Synthesis, spectral, thermal and magnetic studies of Mn(II), Ni(II) and Cu(II) complexes with some benzopyran-4-one Schiff bases

Article abstract of DOI:10.1016/j.saa.2011.03.023

The Schiff bases of N₂O₂ dibasic ligands, H ₂La and H₂Lb are prepared by the condensation of ethylenediamine (a) and trimethylenediamine (b) with 6-formyl-7-hydroxy-5- methoxy-2-methylbenzopyran-4-one. Also tetra basic ligands, H₄La and H₄Lb are prepared by the condensation of aliphatic amines (a) and (b) with 6-formyl-5,7-dihydroxy-2-methylbenzopyran-4-one. New complexes of H ₄La and H₄Lb with metal ions Mn(II), Ni(II) and Cu(II) are synthesized, in addition Mn(II) complexes with ligands H₂La and H₂Lb are also synthesized. Elemental and thermal analyses, infrared, ultraviolet-visible as well as conductivity and magnetic susceptibility measurements are used to elucidate the structure of the newly prepared metal complexes. The structures of copper(II) complexes are also assigned based upon ESR spectra study. All the complexes separated with the stoichiometric ratio (1:1) (M:L) except Mn-H₄La and Mn-H₄Lb with (2:1) (M:L) molar ratio. In metal chelates of the type 1:1 (M:L), the Schiff bases behave as a dinegative N₂O₂ tetradentate ligands. Moreover in 2:1 (M:L) complexes, the Schiff base molecules act as mono negative bidentate ligand and binuclear complex is then formed. The Schiff bases were assayed by the disc diffusion method for antibacterial activity against Staphylococcus aureus and Escherichia coli. The antifungal activity of the Schiff bases was also evaluated against the fungi Aspergillus flavus and Candida albicans.

Full text of DOI:10.1016/j.saa.2011.03.023

Spectrochimica Acta Part A 79 (2011) 522–528
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral, thermal and magnetic studies of Mn(II), Ni(II) and Cu(II)
complexes with some benzopyran-4-one Schiff bases
∗
Aida L. El-Ansary , Hussein M. Abdel-Fattah, Nora S. Abdel-Kader
Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
The Schiff bases of N O dibasic ligands, H La and H Lb are prepared by the condensation of ethylene-
2
2
2
2
Received 2 September 2010
Received in revised form 21 February 2011
Accepted 11 March 2011
diamine (a) and trimethylenediamine (b) with 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-
-one. Also tetra basic ligands, H4La and H4Lb are prepared by the condensation of aliphatic amines
a) and (b) with 6-formyl-5,7-dihydroxy-2-methylbenzopyran-4-one. New complexes of H4La and H4Lb
4
(
with metal ions Mn(II), Ni(II) and Cu(II) are synthesized, in addition Mn(II) complexes with ligands H2La
and H2Lb are also synthesized. Elemental and thermal analyses, infrared, ultraviolet–visible as well as
conductivity and magnetic susceptibility measurements are used to elucidate the structure of the newly
prepared metal complexes. The structures of copper(II) complexes are also assigned based upon ESR
spectra study. All the complexes separated with the stoichiometric ratio (1:1) (M:L) except Mn–H4La and
Mn–H4Lb with (2:1) (M:L) molar ratio. In metal chelates of the type 1:1 (M:L), the Schiff bases behave as a
dinegative N2O2 tetradentate ligands. Moreover in 2:1 (M:L) complexes, the Schiff base molecules act as
mono negative bidentate ligand and binuclear complex is then formed. The Schiff bases were assayed by
the disc diffusion method for antibacterial activity against Staphylococcus aureus and Escherichia coli. The
antifungal activity of the Schiff bases was also evaluated against the fungi Aspergillus flavus and Candida
albicans.
Keywords:
Schiff bases
Benzopyran-4-one
Ethylenediamine
Trimethylenediamine
Transition metal complexes
Spectral measurements
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
(H La,b and H La,b) were previously prepared and characterized
2 4
[
11]. Also the complexes of Ni(II) and Cu(II) with ligands H La and
2
The role of Schiff bases in coordination chemistry has been
H Lb were prepared and characterized [12].
2
extensively studied and quite satisfactory elucidated. Schiff bases
can be considered as useful chelating agents due to their ability to
encapsulate into their coordinating moiety metal ions when a suit-
able function group, e.g. OH, SH, etc., is present sufficiently close
to the azomethine group [1,2]. Tetradentate Schiff bases, especially
those with N O donor set, resulting from the condensation of the
As a continuation to our work, the present paper deals with
the preparation and elucidation of the structure of the chelates
of copper(II), nickel(II) and manganese(II) with Schiff bases H La
4
and H Lb and the metal chelates of manganese(II) with Schiff bases
4
H La and H Lb.
