Synthesis and anti-fungicidal activity of some transition metal complexes with benzimidazole dithiocarbamate ligand

Article abstract of DOI:10.1016/j.saa.2008.10.051

Seven transition metal complexes of benzimidazole ligand (HL) are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analyses (TGA and DTA). From the obtained data, the complexes w

Full text of DOI:10.1016/j.saa.2008.10.051

Spectrochimica Acta Part A 72 (2009) 610–615
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and anti-fungicidal activity of some transition metal complexes with
benzimidazole dithiocarbamate ligand
Gehad G. Mohameda,∗, Nasser A. Ibrahimb, Hanaa A.E. Attiab
a Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
b Central Agr. Pest. Lab., Agricultural Research Center (ARC), Dokki, Giza, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 May 2008
Accepted 31 October 2008
Seven transition metal complexes of benzimidazole ligand (HL) are reported and characterized based
on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analyses
(TGA and DTA). From the obtained data, the complexes were proposed to have the general formulae
2−
[MX2(HL)(H2O)]·yH2O, where M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cr(III); X = Cl−, SO4 and y = 0–4. The
Keywords:
Benzimidazole ligand
Dithiocarbamate
Transition metal complexes
IR
Magnetic moment
Thermal analysis
molar conductance data revealed that all the metal chelates were non-electrolytes. From the magnetic and
solid reflectance spectra, it was found that the geometrical structure of these complexes is octahedral.
The thermal behaviour of these chelates showed that the hydrated complexes loss water molecules of
hydration in the first step followed immediately by decomposition of the anions and ligand molecules in
the subsequent steps. Fungicidal activity of the prepared complexes and free ligand was evaluated against
three soil borne fungi. Data obtained showed the higher biological activity of the prepared complexes than
the parent Schiff base ligand. Formulation of the most potent complex was carried out in the form of 25%
WP. Fungicidal activity of the new formulation was evaluated and compared with the standard fungicide
Pencycuron (Monceren 25% WP). In most cases, the new formulation possessed higher fungicidal activity
than the standard fungicide under the laboratory conditions.
Soil borne fungi and WP formulation
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
of the complexes are studied. The structure of HL ligand is given in
Fig. 1.
Many biological active heterocyclic compounds containing the
dithiocarbamate and/or benzimidazole moieties as well as their
transition metal complexes were reported [1–3]. As a results, many
fungicides [1,4,5], bactericides [3,5], acaricides [6], nematocides [7],
insecticides [6–9] and other pharmaceutical as well as agricultural
compositions were found to contain one or more of these bioactive
groups [10,11]. In view of this fact, our earlier work was concerned
with the synthesis of new benzimidazole derivatives containing the
dithiocarbamate functional group which found to be promising as
antifungal agent [12]. In continuation with this recent work, it was
thought of interest to explore the ligational behaviour of one of
these derivatives with some transition metals aiming to increase its
fungicidal potency. Metal chelates with Cr(III), Mn(II), Co(II), Ni(II),
Cu(II), Zn(II) transition metals are prepared and characterized using
different physico-chemical techniques like elemental analyses (C,
H, N, S and metal content), IR, magnetic moment and reflectance
spectra, and thermal analyses (TGA and DTA). Biological activities
2. Experimental
2.1. Materials and reagents
All chemicals used were of the analytical reagent grade (AR),
and of highest purity available. They included copper(II) chlo-
ride and sulphate di- and penta-hydrates (Prolabo); cobalt(II) and
nickel(II) chloride hexahydrates (BDH); zinc chloride dihydrate
(Ubichem), manganese(II) and chromium(III) chlorides (Sigma).
