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Crystal structure anti-fungal activity and phytotoxicity of diorganotin compounds of dihalo-substituted [(2-hydroxyphenyl) methylideneamino]thiourea.

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Full Paper
Received: 20 May 2010
Revised: 16 June 2010
Accepted: 16 June 2010
Published online in Wiley Online Library: 27 July 2010
(wileyonlinelibrary.com) DOI 10.1002/aoc.1698
Crystal structure, anti-fungal activity
and phytotoxicity of diorganotin compounds
of dihalo-substituted [(2-hydroxyphenyl)
methylideneamino]thiourea†
Bipasa Sarkara , Apurba Kumar Choudhuryb , Abhijit Roya∗ ,
Monique Biesemansc , Rudolph Willemc , Seik Weng Ngd
and Edward R.T. Tiekinkd∗
Seven new diorganotin (IV) compounds (1–7) of Schiff bases derived from dihalo-substituted salicylaldehyde and
thiosemicarbazide were synthesized. The general formulae for the compounds are {R2 Sn[OArCH N–N C(NH2 )S]}, where
R = Me, n-Bu, Ph and Bz, and Ar = -C6 H2 (3-Br-, 5-Cl) or -C6 H2 (3,5-Br2 ), and these were characterized by UV–vis, IR and NMR (1 H,
13 C, 119 Sn) spectroscopy and elemental analysis. Five structures were also investigated by X-ray crystallography. All molecules
are mononuclear, five-coordinate with a tridentate ligand coordinating the tin atom through the thiolate-S, phenoxide-O
and imino-N atoms. The coordination geometries for the n-butyl compounds approach square pyramidal arrangements with
distortions towards trigonal pyramidal occurring for the di-methyl and di-phenyl compounds which display wider C–Sn–C
angles. The potential of the new compounds against six fungal pathogens (Bipolaris sorokiniana, Helminthosporium oryzae,
Altreneria brassicae, Alterneria kikuchiana, Stemphylium pori and Colletotrichum capsici) were investigated for six different
crops (Triticum aestivum, Oryzae sativa, Brassica nigra, Brassica oleracea, Allium cepa and Capcicum annum) and demonstrated
significant activity. None of the investigated compounds displayed adverse phytotoxicity at concentrations as high as 100 ppm.
c 2010 John Wiley & Sons, Ltd.
Copyright Keywords: tin (IV); diorganotin; crystal structure; hydrogen bonding; fungicidal activity; thiosemicarbazones
Introduction
Experimental
General Remarks
842
Thiosemicarbazides, when suitably combined with salicylaldehydes, yield Schiff bases. Schiff bases normally have O, N, S donor
atoms available for coordination with additional potential donors
present depending on substitution patterns. Schiff bases continue
to attract attention as they are known to be capable of stabilizing uncommon oxidation states,[1 – 4] and to give rise to unusual
coordination numbers and redox reactions[5 – 12] in their transition
metal complexes. In the context of the present contribution, it
is the potential biological applications of Schiff base compounds
which is paramount. Motivated by this imperative, the chemistry
of organotin compounds with Schiff bases is well established in
the literature.[13 – 17] Our particular interest in these compounds
relates to delineating their biological properties as a function of
halogen substitution patterns in the salicylaldehyde moiety.[18]
This led us to investigate the synthesis of a series of new compounds with di-substituted salicylaldehydes at 3- and 5-positions
of the phenyl ring, i.e. the 3,5-dibromo derivatives or 3-bromo,
5-chloro derivatives. Herein, we report the syntheses and spectral characterization of seven new compounds, 1–7, represented
in Scheme 1, the crystallographically determined structures of
five of them and the results of preliminary biological studies focused upon the potential use of these compounds as anti-fungal
agents.
Appl. Organometal. Chem. 2010, 24, 842–852
3-Bromo-5-chloro-salicylaldehyde (Aldrich, USA), 3,5-dibromosalicylaldehyde (Aldrich, USA), thiosemicarbazide (Loba Chemie,
Ł
Correspondence to: Abhijit Roy, Department of Chemistry, University of North
Bengal, Darjeeling, West Bengal 734013, India.
E-mail: abhijitchem1947@yahoo.co.in
Edward R.T. Tiekink, Department of Chemistry, University of Malaya,
50603 Kuala Lumpur, Malaysia. Email: edward.tiekink@gmail.com
†
This article is published in Applied Organometallic Chemistry as a special
issue on In Memoriam Professor Edmunds Lukevics, edited by Luba Ignatovich,
Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga, LV-1006, Latvia, and
Vladimir Gevorgyan, University of Illinois at Chicago, Department of Chemistry,
Chicago, United States.
a Department of Chemistry, University of North Bengal, Darjeeling, West Bengal
734013, India
b Department of Plant Pathology, Uttar Banga Krishi Viswavidyalaya, Pundibari,
Cooch Behar, West Bengal, 736165, India
c High Resolution NMR Centre, Department of Materials and Chemistry, Vrije
Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
d Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
c 2010 John Wiley & Sons, Ltd.
Copyright Diorganotin compounds of dihalo-substituted [(2-hydroxyphenyl)methylideneamino]thiourea
X
L:X = Cl
L1:X = Br
N
O
Br
N
_
NH2
S
1: Me2SnL
2: n-Bu2SnL
3: Ph2SnL
4: Bz2SnL
_
5: Me2SnL1
6: n-Bu2SnL1
7: Ph2SnL1
Scheme 1. Structures of the diorganotin thiosemicarbazones described
herein.
