Synthesis, magnetic, spectral and antimicrobial studies on metal complexes of 4-methylphenylaminoacetoisatin hydrazone

Article abstract of DOI:10.3184/030823409X12549096901122

A new series of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Cr(III), Fe(III) and Cu(I) complexes of 4-methylphenyl-aminoacetoisatin hydrazone (HL) have been prepared and characterised The IR spectral data of the complexes indicate neutral bidentate, n

Full text of DOI:10.3184/030823409X12549096901122

JOURNAL OF CHEMICAL RESEARCH 2009
NOVEMBER, 659–664
RESEARCH PAPER 659
Synthesis, magnetic, spectral and antimicrobial studies on metal
complexes of 4-methylphenylaminoacetoisatin hydrazone
Abdou Saad El-Tabl*, Ramadan Mahdy El-Bahnasawy and Alaa El-Deen Hamdy
Chemistry Department, Faculty of Science, Menuofia University, Shebin El -Kom, Egypt
A new series of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Cr(III), Fe(III) and Cu(I) complexes of 4-methylphenyl-
aminoacetoisatin hydrazone (HL) have been prepared and characterised The IR spectral data of the complexes
indicate neutral bidentate, neutral tridentate or monobasic tridentate behaviour of the ligand depending on the
metal ion. The ESR spectra of the complexes [Cu(OAc) (L)].0.5H2O, [CuCl(L)].0.5H2O, [Cr(Cl)(OH)2(HL)].0.5H2O,
Co(NO3)2[(HL)2].2.5H2O and [(HL)(Mn)3(Cl)4(OH)2(H2O)6].H2O, are isotropic. However, those of [Cu(NO3)(L)].2.5H2O
and [Cu(SO4)(H2O)(HL)], are anisotropic with ionic bond characters. The antibacterial and antifungal activities of
the compounds show that some metal complexes exhibit a greater inhibitory effect than tetracycline (bacteria) and
amphotricine (fungi).
Keywords: metal complexes, spectral and magnetic studies, biological studies
Complexes (9) and (10) were prepared by mixing stoichiometric
ratios (1:1)of the complexes (7) and (8) (in 30 cm3 EtOH) with the
appropriate ratios of acetylacetone (in 50 cm3 EtOH) in the presence
of triethylamine. The mixture was refluxed for 3 h and the resulting
precipitate was filtered off, washed several times with ethanol and
dried over P4O10.
Isatin hydrazones of metal complexes have potential activity
as antitumor agents evaluated on human leukaemic
cells,1 and also exhibit anticonvulsant2 and antibacterial
activities.3 Much work on metal complexes of isatin
isonicotinoyl hydrazone has been reported.4 However, little
research has been done on metal complexes of the hydrazone
derived from substituted phenyl amino acetohydrazide and
isatin, so we have prepared and spectrally characterised a new
hydrazone derived from 4-methylpheylaminoacetohydrazide
and isatin and its metal complexes.
Bacteria media
Nutrient agar medium was prepared by standard method.5
The antibacterial activity of (1) and its complexes were tested using
the paper disc diffusion method7 against positive gram bacteria
(Staphylococcus aureus) and gram negative bacteria (Escherichia
coli), The tested compounds in measured quantities were dissolved in
DMF to a concentration of 1000 ppm of compounds. Nutrient Agar
media was poured in each Petri dish. After solidification, 0.1 cm3
of the tested bacteria was spread over the medium using a spreader.
Discs of Whatman no.1 filter paper having diameter of 5.00 mm,
containing compounds were placed in the inoculated Petri plates.
The plates were incubated at 28°C for 24–48 h and the zone of
inhibition was calculated in millimetres.
Experimental
Reagent grade chemicals were used, 4-methylphenylamino-
acetohydrazide was prepared by a published method.5 Elemental
analyses (C, H, N and Cl) were determined by the Analytical Unit
of Mansoura University, Egypt. Standard methods were used to
determine the metal ion content.6 All metal complexes were dried in
a vacuum over anhydrous P4O10. The IR spectra were recorded on a
Perkin-Elmer IR spectrometer 681 (4000–200 cm-1), using KBr discs.