Zinc oxide, disodium salt of ethylenediaminetetraacetic acid; EDTA;
(Analar), ammonia solution (33%, v/v) and ammonium chloride (El-
Nasr Pharm. Chem. Co., Egypt). Organic solvents used included
absolute ethyl alcohol, diethylether, dimethylformamide (DMF)
and dimethylsulphoxide (DMSO). Hydrochloric and nitric acids
(MERCK) were used. De-ionized water collected from all glass
equipments was usually used in all preparations. Antifungal sus-
ceptibility testing was performed in potato-dextrose agar (PDA)
media containing drops of 25% lactic acid to prevent the bacte-
rial contamination. A series of concentrations for each investigated
compound was carried out using DMSO as a solvent.
∗
Corresponding author.
E-mail address: ggenidy@hotmail.com (G.G. Mohamed).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.10.051

G.G. Mohamed et al. / Spectrochimica Acta Part A 72 (2009) 610–615
611
ter) were cut from the margins of actively growing cultures of the
F. solani, R. solani and S. rolfesii fungi and placed in the center of
compound-amended and unamended PDA plates with 4 replicate
plates for each fungus. All plates were incubated at 25 1 ◦C. Colony
diameter (in mm) was measured after 3 days for R. solani, S. rolf-
sii and 7–12 days for F. solani fungi and the percentage of growth
inhibition was calculated for each compound. The estimated effec-
tive concentration (EC50) which gives 50% inhibition of fungi radial
growth, toxicity index (T.I.) and slopes of toxicity lines for each
compound under investigation were determined and tabulated in
Table 5.
Fig. 1. Structure of HL ligand.
2.2. Instruments
The molar conductance of solid complexes in DMF was
measured using Sybron–Barnstead conductometer (Meter-PM.6,
E = 3406). Elemental microanalyses of the separated solid chelates
for C, H, N and S were performed in the Microanalytical Cen-
ter, Cairo University. The analyses were repeated twice to check
the accuracy of the data. Infrared spectra were recorded on a
PerkinElmer FT-IR type 1650 spectrophotometer in wave number
region 4000–200 cm−1. The spectra were recorded as KBr pel-
lets. The solid reflectance spectra were measured on a Shimadzu
3101pc spectrophotometer. The molar magnetic susceptibility was
measured on powdered samples using the Faraday method. The
diamagnetic corrections were made by Pascal’s constant and
Hg[Co(SCN)4] was used as a calibrant. The thermal analyses (TGA,
DrTGA and DTA) were carried out in dynamic nitrogen atmosphere
(20 mL min−1) with a heating rate of 10 ◦C min−1 using Shimadzu
TGA-50H and DTA-50H thermal analyzers.
3. Results and discussion
3.1. Composition and structures of the complexes
The isolated solid complexes of Cr(III), Mn(II), Co(II), Ni(II), Cu(II)
and Zn(II) ions with the HL ligand were subjected to elemental
analyses (C, H, N, S and metal content), IR, magnetic studies, molar
conductance and thermal analyses (TGA and DTA) to identify their
tentative formulae in a trial to elucidate their molecular structures.
The results of elemental analyses (Table 1), are in good agreement
with those required by the proposed formulae. The formation of
these complexes may proceed according to the following equations
given below.
MClx + HL + H2O + yH2O → [MClx(HL)(H2O)]yH2O
(1)
2.3. Synthesis of HL ligand
M = Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II);x = 2–3;y = 0–4.
The used ligand which is formulated as diethyl S-(1H-
benzimidazol-2-yl)metyl dithiocarbamate was prepared by the
standard reported method [12] (Fig. 1).
CuSO4 + HL → [CuSO4(HL)]
(2)
3.1.1. Molar conductivity measurements
2.4. Synthesis of metal complexes
The chelates were dissolved in DMF and the molar conductivi-
ties of 10−3 M of their solutions at 25 2 ◦C were measured. Table 1
shows the molar conductance values of the complexes. It is con-
cluded from the results that the chelates are found to have molar
conductance values of 8.68–23.45 ꢀ−1 mol−1 cm2 indicating that
these chelates are non-electrolytes. It, also, indicates the bonding
of the sulphate or chloride anions to the metal ions.