India), di-n-butyltin oxide (Alfa, USA), dimethyltin dichloride
(Fluka, Germany), diphenyltin dichloride (Aldrich, USA), tin powder
(Merck, India) and benzyl chloride (S.D. fine-chem, India) were
used as received from commercial sources. The diorganotin
oxides, Me2 SnO and Ph2 SnO, were prepared by the alkaline
hydrolysis of dimethyltin dichloride and diphenyltin dichloride,
respectively, in water–ether mixtures.[19] Dibenzyltin dichloride
was prepared from tin powder and benzyl chloride following a
literature method.[20] The solvents used in the reactions were of
AR grade and were obtained from commercial sources (Merck,
Germany). The solvents were dried before use using standard
literature methods. Appropriate precautions to prevent health
hazards were undertaken when benzene was used as a solvent.
Physical Measurements
The 1 H, 13 C and 119 Sn NMR spectra were recorded in CDCl3 solution
using TMS as an internal standard (for 1 H and 13 C) on Bruker DPX
300 and Bruker Avance II 500 (operating at 500.08, 125.76 and
186.46 MHz, respectively) spectrometers. The 119 Sn spectra were
recorded under broadband 1 H decoupling during acquisition and
were referenced to D 37.290665 MHz.[21] IR spectra in the
range 4000–400 cm1 were recorded on a FTIR-8300 Shimadzu
spectrophotometer with samples investigated as Nujol mulls on
a CsI window. The electronic absorption spectra were recorded in
methanol solutions on a Shimadzu UV 2450 spectrophotometer
and emission data were recorded on a Spex Fluorolog 2
spectrophotometer. Microanalyses were performed at the IACS,
Kolkata, India. Tin (%) was estimated gravimetrically as SnO2 .
Syntheses
Preparation of Schiff bases of substituted salicylaldehyde
with thiosemicarbazide
Appl. Organometal. Chem. 2010, 24, 842–852
Crystal structure determination
The crystals of 1, 2, 3, 5 and 6 suitable for the X-ray diffraction study
were prepared by slow crystallization of benzene solutions of the
respective compounds; the crystallographic analysis of 3 showed
the sample had crystallized as a hemi-benzene solvate. Intensity
data were collected at room temperature on a Bruker SMART APEX
CCD fitted with Mo Kα radiation. The data set was corrected for
absorption based on multiple scans[23a] and reduced using standard methods.[23b] The structures were solved by direct-methods
with SHELXL-97[23c] and refined by a full-matrix least-squares
procedure on F2 using SHELXL-97[23c] with anisotropic displacement parameters for non-hydrogen atoms, hydrogen atoms in
their calculated positions and a weighting scheme of the form
w D 1/[σ 2 (Fo 2 ) C (aP)2 C bP] where P D (Fo 2 C 2Fc 2 )/3. In the
analysis of 3, two positions for each of the tin-bound phenyl rings
were resolved. In the refinement, the anisotropic displacement
parameters for matched pairs of atoms were constrained to be
equivalent and to be approximately isotropic by utilizing the
EADP and ISOR commands in SHELXL-97.[23c] Refinement showed
that each component of the disorder had a site occupancy factor
D 0.5. In the refinements of the di-n-butyl compounds, 2 and 6,
high thermal motion was noted for the n-butyl groups. As multiple
positions were not resolved, the 1-,2- and 1-,3- C–C distances were
restrained to 1.54 š 0.01 Å and 2.51 š 0.01 Å, respectively. Crystal
data and refinement details are given in Table 1. The molecular
structures showing crystallographic numbering schemes were
drawn with 35% displacement ellipsoids using ORTEP-3[23d] and
the remaining figures were drawn with DIAMOND.[23e] Additional
data analysis was accomplished using PLATON.[23f]
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
843
The thiosemicarbazones were prepared by reacting equivalent
molar amounts of thiosemicarbazides and the respective substituted salicylaldehyde in a 1 : 1 ethanol–water mixture.[22] The
products were recrystallized from ethanol. The formulae of the
ligands and their derived diorganotin compounds are presented
in Scheme 1.
For the syntheses of the new organotin compounds two
general routes were followed. Method (I): for compounds 1–3 and
5–7, the respective diorganotin oxide was heated under reflux
with the ligand (1 : 1) using dry benzene as the solvent under
an inert atmosphere. The heating was prolonged (10 h) until no
further water formed. The water that formed during the reaction
was removed by a Dean–Stark assembly. The solvent was then
removed by distillation under reduced pressure and the solid
that remained was washed with petroleum ether (60–80 Ž C) and
extracted with benzene. Slow evaporation of the extract held at
room temperature or at 10 Ž C yielded the respective products. In
a typical reaction run, the synthesis of dimethyltin (IV) 3-bromo-5chloro-salicylaldehydethiosemicarbazonate (1) was carried out as
follows. A mixture of Me2 SnO (0.53 g, 3.23 mmol) and 3-bromo5-chloro-salicylaldehyde thiosemicarbazone (1.00 g, 3.23 mmol)
in dry benzene (140 ml) was heated under reflux in a nitrogen
atmosphere for 10 h; the water thus produced was removed
azeotropically (Dean–Stark trap). The solvent was removed from
the yellow reaction mixture and the dry mass first washed with
hot petroleum ether (60–80 Ž C) and then extracted with benzene
(total volume 50 ml). Yellow crystals of the desired product were
obtained by cooling the solution to 10 Ž C. Method (II): for compound 4, the disodium salt of the ligand was prepared in situ by
replacing its two acidic protons in methanolic NaOH solution. The
sodium salt was then reacted with Bz2 SnCl2 to obtain the desired
product. The procedure is described as follows for dibenzyltin (IV)
3-bromo-5-chloro-salicylaldehydethiosemicarbazonate 4. A 0.10 M
methanolic NaOH (63.48 ml, 0.25 g, 6.47 mmol) solution was added
drop-wise to a solution of 3-bromo-5-chloro-salicylaldehyde
thiosemicarbazone (1.00 g, 3.23 mmol) in methanol, while stirring.
