Coordination and biological behaviour of 2-(p-toluidino)-N'-(3-oxo-1,3- diphenylpropylidene) acetohydrazide and its metal complexes

Article abstract of DOI:10.3184/030823409X12596063380927

A series of Ni(II), Co(II), Cu(II), Mn(II), Zn(II), Zr(IV), Fe(III), Ru(III), La(III), Hf(IV) and U(VI) complexes of 2-(p-toluidino)-N'-(3-oxo-1,3- diphenylpropylidene) acetohydrazide (H₂L) have been synthesised and characterised by elemental a

Full text of DOI:10.3184/030823409X12596063380927

770 RESEARCH PAPER
DECEMBER, 770–774
JOURNAL OF CHEMICAL RESEARCH 2009
Coordination and biological behaviour of 2-(p-toluidino)-N'-(3-oxo-
1,3-diphenylpropylidene) acetohydrazide and its metal complexes
Ahmed N. Al-Hakimia*, Abdou S. El-Tablb and Mohamad M. E. Shakdofac
aDepartment of Chemistry, Faculty of Science, Ibb University, Ibb, Yemen
bDepartment of Chemistry, Faculty of Science, El-Menoufia University, Shebin El-Kom, Egypt
cInorganic Chemistry Department, National Research Centre, P.O. 12622 Dokki, Cairo, Egypt
A series of Ni(II), Co(II), Cu(II), Mn(II), Zn(II), Zr(IV), Fe(III), Ru(III), La(III), Hf(IV) and U(VI) complexes of 2-(p-toluidino)-
N'-(3-oxo-1,3-diphenylpropylidene) acetohydrazide (H2L) have been synthesised and characterised by elemental
and thermal analyses (DTA, TG), molar conductances, magnetic moments, IR, 1H NMR, UV-Vis spectra and ESR
measurements. The ESR spectra of solid complexes [(L)(HL)Cu2(OAc)], [Cu(HL)(H2L)(NO3)] and [CuCl (HL)(H2L)].H2O
at room temperature show axial symmetry with covalent bond character, and complex [FeCl2(HL)(H2O)] has gav = 4.38,
indicating a high spin (5/2) iron(III) complex. However, complexes [(HL)Mn2Cl3(H2O)4] and [RuCl2(HL)(H2O)].H2O have
isotropic spectra consistent with octahedral structure. The antifungal and antibacterial activities of the ligand and its
complexes were investigated.
Keywords: metal complexes, synthesis, spectra, thermal studies, magnetism, biological studies
in EtOH (15 mL) was added dropwise. The reaction mixture was
refluxed for 3 h, then cooled to room temperature and the product
was filtered off, washed several times with EtOH and dried over
anhydrous CaCl2.
There has been considerable recent interest in the synthesis
of hydrazones and their complexes. Interest in these species
stems largely from their applications as insecticides, in
medicine and in analytical chemistry. 2,6-di-tert-butyl-
4-(2-azinylhydrazonomethyl) phenol derivatives possess
potential as 5-lipoxygenase inhibitors.1 Metal complexes of
hydrazones act as potential inhibitors for many enzymes.2
The presence of heterocyclic rings in the synthesised
hydrazones are responsible for pharmacological properties.3
Hydrazones create environments similar to biological
systems by coordination through oxygen and nitrogen atoms.
These ligands coordinate with metal ions to produce stable
metal complexes owing to their facile keto–enol tautomerism.
Their complexes have been proposed as acid–base indicators,4
reservoir sensors5 and as analytical reagents6 due to the
colour intensification which accompanies deprotonation.
Isonicotinoylhydrazone was found to be analogous to anti-
tuberculosis drugs.7 Also hydrazones are used as plasticisers
and stabilisers for polymers,8,9 polymerisation initiators and
antioxidants.10 Due to the above applications, we now report
the syntheses and spectroscopic studies of 2-(p-toluidino)-N'-
(3-oxo-1,3-diphenylpropylidene) acetohydrazide and its metal
complexes.
