Studies on biologically potent tetraazamacrocyclic complexes of bivalent tin

Article abstract of DOI:10.1080/10426500307932

Fourteen- to eighteen-membered tetraamide macrocyclic ligands N₄L¹-N₄L⁴ have been prepared by the condensation of 1,2-diaminoethane or 1,3-diaminopropane with malonic or succinic acid in the presence of condensing reagents dicyclohexylcarbodiimide and 4-dimethylaminopyridine. On reduction, these macrocyclic ligands give a new series of tetraazamacrocycles MacL¹-MacL⁴ which form complexes with tin(II) chloride. The ligands and their complexes were characterized by elemental analyses, molecular weight determinations, infrared and ¹H NMR spectral studies. The hexacoordinated state for tin has been confirmed by spectral studies. An octahedral geometry for these complexes has been proposed as the binding sites are the nitrogen atoms of the macrocycles. On the basis of the chemical composition the representation of the complexes as [Sn(MacLⁿ)Cl₂] (n = 1-4) has been established. The ligands and their complexes also have been screened for their antifungal and antibacterial activities and the findings have been reported and explained.

Full text of DOI:10.1080/10426500307932

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Phosphorus, Sulfur, and Silicon and the Related
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Studies on Biologically Potent Tetraazamacrocyclic
Complexes of Bivalent Tin
a
a
Ashu Chaudhary & R. V. Singh
a
University of Rajasthan , Jaipur, India
Published online: 27 Oct 2010.
To cite this article: Ashu Chaudhary & R. V. Singh (2003) Studies on Biologically Potent Tetraazamacrocyclic Complexes of
Bivalent Tin, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:3, 615-626
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:615–626
Copyright �C 2003 Taylor & Francis
1
042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390170200
STUDIES ON BIOLOGICALLY POTENT
TETRAAZAMACROCYCLIC COMPLEXES
OF BIVALENT TIN
Ashu Chaudhary and R. V. Singh
University of Rajasthan, Jaipur, India
(Received January 31, 2002; accepted June 26, 2002)
1
Fourteen- to eighteen-membered tetraamide macrocyclic ligands N L -
4
4
N L have been prepared by the condensation of 1,2-diaminoethane
4
or 1,3-diaminopropane with malonic or succinic acid in the pres-
ence of condensing reagents dicyclohexylcarbodiimide and 4-dimethy-
laminopyridine. On reduction, these macrocyclic ligands give a new se-
1
4
ries of tetraazamacrocycles MacL -MacL which form complexes with
tin(II) chloride. The ligands and their complexes were characterized
by elemental analyses, molecular weight determinations, infrared and
1
H NMR spectral studies. The hexacoordinated state for tin has been
confirmed by spectral studies. An octahedral geometry for these com-
plexes has been proposed as the binding sites are the nitrogen atoms
of the macrocycles. On the basis of the chemical composition the rep-
n
resentation of the complexes as [Sn(MacL )Cl ] (n = 1–4) has been
2
established. The ligands and their complexes also have been screened
for their antifungal and antibacterial activities and the findings have
been reported and explained.
Keywords: Antibacterial activity; antifungal activity; biologically
potent ligands; bivalent tin complexes; tetraamides
INTRODUCTION
Macrocyclic polyamine complexes of bivalent transition metals have
been of great interest due to their importance as an essential metalloen-
1
zyme active site. Typically the 14-membered tetraamine macrocyclic
complexes of cyclen (1,4,8,11-tetrazacyclotetradecane) are well recog-
nized as an example among the macrocyclic polyamines in coordination
A. C. is thankful to CSIR, New Delhi for financial assistance in the form of SRF wide
grant no. 9/149/288/2K2-EMR-I.
Address correspondence to R. V. Singh, Department of Chemistry, University of
Rajasthan, Jaipur—302 004, India. E-mail: kudiwal@datainfosys.net
6
15