2
2
2
2
aliphatic diamines such as ethylenediamine or its derivatives, have
been also extensively studied [3,4]. Schiff base transition metal
complexes have been extensively studied because of their poten-
tial use as catalysts in a wide range of oxidation reactions [5–8].
In recent years many copper, nickel and manganese complexes of
Schiff bases were prepared and characterized by several techniques
2
. Experimental
All chemicals used in this investigation were chemically
pure grade (BDH or Aldrich). They included manganese(II) chlo-
rid, nickel(II) chloride (Nic), copper(II) chloride (Cuc), copper(II)
acetate (Cua), copper(II) perchlorate (Cup), nickel(II) perchlorate
[
9,10].
Quite recently, the Schiff bases derived from the conden-
(Nip), potassium dichromate, ethylenediamine, trimethylenedi-
amine and visnagin. All organic solvents used in this study were
either purified by recommended methods [13] or obtained as grade
materials from BDH. Doubly distilled H O was always used.
sation of 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-
one and 5,7-dihydroxy-6-formyl-2-methylbenzopyran-4-one with
aliphatic diamines (ethylenediamine and trimethylenediamine)
2
2.1. Analysis and physical measurements
∗ Corresponding author. Tel.: +20 106775179; fax: +20 225728843.
E-mail address: aidansary1@yahoo.com (A.L. El-Ansary).
Carbon, hydrogen, and nitrogen were analyzed by standard
microanalysis methods using Perkin Elmer 2400 CHN elemental
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.03.023

A.L. El-Ansary et al. / Spectrochimica Acta Part A 79 (2011) 522–528
523
Table 1
Analytical data of Schiff bases and their complexes.
Compound
H2La
Empirical formula
Mwt
M% found (Calc.)
C% found (Calc.)
H% found (Calc.)
N% found (Calc.)
C26H24N2O8
MnC26H28N2O11
C27H26N2O8
MnC27H36N2O14
C24H20N2O8
CuaC24H20N2O9
CucC24H20N2O9
NipC24H24N2O11
NicC24H20N2O9
Mn2C24H36N2O18
C25H22N2O8
CuaC25H22N2O9
CucC25H28N2O12
NipC25H30N2O13
NicC25H30N2O13
Mn2C25H26N2O12
492.48
599.45
506.51
667.52
464.43
543.97
543.97
575.16
539.13
750.42
467.77
557.99
612.04
625.21
625.21
656.36
–
63.14 (63.34)
51.63 (52.00)
63.92 (64.02)
48.90 (48.58)
61.34 (62.06)
52.84 (52.90)
52.87 (53.00)
49.85 (50.00)
53.14 (53.40)
38.16 (38.40)
61.89 (62.75)
53.85 (53.81)
49.29 (49.06)
48.34 (48.03)
47.80 (48.03)
45.13 (45.70)
4.91 (4.91)
4.48 (4.37)
5.10 (5.17)
5.47 (5.13)
4.55 (4.43)
4.00 (3.70)
3.70 (3.70)
3.57 (4.20)
3.69 (3.70)
5.03 (4.84)
4.84 (4.63)
3.94 (3.97)
4.11 (4.61)
3.99 (4.80)
4.30 (4.80)
4.19 (3.99)
5.59 (5.69)
5.20 (4.70)
5.19 (5.53)
3.98 (4.19)
6.08 (6.03)
5.07 (5.10)
5.05 (5.00)
4.80 (4.80)
5.04 (5.10)
3.84 (3.73)
5.49 (5.85)
4.94 (5.00)
4.39 (4.57)
4.40 (4.48)
4.47 (4.48)
4.31 (4.27)
[
Mn(H2La)·2H2O]·H2O
H2Lb
Mn(H2Lb)·2H2O]·4H2O
H4La
8.56 (9.16)
–
8.00 (8.22)
–
[
[
[
[
[
[
Cua(H4La)]·H2O
11.67 (11.68)
11.57 (11.68)
10.09 (10.20)
10.50 (10.80)
15.00 (14.64)
–
11.41 (11.39)
10.34 (10.38)
9.17 (9.39)
9.27 (9.39)
16.90 (17.21)
Cuc(H4La)]·H2O
Nip(H4La)]·3H2O
Nic(H4La)]·H2O
Mn2(H4La)·2OH·2H2O]·6H2O
H4Lb
[
[
[
[
[
Cua(H4Lb)]·H2O
Cuc(H4Lb)]·4H2O
Nip(H4Lb)·2H2O]·3H2O
Nic(H4Lb)·2H2O]·3H2O‘
Mn2(H4Lb)·2OH·2H2O]
analyzer in the Microanalytical Center, Faculty of Science, Cairo
University, Cairo, Egypt. The metal ion content was determined
after wet decomposition of the chelates as previously described
(60 mL) [11]. The solutions were stirred at room temperature for
at least 30 min; yellow and dark yellow solids were collected by
filtration, washed and recrystallized from ethanol for H L and from
2
[
14,15].