Preparation of metal complexes (2)–(20)
Metal complexes were prepared by mixing stiochiometric ratios
(L:M) (1:1 or 2:1) of the ligand (H2L) in EtOH (30 mL) with the
appropriate metal salts (in 50 mL EtOH/15 mL H2O). The mixture
was refluxed for 2–3 h. On cooling to room temperature, fine crystals
formed, which were filtered off, washed with EtOH and dried over
anhydrous CaCl2.
In-vitro antibacterial and antifungal activities
The antibacterial and antifungal activities of the ligand and its metal
complexes have been studied by the disc diffusion method.13,14 using
the organisms Escherichia coli, Bacillus subtilis and Aspergillus
niger. The test compounds were dissolved in DMSO to concentrations
of 250, 200, 175, 150 and 125 ppm and a DMSO poured disc was
used as negative control. The bacteria were subcultured in nutrient
agar medium, which was prepared using peptone, beef extract, NaCl,
agar agar and distilled water. The Petri dishes were incubated for
48 h at 37°C. The standard antibacterial drug tetracycline was also
screened under similar conditions for comparison. The fungi were
subcultured in Dox´s medium, which was prepared using yeast extract,
sucrose, NaNO3, agar agar, KCl, KH2PO4, MgSO4.7H2O, distilled water
and trace of FeCl3.6H2O. The standard antifungal drug amphotricene
B was also used for comparison. The Petri dishes were incubated for
48 h at 28°C.The zone of inhibition was measured in millimetres
carefully. All determination was made in duplicate for each of the
compounds. An average of the two independent readings for each
compound was recorded.
Experimental
Reagent grade chemicals were used. 2-(p-toluidino) acetohydrazide
was prepared by a published method.11 Elemental analyses were
determined by the Analytical Unit of Cairo University of Egypt.
Standard analytical methods were used to determine the metal ion
content.20 All metal complexes were dried in vacuum over anhydrous
CaCl2. The IR spectra were measured using a Perkin-Elmer 683
spectrophotometer (4000–200 cm-1). Electronic spectra in DMF
solutions were recorded on a Perkin-Elmer 550 spectrophotometer.
The conductances of the complexes (10-3 M DMF) were measured at
25°C with a Bibby conductometer type MCl. The 1H NMR spectrum
of the ligand in DMSO-d6 was recorded using a 300 MHZ Varian
NMR spectrometer. The thermal analyses (DTA and TG) were carried
out in air on a Shimadzu DT-30 thermal analyser from 27 to 800°C at
a heating rate of 10°C per minute. Magnetic moments were measured
using the Gouy method, meff. = 2.84 ccMorr .T. ESR measurements of
solid complexes at room temperature were made using a Varian
E-109 spectrophotometer, with DPPH as a standard material.
TLC was used to confirm the purity of the compounds.
Results and discussion
Reaction of 2-(p-toluidino)acetohydrazide with dibenzoylmethane
in EtOH 1:1, molar ratio, led to the formation of 2-(p-toluidino)-N'-
(3-oxo-1,3-diphenylpropylidene) acetohydrazide (H2L) (Fig. 1). The
reaction of the ligand (H2L), with the metal salts using (1:1) or (2:1)
molar ratios, gave intensely coloured, crystalline solids, which are
stable at room temperature and do not decompose after prolonged
storage. The complexes are insoluble in water, ethanol, methanol,
benzene, toluene, acetonitrile and chloroform, but completely soluble
in dimethylformamide (DMF) or dimethylsulfoxide (DMSO).
Elemental analyses and physical data (Table 1), and spectral data
[Tables2and3, depositedintheElectronicSupplementaryInformation
(ESI)], are compatible with the proposed structures (Fig. 2).
To date, no diffractable crystals could be obtained.