Hot solution (60 ◦C) of the appropriate metal chloride or sul-
phate (1 mmol) in an ethanol–water mixture (1:1, 25 mL) was
added to the hot solution (60 ◦C) of the HL ligand (0.279 g, 1 mmol)
in the same solvent (25 mL). The resulting mixture was stirred
under reflux for 1 h whereupon the complexes precipitated. They
were collected by filtration, washed with a 1:1 ethanol:water mix-
ture and diethyl ether. The analytical data for C, H, N and S were
repeated twice.
3.1.2. Magnetic susceptibility and electronic spectra
measurements
2.5. Biological study
For the hexacoordinated Cr(III) complex, there are three spin-
4
4
allowed transitions in the electronic spectrum, ␯1: B1g → Eg
4
4
4
4
Fungicidal activity of the synthesized complexes in term of their
inhibition to the linear growth of Fusarium solani, Rhizoctoni solani
and Sclerotium rolfesii soil borne fungi.
(4T2g), ␯2: B1g → B2g (4T2g) and ␯3: B1g → Eg (4T1g) [14,15].
The diffuse reflectance spectrum of the Cr(III) chelate shows three
absorption bands at 18,750 (␯1), 26,890 (␯2) and 36,450 (␯3).
The magnetic moment at room temperature is 3.86 B.M. which
corresponds to three unpaired electrons for a d3 Cr(III) ion and
confirm octahedral geometry for this complex [14,15]. The dif-
Potato-dextrose agar (PDA) was used to evaluate the effect
of the selected compounds under investigation on the mycelial
linear growth of three tested fungi. Fifty milliliters of the afore-
mentioned medium were poured into 150 mL conical flasks and
autoclaved at 121 ◦C for 20 min. Three drops of 25% lactic acid were
added to prevent bacterial contamination. Dilutions for each of the
tested compound were carried out (v/v) by dissolving appropri-
ate amounts of each compound in 10 mL DMSO. Equal volumes of
DMSO containing diluted compounds were added to sterile molten
(40 ◦C) PDA to get a series of concentrations of 125, 250, 500 and
1000 ppm for each compound in PDA [13].
fuse reflectance spectrum of the Mn(II) complex shows three
6
bands at 17,570, 22,442 and 26,970 cm−1 assignable to 4T1g → A1g
,
4T2g(G) → A1g and T1g(D) → A1g transitions, respectively [14].
The magnetic moment value is 5.44 B.M. which indicates the pres-
ence of Mn(II) complex in octahedral structure. The electronic
spectrum of the Co(II) complex gives three bands at 15,765, 18,978
and 23,430 cm−1 wave number regions. The bands observed are
6
4
6
assigned to the transitions 4T1g(F) → T2g(F) (␯1), 4T1g(F) → A2g(F)
4
4
4
A zero (0) concentration treatment was prepared for each fun-
gus, which contains equivalent volume of solvent only, and used
as control. Compounds-amended PDA were dispensed aseptically
into 9 cm diameter petridishes. Plugs of mycelium (4 mm diame-
(␯2) and 4T1g(F) → T2g(P) (␯3), respectively, suggesting that there
is an octahedral geometry around Co(II) ion [14,16,17]. The mag-
netic susceptibility measurements lie at 4.95 B.M. (normal range
for octahedral Co(II) complexes is 4.3–5.2 B.M.), is an indicative of

612
G.G. Mohamed et al. / Spectrochimica Acta Part A 72 (2009) 610–615
octahedral geometry [14]. The region at 25,990 cm−1 refers to the
ligand to metal charge transfer band.
The Ni(II) complex reported herein has a room temperature
magnetic moment value of 3.17 B.M.; which is in the normal
range observed for octahedral Ni(II) complexes (ꢁeff = 2.9–3.3 B.M.)