dimethylformamide (DMF) for H L Schiff bases. The structure of the
4
prepared Schiff bases is represented by the formula:
X
O
4
H
C
O
4
X
5
H
C
6
7
Y
6
5
3
N
3
N
2
HO
O
1
CH3
2
H C
O
1
OH
3
7
Schiff base
X
Y
The infrared spectra (IR) of all complexes were recorded
H2La
H2Lb
H4La
H4Lb
OCH3
OCH3
OH
(CH2)2
(CH2)3
(CH2)2
(CH2)3
applying the KBr disc technique using test scan Shimadzu FTIR
spectrometer. Electronic absorption spectra of the chelates were
measured in DMF using UV/vis–NIR 3101 PC Shimadzu spectropho-
tometer. TGA was achieved using a Shimadzu-50 thermal analyzer
OH
(
Japan). The weight loss was measured from ambient temperature
2.3. Preparation of the chelates
◦
◦
up to 800 C in a rate of 10 C per minute.
Magnetic susceptibilities of the chelates were measured at room
temperature using a magnetic susceptibility Cambridge England
Sherwood Scientific.
The solid chelates were prepared by mixing a hot ethanolic
solution of Cu(CH COO) ·H O (Cua), CuCl ·2H O (Cuc), NiCl ·6H O
3
2
2
2
2
2
2
(
Nic), Ni(ClO ) ·6H O (Nip) and (MnCl ·4H O) with the Schiff bases
4
2
2
2
2
The effective magnetic moments were calculated from the
expression ꢀeff = 2.828(XM T)1 B.M., where XM is the molar sus-
ceptibility corrected using Parcel’s constants for diamagnetism of
all atoms in the compounds [16].
sufficient to form 1:1, 1:2 and 2:1 (M:L) complexes. The reaction
mixture was stirred on a water bath. The solid chelates were filtered
off and washed several times with ethanol and second distilled
water until the filtrate becomes colorless. The obtained complexes
were kept in a vacuum desiccator and subjected to elemental anal-
ysis.
/2
EPR spectra of the copper complexes were recorded on
Bruker spectrophotometer. The magnetic field was calibrated with
diphenylpicrylhydrazyl free radical (DPPH) (g = 2.0023).
The molar conductance values of the chelates were calculated
by measuring the conductance of the investigated metal chelates
3. Results and discussion
−
3
(
10 M) in DMF using conductivity meter ORION model 150 of 0.6
cell constant.
The formulae of the complexes, elemental analyses and formula
masses are listed in Table 1. The elemental analysis data are con-
sistent with the calculated results from the empirical formula of
each complex. In the present investigation, different salts of Ni(II)
(NiCl2 and Ni(ClO4)2), also Cu(CH3COO)2 and CuCl2 were used in the
preparation of complexes of Schiff bases H4La and H4Lb in order to
study the effect of the anion on the chelation. MnCl2 salt was used in
the preparation of H2La,b and H4La,b complexes. The data of Table 1
reveal that the anions of different salts are not involved in the chela-
tion. All the separated metal complexes are stable, non-hygroscopic
and partially soluble in most organic solvents, but soluble in DMF
and DMSO.
2.2. Preparation of Schiff bases
H La and H Lb were prepared by condensation of a solution
2
2
of ethylenediamine (a) (0.30 g, 5 mmole) or trimethylenediamine
b) (0.37 g, 5 mmole) with 6-formyl-7-hydroxy-5-methoxy-2-
methylbenzopyran-4-one (2.34 g, 10 mmole) in ethanol (40 mL)
19]. On the other hand, H La and H Lb were prepared by con-
(
[
4
4
densation of a solution of ethylenediamine (a) (0.30 g, 5 mmole) or
trimethylenediamine (b) (0.37 g, 5 mmole) with 5,7-dihydroxy-6-
formyl-2-methylbenzopyran-4-one (2.20 g, 10 mmole) in ethanol

5
24
A.L. El-Ansary et al. / Spectrochimica Acta Part A 79 (2011) 522–528
Table 2
Important IR spectral bands of Schiff bases and their complexes.