The mixture was further stirred for another 2 h and then a methanolic solution of Bz2 SnCl2 (1.20 g, 3.23 mmol) was added slowly. The
yellow reaction mixture was subsequently heated under reflux
for 8 h under inert conditions. The volatiles were removed by
distillation under reduced pressure and the dry mass extracted
with several aliquots of benzene (total volume 50 ml). Slow cooling
to room temperature yielded a yellow precipitate of the product.
B. Sarkar et al.
Table 1. Crystal data and refinement details for 1–3, 5 and 6
Empirical formula
Formula weight
Crystal habit, color
Crystal system
Space Group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
Volume (Å 3 )
Z
Density (calculated, g cm3 )
Absorption coefficient (mm1 )
F(000)
Crystal size (mm)
θ range for data collection (deg)
Reflections collected
Independent reflections
Rint
Reflections with I ½ 2σ (I)
Number of parameters
a, b for weighting scheme
Final R indices [I ½ 2σ (I)]
R indices [all data]
1
2
3
5
6
C10 H11 BrClN3 OSSn
455.33
Cube, yellow
Monoclinic
C2/c
14.7612(9)
13.3430(8)
15.2054(9)
90
91.6906(9)
90
2993.5(3)
8
2.021
4.686
1744
0.20 ð 0.20 ð 0.20
2.1–27.5
14038
3432
0.025
2802
171
0.022, 5.987
R D 0.025
wR2 D 0.055
R D 0.036
wR2 D 0.060
C16 H23 BrClN3 OSSn
539.48
Block, yellow
Monoclinic
P21 /c
17.2188(12)
8.7465(6)
14.9051(10)
90
108.4257(9)
90
2129.7(3)
4
1.683
3.307
1064
0.10 ð 0.25 ð 0.35
2.5–27.5
12543
4871
0.035
3568
225
0.030, 2.458
R D 0.037
wR2 D 0.080
R D 0.062
wR2 D 0.091
C23 H18 BrClN3 OSSn
618.51
Block, yellow
Triclinic
P1
9.1612(7)
9.8617(8)
13.5553(11)
94.159(1)
92.155(1)
99.109(1)
1204.53(17)
2
1.705
2.937
606
0.10 ð 0.20 ð 0.30
1.5–27.5
11506
5488
0.030
3860
274
0.046, 1.141
R D 0.043
wR2 D 0.010
R D 0.071
wR2 D 0.114
C10 H11 Br2 N3 OSS
499.79
Block, yellow
Monoclinic
C2/c
14.9682(12)
13.4107(10)
15.2213(12)
90
92.040(1)
90
3053.5(4)
8
2.174
7.036
1888
0.30 ð 0.35 ð 0.40
2.0–27.5
13737
3491
0.043
2581
171
0.030, 10.080
R D 0.034
wR2 D 0.078
R D 0.058
wR2 D 0.088
C16 H23 Br2 N3 OSSn
583.94
Block, yellow
Monoclinic
P21 /c
17.2465(13)
8.7688(6)
14.7170(11)
90
108.893(1)
90
2105.8(3)
4
1.842
5.116
1136
0.10 ð 0.15 ð 0.35
1.3–27.5
19497
4838
0.048
3592
225
0.045, 0.325
R D 0.033
wR2 D 0.079
R D 0.054
wR2 D 0.089
0.91, 0.68
0.76, 0.89
0.90, 0.80
0.99, 0.76
0.57, 0.62
Largest difference
peak and hole (Å 3 )
Biological studies
Fungicidal activity
The virulent fungal strains of Bipolaris sorokiniana, Helminthosporium oryzae, Altreneria brassicae, Alterneria kikuchiana, Stemphylium
pori and Colletotrichum capsici were collected from the Type
culture collection, Department of Plant Pathology, Uttar Banga
Krishi Viswavidyalaya, Cooch Behar, West Bengal, India. Bipolaris
sorokiniana was maintained in an oatmeal agar medium while the
remaining fungi were grown on potato-dextrose agar medium at
27 Ž C. The fungicidal activities were determined following spore
germination bioassay as described by Rouxel et al.[24] Purified
eluants (15 µl) were placed on two spots 3 cm apart on a clean
grooved slide. One drop of spore suspension (15 µl), which was
prepared from 15-day-old cultures of the fungi, was added to the
treated spots. The slides were incubated in trays at 27 Ž C for 24 h
under humid conditions. After incubation, one drop of Lactophenol mixture was added to each spot to fix the germinated spores.
The number of spore germination events was compared with the
spore germination of the control.
Brassica oleracea were collected from the Directorate of Farm, Uttar
Banga Krishi Viswavidyalaya, Cooch Behar, West Bengal, India.
Seeds were first surface sterilized with 0.1% mercuric chloride for
3 min, washed with distilled water and then the phytotoxic effects
of the new organotin compounds (dissolved in 2 ml methanol
then diluted with 10 ml water) were determined.[25] Seeds were
incubated with different concentration of organotin compounds
for different time periods. After incubation, the seeds were washed
with distilled water and incubated in a BOD incubator for 48 h at
27 Ž C. The percentage of seed germination was calculated and
compared with the control.
Results and Discussion
The new diorganotin compounds 1–7 (Table 2) were obtained in
good yields by the equimolar reaction of either (i) diorganotin (IV)
oxides with the appropriate ligand or (ii) diorganotin (IV) dichloride
with the sodium salt of the respective ligand. The compounds were
air-stable, soluble in common organic solvents and could be recrystallized except for the dibenzyltin (IV) derivative (4), which was
amorphous.