[14,18]. This indicates that, the complex of Ni(II) is six coordi-
nate and probably octahedral [14,18]. The electronic spectrum,
in addition to show the ␲–␲* and n–␲* bands of free ligands,
displays three bands, in the solid reflectance spectrum at ␯1:
3
3
16,350 cm−1
22,754 cm−1
:
:
3A2g → T2g; ␯2: 18,922 cm−1
:
3A2g → T1g(F) and ␯3:
3A2g
→
3T1g(P). The spectrum shows also a band at
25,655 cm−1 which may attribute to ligand to metal charge trans-
fer. The reflectance spectra of Cu(II) chelates consist of a broad band
centered at 17,637 and 19,467–20,722 cm−1. The 2Eg and 2T2g states
of the octahedral Cu(II) ion (d9) split under the influence of the
tetragonal distortion and the distortion can be such as to cause
2
2
2
2
2
the three transitions B1g → B2g
;
2B1g → Eg and B1g → A1g to
remain unresolved in the spectra [19].
It was concluded that all three transitions lie within the single
broad envelope centered at the same range previously men-
tioned. The magnetic moment of 1.98–2.02 B.M. falls within the
range normally observed for octahedral Cu(II) complexes [14,19].
A moderately intense peak observed at 25,364 cm−1 is due to
ligand–metal charge transfer transition [14,19]. The complex of
Zn(II) is diamagnetic. According to the empirical formula, an octa-
hedral is proposed for this complex.
3.1.3. IR spectra and mode of bonding
The infrared spectra of the title ligand and its metal(II)
or metal(III) complexes and important characteristic absorption
bands, along with their proposed assignments, are summarized
in Table 2. The IR spectra of the complexes are very similar to
each other, except some slight shifts and intensity change of a few
vibration bands caused by different metal ions, which indicate that
the complexes have similar structures. However, there are some
significant changes between the metal complexes and their free
ligand for chelation as expected. The coordination mode and sites
of the ligand to the metal ions were investigated by comparing
the infrared spectra of the free ligand with its metal complexes.
Upon coordination, it is noteworthy that the peak at 1678 cm−1
attributed to ␯(C N) vibration originating from N-3 imidazole ring,
is disappeared or shifted by 24–30 cm−1 on complexation, indi-
cating coordination of N-3 atom to metal ions [20]. In addition, IR
spectrum of the ligand revealed a sharp band at 1270 cm−1 due
to ␯(C S) of side chain, which is slightly shifted to higher fre-
quency at about 3–7 cm−1 after complexation in all complexes,
suggesting that sulfur atom of the side chain also contributes to
the complexation. The band observed at 1088 cm−1 in the free
HL ligand is appeared at relatively lower field (1059–1070 cm−1
)
in the complexes which may indicates coordination via the C–S
group [21].
The IR bands at 840 and 750 cm−1, ꢂ(H2O) of coordinated
water, is an indication of the binding of the water molecules to
the metal ions. New bands are found in the spectra of the com-
plexes in the regions 552–622, 480–560 and 428–439 cm−1, which
are assigned to ꢂ(M–N), ꢂ(M–S) and ꢂ(M–S) stretching vibrations
[21,22]. Therefore, from the IR spectra, it is concluded that HL lig-
and behaves as a neutral tridentate ligand coordinated to the metal
ions via the imidazole N-3, C S and C–S groups.
3.1.4. Thermal analyses (TGA, DrGA and DTA)
In the present investigation, heating rates were suitably con-
trolled at 10 ◦C min−1 under nitrogen atmosphere and the weight
◦
∼
loss was measured from the ambient temperature up to 1000 C.
=

G.G. Mohamed et al. / Spectrochimica Acta Part A 72 (2009) 610–615
613
Table 2
1R data (4000–400 cm−1) of HL and its metal complexes.