1H NMR spectrum
Preparation of the ligand (1) [H2L]
The 1H NMR spectrum of the ligand in DMSO-d6 shows signals
which are consistent with the proposed structure (ketonic form,
Fig. 1). The observed peaks at 9.8 and 8.89 ppm are assignable to
the protons of the NH groups of the hydrazide and amine moieties
respectively2 confirming that the ligand is present in the ketonic
2-(p-toluidino) acetohydrazide (1.7 g, 0.01 mol) was dissolved in
EtOH (25 mL) and dibenzoylmethane (2.3 g, 0.01 mol) dissolved
* Correspondent. E-mail: anmalhakimi@yahoo.com
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Fig. 1 Preparation of the ligand.
Table 1 Elemental analyses and physical properties of the ligand and its metal complexes
No.
Compounds
Colour
M.p. Yield Ω mol-1
Found (Calcd)/%
N
/C°)
/%
cm2
C
H
Cl
M
1
2
[H2L] (C24H23N3O2)
Yellow
60
80
79
75
76
78
75
78
82
80
79
71
72
78
83
81
85
82
80
84
85
----
3.3
3.8
4.8
5.2
4.3
3.8
4.1
3.5
2.8
4.8
6.5
7.3
7.8
8.2
5.2
6.2
5.5
5.4
6.5
74.4(74.5)
63.8(63.8)
61.0(60.7)
59.0(59.0)
48.6(48.6)
35.0(35.0)
60.1(60.2)
63.063.0)
64.4(64.4)
65.1(65.1)
42.7(42.8)
51.1(51.0)
49.1(48.6)
49.5(49.6)
52.1(52.9)
62.0(61.3)
57.0(56.3)
54.0(53.5)
47.2(47.1)
41.9(41.7)
5.97(6.2)
5.5(5.7)
4.2(4.5)
4.9(5.1)
4.9(5.1)
4.6(3.8)
5.4(4.9)
4.7(4.8)
4.9(5.0)
4.6(5.2)
4.5(4.4)
4.4(4.4)
4.6(4.4)
4.8(4.8)
4.6(4.8)
5.0(4.9)
4.7(4.3)
4.6(5.2)
3.8(3.9)
3.7(3.9)
10.9(10.6)
8.76 (9.0)
10.5(10.3)
8.8(8.6)
6.0(6.1)
12.1(11.9)
9.2(8.8)
8.8(8.8)
11.0(11.0)
9.1(9.5)
6.2(6.2)
7.7(7.4)
7.5(7.1)
7.0(7.3)
7.3(7.7)
8.5(8.2)
10.7(11.0)
8.2(7.8)
6.7(6.9)
5.6(5.6)
–
–
[(HL)(H2L)Ni(OAc)(H2O)].3H2O Red
240
180
215
250
240
170
240
255
180
170
200
105
230
220
140
220
–
6.5(6.2)
3
[(L)(HL)Ni2(NO3)]
Green
–
12. 6(12.4)
12.3(12.0)
17.0(17.1)
12.6(14.3)
12.1(12.3)
13.8(13.3)
7.8(7.1)
7.5(7.2)
16.8(16.3)
9.7(9.9)
16.8(17.1)
15.7 (15.7)
15.8(16.4)
12.81(12.8)
13(12.8)
12.2(12.1)
23.1(22.7)
31.5(31.8)
4
[(L)(HL) Ni2Cl].3H2O
[(L)Co2(OAc)2(H2O)].3H2O
[(H2L)Co2(NO3)4(H2O)3].H2O
[(L)(HL)Co2Cl].2H2O
[(L)(HL)Cu2(OAc)]
Yellow
Brown
Brown
Brown
Brown
Brown
Green
Yellow
Brown
Black
4.0(3.4)
5
–
–
6
7
4.0 (3.7)
–
8
9
[(HL)(H2L)Cu(NO3) (H2O)]
[(HL)(H2L)CuCl(H2O)].H2O
[(HL)Mn2Cl3(H2O)4]
[(HL)FeCl2(H2O)]
[(HL)RuCl2(H2O)].H2O
[(HL)ZrOCl].3H2O
–
10
11
12
13
14
15
16
17
18
19
20
4.5(4.0)
15.5(15.8)
18.4(18.8)
11.5(12.0)
6.4(6.1)
6.8 (6.5)
–
Green
Green
Yellow
Green
Orange 200
Orange 300
Yellow
[(HL)2HfCl2 ].4H2O
[(HL)Zn(OAc)]
[(HL)Zn(NO3)]
–
[(HL)ZnCl].3H2O
6.9 (6.6)
5.7(5.8)
–
[(HL)LaCl2(H2O)]
[(HL)(UO2)(OAc) ].2H2O
175
form with no evidence for the presence of the enol form from the
appearance of the NH signal and also the absence of the signal OH