Electronic spectra in DMF solutions were recorded on a Perkin-
Elmer 550 spectrophotometer using 1-cm quartz cells. The molar
conductances of complexes in DMF (10-3 M) were measured using
a tip cell and a Bibby conductimeter MCl at room temperature. The
1H NMR spectra of the ligand, [HL], (1) and its zinc(П), copper(І)
and cadmium(II) complexes were measured in DMSO–d6 as a solvent
using a 300 MHZ Varian NMR spectrometer. The thermal analyses
(DTA and TGA) were carried out in air on a Shimadzu DT-30 thermal
analyser from 25 to 800°C at a heating rate of 10°C /min. The solid
ESR spectra of the complexes were recorded on an ELEXSYS E500
Bruker spectrometer in 3 mm Pyrex tubes at 298 K. 1, 1-diphenyl-
picrylhydrazal (DPPH) was used as a g-marker for the calibration of
the spectra. Mass spectra were recorded using a JEOL JM-S-AX-500
mass spectrometer. The magnetic moments of the complexes were
measured in a borosilicate tube with a Johnson Mathey magnetic
susceptibility balance at room temperature, by the modified Gouy
method using the equation μeff = 2.84(χn × T)1/2. T.L.C measurements
confirmed the purity of the prepared compounds.
Fungus media
The tested compounds in measured quantities were dissolved in
DMF to a concentration of 1000 ppm of compounds. Czapek dox
agar medium was prepared by a standard method.5 Aspergillus flavus
or Cadida albicans was spread over each dish by using a sterile
bent loop rod. Disks were cut by a sterilised cork borer and then
taken by sterilised needle. The resulting pits were sites for the test
compounds, the plates are sites for the tested compounds. The plates
were incubated at 30°C for 24–48 h and any clear zones present were
detected, the zone of inhibition was calculated in millimetres.
Results and discussion
The reaction of 4-methylphenylaminoacetohydrazide with isatin
in EtOH (1:1, molar ratio), gave [HL], (1) as shown in Scheme 1.
All complexes are intensely coloured, crystalline solids and stable
at room temperature and not decomposing after prolonged storage.
They are insoluble in non-polar and polar solvents but soluble in polar
coordinating solvents such as DMSO and DMF. Elemental analyses
and physical data (Table 1), and spectral data (Tables 2 and 3†)
Preparation of the ligand and its metal complexes
Ligand [HL] (1): A hot ethanolic solution (50 cm3) containing (6.4 g
1.0 mol) of 4-methyl phenylaminoacetohydrazide was added to a
hot ethanolic solution (50 cm3) containing (4.5 g 1.0 mol) of isatin.
The mixture was refluxed on a water bath for 2 h. The product was
collected at room temperature, washed several times with ethanol and
dried over P4O10.
Complexes (2)–(8) and (11)–(24) were prepared by mixing
stoichiometric ratios:(1:1), (2:1), or (1:3) of (1) (in 30 cm3 EtOH)
with the appropriate metal(Ι), metal(ΙΙ) or metal(ΙΙΙ) salt (chloride,
acetate, nitrate, chloride or sulfate) in EtOH (50 cm3) in the presence
of triethylamine. The mixture was refluxed for 1–3 h and the resulting
precipitate was filtered off, washed several times with ethanol and
dried over P4O10.
H3C
O
CH2
N
+
N
H
C
O
NH2
N
H
O
EtOH
(1 : 1 )
H
H3C
2
CH2
N
N
O
N
C
1
H
O
N
H
3
* Correspondent. E-mail: asaeltabl@yahoo.com
Scheme 1
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660 JOURNAL OF CHEMICAL RESEARCH 2009
Table 1 The elemental analyses of the ligand [HL] and its metal complexes
No. Compound/complex
Mol.wt.
Colour
M. p./°C Aa
Yield
/%
μeff.
M
Calcd (Found%)
C
H
N
M
–
Cl
–
1
2
3
4
5
6
7
8
9
[HL]C17H16N4O2
308.31
438.91
443.30
461.07
465.76
Orange
Black
248
-–
80
70
65
60
64
56
71
64
67
50
68
61
55
60
60
61
59
61
64
67
72
69
70
–
66.22
(65.72)
5.23
(5.13)
18.16
(18.21)
[(L)Cu(OAc)].1/2H2O(C19H19N4O4.5Cu)
[(L)Co(OAc)].H2O(C19H20N4O5Co)
[(L)Ni(OAc)].2H2O(C19H22N4O6Ni)
[(L)Zn(OAc)].2H2O(C19H22N4O6Zn)
[(L)Cd(OAc)](C19H18N4O4Cd)
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
12.0
19.0
14.6
18.9
5.4
1.84
3.48
Dia.