Compound
ꢂ(C N)
Y(C S)
ꢂ(C–S)
ꢂ(M–N)
ꢂ(M–S)
ꢂ(M–S)
HL
1678m
1270sh
1274sh
1273s
1275sh
1274sh
1277m
1275sh
1277sh
1088sh
1062w
1067m
1069m
1070m
1068sh
1070m
1059sh
—
—
—
[MnCl2(HL)(H2O)]·H2O
[CrCl3(HL)]·2H2O
[CoCl2(HL)(H2O)]·H2O
[NiCl2(HL)(H2O)]·H2O
[CuCl2(HL)(H2O)]·4H2O
[CuSO4(HL)]
Disappear
Disappear
Disappear
Disappear
1706sh
570w
615m
557w
622w
621m
616m
552m
480w
560w
483m
520w
540w
485m
485m
439w
428m
428w
430w
434m
436m
433m
1656m
Disappear
[ZnCl2(HL)(H2O)]·3H2O
sh = sharp, m = medium, s = small, and w = weak.
The data are listed in Table 3. The weight losses for each chelate
are calculated within the corresponding temperature ranges. The
different thermodynamic parameters are listed in Table 4. The
thermogram of [MnCl2(HL)(H2O)]·H2O chelate shows four decom-
position steps within the temperature range 30–850 ◦C. The first
step of decomposition within the temperature range 30–90 ◦C cor-
responds to the loss of water molecule of hydration with a mass loss
organic part of the ligand and 2HCl molecules (mass loss = 80.47%;
calcd. = 80.0%) leaving MnO as a residue. The overall weight loss
amounts to 85.09% (calcd. 84.09%).
The TGA curve of the Cr(III) chelate shows four stages of decom-
position within the temperature range of 30–800 ◦C. The first stage
within the temperature range from 30 to 145 ◦C corresponds to
the loss of two water molecules of hydration (mass loss = 7.85;
calcd. = 7.60). The energy of activation for this dehydration step
is 55.25 kJ mol−1. While the subsequent (2nd, 3rd and 4th) stages
of 4.62% (calcd. 4.09%). The energy of activation is 33.23 kJ mol−1
.
The subsequent steps (90–850 ◦C) correspond to the removal of the
Table 3
Thermoanalytical results (TGA and DTA) of HL and its metal complexes.
Complex
TG range (◦C)
DTA (◦C)
n*
Mass loss
Total mass loss
Assignment
Metallic residue
MnO
Estimated (calcd.) %
(1)
30–90
55(+), 140(+), 170(−), 230(−), 360(−), 450(−),
550(−), 660(−)
1
3
4.62 (4.09)
Loss of H2O
90–850
80.47 (80.00)
85.09 (84.09)
Loss of 2HCl and HL
(2)
(3)
(4)
(5)
30–145
145–800
40(−), 72(+), 190(+), 210(−), 230(+), 430(−),
520(−), 650(+), 710(−)
1
3
7.85 (7.60)
77.97 (77.61)
Loss of 2H2O
Loss of 3HCl and HL
CrS
85.82 (85.21)
84.73 (83.15)
79.70 (79.55)
84.42 (84.21)
30–85
85–800
50(+), 120(+), 205(+), 230(−), 250(+),
275(+), 494(+), 620(−)
1
3
4.81 (4.05)
79.92 (79.10)
Loss of H2O
Loss of 2HCl and HL
CoO
NiS
30–160
16–850
60(+), 95(−), 160(+), 195(−), 250(−), 320(−),
450(+), 530(−), 680(−)
1
3
8.63 (8.09)
71.07 (71.46)
Loss of 2H2O
Loss of 2HCl and HL
30–150
150–800
50(−), 80(+), 110(+), 150(−), 210(−), 250(+),
320(−), 440(−), 550(−)
1
2
14.91 (14.30)
69.51 (69.91)
Loss of 4H2O
Loss of 2HCl and HL
CuO
n* = number of decomposition steps.
(1) [MnCl2(HL)(H2O)]·H2O, (2) [CrCl3(HL)]·2H2O, (3) [CoCl2(HL)(H2O)]·2H2O, (4) [NiCl2(HL)(H2O)]·H2O and (5) [CuCl2(HL)(H2O)]·4H2O.
(+) = endothermic and (−) = exothermic.
Table 4
Thermodynamic data of the thermal decomposition of metal complexes of HL.