of the enol form. Multiplet signals in the 7.73–6.8 ppm range are
due to aromatic protons.11 The resonances at 5.17, 4.9 and 2.40 ppm
correspond to the protons of methylene groups of the acetohydrazide
and dibenzoyl moieties and methyl groups respectively.15,16
3100 and 827–755 cm-1 ranges are due to the presence of coordinated
water molecules as in complexes (5), (6), (11), (12), (13) and (19),
whereas the band which appears in the 3670–3340 range is due to
the presence of water molecules of hydration as in complexes (2),
(4–7), (10), (13–15), (18) and (20).17,20,21 However, n(NH) appears in
the 3435–3348 and 3255–3200 cm-1 ranges20,21 (Table 2, deposited in
the ESI). The complexes show a band in the 1711–1640 cm-1 range
(Table 2, deposited in the ESI), which is assigned to n(C=O) except
for complex (5).22 The bands that appear in the 1650–1594, 1596–
1549, 1543–1517 and 1389–1223 cm-1 ranges are due to n(C=N),
n(C=C)Ar and n(CH=C) and n(C-O) vibrations respectively.19,20,23
For metal acetate complexes the monodentate coordination is shown
by the occurrence of na(CO2) at a frequency lower than ns(CO2),24,25
As a result, the separation between the two bands is much larger in
monodentate complexes as in complexes (2), (5), (16) and (20) (i.e.,
na(CO2) = 1556, 1605, 1540 and 1605 cm-1, ns(CO2) = 1417, 1398,
1417 and 1400 cm-1 respectively). In addition, complex (5) shows
n(CO2) at 1549 and 1456 cm-1 due to a bridging acetate group.24,25
Complexes (3), (6), (9) and (17) show several bands in the 1398–
1383, 1229–1181 and 850–835 cm-1 ranges (Table 2, deposited in
the ESI), assigned to a bridging or coordinating nitrate group.25,26
Complexes (4), (7), (8), (10–15), (18) and (19) show bands in the 423–
419, 370–350 cm-1 ranges corresponding to coordinated and bridging
chloride atoms. However, complex (14) shows a band at 760 cm-1
assigned to n(ZrO).27 Complex (21) shows a band at 940 cm-1 due to
its O = U = O group.27
Conductivity measurements
The molar conductance values of the complexes are in the (2.8–8.2
Ω-1cm2mol-1) range (Table 1), these low values indicate the non–
electrolytic nature of the complexes.15 This confirms that the anion is
coordinated to the metal ion.
IR spectra
Important spectral bands of the ligand and its complexes are
presented in Table 2 (deposited in the ESI). The IR spectrum of the
ligand (H2L) shows broad, medium intensity bands in the 3650–3260
and 3245–2780 cm-1 ranges, which are attributed to intra- and inter-
molecular hydrogen bonding.17 The spectrum shows bands at 3405,
3270, 1714 and 1656 cm-1, assigned to the n(NH), n(C=O) and
n(C=N) respectively,18,19 confirmed the ketonic form of the ligand.