Dia.
Dia.
2.82
2.13
6.84
2.95
1.79
Dia.
3.85
Dia.
Dia.
1.80
Dia.
Dia.
2.81
5.61
3.44
Dia.
1.70
3.70
51.99
4.36
12.75
14.47
–
–
–
–
–
–
–
–
–
–
–
–
–
–
(52.55)
(4.37)
(12.26) (14.00)
Brown
Yellow
Brown
51.47
(50.85)
4.54
(4.49)
12.63
(12.38) (12.98)
12.14 12.73
(12.00) (12.21)
12.02 13.60
(11.22) (13.12)
11.69 23.48
(11.21) (23.15)
13.29
49.49
(49.09)
4.80
(3.23)
48.99
(48.29)
4.76
(5.41)
478.75 D. Brown
47.67
(48.18)
3.79
(3.54)
[(L)Mn2(OAc)3(H2O)4].6H2O(C23H44N4
O18Mn2)
774.48
782.00
533.42
578.21
477.89
446.02
Red
20.0
19.5
17.0
4.7
35.66
(34.44)
5.72
(5.32)
7.23
(6.51)
14.28
(13.50)
[(L)Ni2(OAc)3(H2O)4].6H2O(C23H44N4
O18Ni2)
Brown
Brown
Brown
Brown
Black
35.32
(34.20)
5.67
(5.32)
7.16
(6.32)
15.00
(14.47)
[(L)Mn(acac)(H2O)].3H2O(C22H30N4
O8Mn)
49.53
(49.08)
5.66
(5.27)
10.49
(10.51) (10.32)
10.29
10 [(L)Ni(acac)(OAc)].3H2O(C24H31N4O9Ni)
11 [(L)Cu(NO3)].2.5H2O(C17H20N5O7.5Cu)
12 [(L)Ni(NO3)].H2O(C17H17N5O6Ni)
49.85
(50.04)
5.40
(5.91)
9.68
(9.64)
10.15
(10.12)
23.0
1.90
18.1
16.4
15.0
19.4
5.1
42.72
(42.28)
4.21
(5.39)
14.64
(14.01) (12.85)
13.29
45.77
(45.23)
3.84
(4.04)
15.69
(15.96) (13.41)
13.16
13 [(HL)2Co(NO3)2].2.5H2O(C34H37N10O12.
5Co)
844.60 D. Brown
48.35
(48.61)
4.41
(4.03)
16.57
(16.60)
6.97
(6.85)
14 [(HL)2Zn(NO3)2].H2O(C34H34N10O11Zn)
15 [(HL)2Cd(NO3)2](C34H32N10O10Cd)
16 [(L)CuCl].1/2H2O(C17H16N4O2.5ClCu)
17 [(L)NiCl].4.5H2O(C17H24N4O6.5ClNi)
18 [(L)ZnCl].2.5H2O(C17H20N4O4.5ClZn)
822.02
853.03
415.31
482.52
451.17
621.13
560.15
438.78
Black
D. Red
Brown
Yellow
Brown
Brown
Black
49.67
(50.18)
4.16
(4.21)
17.03
(17.21)
7.71
(7.82)
47.87
(47.32)
3.78
(3.96)
16.41
(16.21) (12.86)
13.17
49.16
(48.85)
3.88
(4.19)
13.48
(13.41) (15.21)
11.60 12.16
(11.50) (12.31)
12.41 14.04
(12.20) (13.90)
15.30
8.53
(8.60)
42.31
(42.13)
5.01
(5.75)
7.34
(7.40)
17
45.25
(45.41)
4.46
(5.34)
7.85
(7.41)
19 [(HL)Co2(Cl)2(OH)2(H2O)4].H2O
(C17H28N4O9Cl2Co2)
15.3
14.0
11.9
21.0
11.0
32.87
(32.91)
4.54
(4.21)
9.01
(8.92)
18.97
(19.08) (11.66)
11.41
20 [(HL)Fe(Cl)2(OH)
36.45
(36.88)
5.21
(5.77)
9.99
(9.98)
9.96
(9.32)
12.65
(12.11)
(H2O].5H2O(C17H29N4O9Cl2Fe)
21 [(HL)Cr(Cl)(OH)2].1/2H2O(C17H19N4O4.5
Cl2Cr)
Brown
46.53
(46.89)
4.36
(4.70)
12.75
(12.12) (11.30)
11.85
8.09
(7.80)
22 [(HL)2Cu2Cl2].1.5H2O(C34H35N8O5.5
Cl2Cu2)
841.55 Y. brown
48.52
(48.21)
4.19
(4.25)
13.30
(13.46) (14.91)
11.52 13.07
(11.16) (13.41)
15.09
8.42
(8.71)
23 [(HL)Cu(SO4)H2O](C17H18N4O7 SCu)
485.93
775.06
Brown
Brown
42.02
(42.32)
3.73
(4.13)
–
24 [(HL)(Mn)3(Cl)4(OH)2(H2O)6].H2O
(C17H32N4O11Cl4Mn3)
23.40 58
26.34
(26.58)
4.16
(3.98)
7.22
(7.13)
21.26
(20.94) (18.11)
18.29
AaM= molar conductivity, D. = dark, Y. = yellowish, acac = acetylacetone
are compatible with the proposed structures (Fig. 1). To date,
no diffractable crystals have been grown.