Phytototoxic effect
844
Seeds of Indian wheat (Triticum aestivum L.), cultivar Sonalika
were obtained from the Directorate of Wheat Research, Karnal,
India. Seeds of Oryzae sativa, Brassica nigra, Capcicum annum and
wileyonlinelibrary.com/journal/aoc
IR spectra
The main characteristic IR absorptions are presented in Table 3.
The ν(NH2 ), ν(C N–N C) and ν(Sn–C) bands were assigned on
c 2010 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2010, 24, 842–852
Diorganotin compounds of dihalo-substituted [(2-hydroxyphenyl)methylideneamino]thiourea
Table 2. Physical and analytical data for 1–7
Elemental composition found (calcd) (%)
Compound number Composition
Ž
Yield (%)
Melting point ( C)
C
H
N
Sn
82
157
74
82
80
212
63
>240
85
156
75
108
83
188
26.30
(26.38)
35.36
(35.49)
44.38
(44.66)
43.44
(43.50)
23.91
(24.03)
32.68
(32.80)
38.41
(38.50)
2.32
(2.44)
4.61
(4.65)
2.60
(2.93)
3.12
(3.15)
2.25
(2.22)
4.27
(4.30)
2.41
(2.42)
9.21
(9.23)
7.75
(7.76)
7.20
(6.79)
6.80
(6.92)
8.39
(8.41)
7.14
(7.17)
6.65
(6.73)
25.91
(26.07)
21.89
(21.92)
20.38
(19.19)
19.42
(19.54)
23.59
(23.75)
20.18
(20.26)
18.88
(19.02)
1
C10 H11 N3 OSClBrSn
2
C16 H25 N3 OSClBrSn
3
ž
C20 H15 N3 OSClBrSn 0.5C6 H6
4
C22 H19 N3 OSClBrSn
5
C10 H11 N3 OSBr2 Sn
6
C16 H25 N3 OSBr2 Sn
7
C20 H15 N3 OSBr2 Sn
Table 3. IR spectral data (cm1 ) for compounds 1–7a
Compound
ν(NH2 )asym
ν(NH2 )sym
ν(C N–N C)
ν(C–S)
ν(Sn–C)
1
2
3
4
5
6
7
3438 (m)
3462 (m)
3463 (w)
3452 (b,w)
3427 (b)
3431 (b)
3409 (b)
3168 (w)
3344 (w)
3286 (w)
3008 (w)
3200 (w)
3175 (w)
3135 (w)
1608 (s)
1601 (m)
1627 (m)
1621 (m)
1606 (m)
1627 (m)
1626 (m)
734 (s)
750–729 (m)
736 (m)
728–671 (w)
724 (w)
722 (w)
724 (w)
520, 464 (w)
570, 457 (w)
570, 462 (w)
528, 460 (w)
535, 475 (w)
538, 472 (w)
540, 468 (w)
a
Spectra recorded as nujol mulls on a CsI window; s, strong; m, medium; w, weak; b, broad.
the basis of literature data.[26,27] The ν(NH2 )asym and ν(NH2 )sym
stretching vibrations due to the ligands in 1–7 appeared in the
range 3248–3454 cm1 . The bands in the free ligands did not
shift significantly upon coordination, indicating that the aminonitrogen atom is hardly or not involved in an interaction with tin.
The spectra also show medium to strong absorptions in the range
of 1600–1627 cm1 due to ν(C N–N C).[27] The spectra showed
weak absorptions within the range 721–750 cm1 , as expected
for ν(C–S). The ν(Sn–C)asym and ν(Sn–C)sym bands are tentatively
assigned[28] to absorptions in the regions 520–570 cm1 and
430–468 cm1 , respectively.
NMR Spectra
Appl. Organometal. Chem. 2010, 24, 842–852
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
845
All NMR data are summarized in Table 4. The 1 H signals were
assigned on the basis of proton integration and multiplicity
patterns, as well as for a selected number of compounds, by
2D 1 H– 13 C HMQC and HMBC experiments, and were compared
with literature[18,29 – 31] data. The azomethine proton resonance
(around 8.4 ppm) is flanked by 3 J(HC NÐ Ð Ð119 Sn) coupling
satellites ranging from 34 to 41 Hz indicating the existence in
solution of an intramolecular coordination between the tin and
nitrogen atom.[32] For the dimethyltin derivatives, the2 J(1 H– 119 Sn)
coupling satellites are clearly visible, which allowed estimation
of the C–Sn–C angle from the Lockart equation,[33] D
0.016j2 J(1 H– 119 Sn)j2 1.32j2 J(1 H– 119 Sn)j C 133.4. For both 1
and 5 a value of 122Ž was found, comparing well with the 128
and 127Ž angles found, respectively, in the solid-state according
to X-ray crystallography (Table 6).
The 13 C resonances were well separated and readily assigned with the aid of 2D 1 H– 13 C HMQC and HMBC spectra
and n J(117/119 Sn– 13 C) coupling constants. The values for the
1 J(119 Sn– 13 C) coupling constants were consistent with pentacoordinated tin for which the fifth coordination site originates
from the interaction with the imine nitrogen atom of the Schiff
base.[34] 1 J(119 Sn– 13 C) coupling constants also allowed estimation
of the C–Sn–C angle, from a relationship established by Lockart
et al. for dimethyltin compounds, 1 J(119 Sn– 13 C) D 10.7 (š0.5) 778 (š64),[35 – 37] and by Holeček et al.[38 – 41] for dibutyl and
diphenyl derivatives, 1 J(119 Sn– 13 C) D 9.99 (š0.73) 746 (š100)
and 1 J(119 Sn– 13 C) D 15.56 (š0.84) 1160 (š101), respectively.