6
16
A. Chaudhary and R. V. Singh
2
chemistry. Therefore, the physical and chemical properties of the metal
complexes are closely related to the structural features of the corre-
sponding macrocyclic ligands. Numerous efforts in this area have been
directed toward the synthesis of new types of cyclen analogues. These
include in the variation of the ring size, functionalization of the cyclen
3
4
skeleton, attachment of pendant donors to tetraamines, introduction
of variable degree of unsaturation, and introduction of substituents
4� 9
to the methylene carbon skeleton.
plored for the use as photosensitizers
in which the superoxide radical and its progeny are suspected of play-
Metalloporphyrins are being ex-
1
0,11
and for treating pathologies
1
2� 15
ing important roles.
The multifarious roles played by the naturally
occurring macrocycles in the functioning of biological systems are now
well know.1
6� 19
Their role in the physiology and biochemistry in the life
forms is of paramount importance.
The chemistry of macrocyclic complexes also is of significant inter-
est due to the use of such complexes as dyes and pigments as well as
MRI contrast agents and models for naturally occurring macrocyclic
systems. The design of host molecules as receptors for the recognition
of substrate anion guest molecules in aqueous solution is a very im-
portant target from an environmental, industrial, and health-related
point of view with multiple potential applications.2
0,21
Polyazamacro-
cyclic ligands also have been reported to catalyze biologically signif-
2
2
icant reactions of their bounded guests such as ATP hydrolysis and
formation. Mostly, the polyamide macrocycles formed on reduction with
B2H6 or LiAlH4 lead to the formation of their corresponding polyaza-
macrocycles, which may be used to construct of various macropolycyclic
systems. Keeping theses facts in mind, we have synthesized and char-
acterized the tetraazamacrocyclic complexes of tin(II) in which dicyclo-
hexylcarbodiimide and 4-dimethylamino-pyridine act as good condens-
ing reagents for the condensation of primary amine and carboxylic acid.
This article deals with the striking structural features, synthesis, and
appreciable biological applications of these complexes.
EXPERIMENTAL
All the apparatus used during the experimental work were fitted
with quick fit interchangeable standard ground joints. Melting points
were determined in sealed capillary tubes. The solvents and volatile
fractions were removed under reduced pressure using traps of con-
vential design dipped in ice. Fused calcium chloride towers were used
to prevent the back diffusion of moisture from the vacuum pump.
The chemicals including dicyclohexylcarbodiimide, 1,2-diaminoethane,

Azamacrocyclic Tin Complexes
617
1
,3-diaminopropane, and LiAlH4 were used as obtained from E. Merck.
SnCl2(BDH) was used without further purification.
1
4
Synthesis of the Ligands (N L -N L )
4
4
The reaction is carried out in 2:2 molar ratio. The appropriate
amount of dicyclohexylcarbodiimide (1.5624 g) and catalytic amount of
4
0
-dimethylaminopyridine in minimum amount of dichloromethane at
C, put on in magnetically stirred two-nacked round-bottom flask.
�
The reaction is followed by the addition of 1,2-diaminoethane or 1,3-
diaminopropane (corresponding to the dicyclohexylcarbodiimide) in
dichloromethane and malonic or succinic acid (corresponding to the
dicyclohexylcarbodiimide) in dichloromethane. The resulting mixture
�
was stirred for 10–12 h at 0 C. The solid product was isolated by filtra-
tion and washed several times with the solvent and dried in vacuo. The
solid products were recrystalized from benzene and dried in vacuo.
Synthesis of MacL -MacL4
1
1
4
The reaction is carried out in 1:2 molar ratio. The ligands N4L -N4L
�
(
1.0 g) were dissolved in tetrahydrofuran and cooled at 0 C. Lithium
aluminium hydride (corresponding to ligands) in tetrahydrofuran was
stirred for about 10 h in an ice bath. The reaction is followed by mixing
the solution of ligand and LiAlH4. The reaction mixture was stirred un-
der reflux for 72 h. After cooling, 20 ml of 15% aq. NaOH and then 30 ml
�
water were added to the mixture at 0 C. The solid product was isolated
by filtration and the residue repeatedly washed with hot tetrahydrofu-
ran. The filtrate was concentrated under reduced pressure. The liquid
thus dried in vacuo.
Synthesis of the Complexes
1
The reaction is carried out in 1:1 molar ratio. 0.9–0.8 g ligands MacL -
4
MacL were dissolved in methanol. The reaction is followed by the ad-
1
4
dition of tin(II) chloride (corresponding to ligands MacL -MacL ) so-
�
lution. The resulting mixture was stirred for 12 h at 0 C, the solid
product was obtained by filtration and washed repeatedly with same
solvent and dried in vacuo. The products were recrystallized from
benzene.
Thus, a series of 14–18 membered tetraazamacrocyclic ligands and
their complexes was derived by the condensation of dicarboxylic acids
with primary diamines in the presence of condensing reagents DCC
and DMAP as shown in Figure 1.