H3C
H
N
CH2
N
O
N
H
C
O
Conductivity measurements
The molar conductance values of the complexes in DMF (10-3 M) lie
in the (1.90–23.40 W-1 cm2 mol-1) range (Table 1). The low values
indicate that all the complexes are non electrolytes.8 This confirms
that the anion is coordinated to the metal ion.
N
H
H3C
1H NMR of the (1) and some metal complexes
The H NMR spectrum of (1) in DMSO-d6 confirms the proposed
structure (Fig. 1). The spectrum shows two peaks for the NH
group at 11.12, 10.81 ppm and another peak for the OH group at
13.54 ppm.9 The integration of the two sets of signals related to
NH and OH groups gives the ratio 50:25, this is evidence for the
presence of enol and keto-forms of the ligand as shown in Scheme 2.
CH2
N
N
H
C
1
N
O
OH
N
H
Scheme 2
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JOURNAL OF CHEMICAL RESEARCH 2009 661
H3C
H
O
H
N
N
H
N
CH2
C
NO3
CH2
NH
N
O
N
H
C
O
H3C
N
O
O
N
N
H
M
.nH2O
CH3
N
H
NO3
H3C
HN
CH2
C
O
N
CH2
N
N
C
N
H
H
OH
M=Co(II)
M=Zn(II)
M=Cd(II)
n=2.5
n=1
n=0
(13)
(14)
(15)
N
O
H
( )
1
H3C
H3C
CH2
CH2
N
H
C
N
N
N
H
C
O
N
N
O
.n H2O
M
.nH2O
M
N
H
O
OAc
O
N
H
Cl
M=Cu(II) n=1/2
M=Ni(II) n=4.5
M=Zn(II) n=2.5
(16)
(17)
(18)
M=Cu(II)
M=Co(II)
M=Ni(II)
M=Zn(II)
M=Cd(II)
n=1/2 (2)
n=1
n=2
n=2
n=0
(3)
(4)
(5)
(6)
O
C
H
N
CH2
NH
H3C
OH
H3C
CH2
N
OH2
2 N
Cl
C
2 O
N
N
OH
.H2O
Co
H
OH2
M
Co
OH
O
N
Cl
OAc
OH
OH2
.n H2O
OH2
H
M
N
H
O
(
)
19
OAc
OAc
OH2
OH2
M=Mn(II) n=6
(7)
(8)
O
C
H
N
M=Ni(II)
n=6
NH
CH2
H3C
Cl
H3C
OH
N
O
CH2
N
H
Fe
C
.5H2O
N
H2O
CH2
N
H
H3C
HC
O
Cl
20
N
C
O
O
(
)
.3H2O
Mn
N
O
C
H3C
OH2
H
H3C
(9)
NH
C
O
N
H
OH
N
H3C
1/2H2O
Cr
CH2
O
N
H
O
N
Cl
C
N
OH
H
H3C
HC2
(
)
21
O
N
C
.3H2O
Ni
O
C
N
H
O
H
N
O
C
OAc
H3C
(10)
NH
CH2
Cl
H
H3C
H3C
N
O
N
O
Cu Cu
Cl
CH2
1.5 H2O
N
H
N
H
N
CH3
N
N
O
C
O
CH2
HN
N
C
O
.nH2O
M
N
H
H
NO3
(
22
)
M=Cu(II) n=2.5
M=Ni(II) n=1
(11)
(12)
Fig. 1
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662 JOURNAL OF CHEMICAL RESEARCH 2009
The complexes show broad bands in the 3570–3115 and 3270–
2650 cm-1 ranges indicating intra- and intermolecular hydrogen
bondings in the complexes.11 Complexes (2)-(8) and (10) show
two bands in the 1589–1523 and 1405–1326 cm–1 ranges, due to
n(C=O) and n(C–O) of the acetate group. The difference between
these bands (in the 236–155 cm–1 range), enable us to suggest that
the acetate group is coordinated to the metal ions in a unidentate
fashion.17 However, complexes (7) and (8) show bands at 1558,
1416, and 1560, 1417 cm–1; the difference between these bands
is equal to 142 and 143 cm–1 respectively, indicating bridging