The calculated values were 128š12 and 127š12Ž for, respectively,
1 and 5, 130 š 20 and 128 š 20Ž for, respectively, 2 and 6, and
132 š 14 and 130 š 14Ž for, respectively, 3 and 7; all compared
well with the angles found in the solid state, ranging from 119 to
128Ž (Table 6).
The intramolecular coordination was further confirmed by
the rather high (17–21 Hz) n J(117/119 Sn– 13 C) coupling constant
found for carbon 7, which without this interaction would implicate four bonds over a heteroatom for which no measurable
coupling constant was expected. In the 2D 1 H– 13 C HMBC correlation experiment, satellites originating from the coupling with
the passive 119 Sn spin were clearly observed for correlation peaks
846
wileyonlinelibrary.com/journal/aoc
c 2010 John Wiley & Sons, Ltd.
Copyright 0.93
(s)f72gd
5.18
(s)
7.06
(d,2.5)c
8.39
(s)f38gd
7.58
(d,2.5)c
1H
1 H, 13 C
158.4
[20]b
168.8
121.2
131.1
13 C
117.7
[24]b
160.1
[32]b
116
[8]b
136.3
6.18
[567/593]b
194.0
1
158.5
[16]b
169.1
120.8
131.1
13 C
117.7
[19]b
160.6
[32]b
116.6
[8]b
136.3
26.4
[532/557]b
27.3
[31]
26.5
[87]
13.6
212.8
1.64–1.52
(m)
1.74–1.64
(m)f106gd
1.44–1.28
(m)
0.91(t)
5.05
(s)
7.06
(d,2.5)c
8.40
(s)f34gd
7.58
(d,2.5)c
1H
2
158.7
[21]b
167.2
121.6
131.4
13 C
117.8
[22]b
160.4
[33]b
117.0
[10]b
136.6
141.4
[854/895]b
8.03(d)
135.9
f82gd
[59]
7.50–7.40
128.9
(m)
[84]
7.50–7.40
130.4
(m)
[17]
320.1
5.21
(s)
7.03
(d,2.5)c
8.41
(s)f41gd
7.65
(d,2.5)c
1H
3
and 119 Sn NMR data for 1–7 (chemical shifts in ppm, coupling constants in Hz)
Compound 4 is poorly soluble in CDCl3 : 13 C and 119 Sn spectra were not recorded.
Unresolved n J(13 C– 117/119 Sn) and resolved 1 J(13 C– 117/119 Sn) are indicated between brackets.
c 4 J (1 H– 1 H) coupling constants in parentheses.
d 2,3 J(1 H– 117/119 Sn) coupling constants between braces.
b
a
Sn
δ
γ
β
α
8
NH2
7
5
6
4
3
2
Atom
1
Table 4.
7.26–7.88
(m)
7.26–7.88
(m)
7.26–7.88
(m)
4.71
(s)
7.19
(d,2.5)c
7.88
(s)f36gd
7.70
(d,2.5)c
1H
4a
0.93
(s)f72gd
5.14
(s)
7.20
(d,2.2)c
8.39
(s)f38gd
7.70
(d,2.2)c
1H
158.4
[21]b
168.8
107.1
134.1
13 C
118.5
[23]b
160.5
[31]b
117.0
[8]b
138.8
6.19
[567/594]b
193.6
5
158.4
[17]b
169.1
107.1
134.2
13 C
118.6
[19]b
161.0
[33]b
117.0
[n.o.]
138.8
26.4
[531/557]b
27.3
[31]
26.8
[88]
13.6
212.5
1.64–1.52
(m)
1.74–1.64
(m)f106gd
1.44–1.28
(m)
0.91(t)
5.05
(s)
7.18
(d,2.3)c
8.39
(s)f35gd
7.70
(d,2.3)c
1H
6
158.6
[21]b
167.2
107.9
134.5
13 C
118
[21]b
160.8
[34]b
117.3
[10]b
139.0
141.4
[860/894]b
8.02(d)
135.9
f82gd
[59]
7.50–7.40
128.9
(m)
[85]
7.50–7.40
130.4
(m)
(17)
319.9
5.19
(s)
7.17
(d,2.5)c
8.41
(s)f41gd
7.76
(d,2.5)c
1H
7
B. Sarkar et al.
Appl. Organometal. Chem. 2010, 24, 842–852
Diorganotin compounds of dihalo-substituted [(2-hydroxyphenyl)methylideneamino]thiourea
Table 5. Electronic absorption spectra of compounds 1–3 and 5–7
recorded in methanol solution
Compound λmax (nm) Absorption (λmax , nm)
Emission (λmax , nm)
1
2
3
5
6
7
495 (λexc
495 (λexc
490 (λexc
493 (λexc
496 (λexc
491 (λexc
410
415
407
409
414
408
410, 340, 236
415, 340. 238
407, 339, 260
409, 340, 238
414, 343, 240
408, 340, 268
D 400
D 415
D 410
D 410
D 410
D 410
nm)
nm)
nm)
nm)
nm)
nm)
associated with proton 7. From the tilt of the satellites the relative
sign of the 1 H– 119 Sn and 13 C-119 Sn coupling constants can be
obtained.[42] In this respect, a positive tilt for carbon 1 and a negative one for carbon 2 were noted, meaning that, if the 1 H– 119 Sn
coupling for proton 7 can be considered as a 3 J coupling pathway,
giving usually negative coupling constants, the coupling constant
between the tin atom and carbon 1 is also negative, while the one
with carbon 2 is positive. This observation is in accord with the
fact that 2 J(13 C– 119 Sn) coupling constants are generally positive,
while 3 J(13 C– 119 Sn) coupling constants are usually negative.