6
18
A. Chaudhary and R. V. Singh
RESULTS AND DISCUSSION
The resulting macrocyclic complexes are colored solids, soluble in
tetrahydrofuran and dimethylformamide. The conductivity values
�
2
3
measured for 10 M solution in anhydrous DMF are in the range
1
�
1
� 1
3–22 ohm cm mol , showing them to be nonelectrolytes. Elemen-
tal analyses agree well with the stoichiometry and chemical formula of
n
the compounds [Sn(MacL )Cl2]. The physical properties and analytical
data of the complexes are given in Table I.
Infrared Spectra
The preliminary identification of the macrocyclic ligands and their
complexes have been obtained from their infrared spectra. The first
feature of all the complexes that attracts attention is the absence of
NH2 stretching vibrations of the amine and OH groups of the di-
caboxylic acids, implying their involvement in the formulation of ter-
traamidemacrocycles. A single sharp band observed for amide ligands
FIGURE 1 Synthesis of Ligands and Complexes. (Continued)

Azamacrocyclic Tin Complexes
619
FIGURE 1 (Continued)
1
4
� 1
N4L -N4L in the region 3275–3286 cm may be assigned to �(N H)
of amide group. The amide I, amide II, amide III, and amide IV
groups are present at 1648–1707, 1544–1587, 1252–1275, and 626–
�
1
23,24
6
81 cm respectively.
It provides a strong evidence for the pres-
ence of a closed cyclic product. Strong and sharp absorption bands
�
1
appeared in the regions 2820–3055 and 1405–1460 cm in all the com-
plexes are assigned to the C H stretching and C H bending vibrati-
2
5
nal modes repsectively. It has been noticed that tetraazamacrocyles
1
4
MacL -MacL do not show amide bands corresponding to tetraamide
macrocycles. However, a slight negative shift in the NH stretching vi-
bration has been observed. All other bands do not show appreciable
change.
1
In the spectra of macrocyclic complexes [Sn(MacL )Cl2]
Sn(MacL )Cl2] as compared to their tetraazamacrocycles, the
4
[
slight negative shift in the �(N H) band that appeared in the region