Also, a band appears at 1597 cm-1 corresponding to n(C=C)Ar.19,20
In order to know the mode of coordination between the ligand and
the metal ion, the IR spectrum of the ligand was compared with
those of the metal complexes. The complexes show broad bands
in the 3565–3225 and 3260–2730 cm-1 ranges due to intra- and
intermolecular hydrogen bondings17 and other bands in the 3350–
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Fig. 2 Structural representation of metal complexes.
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The spectral results together with elemental analyses indicated that
the hydrazone can behave as a neutral bidentate (H2L), monobasic
bidentate (HL-), monobasic tridentate (HL-) or dibasic tridentate (L2-)
ligand towards the metal ions, and also, the ligand is coordinated to
the metal ion by the carbonyl oxygen of the hydrazide moiety and
carbonyl oxygen of the dibenzoylmethane moiety in the enolic or
ketonic form, as well as by azomethine nitrogen atoms.
and having an axial symmetry type of a d(x2-y2) ground state, which
is the most common for copper(II) complexes.33,42 The g-values
suggest a square planar or octahedral geometry23 and the complexes
show g||>g┴>2.0023, indicating a distortion around the copper(II)
ion43,44 The ESR parameters for the complexes are shown in Table 4
(deposited in the ESI). The g-values are related by the expression,43,44
G = (g||-2)/(g┴-2). If G > 4.0, then local tetragonal axes are aligand
parallel or only slightly misaligand and if G < 4.0, significant
exchange coupling is present. Complex (8) shows a value of 3.33,
indicating spin-exchange interaction takes place between copper(II)
ions, which is compatible with the magnetic moment value. However,
complexes (9) and (10) show G > 4.0 (Table 4, deposited in the ESI),
indicating tetragonal axes are present in these complexes. Also, the
g||/A|| values are considered as diagnostic of stereochemistry.43,44
The g||/A|| value for the complexes (Table 6, deposited in the ESI) lie
just within the range of expected structures. The g| -values reported
here are 2.2, 2.26 and 2.27 respectively, indicating considerable
covalent bonding character in these complexes.23,42,43 The isotropic
value of the hyperfine coupling constant Aiso is related to the σ-
bonding parameter (a2).44,46 If a2 = 1, the bond would be completely
ionic and if a2 = 0.5, the bond would be completely covalent.
The calculated values of a2 for complexes (8), (9) and (10) are 0.73,
0.64 and 0.63 respectively, suggesting covalent bonding.42,44 The
orbital reduction factor (K)45 can be used to measure the covalent
character of the metal-ligand band. For an ionic environmental,
K = 1 and for a covalent environmental K < 1; the lower the
value of K, the greater is the covalent character. The K-values for
the complexes (Table 4, deposited in the ESI) are indicative of a
covalent nature.23,42,43 Also, the in-plane and out-of plane π-bonding
Magnetic moments
Room temperature magnetic moments of the complexes (2–20) are
shown in Table 3 (deposited in the ESI). Nickel(II) complexes (3) and
(4) show diamagnetic values confirming a square planar geometry
around the nickel(II) ion. However, complex (2) shows 2.74 B.M.,
indicating octahedral geometry around the nickel(II) ion.24,28
Cobalt(II) complexes (5), (6) and (7) show values 3.4 and 4.2 and
3.2 B.M. (Table 1), which could indicate high spin square planar or
octahedral cobalt(II) complexes.8,29 However, the low values of (5)
and (7) indicate spin-exchange interactions take place between the
cobalt(II) ions in a square planner geometry. The magnetic moments
for the copper(II) complexes (8), (9) and (10) are 1.5, 1.81 and 1.72
B.M respectively. The value of complex (8) is well below the spin-
only value (1.73 B.M.), indicating spin-exchange interactions take
place between the copper(II) ions in a square planar environmental.30
However, the values of complexes (9) and (10) correspond to one
unpaired electron in an octahedral structure.8 The magnetic moment
value for manganese(II) complex (11) is 4.92 B.M., suggesting a high
spin octahedral geometry around the manganese(II) ion.17 The low
value is due to the presence of spin-exchange interactions between
the Mn(II) ions. Iron(III) complex (12) shows a value 5.66 B.M,
indicating a high spin iron(III) octahedral geometry.8 Ruthenium(III)
complex (13) shows a magnetic value 1.6 B.M indicating an
octahedral structure.31 Zirconium(IV) (14), hafnium(IV) (15),
zinc(II) complexes (16–18), lanthanum(III) (19) and uranyl(II) (20)
complexes are diamagnetic.