However, it should be emphasized that, for carbon 1, two coupling
pathways, both involving three bonds, need to be considered,
one through the oxygen atom and another one through the
coordinating nitrogen atom and a double bond.[43] The 119 Sn
chemical shifts, around 200 ppm for the aliphatic tin compounds
and around 320 ppm for the diphenyltin compounds, were also
in agreement with penta-coordination at tin.
Electronic Spectra
The spectral data for 1–3 and 5–7 are summarized in Table 5.
Towards the visible region, the electronic spectra showed
multiple absorptions, giving rise to the yellow appearance of
the compounds and probably due to an n ! π Ł transition
within the thiosemicarbazide chromophore owing to extensive
conjugation,[18] which is most likely the reason for the observed
fluorescence in methanol solution (Table 5).
Crystal and Molecular Structures
The molecular structures of five compounds, i.e. 1–3, 5
and 6, revealed a certain degree of homogeneity in their molecular
Table 7. Spore germination (%) of Bipolaris sorokiniana and Helminthosporium oryzae in the presence of compounds 1–3 and 5–7
Spore germination
percentage of
B. sorokiniana
Concentration (ppm)
Spore germination
percentage of
H. oryzae
Concentration (ppm)
25
50
100
25
50
100
9.6
5.9
4.7
10.1
5.6
4.9
83.1
3.5
2.5
2.0
5.0
3.3
2.0
0
0
0
1.0
0
0
10.9
6.7
5.8
10.5
6.2
5.3
85.4
5.0
4.0
3.2
4.8
3.5
3.2
1.5
0.5
0
1.2
0
0
Chemical
1
2
3
5
6
7
Control (water)
structures, at least to a first approximation, that did not persist
in their supramolecular aggregation patterns. The molecular
structures, Fig. 1, revealed a tridentate mode of coordination
to the tin atom through the thiolate-S1, phenoxide-O1 and iminoN1 atoms of the dianion derived from the respective Schiff base,
with the penta-coordinate geometry being completed by two
carbon atoms in each case. The similarity in the structures was
emphasized by the isomorphous relationship between the two
di-methyl compounds, 1 and 5, and between the two di-n-butyl
derivatives, 2 and 6 (Table 1). An evaluation key bond distances
of 1 with Br/Cl substituents and 5 with Br/Br ones, indicated that
the substituents do not influence the electronic structure of the
ligand as the comparable distances are equal within experimental
error (see Table 6 for geometric parameters). Small, but chemically
insignificant,[44] differences were noted between the Sn–S1 bond
distances in the structures of 2 and 6. Within the dianion, the C1–S1
and N1–N2 bond distances were consistent with single bonds,
whereas double bond character is evident in each of the C1–N2 and
C2–N1 bonds (Table 6). Arguably, the most significant differences
in the geometric parameters about the tin atoms were found in
the S1–Sn–O1 and C–Sn–C angles (Table 6). These are pivotal in
determining the coordination geometry about the tin atom in each
structure as the coordination geometries vary depending on the
nature of the tin-bound group. Thus, the dimethyltin compounds
adopt almost intermediate geometries between square pyramidal
and trigonal bipyramidal. This is quantified by the value of τ , i.e.
τ D 0.47 for 1 and 0.49 for 5, which compares with τ D 0.00 for
Table 6. Selected geometric parameters (Å, deg) for 1–3, 5 and 6
Parameter
1
2
3
5
6
Sn–S1
Sn–O1
Sn–N1
C1–S1
N1–N2
C1–N2
C2–N1
S1–Sn–O1
C–Sn–C
2.5493(10)
2.086(2)
2.231(2)
1.723(3)
1.391(3)
1.299(4)
1.298(4)
156.24(7)
128.25(18)
2.5151(13)
2.118(3)
2.242(3)
1.728(5)
1.385(4)
1.307(5)
1.300(5)
148.08(9)
119.0(2)
2.5074(15)
2.082(3)
2.236(3)
1.718(5)
1.387(5)
1.300(5)
1.292(5)
153.52(11)
119.2(8)
124.6(8)a
2.5451(15)
2.085(3)
2.232(4)
1.721(5)
1.396(5)
1.300(6)
1.290(6)
156.17(11)
127.0(3)
2.4975(12)
2.104(2)
2.232(3)
1.724(4)
1.376(4)
1.299(5)
1.294(5)
148.70(9)
118.5(2)
The C–Sn–C angle for the second component of the disordered phenyl groups.
Appl. Organometal. Chem. 2010, 24, 842–852
c 2010 John Wiley & Sons, Ltd.
Copyright 847
a
wileyonlinelibrary.com/journal/aoc
B. Sarkar et al.
Figure 1. The molecular structures of 1–3, 5 and 6 showing atom labeling schemes. For 3, only one component of the disordered tin-bound phenyl
groups is shown for clarity.
848
an ideal square pyramid and τ D 1.00 for an ideal trigonal
bipyramid.[45] For the diphenyltin compound, 3, a distortion
towards square pyramidal is evident, τ D 0.29. The distortion
is even greater for the di-n-butyltin compounds where τ D 0.15
and 0.16 for 2 and 6, respectively. Therefore, there is a correlation
between the magnitude of C–Sn–C and the distortion away from
an ideal square pyramid.
wileyonlinelibrary.com/journal/aoc
In the crystal structures of isomorphous 1 and 5, molecules
are connected into supramolecular chains aligned along [1 0 1],
through a variety of hydrogen bonding interactions. The most
prominent supramolecular synthon in the crystal packing is an
eight-membered fÐ Ð ÐHNCNg2 motif disposed about a two-fold
axis; geometric parameters for the intermolecular interactions are
given below. The second hydrogen of the amine forms a hydrogen
c 2010 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2010, 24, 842–852
Diorganotin compounds of dihalo-substituted [(2-hydroxyphenyl)methylideneamino]thiourea
bond to the Br1 atom with the resulting chain stabilized by an
internal C–HÐ Ð ÐCl interaction. The supramolecular chains thus
formed, Fig. 2(a), pack into layers with an undulating topology
that stack along the b-axis, Fig. 2(c). In the absence of the chloride
in 5, a C–HÐ Ð ÐS interaction occurs instead, and these provide
connections between the chains to form two-dimensional arrays
in the ac plane, Fig. 2(b). The layers have an undulating topology
and stack as illustrated for 1, Fig. 2(c). By contrast to the situation
in 1 and 5, simpler supramolecular aggregation patterns are
observed in the crystal structures of isomorphous 2 and 6, and
in 3. This is correlated with the increased size of the tin-bound
substituents and the participation of only one of the amine-H
atoms in significant intermolecular interactions.