6
20
A. Chaudhary and R. V. Singh
TABLE I Physical Properties and Analytical Data of Tetraamides,
Tetraazamacrocylic Ligands, and Their Tin(II) Macrocyclic Complexes
Mol. wt.
found
(calcd.)
Analysis % found (calcd.)
�
Empirical
formula
m.p. ( C)
and color
Compound
N4L1
N
Cl
—
Sn
—
C10H16O4N4
C12H20O4N4
C12H20O4N4
C14H24O4N4
C10H24N4
195
White
209
White
218
White
202
White
173
20.77
(21.86)
18.06
(19.66)
18.41
245
(256)
251
(285)
264
(285)
299
(312)
N4L2
—
—
—
—
N4L3
(19.66)
16.99
N4L4
—
—
(17.96)
MacL1
MacL2
MacL3
MacL4
26.78
—
—
181
Light brown (28.01)
154 23.44
Light brown (24.57)
161 23.14
Light brown (24.57)
178 20.99
Light brown (21.89)
Sn(MacL )Cl2] C10H24N4Cl2Sn 196 13.52
Off-white
Sn(MacL )Cl2] C10H28N4Cl2Sn 217
White
Sn(MacL )Cl2] C12H28N4Cl2Sn 162
Off-white
Sn(MacL )Cl2] C14H32N4Cl2Sn 261
Off-white
(200)
199
(228)
211
(228)
230
(256)
361
(390)
387
(418)
C12H28N4
—
—
C12H28N4
—
—
C14H32N4
—
—
1
[
[
[
[
17.45
29.89
(14.37) (18.18) (30.43)
12.41 16.29 27.88
(13.40) (16.96) (28.39)
20.05 16.20 27.81
(13.40) (16.96) (28.39)
11.04 15.27 26.04
(12.56) (15.90) (26.61)
2
3
403
(418)
439
4
(446)
�
1
3
218–3229 cm was noticed. It is ascribed to the coordinated N H
stretching vibration. This is further substantiated by the fact that
all the complexes show a medium intensity band in the region 441–
�
1
4
59 cm which is attributed to the Sn N stretching vibrations. The
Sn Cl stretching vibrations of compounds have been assigned at
�
1
26
4
80–488 cm as reported earlier also. The infrared spectral data of
ligands and their complexes are listed in Table II.
1H NMR Spectra
1
The H NMR spectra of the amide ligands, tetraazamacrocycles and
their macrocyclic complexes (Table III) reveal the signals expected
for the given Figure 1. In the spectra of all the complexes, no band
could be assigned for hydroxyl or amino groups, suggesting that the
proposed macrocylic complexes have formed after the condensation.
A broad signal is observed in the region � 7.86–8.16 ppm for amide

Azamacrocyclic Tin Complexes
621
TABLE II IR Spectral Data (in cm 1) of Tetraamides,
�
Tetraazamacrocylic Ligands, and Their Tin(II) Complexes
CH
Compound
� (N H)
Stretching Bending �Sn N
�Sn Cl
1
N4L
3275
3278
3286
3281
3261
3257
3235
3243
3229
3221
3216
3218
3055
3018
3047
3024
2892
2951
2903
2933
2852
2820
2864
2829
1460
1447
1454
1458
1429
1438
1434
1441
1422
1405
1417
1412
—
—
—
—
—
—
—
—
441
459
443
446
—
—
—
—
—
—
—
—
483
480
484
488
2
3
4
N4L
N4L
N4L
1
2
3
4
MacL
MacL
MacL
MacL
Sn(MacL )Cl2]
Sn(MacL )Cl2]
1
[
[
[
[
2
3
Sn(MacL )Cl2]
Sn(MacL )Cl2]
4
protons27,28 in macrocyclic ligands N4L -N4L . A multiplet appearing
1
4
in the region � 3.25–3.67 ppm could be ascribed to the methylene protons
2
4
(
CO N CH2) adjacent to the nitrogen atom. The spectra of N4L -N4L
show multipletes in the region � 2.05–2.08 ppm assignable to methy-
lene protons of 1,3-diaminopropane moiety. However, a singlet appear-
ing in the region � 2.81–2.92 and 3.09–3.11 ppm may be ascribed to the
methylene protons of the malonic acid and succinic acid moiety which
are adjacent to the nitrogen atoms.
The 1H NMR spectra of MacL -MacL do not show any signal
assignable to amide protons. It confirms the reduction of carboxylic
groups. The spectra of tetraazamacrocycles show multiplet in the re-
gion � 6.18-6.31 ppm due to (C H) secondary amino protons. Another
multiplet observed in the regions � 2.55–2.73 ppm is attributed to the
methylene protons (N CH2 C) of acid moiety. Tetraazamacrocycles
1
4
1
3
MacL and MacL show a multiplet in the region � 3.11–3.13 ppm, in-
1
dicating the methylene protons of (N CH2) amine moiety. MacL and
2
MacL show a multiplet in the region � 1.93–2.19 ppm due to the cen-
3
4
tral methylene protons [C (CH2) C]. However, MacL and MacL show
another multiplet in the region � 1.79–1.89 ppm ascribed to methylene
protons of succinic acid portion.
According to the above interpretation we can say that the ligands
act as tetradentate chelating agents having four coordination sites.
Secondly, since the anions Cl remained bonded with the tin atom, a
hexacoordinated environment around the tin metal atom seems to be
reasonable.