о
Complex
Decomp. temp. ( C)
E* (kJ mol−1
)
A (s−1
)
ꢃS* (kJ mol−1
)
ꢃH* (kJ mol−1
)
ꢃG* (kJ mol−1
)
[MnCl2(HL)(H2O)]·H2O
30–90
90–170
170–450
450–850
33.23
74.67
109.1
145.3
3.29 × 107
5.55 × 1010
7.11 × 1011
6.23 × 106
−48.72
−100.7
−164.6
−220.5
53.52
81.69
108.6
162.8
70.4
126.5
188.7
223.6
[CrCl3(HL)]·2H2O
30–145
145–300
300–650
650–800
55.25
63.99
145.6
198.7
3.66 × 107
7.63 × 109
2.99 × 1013
4.68 × 1011
−66.95
−128.7
−203
94.82
151.5
225.9
302.5
79.81
137.4
235.6
335.6
−256.4
[CoCl2(HL)(H2O)]·H2O
[NiCl2(HL)(H2O)]·H2O
[CuCl2(HL)(H2O)]·4H2O
30–85
85–250
250–510
510–800
46.89
105.4
184.3
256.7
4.66 × 1010
3.98 × 107
5.19 × 1013
6.35 × 108
−39.83
−129.8
−194.6
−275.3
50.63
90.36
162.7
256.3
72.63
135.7
244.6
303.4
30–160
160–470
470–620
620–800
50.59
118.7
192.6
263.4
2.69 × 107
5.47 × 1010
6.07 × 1011
4.69 × 107
−40.69
−75.44
−103.2
−172.6
66.77
136.3
217.6
249.6
86.88
186
245
277.8
30–150
150–400
400–800
33.67
96.85
188.2
5.62 × 1010
2.98 × 1014
3.89 × 1012
−30.83
−99.87
−204.6
55.63
130.4
262.7
78.63
145.7
274.6

614
G.G. Mohamed et al. / Spectrochimica Acta Part A 72 (2009) 610–615
Fig. 2. Suggested structure of metal complexes.
involve the loss of 3HCl and ligand molecules with a mass loss of
77.97% (calcd. 77.61%). The overall weight loss amounts to 85.82%
(calcd. 85.21%).
(calcd. 84.21%). The data given also in Table 3 show the DTA results
obtained during the thermal decomposition of the complexes. All
the complexes give an endo- and exo-thermic peaks within the
temperature ranges of decomposition.
On the other hand, [CoCl2(HL)(H2O)]·H2O chelate exhibits four
decomposition steps. The first step in the temperature range
30–85 ◦C (mass loss = 4.81%; calcd. for H2O; 4.05%) may accounted
for the loss of water molecule of hydration. The energy of activation
for this step is 46.89 kJ mol−1. As shown in Table 4, the mass losses
of the remaining decomposition steps amount to 79.92% (calcd.
79.10%). They correspond to the removal of 2HCl and HL molecules
leaving CoO as a residue. The values of energy activation for these
steps are 105.4, 184.3 and 256.7 kJ mol−1 for the 2nd, 3rd and 4th
steps, respectively.
3.1.5. Kinetic data
The thermodynamic activation parameters of decomposition
processes of dehydrated complexes namely activation energy (E*),
enthalpy (ꢃH*), entropy (ꢃS*) and Gibbs free energy change of
the decomposition (ꢃG*) were evaluated graphically by employing
the Coats–Redfern relation [23]. The entropy of activation (ꢃS*),
enthalpy of activation (ꢃH*) and the free energy change of activa-
tion (ꢃG*) were calculated.
[NiCl2(HL)(H2O)]·H2O complex is thermally decomposed in four
decomposition steps within the temperature range of 30–850 ◦C.
The first decomposition step with an estimated mass loss of 8.63%
(calcd. mass loss = 8.09%) within the temperature range 30–160 ◦C,
may be attributed to the loss of hydrated and coordinated water
molecules. The activation energy is 50.59 kJ mol−1. The remaining
decomposition steps (three steps) found within the temperature
range 160–850 ◦C with an estimated mass loss of 71.07% (calcd.
mass loss = 71.46%) which are reasonably accounted for the removal
of 2HCl and HL ligand as gases leaving NiS as a residue. The values
of the activation energy are 118.7, 192.6 and 263.4 kJ mol−1 for the
2nd, 3rd and 4th steps, respectively.