acetate.18 Complexes (2)–(12) and (16)–(18) show bands in the
1280–1298 cm–1 range, assigned to (C–O), the shift of this band by
7–89 cm–1 compared to that of the ligand, indicates coordination of
this group to the metal ion. Complexes (11)–(15) show four bands
in the 1386–1377, 1290–1103, 850–789 and 751–740 cm–1 ranges,
which are assigned to a terminal nitrate group.19 Complexes (16)–
(22) show band in the 460–379 cm–1 range, due to the coordination
of chloride.19 Complex (23) shows strong bands at 1201, 1121, 1025
and 977 cm–1, due to bidentate, coordinated sulfate.11,20 Complexes
(20), (21) and (24) show n(OH) at 1074, 1070 and 1098 cm–1.11
The bonding of (1) to the metal ions through the oxygen and
nitrogen atoms is supported by the presence of new bands in the
680–558 and 553–467 cm–1 ranges, due to n(M–O) and n(M–N)
respectively.21,22
H3C
CH2
NH
N
C
O
N
H
O
O
O
Cu
S
N
H
O
O
OH2
(
)
23
O
C
H
N
CH2
NH
H3C
OH
OH2
Mn
OH2
)
OH2
Mn
OH
Mn
2Cl
Cl
N
O
Cl
Cl
.H2O
N
H
OH
OH2
OH2
(
24
Fig. 1 Continued
Magnetic moments
The room temperature magnetic moments of the complexes (2)–
(24) are shown in Table 1. Nickel(ІІ) complexes (4), (12) and (17)
are diamagnetic, indicating square planar geometry, however,
complexes (8) and (10) show values 2.13 and 2.95 B.M., indicating
an octahedral structure.20,23-25 The low value of complex (8) indicates
spin-exchange interactions taking place between the nickel(ІІ) ions.
The cobalt(ІІ) complexes (3), (13) and (19) show the values 3.48,
3.85 and 2.81 B.M. respectively, indicating high- spin square planar
or octahedral cobalt(ІІ) complexes.5,9,26 The low value of complex
(19), suggests spin-exchange interactions taking place between the
cobalt(ІІ) ions. The manganese(ІІ) complexes (7), (9) and (24) show
values 2.82, 6.84 and 3.70 B.M. respectively, indicating high-spin
octahedral manganese(ІІ) complexes.9 The low values of complexes
(7) and (24), indicate spin-exchange interactions taking place
between the manganese(ІІ) ions. Copper(ІІ) complexes (2), (11), (16)
and (23) show values 1.84, 1.79, 1.80 and 1.70 B.M. respectively,
which corresponding to one unpaired electron in a square planar or
octahedral structure.9 Iron(ΙΙІ) complex (20) has a value 5.61 B.M.
indicating a high-spin octahedral iron(ІІІ) complex.27 Chromium(ІІІ)
complex (21) shows a value of 3.44 B.M, which indicates an
octahedral chromium(ІІІ) complex.28 However, zinc(ІІ) complexes
(5), (14) and (18), cadimium(ІІ) complexes (6) and (15) and the
copper(І) complex (22) are diamagnetic as expected.
The peaks in the 6.20–7.39 ppm range are assigned to the protons
of the aromatic ring and the singlet peaks at 3.35 and 4.34 ppm, to
protons of methyl and methylene groups respectively.5 Zinc(П)
complex (14) shows multiplet peaks in the 6.55–7.53 ppm range,
assigned to the aromatic protons and the NH group appears at
7.69 ppm. The peaks at 3.34 and 4.24 ppm, are due to the protons
of methyl and methylene groups respectively.5 The zinc(ІІ
)
complex (18) shows aromatic protons as multiplet peaks in the
6.60–6.93 ppm range, and peaks at 3.40 and 4.25 ppm due to the
protons of methyl and methylene groups respectively.5 The signal due
to NH proton had disappeared, confirming the proposed structure.
The cadmium(ІІ) complex (15) shows aromatic proton resonances
in the 6.64-6.90 ppm range, the NH proton at 7.69 ppm. and the
protons of methyl and methylene groups respectively5 at 3.33 and
4.26 ppm, The copper(І) complex (22) shows aromatic protons
in the 6.94–7.29 ppm range, the NH proton at 7.70 ppm. and the
protons of methyl and methylene groups at 3.34 and 4.22 ppm
respectively.5 The 1H NMR spectra of the ligand and its Zn(ІІ)
complex are shown in Fig. 2†.
Mass spectrum of the ligand, (1)
The mass spectrum of the ligand reveals the molecular ion peak (m/z)
at 308 a.m.u. consistent with the molecular weight. and the fragments
at m/z = 78, 91, 106, 120, 145, 148 and 163 corresponding to
C6H6 , C7H7 , C7H8N+, C8H10N+, C8H5N2O+, C9H10NO+ and
C9H11N2O+ respectively, (Table 4†). The suggested mechanism of
the fragmentation of the ligand is shown in Fig. 3†.
+
+
ESR spectra
The ESR spectra of solid copper(ІІ) complexes (2) and (16) at room
temperature are characteristic of species with the d9 configuration and
the isotropic type of resonance, (giso = 2.15 and 2.10 respectively),
indicates octahedral or square planar geometry around the copper(ΙΙ)
ion.5,29 Copper(ІІ) complexes (11) and (23) in polycrystalline state
at room temperature exhibit anisotropic signals with two g values,
g║ = 2.33, 2.35 and g┴ = 2.06, 2.063 with giso = 2.15 and 2.16
IR spectra
Important spectral bands of (1) and its metal complexes are presented
in Table 2†. The IR spectrum of (1) shows broad strong bands in
3550–3320 and 3300–2820 cm-1 ranges, which are attributed to
intra- and intermolecular hydrogen bonding of OH groupings.10
Also, the spectrum shows n(NH)(1), s, as at 3420 and 1522, n(NH)(2), s, as
at 3387 and 1462, n(NH)(3), s, as at 3238 and 1458 cm-1 respectively.11
Other bands at 1720, 1702 and 1618 cm-1 are assigned to the n(C=O)
hydrazide, n(C=O)ring and n(C=N) respectively.11-13. Strong
bands appear in the 1590–1522 cm-1 range and at 1369 cm-1,
corresponding to n(C=C)Ar and n(C–O) respectively.12,14
Comparison of the spectra of the complexes with that of (1)
shows shifts of characteristic bands. Bands observed in the ranges
3421–3417, 1531–1514, 3385–3381, 1460–1455, 3223–3205
and 1466–1452 cm-1 are due to n(NH)(1), n(NH)(2) and n(NH)(3)
respectively13 (Table 2†). The complexes show bands in the 1727–
1650 and 1644–1591 cm-1 ranges assignable to n(C=O) and n(C=N)
respectively. The shift of the band due to n(C=O) in the 9–52 cm-1
range indicates a minor change in symmetry of this group due to
metal coordination. Also, the shift of n(C=N) in the 6–27 cm-1
range is evidence for the coordination of the azomethine nitrogen
atom to the metal ions.15 Broad bands were observed in the 3660–
3190 and 3470–3125 cm–1 ranges which are assigned to n(OH)
of hydrated water [except for (6), (15) and (23)] or coordinated
water molecules [except (2)–(6), (10)–(18), (21) and (22)].14,16
respectively. The g║> g┴>ge observation suggests
a tetragonal
distortion around the copper(ІІ) ions, corresponding to elongation
along the fourfold symmetry z-axis with a d(x2–y2) ground state.30,31
In addition, exchange coupling interactions between two copper(ІІ)
ions is explained by the Hathaway expression32 G = (g║-2)/(g┴-2).
If the value G >4.0, the exchange interaction is negligible, which is
the case for complexes (11) and (23), (G = 5.50, 5.55 respectively).30,31
Also, the g║value in the copper(ІІ) complexes can be used as a measure
of the covalent character of the metal–ligand bond. If this value is
greater than 2.3, the environment is essentially ionic and values
less than this limit indicate a covalent environment. The g║-values
for complexes (11) and (23) indicate ionic bond character.29 The
ESR spectrum of chromium(ІІІ) complex (21) shows isotropic-
type symmetry with giso = 2.26, typical of chromium(ІІІ) octahedral
geometry.5 Cobalt(ІІ) complex (13) has an isotropic-type resonance
with giso = 2.06, indicating an octahedral cobalt(ІІ) ion.5,31 and the
manganese(ІІ) complex (24) shows an isotropic type symmetry
with giso = 2.004, typical of manganese octahedral geometry.23 The
cobalt(ІІ) complex (3) at room temperature do not show ESR signal
because the rapid spin lattice relaxation of the cobalt(ІІ) broadness
the lines at room temperature.33 The ESR spectrum of manganese(ІІ)
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JOURNAL OF CHEMICAL RESEARCH 2009 663
complex (24) is shown in Fig. 4†. The ESR parameters for the
[(HL)2Co(NO3)2].2.5H2O
[(HL)2Co(NO3)2].2H2O
[(HL)2Co(NO3)2].2H2O + 1/2 H2O
63 °C
95 °C
complexes are shown in Table 5†.
[(HL)2Co(NO3)2] + 2H2O
[(L)2Co]+ 2HNO3
Electronic spectra
The electronic spectral data for the ligand and its metal complexes
are summarised in Table 3†. The ligand in DMF solution shows three
bands at 275 nm (e = 0.46 × 103 mol-1cm-1), 345 nm (e = 1.40 ×
103 mol-1cm-1) and 355 nm (e = 1.36 × 1 03 mol-1cm-1). The first
band may be assigned to an intraligand π→π* transition which is
nearly unchanged on complexation, whereas the second and third
bands may be assigned to the n→π* and charge transfer transitions
of the azomethine and carbonyl groups respectively.34 These bands
are shifted on complexation, suggesting the coordination of the
azomethine nitrogen atom and carbonyl group to the metal ion.
Nickel(ІІ) complexes (8) and (10) show three bands in the 475–
482, 620–625 and 845–870 nm ranges, which are attributable to
3A2g(F)→3T1g(P)(n3), 3A2g(F)→3T1g(F)(n2) and 3A2g(F)→ 3T2g(F)(n1)
transitions respectively, of octahedral nickel(ІІ) complexes.9,35,36
The n2/n1 ratio for the complexes (8) and (10) are 1.40 and 1.35
(Table 3†), which are less than the usual range of 1.50–1.75,
indicating distorted octahedral nickel(ІІ) complexes.37 Complexes
(4), (12) and (17) show the first band in the 540–550 nm range,
227 °C
461 °C
[(HL)2Co(NO3)2]
[(L)2Co]
CoO + Volatile organic residue
Antimicrobial studies
The antimicrobial screening data show that the compounds exhibit
antimicrobial properties, the metal chelates exhibiting a greater
inhibitory effect than the parent ligand, in comparison to tetracycline
(as antibacterial agent) and amphotriciine (as antifungal agent).