Compound
H2La
ꢁC
O
ꢁC
N
ꢁC–N
ꢁC–O
ꢁM–N
ꢁM–O
1654s
1674s
1662s
1654s
1658s
1662s
1651s
1658s
1658s
1630s
1651s
1662s
1662s
1658s
1654s
1651s
1620s
1631s
1620s
1593s
1620s
1612s
1612s
1612s
1612s
1620s
1612s
1620s
1620s
1573s
1620s
1593s
1396m
1384w
1396m
1388w
1357m
1350m
1342w
1346w
1346m
1350w
1346m
1300w
1300m
1338w
1333m
1307m
1218w
1226m
1222m
1230m
1218w
1222m
1222w
1230w
1230w
1226m
1222m
1230w
1230w
1253m
1222m
1233w
–
543w
–
509w
–
559w
536w
551w
551w
–
–
424w
–
428w
–
411w
420w
420w
424w
424w
–
412w
412w
444w
439w
420w
[
Mn(H2La)·2H2O]·H2O
H2Lb
Mn(H2Lb)·2H2O]·4H2O
H4La
[
[
[
[
[
[
Cua(H4La)]·H2O
Cuc(H4La)]·H2O
Nip(H4La)]·3H2O
Nic(H4La)]·H2O
Mn2(H4La)·2OH·2H2O]·6H2O
H4Lb
–
[
[
[
[
[
Cua(H4Lb)]·H2O
540w
540w
543w
536w
555w
Cuc(H4Lb)]·4H2O
Nip(H4Lb)·2H2O]·3H2O
Nic(H4Lb)·2H2O]·3H2O
Mn2(H4Lb)·2OH·2H2O]
3.1. Infrared spectra of the complexes
The Schiff bases H La, H Lb and H La show the stretching
2 2 4
−
1
vibration of azomethine group at 1620 cm
[11,12]. On other
The bonding between the ligands and metal ions can be inferred
hand the IR spectrum of Schiff base H Lb displays this band at
4
−
1612 cm [11,12]. The infrared spectra of Mn–H Lb, Cua,c–H Lb,
2 4
1
by comparing the IR spectra of the metal chelates with those of the
organic ligands. IR band assignments of the Schiff bases and metal
chelates are listed in Table 2. The infrared spectra of Schiff base
Nip,c–H La and Nip–H Lb complexes show a shift of the ␯C N band
4
4
towards lower wave numbers, Table 2, indicating the coordination
of azomethine group to the metal ions [12]. But in the infrared spec-
tra of Mn–H La, Cua,c–H Lb and Nic–H Lb complexes, the band due
H La and its complexes are shown in Fig. 1.
4
2
4
4
3
.1.1. Infrared spectra of (1:1) (M:L) complexes
The 1651–1662 cm band in the free ligands is assigned to the
to the azomethine group show shift to higher wave number, Table 2.
The shift in the position of this band to lower or higher wave num-
ber upon chelation can be likely ascribed to the perturbing effect of
the coordinating metal ions on such vibration. The observed shift of
the C N stretching frequency in the Schiff bases chelates compared
to the free ligands, reveals that the C N group would contribute in
coordination with metal atoms via the nitrogen lone pair [17].
The ligands show a 1218–1222 cm band due to the phenolic
C–O stretching vibration, undergoes a shift towards higher wave
number in the spectra of complexes. This shift confirms the partic-
ipation of oxygen in the C–O–M bond [18].
−1
benzopyrone carbonyl in position four [11,12]. This band does not
show significant change in 1:1 (M:L) chelates confirming that this
group does not participate in the chelation.
−
1
3.1.2. Infrared spectra of (2:1) (M:L) complexes
For the Mn(II) complex with H Lb the stretching frequency of
4
−
1
the benzopyrone carbonyl in position four [11,12] at 1651 cm
does not show significant change confirming that this band does
not participate in its chelation. On the other hand, the IR spectra
of Mn –H La shows shift to lower wave number and decreasing
2
4
in the intensity of this band, suggesting that the carbonyl group
−
1
is coordinated to manganese(II) ion. While the band at 1612 cm
in the infrared spectra of the free Schiff base H Lb [11,12] (due to
4
the azomethine group absorption) shows shift to lower wave num-
ber in the infrared spectra of Mn –H Lb complex, this shift reveals
2
4
that the C N group involved on coordination with Mn(II). In the IR
spectrum of Mn –H La complex the ␯C N band is unaltered this
2
4
result may be taken as an evidence that the azomethine group is not
−
1
involved in its chelation. The band at 1222 cm due to the pheno-
lic C–O stretching vibration, undergoes a shift towards higher wave
number in the spectra of complexes. So, In Mn –H Lb complex both
2
4
phenolic oxygen and nitrogen of azomethine group are involved in
the chelation with metal ion [19] but Mn –H La complex shows
2
4
an unusual mode of chelation in which the Schiff base is bound
to Mn(II) ion via the carbonyl group in position four and phenolic
oxygen in position five of the benzopyrone moiety.