Supramolecular chains, mediated by N–HÐ Ð ÐO hydrogen bonding, along the c-axis are found in each of 2 (Fig. 3) and 6. In 6, the
chains are reinforced by N–HÐ Ð ÐBr interactions so that the H1n
atom is bifurcated. Finally, the crystal structure of 3 comprises
diphenyltin molecules and benzene molecules in the ratio 2 : 1.
The presence of the eight-membered fÐ Ð ÐHNCNg2 synthon leads to
centrosymmetric dimeric aggregates, Fig. 4(a). These stack along
the a-axis to define channels in which reside the solvent benzene
molecules, Fig. 4(b).
(a)
(b)
Details of the geometric parameters describing the supramolecular
aggregation in the structures of 1 and 5
1: N3–H1nÐ Ð ÐN2i D 2.37(4) Å, N3Ð Ð ÐN2i D 3.176(4) Å, angle at
H1n D 152(3)Ž for symmetry operation i: 1 x, y, 1 1/2 z.
N3–H2nÐ Ð ÐBr1ii D 2.84(4) Å, N3Ð Ð ÐBr1ii D 3.626(3) Å, angle at
H2n D 162(3)Ž for symmetry operation ii: 1/2 C x, 1/2 y, 1/2 C z.
C9–H9cÐ Ð ÐCl1iii D 2.80 Å, C9Ð Ð ÐCl1iii D 3.669(5) Å, angle at H9c
D 150Ž for symmetry operation iii: 1/2 x, 1/2 y, 1 z.
5: N3–H1nÐ Ð ÐN2i D 2.33(6) Å, N3Ð Ð ÐN2i D 3.175(6) Å, angle at
H1n D 163(6)Ž for symmetry operation i: 1 x, y, 1 1/2 z.
N3–H2nÐ Ð ÐBr1ii D 2.88(6) Å, N3Ð Ð ÐBr1ii D 3.679(5) Å, angle at
H2n D 163(6)Ž for symmetry operation ii: 1/2 C x, 1/2 y, 1/2 C z.
C9–H9bÐ Ð ÐS1iii D 2.81 Å, C9Ð Ð ÐS1iii D 3.710(6) Å, angle at H9b D
157Ž for symmetry operation iii: 1 1/2 x, 1/2 y, 1 z.
Details of the geometric parameters describing the supramolecular
aggregation in the structures of 2 and 6
2: N3–H1nÐ Ð ÐO1i D 2.36(5) Å, N3Ð Ð ÐO1i D 3.076(5) Å, angle at
H1n D 145(5)Ž for symmetry operation i: x, 1 1/2 y, 1/2 C z.
6: N3–H1nÐ Ð ÐO1i D 2.36(4) Å, N3Ð Ð ÐO1i D 3.055(5) Å, angle at
H1n D 141(4)Ž for symmetry operation i: x, 1 1/2 y, 1/2 C z.
N3–H1nÐ Ð ÐBr1i D 2.92(5) Å, N3Ð Ð ÐBr1i D 3.661(5) Å, angle at H1n
D 148(4)Ž .
(c)
Details of the geometric parameters describing the supramolecular
aggregation in the structure of 3
N3–H1nÐ Ð ÐN2i D 2.25(6) Å, N3Ð Ð ÐN2i D 3.052(6) Å, angle at H1n
D 163(5)Ž for symmetry operation i: 2 x, 1 y, 1 z.
Anti-fungal Activities
Appl. Organometal. Chem. 2010, 24, 842–852
Figure 2. Crystal packing in the isomorphous structures of 1 and 5: (a) view
of the supramolecular chain in 1 mediated by N–HÐ Ð ÐN and N–HÐ Ð ÐBr
interactions and sustained by internal C–HÐ Ð ÐCl contacts; (b) view of the
supramolecular chain in 5 mediated by N–HÐ Ð ÐN and N–HÐ Ð ÐBr interactions
for 1, and connected into a two-dimensional array by C–HÐ Ð ÐS contacts;
(c) stacking of layers in 1 representative of both 1 and 5.
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
849
The anti-fungal properties of the diorganotin compounds 1–3 and
5–7 are summarized in Tables 7–9. The fungitoxic effect of the
organotin compounds was screened at three concentrations, 25,
50 and 100 ppm, on spore germination of six different pathogens
of rice (Helminthosporium oryzae), wheat (Bipolaris sorokiniana),
mustard (Alternaria brassicae), cabbage (Alternaria kikuchiana),
B. Sarkar et al.
(a)
(b)
Figure 3. Crystal packing in the isomorphous structures of 2 and 6: view of
the supramolecular chain in 2 mediated by N–HÐ Ð ÐN hydrogen bonding,
representative of both 2 and 6.