The TGA curve of the [CuCl2(HL)(H2O)]·4H2O chelate repre-
sents three decomposition steps as shown in Table 3. The first step
of decomposition within the temperature range 30–150 ◦C corre-
sponds to the loss of four hydrated water molecules with a mass
loss of 14.91% (calcd. for 4H2O; 14.30%). The energy of activation
for this dehydration step is 33.67 kJ mol−1. The remaining steps
of decomposition within the temperature range 150–800 ◦C cor-
respond to the removal of HL ligand as gases with an energy of
activation for these steps of 96.85 and 188.2 kJ mol−1 for the 2nd and
3rd steps, respectively. The overall weight losses amount to 84.82%
The data are summarized in Table 4. The activation energies of
decomposition are found to be in the range 22.95–243.4 kJ mol−1
.
The high values of the activation energies reflect the thermal
stability of the complexes. The entropy of activation is found to
have negative values in all the complexes which indicates that the
decomposition reactions proceed with a lower rate than the normal
ones.
3.1.6. Structural interpretation
The structures of the complexes of HL with Cr(III), Mn(II), Co(II),
Ni(II), Cu(II) (Cl− and SO42−) and Zn(II) ions are confirmed by
the elemental analyses, IR, molar conductance, magnetic, solid
reflectance, mass and thermal analysis data. Therefore, from the
IR spectra, it is concluded that HL behaves as a neutral tridentate
ligand coordinated to the metal ions via the imidazole N-3 and
two side chain S atoms. The molar conductance data, it is found
that the complexes are non-electrolytes. On the basis of the above
observations and from the magnetic and solid reflectance measure-
ments, octahedral geometries are suggested for the investigated
complexes except CuSO4 complex has square planar geometry. As
a general conclusion, the investigated metal complex structures can
be given as shown in Fig. 2.
Table 5
Fungicidal activity of the new synthesized complexes on the three soil borne fungi.
Complexes
F. solani
R. solani
S. rolfesii
EC50 (ppm)
Slope
T.I.a
15.1
53.3
100
67.3
66
75.4
63.7
67.2
EC50 (ppm)
Slope
T.I.a
88.4
81.1
100
93.1
72.8
90.4
67.3
39.4
EC50 (ppm)
Slope
T.I.a
75.3
69.7
100
50.5
66.8
86.4
50
[CuSO4(HL)]
2344.1
662.8
353.5
525.6
535.8
469.1
555.2
526.1
0.67
3.2
2.2
2.36
0.77
2.14
2.05
0.38
232.5
253.4
205.5
220.7
282.3
227.2
305.1
521
1.6 3
2.62
1.81
1.68
2.62
1.34
3.26
0.62
261
0.85
1.58
1.97
1.72
2.07
1.89
2.61
3.32
[CuCl2(HL)(H2O)]·4H2O
[CoCl2(HL)(H2O)]·H2O
[CrCl3(HL)]·2H2O
[MnCl2(HL)(H2O)]·H2O
[NiCl2(HL)(H2O)]·H2O
[ZnCl2(HL)(H2O)]·3H2O
HL
282.1
196.6
389
294.3
227.6
393.6
800.1
24.6
a
Toxicity index is the % of activity of the tested compounds to the most potent one whose T.I is 100.

G.G. Mohamed et al. / Spectrochimica Acta Part A 72 (2009) 610–615
615
Table 6
Fungicidal activity of the local formulation (25% WP) and the standard fungicide (Monceren 25% WP) on the three tested fungi.