In the IR spectra of all (1:1) or (2:1) (M:L) metal chelates, a broad
−
1
band is observed in the range of 3363–3560 cm . Such broad band
may be attributed to the stretching vibration of water molecules
of crystallization, a result confirmed by microanalyses of these
chelates. For Mn –H Lb, this band may be due to OH in position
Fig. 1. Infrared spectra of Schiff base H4La and its complexes.
2
4

A.L. El-Ansary et al. / Spectrochimica Acta Part A 79 (2011) 522–528
525
Table 3
TG results for the solid complexes of the Schiff bases H4La and H4Lb.
◦
Complex
M:L
Temperature ( C)
H2O mass loss (%)
Number of water molecules
Residue (%)
Calc
Calc
Found
Found
[
[
[
[
[
Mn2(H4La)(OH)2(H2O)2]6H2O
Mn2(H4Lb)(OH)2(H2O)2]
Nip(H4Lb)(H2O)2]3H2O
Nic(H4La)]H2O
2:1
300
200
320
250
290
19.25
5.44
14.40
3.33
18.9
6.0
14.3
3.4
8
2
5
1
1
18.98
21.45
12.00
13.90
11.60
20
22
12
14
11
2:1
1:1
1:1
1:1
Cua(H4La)]H2O
3.31
3.5
Table 4
Thermodynamic and kinetic data of thermal decomposition of some solid complexes.
◦
Complex
Temp range
50–350
E* (kJ)
ꢂS* (J)
ꢂH* (kJ)
ꢂG* (kJ)
Ts ( C)
Cs
[Mn2(H4La)(OH)2(H2O)2]6H2O
[Mn2(H4Lb)(OH)2(H2O)2]
[Nip(H4Lb)(H2O)2]3H2O
[Nic(H4La)]H2O
10.1
26.1
27
37
11.6
9.8
60.8
65.8
85
86.6
37.6
−256
−258
−187
−242
−249
−278
−101
−125
−157
−121
−180
6.3
18.2
24
30
7.9
3.1
57.7
62
78.9
81.7
30.1
123
264
90
246
118
227
96
121
191
152
192
183
680
80
0.4
035
0.33
0.36
037
3
3
3
90–700
50–150
50–750
60–200
00–700
64–127
64–227
84–554
620
172
530
104
199
444
313
628
0.35
0.4
0.4
0.4
0.4
1
2
[Cua(H4La)]H2O
197–343
50–927
3
0.33
◦
five of benzopyrone moiety. In the low frequency region, new bands
in the coordination sphere. On further heating above 300 C of the
anhydrous complex [ML], the organic part of the complexes may
decompose in one or more steps with the possibility of the forma-
tion of one or two intermediates. These intermediates may include
the metal ion with a part of Schiff base in case of the 1:1 or 1:2
−
1
observed in the IR spectra all chelates in the region 411–444 cm
may be attributed to ␯M–O (phenolic). The new band observed at
−
09–566 cm in the infrared spectra of (1:1) (M:L) and Mn –H Lb
2 4
1
5
complexes may be attributed to ␯M–N stretching.
(L:M) complexes [20]. These intermediates may finally decompose
to stable metal oxides as a final product.
The thermal decomposition of these complexes may proceed
according to the following mechanisms:
For Ni(II) and Cu(II) complexes
3
.1.3. TG analysis of the solid complexes
This method of analysis is used to confirm the results of ele-
mental analyses. The TG analysis was measured for Mn –H La,
2
4
Mn –H Lb, Nic–H La, Nip–H Lb and Cua–H La complexes, Table 3.
2
4
4
4
4
At the beginning near the room temperature, the weight loss
[
[
[
ML·nH O]·mH O → [ML·nH O]
2
2
2
corresponds to the removal of the hydrated H O from the com-
2
plex. This process is followed by removal of the more strongly
ML·nH O] → [ML]
2
bound (coordinated) H O molecules which occupy some positions
2
ML] → Intermediate(unstable)
Table 5
Electronic absorption bands and magnetic moments of the metal chelates.
Intermediate → metaloxide
ꢁ (cm 1
−
)
B.M.
Molar
conductance
Compounds
For Mn(II) binuclear complexes
H2La
27473, 25126
27855
27778, 23809
27778
24876
27100
27421
24155
24154
23697
–
5.80
–
5.90
–
1.90
2.03
0.00
0.00
5.50a
–
–
3.7
–
4.0
–
25.6
23.5
22.0
19.2
14.3
–
[
Mn(H2La)·2H2O]·H2O
H2Lb
Mn(H2Lb)·2H2O]·4H2O
H4La
[Mn2L·2OH·2H2O]·6H2O → [Mn2L·2OH·2H2O]
[
[
Mn L·2OH·2H O] → [Mn L·2OH]
2
2
2
[
[
[
[
[
Cua(H4La)]·H2O
Cuc(H4La)]·H2O
[
Mn L·2OH] → Intermediate(unstable)
2
Nic(H4La)]·H2O
Nip(H4La)]·3H2O
Mn2(H4La)·2OH·2H2O]·6H2O
Intermediate → metaloxide(MnO2)
H4Lb
24876
[
[
[
[
[
Cua(H4Lb)]·H2O
27700
27548
27701
27248
2.07
1.99
3.29
3.28
5.51a
10.5
9.2
10.1
5.3
15.2
Cuc(H4Lb)]·4H2O
3
.1.4. Thermodynamic parameters and kinetics of thermal
Nic(H4Lb)·2H2O]·3H2O
Nip(H4Lb)·2H2O]·3H2O
Mn2(H4Lb)·2OH·2H2O]
dissociation of complexes
The values of ꢂH* and ꢂS* determined from Coats–Redfern
equation [20], are listed in Table 4 for the first step in the Mn –H La,
23809
a
Magnetic moment per metal ion.
2
4
Mn –H Lb, Nip–H Lb, Nic–H La complexes, second step in the
2
4
4
4
Mn –H La, Mn –H Lb, Nip–H Lb, Nic–H La, Cua–H La complexes
2
4
2
4
4
4
4
Table 6
Electron spin resonance data.
and third step in the Cua–H La complex. These values suggest
4
an associative mode of activation of substitution. The low ꢂH*
values imply a pronounced degree of ligand participation in the
transition state and the negative entropy of activation implies
increased ordering. The activation energies of decomposition E*
Complex
g||
g⊥
gav
G
Cuc–H4La
Cua–H4Lb
2.0457
2.0974
2.013
2.025
2.024
2.049
4.056
4.21

5
26
A.L. El-Ansary et al. / Spectrochimica Acta Part A 79 (2011) 522–528
Table 7
Antimicrobial activity of Schiff bases.
−
Staphylococcus aureus (G+)
Sample
Escherichia coli (G )
Candida albicans (Fungus)
Aspergillus flavus (Fungus)
Standard
Tetracycline (Antibacterial agent)
Amphotricine B (Antifungal agent)
38
–
34
–
–
20
0.0
14
18
0.0
0.0
–
18
0.0
12
14
0.0
0.0
DMSO
H2La
H2Lb
H4La
H4Lb
0.0
18
24
13
16
0.0
19
27
14
15
G: Gram reaction; solvent: DMSO.
were found to be in the range 10–85 kJ mol−1. These values of acti-
vation energies reflect moderate thermal stability of the complexes.
Non-isothermal kinetic analysis of the decomposition of the com-
plexes was carried out by the application of Nathg and Arora [21]
method. The Cs values (mass fraction at Ts) of thermal decompo-
sition of the complexes, Table 4, are in the range 0.33–0.40 which
indicates that the decomposition follows first order kinetics [21].
dral geometry may be suggested [26] for these complexes. While
the electronic spectra of Mn2–H4La and Mn2–H4Lb show bands at
−
1
23697 and 23809 cm , respectively, these bands can be taken as
evidence for square planar geometry for such complexes [27]. The
magnetic moment values of Mn–H2La and Mn–H2Lb complexes are
5.8 and 5.9 B.M, respectively, corresponding to the existence of five
unpaired electrons which is consistent with the octahedral struc-
ture. While the magnetic moment values of (2:1) (M:L) Mn2–H4La
and Mn2–H4Lb complexes are 5.5 and 5.51 B.M. per metal ion,
respectively. These magnetic moment values are evidence for a
planar stereochemistry for such complexes [27].
Generally, the H La complexes are thermally more stable than
4
those with H Lb Schiff base as reflected from comparing their E*.