coefficients (b1 and B2) can be calculated.23,42,43 The complexes
2
show b2 and b2 values (Table 6, deposited in the ESI) that indicate
ionic character1in the in-plane π and covalent character in out-of
plane π-bonding.46 It is possible to calculate approximate orbital
populations for p or d orbitals using the following equations,47 where
Ao and 2B0 are the calculated dipolar couplings for unit occupancy of
s and d orbitals respectively.
Electronic spectra
The electronic spectral data of the ligand and its complexes in
DMF solution are presented in Table 3 (deposited in the ESI).
The ligand exhibits bands at 310 and 220 nm, assigned to n→π*
and π→π*transitions.17 The nickel(II) complex (2) shows bands at
345, 480 and 650 nm; the bands are attributable to 3A2g(F)→3T1g(P)
A11 = Aiso-2B[1± (7/4) ∆g11]
(1)
(2)
a2p, d = 2B/2B0
3
3
(υ3), A2g(F)→3T1g(F) (υ2) and A2g(F)→3T2g(F) (υ1) transitions
respectively of an octahedral nickel(II) complex.32 The υ2/υ1 ratio
is 1.37 indicating a distorted octahedral nickel(II) complex.33
However, complexes (3) and (4), show bands at 460 and 510 and
450 and 520 nm respectively. The bands are assigned to 3T1→3T2
When the data are analysed using the Cu63 hyperfine coupling and
considering all the sign combinations, for complexes (8), (9) and
(10) the only physically meaningful results are found when A11 and
A┴ are negative. The resulting isotropic coupling constant and the
parallel component of the dipolar coupling) are negative. The orbital
3
and T1(F)→3T2(P) transitions, of a square planar nickel(II) ion.27,34
2
population (ad %) for the complexes (Table 4, deposited in the ESI)
indicate that the main orbital is the d(x2-y2) ground state.44 However,
the ESR spectra of manganese(II) and ruthenium(III) complexes are
of the isotropic type with giso = 2.024 and 2.11 respectively, typical
of octahedral structure. The iron(III) complex (12) shows gav = 4.38
arising from very large zero field splitting effect. This g- value indicates
a high spin (5/2) octahedral geometry around the iron(III) ion.
The cobalt(II) complexes (5) and (7) show bands in the 460, 545 and
620 nm and 475, 555 and 610 nm respectively are which assigned to
a square planar geometry.35 However, complex (6) shows bands at
4
455, 550 and 650 nm; these bands are assigned to T1g(F)→4T2g(F),
4T1g(F)→4A2g and 4T1g(F)→4T1g(P) transitions respectively of a high
spin cobalt(II) octahedral complex.36 The copper(II) complexes (8),
(9) and (10) show different bands (Table 3, deposited in the ESI).
Complex (8) shows bands at 395, 480 and 590 nm, corresponding
Thermal analyses
2
2
to B1g→2B2g, 2B1g→2Eg and B1g→2A1g transitions respectively of
a square planar geometry.37 However, complexes (9) and (10) show
bands at 390, 475 and 640 nm and 395, 480, 650 nm respectively.