Table 8. Spore germination (%) of Alterneria brassicae and Alterneria
kikuchianain the presence of compounds 1–3 and 5–7
Chemical
1
2
3
5
6
7
Control (water)
Spore germination
percentage of
A. brassicae
Concentration (ppm)
Spore germination
percentage of
A. kikuchiana
Concentration (ppm)
25
50
100
25
50
100
5.8
4.4
9.9
9.5
5.8
4.5
80.9
3.3
2.4
4.0
4.0
3.0
2.1
0
0
1.1
1.0
0
0
4.4
3.9
9.5
9.4
4.5
4.1
79.5
3.1
2.5
4.6
4.0
3.3
2.9
0
0
1.0
0.9
0
0
chilli (Colletotrichum capsici) and onion (Stemphylium pori). All test
chemicals markedly inhibit the spore germination of each of the
above fungi at concentrations above 50 ppm. At 100 ppm, almost
complete inhibition of spore germination ensued, irrespective of
the pathogen, which indicates high fungitoxicity against different
groups of pathogen.
Phytotoxic Properties
850
The phytotoxic effects of compounds 1–3 and 5–7 as a function
of the concentration are summarized in Tables 10 and 11. For this
purpose, the seed germination of four economically important
crops, Oryzae sativa, Brassica nigra, Capcicum annum and Brassica
oleracea was evaluated at a concentration of 100 ppm. The results
indicate that none of the organotin compounds displays any
inhibitory effect on seed germination and some even show
stimulated germination. In other experiments (Table 10) with
Triticum aestivum (Sonalika) it was found that concentrations
as low as 25 ppm were equally effective.
The data available from the present study and the previous
study[18] are still limited, making it difficult for comprehensive
wileyonlinelibrary.com/journal/aoc
Figure 4. Crystal packing in the structure of 3: (a) dimeric aggregates
mediated by N–HÐ Ð ÐN hydrogen bonds; and (b) stacking of the aggregates
shown in (a) to form channels along the a axis in which reside the solvent
benzene molecules, highlighted in space filling mode.
Table 9. Spore germination (%) of Colletotrichum capsici and Stemphylium pori in the presence of compounds 1–3 and 5–7
Chemical
1
2
3
5
6
7
Control (water)
Spore germination
percentage of
C. capsici
Concentration (ppm)
Spore germination
percentage of
S. pori
Concentration (ppm)
25
50
25
50
8.1
7.0
12.2
13.7
7.9
6.92
78.2
4.9
4.2
5.6
5.9
4.3
3.9
7.9
6.70
11.9
12.3
7.3
6.1
75.9
5.0
3.7
6.1
6.7
4.9
3.4
100
0.8
0.5
2.1
1.9
0.9
0
100
0.9
0
2.2
2.0
0.8
0
comparisons to be made. However, in our previous study,[18] it
was observed that the general activity of the organotins towards
fungi decreased when alkyl groups were replaced by aryl groups,
irrespective of the fungi under study. By contrast, in the present
study fungitoxicity did not follow one common general trend but
rather appeared to be dependent on the individual fungi under
investigation. Hence, the order of activity decreased from alkyl to
c 2010 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2010, 24, 842–852
Diorganotin compounds of dihalo-substituted [(2-hydroxyphenyl)methylideneamino]thiourea
Table 10. Phytotoxicity of compounds 1–3 and 5–7, after seed
treatment of Indian wheat (Triticum aestivum L.), cultivar Sonalika
Percentage of
seed germination
after 4 h treatment
Concentration. (ppm)
Percentage of
seed germination
after 12 h treatment
Concentration (ppm)
Compound
25
50
100
25
50
100
1
2
3
5
6
7
Controla
93
92
95
98
91
92
96
95
99
95
94
99
95
95
93
99
92
93
94
94
94
94
96
93
92
93
96
97
91
95
97
94
95
92
95
94
94
92
a The control seeds were incubated in methanol–water (1 : 5) for the
indicated period.
Table 11. Phytotoxic effect compounds 1–3 and 5–7 after seed
treatment of rice (Oryzae sativa), mustard (Brassica nigra), chilli
(Capcicum annum) and cabbage (Brassica oleracea) at 100 ppm
concentration
Compound
1
2
3
5
6
7
Controla
Rice
(Oryzae
sativa)
82
84
86
77
81
85
83
Percentage of seed germination
after 12 h treatment
Mustard
Chilli
Cabbage
(Capcicum
(Brassica
(Brassica
nigra)
annum)
oleracea)
85
86
87
89
85
84
87
79
80
83
81
82
84
81
89
91
94
89
92
91
93
a The control seeds were incubated in methanol–water (1 : 5) for the
indicated period.
phenyl in one case and reversed for the other. For the disubstituted
ligand (e.g. 3,5-dibromo-), compounds containing phenyltin
groups 7 were more fungitoxic than the alkyl-substituted
tin compounds (5, 6). By contrast, as has been pointed out
above, the reverse trend was true for mono-substituted ligands
(e.g. 5-bromo-),[18] indicating presumably a dependence of the
activities on substitution on the aromatic ring of the ligand moiety.
As far as the phytotoxicities are concerned, all studied
compounds were well tolerated by various agricultural crops,
showing possibilities for commercial applications.
Acknowledgments
Appl. Organometal. Chem. 2010, 24, 842–852
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c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
851
One of us (B.S.) is thankful to the Head of the Department of Chemistry, North Bengal University, West Bengal,
India for providing the laboratory facilities. A.R. is grateful
to Professor N. Chattopadhyay, Chemistry Department, J. U.
Kolkata for providing the fluorescence spectra. M.B. and R.W.
are indebted to the Research Council of the VUB for financial support (grant GOA31). The authors are grateful to the
University of Malaya for support of the crystallographic facility.
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852
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c 2010 John Wiley & Sons, Ltd.
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crystals, compounds, anti, thioureas, dihalo, hydroxyphenyl, fungal, phytotoxicity, structure, activity, diorganotin, methylideneamino, substituted
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