4
3.2. Spectroscopic, magnetic moment studies and molar
The molar conductance values of the complexes at room tem-
conductivity
−
1
2
−1
perature in DMF lie in the 3.7–25.6 ꢃ cm mol range. These
values are much lower than the values reported for the 1:1 elec-
trolytes in the same solvents [28], indicating their non-electrolytic
nature.
The electronic spectra of the ligands and their complexes were
recorded in dimethylformamide (DMF), Table 5. As previously
reported, the electronic spectra of free Schiff bases (H La and
2
−
1
H Lb) exhibit a shoulder at 364 nm (27473 cm ) and 360 nm
27778 cm ), respectively, which is due to ␲–␲* transition of
2
−1
(
3.3. EPR spectra
the benzopyrone ring moiety [12]. Whereas the absorption bands
−1
−1
observed at 402 nm (24875 cm ) and 403 nm (24814 cm ) are
due to the ␲–␲* transition within the azomethine group [22]. The
electronic spectra of Schiff bases (H La and H Lb) show one band at
The room temperature X-band ESR spectra of powdered.
Cuc–H4La and Cua–H4Lb complexes were recorded and the spin
Hamilton ion parameters of the complexes with Cu(II) (s = 1/2,
I = 3/2) were calculated. The ESR spectra of these complexes are
quite similar and exhibit an axially symmetric g-tensar parame-
ters with g|| > g⊥ > 2.003 indicating that the unpaired electron most
likely resides in dx2–y2 ground state [29] characteristic of square
planar pyramidal or octahedral geometry [30]. The value of gav
were calculated according to the equation gav = 1/3 (g|| + 2 g⊥) and
the results are given in Table 6. g|| is a moderately sensitive func-
tion for M–L bond nature. Kivelson and Neiman [31] have reported
4
4
−1
2
4876 cm which is due to the ␲–␲* transition within the azome-
thine group [22].
The electronic spectra of the metal complexes under investiga-
tion do not resemble those of their ligands, which is supporting
evidence for complex formation.
The bands in the range of 27100, 27421, 27700 and 27548 cm−1
which appear in the spectra of Cua–H La, Cuc–H La, Cua–H Lb
4
4
4
and Cuc–H Lb complexes, respectively, can be assigned as charge
4
transfer bands. The position of the bands supports square planar
geometry for these complexes [22], these results in accordance
with that obtained for copper complexes with H La and H Lb [12].
2
2
The measured magnetic moment values for (1:1) (M:L) Cu(II) com-
plexes with Schiff bases H La and H Lb are in the 1.90–2.07 B.M.
4
4
range indicating the presence of one unpaired electron in these
chelates, this suggested the presence of copper in the oxidation
state II and square planar geometry for these chelates [23]. The
solution state spectra of Nic–H La and Nip–H La complexes exhibit
4
4
−
1
bands at 24155 and 24154 cm , respectively. These bands may
1
1
be attributed to A g → B g transition [24], indicating square pla-
1
1
nar geometry. While Nic–H Lb and Nip–H Lb complexes show
4
4
−
1
broad and strong bands at 27701 and 27248 cm , respectively,
corresponding to 3A g(F) → T g(P) transition in approximately
3
2
1
octahedral field [25]. The diamagnetic nature of (1:1) (M:L)
Nic–H La and Nip–H La complexes supports the square planar
4
4
geometry. While Nic–H Lb and Nip–H Lb complexes show mag-
4
4
netic moment of 3.29 and 3.28 B.M., respectively, which could be
attributed to high spin octahedral of Ni(II) [25]. These results are
in accordance with that obtained for nickel complexes with H La
2
and H Lb [12] One charge transfer band is observed at 27855 and
2
−1
2
7778 cm
for Mn–H La and Mn–H Lb, respectively. This may
2 2
2
2
2
be assigned to T g → T g or A g transitions. Thus an octahe-
Fig. 2. ESR spectrum of Cua–H4Lb complex.
2
1
2

A.L. El-Ansary et al. / Spectrochimica Acta Part A 79 (2011) 522–528
527
the g|| value < 2.3 for covalent character of metal–ligand band and
5. Conclusion
g|| value > 2.3 for ionic character. By applying this criterion, the g||
values are 2.046 and 2.097 for Cuc–H La and Cua–H Lb complexes
From these studies (elementalanalysis, thermalanalysis, UV/vis,
IR spectral measurements and magnetic moment measurements)
on the prepared metal chelates, the following conclusions can be
drawn concerning the ligating properties of the Schiff bases as well
as the stereochemistry of their corresponding metal complexes.
In metal chelates of the type 1:1 M:L the Schiff bases behaves as
4
4
are less than 2.3 is an indication of significant covalent bonding
in Cu(II) complexes. Based on IR, electronic spectra and ESR data,
the two complexes have a square planar structure. The geomet-
ric parameter G, which is a measure of the exchange interaction
between copper centers, is calculated using Hathway expression
(
G = g|| − 2.0023/g⊥ − 2.0023) [32]. According to Hathway [33], if
a dinegative N O2 tetradentate ligands, coordination occurring via
2
the value of G > 4, the exchange interaction is negligible in solid
complexes but if G < 4 indicates considerable interaction in solid
complexes.
The calculated G values are given in Table 6. The G value of
the studied Cu(II) complexes is greater than 4 indicating that no
exchange interaction between the copper(II) centers in the solid
the two azomethine nitrogen and the two deprotonated phenolic
oxygen atoms in position seven of the benzopyrone moiety. The
rigid highly conjugated dinegative chelate ring imposes a square
planar environment around the metal ion. Thus a square planar
structure has been proposed for Cua–H La, Cuc–H La, Cua–H Lb,
4
4
4
Cuc–H Lb, Nic–H La and Nip–H La chelates. Manganese(II) com-
4
4
4
phase. Fig. 2 shows the ESR spectrum of Cua–H Lb complex.
plexes of the type [ML·2H O]·nH O (L = H La or H Lb), Nic–H Lb
4
2
2
2
2
4
and Nip–H Lb complexes are in agreement with an octahedral
4
environment around the metal ion where the dinegative tetraden-
tate ligand lies in the equatorial plane and two water molecules
4
. Antimicrobial activity of Schiff bases
occupy the axial positions. Moreover the Mn –H Lb complex of
2
4
stoichiometric composition 2:1 (M:L) has anomalous behavior. It
It is evident that in azomethine derivatives, the C N linkage is an
essential structural requirement for biological activity [34]. Several
Schiff bases have been reported to possess remarkable antibacterial
behaves as binuclear complex of the type [Mn L·2H O·2OH]. The
2
2
spectral data elucidate the coordination occurring via one azome-
thine nitrogen and one deprotonated oxygen atom in position
seven of the benzopyrone moiety to Mn(II) ion. Thus a square
planar structure was proposed for this complex in accordance
with electronic absorption spectrum. An unusual mode of chela-
[
35], antifungal [36], anticancer [37] and diuretic activities [38]. All
the studied Schiff bases were screened for antimicrobial activity
against the bacteria, Escherichia coli and Staphylococcus aureu by
the disc diffusion method [39], using tetracycline as a standard. The
antifungal activity of the compounds was also evaluated against the
fungi, Aspergillus flavus and Candida albicans and Amphotericin B
was used as standard. The antimicrobial activity was evaluated by
measuring the zone of inhibition in mm. The bacterial and fungal
inhibition zone values are summarized in Table 7.
tion of Schiff base H La in adapted by Mn(II) complex of the type
4
[
Mn L·2H O·2OH]·6H O is which the Schiff base molecules act as a
2
2
2
mono negative bidentate ligand and binuclear complex is formed.
In other words the Schiff base is bound to Mn(II) ion via the car-
bonyl group in position four and phenolic oxygen in position five
of the benzopyrone moiety. In the IR spectrum of this complex the
The screening data revealed that most of the tested compounds
␯
C N band is unaltered meanwhile the ␯C O band of the ligand is
showed good inhibitory activity. The compound H La exhibited
4
shifted to lower frequency. A square planar structure is proposed
for this complex in accordance to UV/vis spectrum.
The geometric structure of the prepared complexes can be
shown as follows:
good antibacterial activity, almost close to that of the standard. All
the compounds moderately inhibited the growth of Gram positive
O
OH
H
H
OH
O
C
(CH
2
)
3
C
N
N
OH HO
Mn
Mn
H
3
C
O
O
CH3
H O
2
H O
2
Mn
2
-H
4
Lb complex
OH
2
OH
H O
2
OH
O
Mn
Mn
O
O
H
C
H
O
2 2
(CH )
C
N
N
.
6 H O
2
H
3
C
OH
HO
CH
3
2 4
Mn -H La complex
and Gram negative bacteria. The Schiff base which has antifungal
activity very close to that of the standard is H La. As shown in
4
Table 7, the Schiff base H Lb showed no inhibition in fungi growth.
4

5
28
A.L. El-Ansary et al. / Spectrochimica Acta Part A 79 (2011) 522–528
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