6
22

Azamacrocyclic Tin Complexes
623
Antifungal Activity
The antifungal activity of tetraazamacrocyclic ligands and their com-
plexes with divalent tin has been evaluated by Radial Growth Method29
using Czapek’s agar medium having the composition, glucose 20 g,
starch 20 g, agar-agar 20 g, and distil water 1000 mL. To this medium
was added requisite amount of the compounds after being dissolved in
dimethylformamide so as to get a certain final concentration (50, 100,
and 200 ppm). The medium then was poured into the petri plates and
the spores of fungi were placed on the medium with the help of an
inoculum needle. These petri plates were wrapped in polythene bags
containing a few drops of alcohol and were placed in an incubator at
�
3
0 � 1 C. The controls were also run and three replicates were used in
each case. The linear growth of the fungus was obtained by measur-
ing the fungal colony diameter after four days. The amount of growth
inhibition was calculated by the equation:
Percent Inhibition = (C � T) � 100/C,
where C is the diameter of fungal colony in control plate and T is the
diameter of fungal colony in test plate.
The organisms used in these investigations included Collectatrichum
capsici and Macrophomina phaseolina.
Antibacterial Activity
The activity against bacteria was evaluated by the Inhibition Zone
Technique.30 The nutrient agar medium having the composition pep-
tone 5 g, beef extract 5 g, NaCl 5 g, agar-agar 20 g, and distil water
1
000 mL was pipetted into the petri dish. When it solidified, 5 mL
of warm seeded agar was applied. The seeded agar was prepared by
cooling the molten agar to 40°C and that added the amount of bacte-
rial suspension. The compounds were dissolved in dimethylformamide
in 500 and 1000 ppm concentrations. Paper discs of Whatman No. 1
filter paper measuring diameter of 5 mm were soaked in these solu-
tions of varied concentrations. The discs were dried and placed on the
medium previously seeded with organisms in petri plates at suitable
�
distance. The petri plates were stored in an incubator at 28 � 2 C for
2
4 h. The zone of inhibition, thus formed around each disc containing
the test compounds was measured accurately in mm. The organisms
used in these investigations included Pseudomonas cepacicola (� ) and
Klebsella aerogenous (� ).

6
24
A. Chaudhary and R. V. Singh
TABLE IV Fungicidal Screening Data of Tetraamides, Tetraazamacrocylic
Ligands, and Their Divalent Tin Complexes, Percent Growth Inhibition After
�
4
days at 30 � 1 C
Collectatrichum capsici
Macrophomia phaseolina
Compounds
50 ppm
100 ppm
200 ppm
50 ppm
100 ppm
200 ppm
1
N4L
N4L
N4L
N4L
32
35
51
47
32
39
64
60
37
53
79
74
83
49
44
72
65
57
57
76
69
56
75
89
83
100
65
51
80
81
73
77
86
79
79
88
94
91
100
29
34
49
47
32
—
74
58
34
53
82
70
87
51
—
71
60
83
90
76
76
85
79
74
92
96
91
100
2
3
4
70
68
54
55
81
65
53
76
90
79
100
1
2
3
4
MacL
MacL
MacL
MacL
Sn(MacL )Cl2]
Sn(MacL )Cl2]
Sn(MacL )Cl2]
Sn(MacL )Cl2]
Bavistin
1
[
[
[
[
2
3
4
Mode of Action
The chelation theory31 accounts for the increased activity of the metal
complexes. The chelation reduces the polarity of metal atom mainly
because of partial sharing of its positive charge with the donor groups
TABLE V Bactericidal Screening Data of Tetraamides, Tetraazamacrocylic
Ligands, and Their Tin(II) Macrocyclic Complexes, Inhibition Zone of I (mm)
�
after 24 h at 28 � 2 C
Pseudomonas cepacicola (� )
Klebsella aerogenous (� )
Compound
500 ppm
1000 ppm
500 ppm
1000 ppm
Streptomycin
2
6
6
4
8
7
8
5
9
7
9
6
10
3
8
9
3
5
5
4
8
4
7
7
9
6
8
7
10
5
8
7
1
N4L
N4L
N4L
N4L
2
3
6
7
4
10
11
11
9
12
13
12
11
12
11
10
12
9
13
10
13
12
13
1
MacL
MacL
MacL
MacL
2
3
4
1
[
[
[
[
Sn(MacL )Cl2]
2
Sn(MacL )Cl2]
3
Sn(MacL )Cl2]
4
Sn(MacL )Cl2]