Conc. (ppm)
F. solani
R. solani
S. rolfesii
Mean growth zone (mm)
% of inhibition
Mean growth zone (mm)
% of inhibition
Mean growth zone (mm)
% of inhibition
500
400
300
200
100
Control (0)
24.5
27
30
32.7
45
90.9
72.8
70
66.7
63.7
50
27.4
40.7
43
47
57
90.9
69.5
54.8
52.2
47.8
36.6
0
0
11.3
24
32.2
90
90.9
100
87.4
73.3
64.1
0
0
0
EC50
EC50**
*
90.94 ppm
2467.70 ppm
207.52 ppm
48.0 ppm
206.23 ppm
2309.18 ppm
EC50* is the effective concentration of the new formulation.
EC50** is the effective concentration of the standard fungicide (Monceren 25% WP).
3.2. Fungicidal activity
respectively. Data shown reflects the higher fungicidal activity of
the new formulation as compared with the standard fungicide on
F. solani and S. rolfesii fungi but not for R. solani fungus.
Data in Table 5 shows that the EC50 values of the prepared com-
plexes on R. solani and S. rolfesii fungi are lower than that of the
corresponding free ligand. This means that, the complexation pro-
cess increases the fungicidal potency on these two tested fungi.
The ranges of EC50 values of the complexes on R. solani fungus are
205.46–305.14 and 196.64–393.58 ppm on S. rolfsii but that of the
free ligand are 521.00 and 800.12 ppm on R. solani and S. rolfesii,
respectively. The high fungitoxic effect of the complexes than the
free ligand can be understood in term of chelation theory which
stated that, upon complexation the polarity of the metal ion gets
reduced which increases the lipophilicity of the metal complexes,
facilitating them to cross the cell membrane easily [24].
4. Conclusion
•
Many transition metal complexes were synthesized from the ben-
zimidazole dithiocarbamate ligand (HL).
•
Complexation process increases the fungicidal activity of the lig-
and.
•
Cobalt complex was found to be the most potent one against the
three tested soil borne fungi so it was formulated as 25% WP.
•
Fungicidal activity of the new formulation was evaluated and
compared with the standard fungicide (Monceren 25% WP).
•
In contrast, F. solani fungus shows higher resistance to the syn-
thesized complexes than the free ligand with exception of the cobalt
and nickel complexes. Generally, cobalt complex shows the high-
est fungicidal activity as it has the lowest EC50 values on the three
tested fungi. These values are 353.55, 205.45 and 196.84 ppm for
F. solani, R. slani and S. rolfesii fungi, respectively. Consequently, we
formulated this complex to make it commercially available as a
local fungicide after satisfying all required studies.
Data obtained showed the higher fungicidal activity of the new
formulation than the standard fungicide in most cases.
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3.3. Formulation
The main technique is used to apply the active ingredients of
pesticides in the field. Beside the ability of formulation to spread
the small amount of active ingredient over a large area, it also
improves its pesticidal activity in the field. Depending on the
physico-chemical properties of the active ingredient as well as the
type of pest, we should select the type of formulation. In this work
we formulated the cobalt complex in the form of 25% wettable
powder (25% WP). The local formulation passed successfully the
required tests according to the standard method [25]. The compo-
nents of the formulation are listed as follows:
The active ingredient (Co-complex)
Anionic surfactant
Dispersing agent
Antifoaming agent
Carrier
25.00%
20.00%
4.00%
1.00%
50.00%
100%
w/w
w/w
w/w
w/w
w/w
w/w
Total
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841 (2007) 41.
To determine the fungicidal potency of the new formulation
we evaluated its activity against the same fungi and compared it
with the commercially used fungicide (Monceren 25% WP) by using
different ranges of dilutions.
From data in Table 6 it is evident that the inhibition activity
of the formulation, to the fungi mycelial growth, increases as the
concentration increases. The EC50 values of the new formulation
are 90.94, 207.52, 208.23 ppm but that of the standard fungicide are
2467.70, 48.50, 2309.18 ppm on F. solani, R. solani and S. rolfesii fungi,
[23] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68.
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[25] FAO and WHO joint meeting on pesticides specifications (JMPS(, [Manual on
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