The bands are assigned to ligand→copper charge transfer, 2B1→2E
and 2B1→2B2 transitions, in a distorted octahedral structure.38
Manganese(II) complex (11) shows bands at 485, 550 and 650 nm,
The results of TG and DTAanalyses of complexes are shown in Table 5
(deposited in the ESI). The results show that complexes (2), (4), (13–
15) and (18) lose hydrated water molecules in the temperature range
60–100°C; this process is accompanied by an endothermic peak.
The coordinated water molecules were eliminated from complexes
(2), (6), (11) and (13) at relatively higher temperature than those
of the hydrated water molecules (110–170°C) (Table 5, deposited
in the ESI). The removal of an HCl molecule (accompanied by an
endothermic peak) was observed for (4), (11), (13–15) and (18)
complexes in the temperature 240–310°C range, compatible with
the TG result. For complex (6), the removal of an HNO3 molecule,
also accompanied by an endothermic peak, was observed in the
280–295°C range, compatible with the TG result. The removal of
a CH3COOH molecule, (accompanied by an endothermic peak), for
complex (12) occurs at 320°C, compatible with the TG result. The
complexes decompose through degradation of the hydrazone ligand
at a temperature above 400°C leaving metal oxides (490–660°C)
(Table 5, deposited in the ESI).
6
6
6
corresponding to A1g→4Eg, A1g→4T2g and A1g→4T1g transitions
which are compatible to an octahedral geometry around the
manganese(II) ion.39 Iron(III) complex (12) shows bands at 475, 550
and 640 nm. The first two bands are due to charge transfer transitions
while the last band is considered to arise from the 6A1→4T1 transition;
these bands suggest a distorted octahedral geometry around the
iron(III).35,37 Ruthenium(III) complex (13), shows bands at 475, 575
and 620 nm. The first bands are due to LMCT transitions and the
other band is assigned to a 2T2g → 2A2g transition. The band positions
are similar to those observed for other octahedral ruthenium(III)
complexes.31,40 Zirconium(IV) complex (14), hafnium(IV) (15),
zinc(II) (16-18), lanthanum(III) (19) and uranyl(VI) (20) complexes
show bands (Table 3, deposited in the ESI) indicating intraligand
transitions.37,41
Antibacterial and antifungal screening
The ligand and its complexes have been screened for their
antibacterial and antifungal activities and the results obtained are
presented in Table 6 (deposited in the ESI). It is observed that the
activity of the complexes increases with increase in the concentration
Electron spin resonance
The ESR spectra of solid copper(II) complexes (8), (9) and (10) at
room temperature are characteristic of a specie with a d9 configuration
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of the compounds tested. All the metal complexes are more potent
bactericides and fungicides than the ligand.49-50 The results (Table 6,
deposited in the ESI) show that Ru(III) complex (13) has higher
antibacterial activity but Zn(II) complex (18) shows higher
antifungal activity than the other complexes. For bacteria, the order
of activities of these complexes is (13)>(19)>(10) = (18)>(12)>
(4)>(11)>(7)>(15)>(14) = (1) and for fungi, the order of activities
is (18)>(10) = (13) = (19)>(11)>(12) = (14)>(4) = (15)>(7) = (1).
The variation in the activity of different complexes against different
microorganisms depends either on the impermeability of the
microbel cells or differences in the ribosomes of microbial cells.
The increased activity of the metal chelates can be explained on the
basis of chelation theory.49 It is known that chelation tends to make
the coordinated ligand act as more powerful and potent bacterial and
fungicidal agent, thus killing more of the bacteria and fungi than the
free ligand precursor. 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.51 This increases the lipophilic character of the metal
chelate and favours its permeation through the lipoid layer of the
organism membrane. There are other factors which also increase the
activity, which are the number of coordination sites, size of complex,
solubility, conductivity and also the bond lengths between the metal
and the coordinated ligand atoms.
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45 R.K. Ray, Inorg. Chem. Acta,1990, 174, 257.
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Received 2 September 2009; accepted 26 November 2009
Paper 09/0772 doi:10.3184/030823409X12596063380927
Published online: 8 December 2009
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