Azamacrocyclic Tin Complexes
625
and possible � electron delocalisation within a whole chelating ring.
The chelation increases the lipophilic nature of the central atom which
subsequently favours its premeation through the lipid layer of the cell
membrane.
The results of biological activity have been compared with the con-
ventional fungicide, bavistin, and the conventional bactericide strep-
tomycin used as standards. The results achieved out of these studies
have been enlisted in Tables IV and V in which the antifungal activ-
ity indicated that the metal chelates are more active than their parent
diamines, dicarboxylic acids, metal salts, tetraamides, and tetraaza-
macrocycles. In case of antibacterial activity the ligands and complexes
showed similar type of behaviors as indicated in antifungal activity.
REFERENCES
[
[
[
[
[
1] I. Bertini and C. Luchinat, Bioinorganic Chemistry, edited by I. Bertini, H. B. Gray,
S. J. Lipprd, and J. Valentine (University Science Books, Mill Valley, CA, 1994).
2] N. F. Curtis, Coordination Chemistry of Macrocyclic Compounds, edited by G. A.
Melson (Plenum, New York, 1979).
3] E. Kimura, Y. Kotake, T. Koike, M. Shionoya, and M. Shiron, Inorg. Chem., 29, 4991
(1990).
4] S. G. Kang, M. S. Kim, J. S. Choi, D. Whang, and K. Kim, J. Chem. Soc. Dalton
Trans., 363 (1995).
5] K. Y. Choi, J. C. Kim, W. P. Jensen, I. H. Suh, and S. S. Choi, Acta Cryst, C52, 2166
(1996).
[
[
[
[
6] K. Y. Choi, M. R. Oh, and I. H. Suh, Chem. Lett., 147 (1997).
7] K. Y. Choi, I. H. Suh, and J. C. Kim, Polyhedron, 16, 1783 (1997).
8] K. Y. Choi, Polyhedron, 16, 2073 (1997).
9] K. Y. Choi and I. H. Suh, Polyhedron, 16, 2396 (1997).
[
[
[
10] D. Dolphin, Can. J. Chem., 72, 1005 (1994).
11] R. Bonnett, Chem. Soc. Rev., 24, 19 (1995).
12] T. P. Misko, M. K. Highkin, A. M. Veenhuizen, P. T. Manning, M. K. Stem, M. G.
Currie, and D. Salvemini, J. Biol. Chem., 273, 15646 (1998).
13] D. Salvemini, Z. Q. Wang, M. K. Stern, M. G. Currie, and T. P. Miska, Proc. Natl.
Acad. Sci. USA, 95, 21659 (1998).
[
[
[
14] J. Lee, J. A. Hunt, and J. T. Groves, J. Chem. Soc., 120, 6053 (1998).
15] G. Ferrer-Sueta, I. Batinic-Haberle, I. Spasojevic, I. Fridovich, and R. