated leading to isolation of
solid products. The product thus formed was filtered, washed several times with
methanol, and dried in vacuum.
2.3. Organism culture and in vitro screening of the ligands and metal complexes
Antibacterial activity of the synthesized compounds was completed by disc diffusion.
The macro-dilution test with standard inoculums of 105 CFU mLꢀ1 was used to assess
the minimum inhibitory concentration (MIC) of the test compounds. DMSO was the
solvent. Serial dilutions of the compounds were prepared to the final concentrations of
512, 256, 128, 64, 32, 16, 8, 4, 2, and 1 mg Lꢀ1. These tubes were kept at 37ꢁC for 18 h.
For assaying antifungal activity, Candida albicans, Candida krusei, Candida parapsilosis,
and Cryptococcus neoformans were inoculated in Sabouraud Dextrose broth medium
(Hi-Media, Mumbai) and incubated for 24 h at 35ꢁC; subsequently, a suspension of
106 CFU mLꢀ1 was prepared in sterile saline solution according to the McFarland
protocol.
2.4. Physical measurement
Elemental analyses were recorded on a Perkin Elmer 2400 CHN elemental analyzer; 1H-
and 13C-NMR spectra were recorded in DMSO-d6 using a Bruker Avance II 400 NMR
spectrometer from SAIF, Panjab University, Chandigarh, India. FT-IR (4000–
200 cmꢀ1) was recorded as KBr/CsI discs on a Perkin Elmer 621 spectrophotometer.
ESI-mass spectra were recorded on a Micromass Quattro II Triple Quadruple mass
spectrometer. Electronic spectra of the complexes in DMSO were recorded on a Pye-
Unicam 8800 spectrophotometer at room temperature. EPR spectra were recorded at
room temperature on a Varian E-4 X-band spectrometer using DPPH as the g-marker
from SAIF IIT-Madras, Chennai, India. Metals and chlorides were estimated
volumetrically [17] and gravimetrically [18], respectively. Magnetic susceptibility
measurements were carried out using a Faraday balance at room temperature. The
molar conductivity data for 10ꢀ3 mol Lꢀ1 solutions in DMSO were recorded on a
Systronic type 302 conductivity bridge thermostated at 25.00ꢁC ꢂ 0.05ꢁC. TGA–DTA
and DSC were performed on a Shimadzu Thermal Analyzer under nitrogen using
alumina powder as reference.

12 and 14 member Schiff bases
3959
3. Results and discussion
Two functionalized Schiff-base macrocyclic ligands, L1 and L2, have been synthesized
by condensation between 3,4-diaminobenzophenone and 2,3-butanedione or 2,4-
pentanedione in 1 : 1 molar ratio in methanol. The ligands formed are solid and
remained unchanged for extended times in air and were found to be soluble in almost all
polar solvents. The purities of the ligands and complexes were checked by TLC on silica
gel-coated plates using benzene (85%), methanol (10%) and acetic acid (5%) as eluent.
Only one spot was observed after developing in an iodine chamber, indicating purity of
all the complexes. However, attempts to grow single crystals suitable for X-ray
crystallography failed. The formation of these macrocyclic ligand frameworks was
confirmed based on elemental analyses, characteristic bands in the FT-IR (table 6), and
resonances in the 1H- and 13C-NMR spectra (tables S1 and S2; Supplementary
material). The positions of molecular ion peaks in the mass spectra (figures 1 and 2)
were consistent with the empirical molecular formula (table 1).
Mononuclear macrocyclic complexes [FeL1Cl2]Cl, [FeL2Cl2]Cl, [ML1Cl2], and
[ML2Cl2], where M ¼ Co(II) and Cu(II) (scheme 1), were obtained by reaction of L1
and L2 with transition metal ions in 1 : 1 molar ratio. All the macrocyclic complexes are
solid, stable to the atmosphere and soluble in polar solvents. Elemental analyses agree
well with the suggested macrocyclic frameworks. Formation of tetraimine macrocyclic
complexes were further confirmed by mass, FT-IR, 1H- and 13C-NMR data; electronic
and electronic paramagnetic resonance spectral studies and magnetic moments gave the
geometry around the metal ions.
The thermal analyses and molar conductance data (table 1) of the complexes indicate
the non-electrolytic nature of Co(II) and Cu(II) complexes while those for Fe(III)
complexes correspond to a 1 : 1 electrolyte [19].
3.1. In vitro antimicrobial activity of synthesized compounds
The in vitro antibacterial activities of L1, L2, and all the complexes were tested using the
bacterial cultures of Streptococcus mutans, methicillin-resistant Staphylococcus aureus
(MRSA þve), Streptococcus pyogenes, Pseudomonas aeruginosa, Salmonella typhimur-
ium, Escherichia coli and fungal cultures of C. albicans, C. krusei, C. parapsilosis, and
Cr. neoformans by the disc diffusion method [20] and then the MICs were determined.
Chloramphenicol (30 mg) and fluconazole were used as positive control in the case of
bacterial strains and fungi, respectively. The MICs were assessed by the macro-dilution
test using standard inoculums of 105 CFU mLꢀ1. The susceptibility was assessed on the
basis of diameter of zone of inhibition against Gram-positive and Gram-negative
strains of bacteria and fungi. The zones of inhibition (mm) of every compound against
Gram-positive and Gram-negative strains of bacteria are shown in table 2 and MIC
data in table 3. Biological activities show that L1 and L2 are biologically active and their
metal complexes are more active. L2 and its complexes were highly active against
bacterial strains in comparison to L1 and its complexes. Cobalt(II) complexes were the
best antibacterial complexes while iron(III) and copper(II) complexes were moderate in
activity. The MIC confirmed [CoL2Cl2] to be the most active. Zones of inhibition for
different fungal strains are shown in table 4 and MIC data in table 5. The in vitro
antifungal activity assay showed that L1 and its metal complexes were more active than

3960
F. Firdaus et al.
Figure 1. Mass spectrum of [CuL1Cl2].
Figure 2. Mass spectrum of [CuL2Cl2].
L2 and its metal complexes. The metal complexes were more active against fungi than
the Schiff bases. The cobalt(II) complexes showed moderate activity against all fungal
strains, iron(III) complexes show better inhibition and copper(II) complexes show
excellent activity against fungal growth.

12 and 14 member Schiff bases
3961
Table 1. The m/z, color, yield, melting point and molar conductance values of the complexes.
Compounds
m/z found (Calcd)
Color
Yield (%)
Ãm (molꢀ1 cm2 ꢀꢀ1
)
m.p. (ꢁC)
L1
524.5 (524.6)
552.6 (552.6)
686.3 (686.8)
714.6 (714.8)
655.0 (654.4)
682.2 (682.5)
658.8 (659.0)
688.0 (687.1)
Dark yellow
Dark brown
Black
Black
Dark yellow
Black
65
68
60
62
61
62
55
58
–
–
175
160
180
180
250
280
200
285
L2
[FeL1Cl2]Cl
[FeL2Cl2]Cl
[CoL1Cl2]
[CoL2Cl2]
[CuL1Cl2]
[CuL2Cl2]
50
50
20
26
31
18
Dark brown
Black
3.2. Analytical results
Anal. Calcd for L1 (%): C, 77.84; H, 5.37; N, 10.67. Found: C, 77.31; H, 5.05; N, 10.15.
Anal. Calcd for L2 (%): C, 78.23; H, 5.83; N, 10.13. Found: C, 77.83; H, 5.51;
N, 9.66. Anal. Calcd for [FeL1Cl2]Cl (%): Fe, 8.13; Cl, 15.48; C, 59.45; H, 4.10; N, 8.15.
Found: Fe, 7.90; Cl, 15.16; C, 59.23; H, 4.00; N, 8.01. Anal. Calcd for [FeL2Cl2] Cl (%):
Fe, 7.81; Cl, 14.87; C, 68.48; H, 4.51; N, 7.83. Found: Fe, 7.52; Cl, 14.55; C, 68.07; H,
4.22; N, 7.61. Anal. Calcd for [CoL1Cl2] (%): Co, 9.00; Cl, 10.83; C, 62.39; H, 4.31; N,
8.56. Found: Co, 8.78; Cl, 10.53; C, 62.07; H, 4.11; N, 8.13. Anal. Calcd for [CoL2Cl2]
(%): Co, 8.63; Cl, 10.38; C, 63.35; H, 4.72; N, 8.20. Found: Co, 8.41; Cl, 10.06; C, 63.12;
H, 4.51; N, 8.00. Anal. Calcd for [CuL1Cl2] (%): Cu, 9.64; Cl, 10.75; C, 61.96; H, 4.28;
N, 8.50. Found: Cu, 9.22; Cl, 10.43; C, 61.52; H, 4.06; N, 8.10. Anal. Calcd for
[CuL2Cl2] (%): Cu, 9.24; Cl, 10.31; C, 62.92; H, 4.69; N, 8.15. Found: Cu, 9.00; Cl,
10.10; C, 62.72; H, 4.38; N, 7.81.
3.3. IR spectra
The formation of both L1 and L2 by condensation of 3,4-diaminobenzophenone and
alkyl diketones have been confirmed by the appearance of strong bands at 1645 and
1595 cmꢀ1, characteristic of imine ꢀ(C¼N) [21]. The position of this band is shifted by
15–20 cmꢀ1 in all metal complexes as compared to free ligands, indicating participation
of the imine nitrogen in coordination [22]. The mode of coordination is further
supported by the absence of a band at ꢃ3400 cmꢀ1, a characteristic of ꢀ(NH2) of 3,4-
diaminobenzophenone. The band assigned to pendant carbonyl groups of 3,4-
diaminobenzophenone were at 1707–1728 cmꢀ1 [23]. Formation of the macrocyclic
framework has been further deduced by two sharp bands at 418–426 cmꢀ1 and 315–
333 cmꢀ1 assigned to ꢀ(M–N) and ꢀ(M–Cl), respectively [24]. All the complexes show
bands at 2847–2890 cmꢀ1 and 1408–1444 cmꢀ1 corresponding to ꢀ(C–H) stretching and
ꢁ(C–H) bending modes, respectively. Bands corresponding to phenyl ring vibrations
appear at their proper positions (table 6).
3.4. 1H-NMR spectra
The formation of Schiff-base macrocyclic ligands L1 and L2 has been further supported
1
by proton magnetic resonance spectra. H-NMR spectra of the ligands do not show a

3962
F. Firdaus et al.
O
C
X
H C
CH
3
3
NH
2
2
+
2
O
O
NH
2
MeOH
CH
H C
3
3
X
O
C
O
C
N
N
N
N
(B)
(A)
(B)
(A)
X
CH
H C
3
3
1
2
L and L
[MCl ]
2
or
[FeCl ]
3
n+
CH
H C
3
3
X
O
O
Cl
C
C
N
N
N
M
Cl
N
(A)
(B)
(A)
(B)
X
CH
H C
3
3
1
2
X= 0 for L ; X= CH for L
2
n = 1, M = Fe(III)
n = 0, M = Co(II) and Cu(II)
Scheme 1. Preparation and structures of L1 and L2 and their metal complexes.

12 and 14 member Schiff bases
Table 2. Antibacterial activity of the complexes.
Gram-positive bacteria
3963
Gram-negative bacteria
Compounds
S. mutans
S. pyogenes
S. aureus
P. aeruginosa
S. typhimurium
E. coli
L1
10.9 ꢂ 0.4
12.9 ꢂ 0.5
13.5 ꢂ 0.2
12.3 ꢂ 0.5
14.5 ꢂ 0.2
21.4 ꢂ 0.5
22.1 ꢂ 0.2
20.4 ꢂ 0.2
26.8 ꢂ 0.5
–
10.2 ꢂ 0.8
12.5 ꢂ 0.3
14.4 ꢂ 0.1
12.8 ꢂ 0.3
14.3 ꢂ 0.3
20.1 ꢂ 0.5
22.3 ꢂ 0.7
19.3 ꢂ 0.3
22.4 ꢂ 0.4
–
11.8 ꢂ 0.8
11.9 ꢂ 0.5
15.3 ꢂ 0.2
13.1 ꢂ 0.4
14.5 ꢂ 0.5
19.1 ꢂ 0.2
21.5 ꢂ 0.4
19.9 ꢂ 0.3
21.0 ꢂ 0.5
–
10.3 ꢂ 0.2
11.5 ꢂ 0.4
16.1 ꢂ 0.5
8.8 ꢂ 0.l
13.1 ꢂ 0.5
18.1 ꢂ 0.5
17.2 ꢂ 0.3
19.2 ꢂ 0.2
17.1 ꢂ 0.2
–
10.1 ꢂ 0.5
10.2 ꢂ 0.5
17.3 ꢂ 0.2
14.8 ꢂ 0.2
14.1 ꢂ 0.3
19.2 ꢂ 0.2
21.4 ꢂ 0.5
20.4 ꢂ 0.2
25.2 ꢂ 0.8
–
10.1 ꢂ 0.5
11.9 ꢂ 0.5
18.5 ꢂ 0.2
13.6 ꢂ 0.2
15.4 ꢂ 0.2
21.8 ꢂ 0.5
23.5 ꢂ 0.4
21.5 ꢂ 0.2
20.0 ꢂ 0.2
–
[FeL1Cl2]Cl
[CoL1Cl2]
[CuL1Cl2]
L2
[FeL2Cl2]Cl
[CoL2Cl2]
[CuL2Cl2]
Chloramphenicol
DMSO
Positive control chloramphenicol and negative control DMSO measured by the Halo Zone Test (Unit, mm).
Table 3. MIC of the complexes, positive control chloramphenicol.
Gram-positive bacteria
Gram-negative bacteria
Compounds
S. mutans
S. pyogenes
S. aureus
P. aeruginosa
S. typhimurium
E. coli
L1
512
512
512
512
512
128
128
256
32
512
512
256
512
512
128
64
512
512
256
512
256
128
64
512
512
64
512
512
32
32
32
32
512
512
256
512
512
128
128
128
32
512
512
64
512
128
32
32
32
32
[FeL1Cl2]Cl
[CoL1Cl2]
[CuL1Cl2]
L2
[FeL2Cl2]Cl
[CoL2Cl2
[CuL2Cl2]
Chloramphenicol
128
32
128
32
Table 4. Antifungal activity of the complexes.
Compounds
C. albicans
C. krusei
C. parapsilosis
Cr. neoformans
L1
13.7 ꢂ 0.5
15.6 ꢂ 1.4
14.5 ꢂ 0.5
21.3 ꢂ 1.2
12.5 ꢂ 0.2
15.5 ꢂ 0.5
12.8 ꢂ 0.2
18.1 ꢂ 0.2
20.0 ꢂ 0.5
–
12.8 ꢂ 0.3
14.8 ꢂ 0.2
12.7 ꢂ 0.4
18.6 ꢂ 0.4
11.5 ꢂ 0.4
13.4 ꢂ 1.2
11.5 ꢂ 0.3
16.2 ꢂ 0.2
20.0 ꢂ 0.5
–
12.7 ꢂ 0.3
12.9 ꢂ 0.3
11.8 ꢂ 0.4
17.7 ꢂ 0.4
11.8 ꢂ 0.2
12.7 ꢂ 0.2
11.4 ꢂ 0.4
15.2 ꢂ 0.2
18.0 ꢂ 0.5
–
11.1 ꢂ 0.2
11.8 ꢂ 1.2
10.1 ꢂ 0.5
16.8 ꢂ 0.2
10.9 ꢂ 0.4
12.6 ꢂ 0.5
10.8 ꢂ 1.2
12.2 ꢂ 0.2
19.0 ꢂ 0.5
–
[FeL1Cl2]Cl
[CoL1Cl2]
[CuL1Cl2]
L2
[FeL2Cl2]Cl
[CoL2Cl2]
[CuL2Cl2]
Fluconazole
DMSO
Positive control (fluconazole) and negative control (DMSO) measured by the Halo Zone
Test (Unit, mm)
signal corresponding to primary amino protons of the condensed 3,4-diaminobenzo-
phenone, suggesting that the proposed frameworks have been formed. Spectra of
L1 and L2 exhibit singlets at 2.15 and 2.19 ppm assigned to methyl protons (CH3, 12H)
[21] of the condensed 2,3-butanedione and 2,4-pentanedione moieties, respectively;

3964
F. Firdaus et al.
Table 5. MIC of the complexes, positive control fluconazole.
Compounds
C. albicans
C. krusei
C. parapsilosis
Cr. neoformans
L1
32
8
16
2
32
8
32
4
512
256
512
128
512
512
512
256
64.0
128
128
512
16
512
128
512
32
512
512
512
32
512
128
512
128
8.0
[FeL1Cl2]Cl
[CoL1Cl2]
[CuL1Cl2]
L2
[FeL2Cl2]Cl
[CoL2Cl2]
[CuL2Cl2]
Fluconazole
1.0
8.0
Table 6. IR spectral data (cmꢀ1) of the complexes.
Compounds
ꢀ(C¼N)
ꢀ(C¼O)
ꢀ(M–N)
ꢀ(C–H)
ꢀ(M–Cl)
Ring vibrations
L1
1645(s)
1595(s)
1620(s)
1578(s)
1630(s)
1575(s)
1620(s)
1580(s)
1718
1725
1722
1707
1720
1728
1710
1716
–
–
2868
2880
2847
2850
2890
2885
2872
2860
–
–
1430, 1092, 728
1440, 1098, 735
1455, 1100, 720
1460, 1095, 725
1448, 1105, 732
1435, 1090, 740
1458, 1110, 730
1450, 1108, 738
L2
[FeL1Cl2]Cl
[FeL2Cl2]Cl
[CoL1Cl2]
[CoL2Cl2]
[CuL1Cl2]
[CuL2Cl2]
420(m)
422(m)
426(m)
419(m)
425(m)
418(m)
328
333
315
330
320
325
s, strong intensity band; m, medium intensity band.
a singlet at 3.27 ppm corresponds to methylene protons (C–CH2–C, 4H) of the
condensed 2,4-pentanedione moiety in L2. Resonances corresponding to various
aromatic ring protons [25] appear at their appropriate positions (table S1).
3.5. 13C-NMR spectra
13C-NMR spectra have strong resonances at 155.6 and 160.0 ppm assigned to imine
carbons (C¼N) [26] of L1 and L2, respectively. Resonances at 22.7 and 18.7 ppm
correspond to methyls of L1 and L2, respectively. Another resonance at 44.8 ppm is
due to methylene carbon of condensed 2,4-pentanedione moiety. Chemical shifts due to
3,4-diaminobenzophenone carbons [27] are listed in table S2.
3.6. EPR spectra
EPR spectra of the polycrystalline Cu(II) complexes were recorded at room temper-
ature and at liquid nitrogen temperature and their g and g values calculated
?
(Supplementary material). Both [CuL1Cl2] and [CuL2Cl2] exhibit a similar single broad
signal (Supplementary material). The absence of hyperfine lines may be due to strong
dipolar and exchange interactions between copper(II) ions in the unit cell [28]. The
calculated g values of 2.135 and 2.130 and g values of 2.037 and 2.041 for [CuL1Cl2]
?
and [CuL2Cl2], respectively, suggest that the unpaired electron is in the dx2ꢀy2

12 and 14 member Schiff bases
3965
orbital [29]. The g 4 g for the complexes show that the unpaired electron is localized in
?
the dx2ꢀy2 orbital of Cu(II) characteristic of axial symmetry [30]. Tetragonally elongated
geometry is thus confirmed [31].
The G values related by the expression G ¼ (g ꢀ 2)/(g ꢀ 2) measuring the exchange
?
interaction between metal centers in polycrystalline solids have also been calculated.
According to Hathaway and Billing, if G 4 4 the exchange interaction is negligible, but
if G 5 4, considerable interaction occurs in the complexes [32]. The complexes reported
here have G values of 1.048 and 1.043 for [CuL1Cl2] and [CuL2Cl2], indicating
considerable exchange interaction among the Cu(II) ions in these complexes.
3.7. Electronic spectra and magnetic moments
Electronic spectra of [FeL1Cl2]Cl and [FeL2Cl2]Cl show three spectral bands,
17,900 cmꢀ1 (" ¼ 51 L molꢀ1 cmꢀ1), 19,900 cmꢀ1 (" ¼ 58 L molꢀ1 cmꢀ1), 24,000 cmꢀ1
(" ¼ 60 L molꢀ1 cmꢀ1
)
and
17,200 cmꢀ1
(" ¼ 53 L molꢀ1 cmꢀ1),
20,000 cmꢀ1
(" ¼ 59 L molꢀ1 cmꢀ1), 23,760 cmꢀ1 (" ¼ 63 L molꢀ1 cmꢀ1), which may be assigned to
4
6
4
6
4
4
6A1g ! T1g, A1g ! T2g, A1g ! A1g, Eg transitions, respectively. These bands are
consistent with octahedral geometry [33] around Fe(III), which is further supported
by the observed magnetic moment of 5.9 B.M. for [FeL1Cl2]Cl and 5.8 B.M. for
[FeL2Cl2]Cl.
Electronic spectra of the cobalt complexes exhibit two absorption bands at 8100 cmꢀ1
(" ¼ 13 L molꢀ1 cmꢀ1), 16,700 cmꢀ1 (" ¼ 17 L molꢀ1 cmꢀ1) for [CoL1Cl2] and 9160 cmꢀ1
(" ¼ 12 L molꢀ1 cmꢀ1), 17,240 cmꢀ1 (" ¼ 15 L molꢀ1 cmꢀ1) for [CoL2Cl2], comparable
to the characteristic features of distorted octahedral Co(II) complexes [34], which may
4
4
be reasonably assigned to 4T1g(F) ! T2g(F) (ꢀ1) and 4T1g(F)! A2g(F) transitions. The
observed magnetic moments of 4.8 and 4.9 B.M. further complement the electronic
spectral findings.
Electronic spectra of Cu(II) complexes show bands at 13,899 cmꢀ1
(" ¼ 30 L molꢀ1 cmꢀ1) and 16,720 cmꢀ1 (" ¼ 45 L molꢀ1 cmꢀ1) for [CuL1Cl2] and
14,012 cmꢀ1 (" ¼ 33 L molꢀ1 cmꢀ1
)
and 16,600 cmꢀ1 (" ¼ 49 L molꢀ1 cmꢀ1
)
for
[CuL2Cl2]. These may be assigned to B1g ! A1g and B1g ! Eg transitions,
2
2
2
2
2
2
respectively. Because of low intensity of B1g ! B2g, this band is usually not observed
as a separate band in tetragonally distorted complexes [35]. The geometry of the Cu(II)
complexes is further supported by the magnetic moment values [24] of 1.8 and 1.9 B.M.
for [CuL1Cl2] and [CuL2Cl2], respectively.
3.8. Thermal analysis by TGA–DTA/DSC
The observed percentage weight losses corresponding to various steps in all thermo-
grams are compared with those calculated [36]. The TGA of L1 and L2 consist of two
well-defined stages. The first starts at 250–329ꢁC and 200–358ꢁC in L1 and L2,
respectively, corresponding to degradation of two pendant groups (2C7H5O) contrib-
uting 39.72% (Calcd 40.07%) and 38% (Calcd 38.03%) weight loss of L1 and L2,
respectively. The initial decomposition of the exocyclic rings is common in such
complexes [37]. The second stage from 402ꢁC to 650ꢁC and 440–670ꢁC consists of

3966
F. Firdaus et al.
degradation of the remaining part with estimated loss of 59.32% (Calcd 60.28%) and
61.63% (Calcd 62.00%) in L1 and L2, respectively.
The DTA curves of L1 and L2 show endothermic peaks at 347ꢁC and 525ꢁC,
respectively, which may be assigned to loss of pendant moieties. Other endothermic
peaks at 543ꢁC and 649ꢁC correspond to decompositions of the whole L1 and L2,
respectively.
The DSC profiles of L1 and L2 exhibit exothermic peaks at 245–325ꢁC and an
endothermic peak at 500–569ꢁC due to pyrolysis of the whole organic moiety.
The metal complexes exhibit similar thermal decompositions. Complexes of Co(II)
and Cu(II) show two stage thermograms, 280–447ꢁC and 507–685ꢁC. The first stage
accounts for 11% weight loss corresponding to the removal of chlorides and the second
stage is consistent with degradation of the remaining compound. TGA of Fe(III)
complexes show three well-defined stages. The first stage at 170–190ꢁC continuing to
200–248ꢁC corresponds to loss of one chloride outside the coordination sphere (4.92%,
Calcd 5.16% and 4.73%, Calcd 4.95%) in [FeL1Cl2]Cl and [FeL2Cl2]Cl, respectively.
The second stage between 300ꢁC and 410ꢁC may be due to loss of two coordinated
chlorides corresponding to 9.98% (Calcd 10.88%) and 10.01% (Calcd 10.88%) and the
final peak 585–700ꢁC may be assigned to the loss of organic ligand in [FeL1Cl2]Cl and
[FeL2Cl2]Cl. TGA curves of all the complexes show a straight horizontal line even on
heating to 850ꢁC indicating formation of metal oxide residue [38].
The DTA curves of the complexes show endothermic peaks at 313–440ꢁC assigned to
loss of coordinated chlorides. The broad endothermic peak obtained between 501ꢁC
and 638ꢁC is due to decomposition and formation of metal oxides. The DTA of
[FeL1Cl2]Cl and [FeL2Cl2]Cl complexes exhibit a small endotherm at 195ꢁC and 230ꢁC,
respectively, due to loss of one chloride outside the coordination sphere.
In the DSC plots, a small endothermic peak at 296–320ꢁC is due to liberation of
chlorides, while endothermic peak at 399–450ꢁC is due to pyrolysis of the whole moiety
with well-defined exotherms at 505–595ꢁC corresponding to formation of metal oxides
[39]. Strictly horizontal levels between 450ꢁC and 500ꢁC are not possible for [FeL1Cl2]Cl
and [FeL2Cl2]Cl due to loss of iron chloride. A new level extending from 500ꢁC to
600ꢁC corresponding to ferric oxide was observed. These oxides decompose at high
temperature and regain their initial weight at 811ꢁC.
4. Conclusion
Iron(III), cobalt(II), and copper(II) complexes with two Schiff-base ligands, L1 and L2,
bearing functionalized pendant arms have been synthesized by cyclocondensation of
3,4-diaminobenzophenone with 2,3-butanedione and 2,4-pentanedione. The synthesized
Schiff bases are tetradentate through coordination of azomethine to metal. Octahedral
geometry for Fe(III) complexes and distortion from octahedral geometry for Co(II) and
Cu(II) complexes have been assigned on the basis of elemental, thermal, and spectral
data. The antimicrobial activities of all the complexes indicate that they are active
against a series of pathogens and the metal complexes are more active than their
respective parent ligands.

12 and 14 member Schiff bases
3967
Acknowledgments
The authors acknowledge The Chairman, Department of Chemistry, Aligarh
Muslim University, Aligarh, India for providing necessary research facilities.
They are grateful to Dr Asad Ullah Khan, Interdisciplinary Biotechnology
Unit, Aligarh Muslim University, Aligarh for performing antimicrobial activity and
SAIF, Panjab University Chandigarh, India for providing, NMR and elemental
analysis, and to SAIF IIT-Madras, Chennai, India for performing EPR spectra.
They thank Prof. R.J. Singh, Department of Physics, AMU, Aligarh for the discussion
of EPR spectra.
References
[1] T.E. Jones, L.L. Zimmer, L.L. Diaddario, D.B. Rorabacher. J. Am. Chem. Soc., 97, 7163 (1975).
[2] V.J. Thom, J.C.A. Boeyens, G.J. McDougall, R.D. Hancock. J. Am. Chem. Soc., 106, 3198 (1984).
[3] R.D. Hancock, S.M. Dobson, A. Evers, P.W. Wade, M.P. Ngwenya, J.C.A. Boeyens, K.P. Wainwright.
J. Am. Chem. Soc., 110, 2788 (1988).
[4] J.M. Lehn. Supramolecular Chemistry, Concepts and Perspectives, VCH, Weinheim (1995).
[5] K.R. Adam, D.S. Baldwin, P.A. Duckworth, L.F. Lindoy, M. McPartlin, A. Bashall, H.R. Powell,
P.A. Tasker. J. Chem. Soc., Dalton Trans., 1127 (1995).
[6] P.M. Reddy, A.V.S.S. Prasad, K. Shanker, V. Ravinder. Spectrochim. Acta, Part A, 68, 1000 (2007).
[7] T.A. Kaden. Pure Appl. Chem., 65, 1477 (1993).
[8] K.P. Wainwright. In Advances in Inorganic Chemistry, A.G. Sykes (Ed.), Vol. 52, pp. 293–334, Academic
Press, San Diego (2001).
[9] S.G. Kang, S.J. Kim. Bull. Korean Chem. Soc., 24, 269 (2003).
[10] V. Comblin, D. Glisoul, M. Hermann, V. Humblet, V. Jacques, M. Mesbahi, C. Sauvage, J.F. Desreux.
Coord. Chem. Rev., 185–186, 451 (1999).
[11] J. Costamagna, G. Ferraudi, B. Matsuhiro, M. Compos-Vallette, J. Canales, M. Villagran, J. Vargas,
M.J. Aruirre. Coord. Chem. Rev., 196, 125 (2000).
[12] H. Aneetha, Y.H. Lai, S.C. Lin, K. Panneerselvam, T.H. Lu, C.S. Chung. J. Chem. Soc., Dalton Trans.,
2885 (1999).
[13] X. Sun, M. Wuest, G.R. Weisman, E.H. Wong, D.P. Reed, C.A. Boswell, R. Motekaitis, A.E. Martell,
M.J. Welch, C.J. Anderson. J. Med. Chem., 45, 469 (2002).
[14] E. Maimon, I. Zilbermann, G. Golub, A. Ellern, A.I. Shames, H.A. Cohen, D. Meyerstein. Inorg. Chim.
Acta, 324, 65 (2001).
[15] E.Q. Gao, H.Y. Sun, D.Z. Liao, Z.H. Jiang, S.P. Yan. Polyhedron, 21, 359 (2002).
[16] N.E. Borisova, M.D. Reshetova, Y.A. Ustynyuk. Chem. Rev., 107, 46 (2007).
[17] C.N. Reilly, R.W. Schmid, F.A. Sadak. J. Chem. Educ., 36, 619 (1959).
[18] A.I. Vogel. A Text Book of Quantitative Inorganic Analysis, 3rd Edn, pp. 433–434, Longman,
London (1961).
[19] W.J. Geary. Coord. Chem. Rev., 7, 82 (1971).
[20] S.A. Khan, K. Saleem, Z. Khan. Eur. J. Med. Chem., 42, 103 (2007).
[21] N. Raman, C. Thangaraja. Transition Met. Chem., 30, 317 (2005).
[22] N. Gupta, R. Gupta, S. Chandra, S.S. Bawa. Spectrochim. Acta, Part A, 61, 1175 (2005).
[23] O.Z. Yesilel, H. Olmez. Transition Met. Chem., 30, 992 (2005).
[24] S. Chandra, Sangeetika. Spectrochim Acta, Part A, 60, 2153 (2004).
[25] P.V.G. Reddy, Y.B.R. Kiran, C.S. Reddy, C.D. Reddy. Chem. Pharm. Bull., 52, 307 (2004).
[26] M. Shakir, N. Begum, S. Parveen, P. Chingsubam, S. Tabassum. Synth. React. Inorg. Met-Org. Chem.,
34, 1135 (2004).
[27] P.V.G. Reddy, C.S. Reddy, C.N. Raju. Chem Pharm. Bull., 51, 860 (2003).
[28] I.S. Ahuja, S. Tripathi. Ind. J. Chem., 30(A), 1060 (1991).
[29] F.K. Kneubuhl. J. Chem. Phys., 33, 1074 (1960).
[30] D. Kivelson, R. Neiman. J. Chem. Phys., 35, 149 (1961).
[31] S. Chandra, L.K. Gupta. Spectrochim. Acta, Part A, 60, 2767 (2004).
[32] B.J. Hathaway, D.E. Billing. Coord. Chem. Rev., 5, 143 (1970).
[33] C.J. Ballhausen. Introduction to Ligand Field Theory, McGraw-Hill, New York (1962).
[34] D.P. Singh, R. Kumar, V. Malik, P. Tyagi. J. Enzyme Inhib. Med. Chem., 22, 177 (2007).

3968
F. Firdaus et al.
[35] K.G. Kocwin, W. Wojciechowski. Transition Met. Chem., 21, 312 (1996).
[36] J. Bassett, R.C. Denney, G.H. Jeffrey, J. Mendham. Vogels Textbook of Quantitative Inorganic
Analysis, 4th Edn, Longman, London (1978).
[37] X. Wei, X. Du, D. Chen, Z. Chen. Thermochim. Acta, 440, 181 (2006).
[38] A.A. Ahmed, S.A. BenGuzzi, A.A. El-Hadi. J. Sci. Appl., 1, 79 (2007).
[39] S.M. Annigeri, A.D. Naik, U.B. Gangadharmath, V.K. Revankar, V.B. Mahale. Transition Met. Chem.,
27, 316 (2002).