From the data obtained (Table 7†), it is observed that the inhibition
zone area is much larger for metal complexes against the gram-
positive bacteria (Staphylococcus aureus), gram-negative bacteria
(Escherichia coli) and fungi (Aspergillus flavus and Candida
albicans). The increased activity of the metal chelates can be
explained on the basis of chelation theory.48 It is know that chelation
tends to make ligands act as more powerful and potent bactericidal
agents and antifungal agents, thus killing more of the bacteria than
the ligand. It is observed that, in a complex, the positive charge of
the metal is partially shared with the donor atoms present in the
ligand, and there may be π-electron delocalisation over the whole
chelate.48 This increases the lipophilic character of the metal chelate
and favours its permeation through the lipoid layer of the bacterial
membranes. Also, there are other factors which also increase the
activity, such as solubility, conductivity and bond length between
the metal and the ligand. The mode of action may involve the
formation of a hydrogen bond through the azomethane nitrogen and
oxygen atom with the active centres of the cell constituents, resulting
in interference with the normal cell process. The variation in the
effectiveness of different compounds against different organisms
depend either on the impermeability of the cells of the microbes or
the difference in ribosomes of microbial cells.21 There is a marked
increase in the bacterial activities of the ligand and complexes
for gram positive bacteria, (Staphylococcus aureus): the order of
activities are (8) = (12)>(10) = (23)>tetracycline = (19)>(4) = (14)
= (24)>(3) = (5) = (20)>(9)>(6)>(2)>(7) = (11)>(1). For gram-
negative bacteria, (Escherichia coli), the order of activities are (20)
= (24) > tetracycline>(10) = (23)>(19)>(4) = (12)>(8)>(5) = (6) =
(14)>(3) = (11)>(2) = (7)>(9)> (1). For Asergillus flavus we have
(24)>(9) = (23)>(8) = (14) = (20>(7) = (12) = (19)>(10)>(5)>(6) =
(11) = amphotricine >(2) = (3) = (4)>(1). and for Candida albicans
(23)>(20>(19) = (24)>(6) = (8) = (11)> amphotricine = (14)>(5) = (7)
= (9) = (10)>(3) = (12)>(2)>(4)>(1)
1
which is assigned to the A2g←1A1g transition (b2g→b1g) and the
1
second band in the 430–465 nm range is due to the B1g←1A1g
transition (a1g→b1g), of square planar nickel(ІІ) ions.11,38,39 Cobalt(ІІ)
complexes (13) and (19) show three bands in the 435–450, 515–520
and 770–830 nm ranges, which are assigned to4T1g(F)→4T1g(P)
(n3), 4T1g(F)→4A2g(n2) and 4T1g(F)→4T2g(F)(n1) transitions
respectively, of high-spin octahedral cobalt(ІІ) complexes.25,40 The
n2/n1 ratio for the complexes are in the 1.49–1.59 range (Table 3†),
which are less than the usual range, indicating distorted
octahedral cobalt(ІІ) complexes. However, complex (3) shows
4
bands at 490 and 550 nm (Table 3†) assigned to T1g→4T1g(P)
4
and T1g→4T2g transitions, characteristic of a high-spin square
planar cobalt(ІІ) ion.41 Manganese(ІІ) complexes (7), (9) and (24)
show bands in the 465–480, 540–560 and 635–650 nm ranges,
6
6
6
assigned to A1g→4Eg, A1g→4T2g and A1g→4T1g, transitions, of
octahedral geometry around the manganese(ІІ) ion.42 Chromium(ІІІ)
complex (21) shows bands at 395, 445, 540 and 600 nm, the first
band is assigned to a charge transfer transition and the last bands to
4A2g(F)→4T1g(P), 4A2g(F)→4T1g(F) and 4A2g→4T2g(F) transitions, of
an octahedral chromium(ІІІ) complex.28,29 Copper(ІІ) complexes (2),
(11), and (16) show bands in the 450–460, 480–495 and 525–535 nm
ranges (Table 3†), assigned to 2B1g→ 2B2g, 2B1g→2Eg and 2B1g→2A1
transitions respectively, of a square planar geometry43, and complex
2
(23) shows bands at 445, 575 and 635 nm, assigned to B1g→2Eg,
†Electronic Supplementary Information
2
2B1g→2A1g and B1g→2B1g transitions, of an octahedral copper(ІІ)
Tables, Figures and Schemes denoted† have been deposited
electronically and may be accessed via http://www.ingentaconnect.
com/content/stl/jcr
complex.43 The iron(ІІІ) complex (20) shows bands at 430, 460
and 660 nm. The first and second bands are assigned to charge
transfer transitions while the last band is considered to arise from
6
the A1→4T1 transition, from distorted octahedral geometry around
Received 7 July 2009; accepted 28 September 2009
Paper 09/0672 doi: 10.3184/030823409X12549096901122
Published online: 16 November 2009
the iron(ІІІ) ion.44,45 Zinc(ІІ) complexes (5), (14), (18), cadmium(ІІ)
complexes (6) and (15) and copper(І) complex (22) show bands
(Table 3†), indicating intraligand transitions.
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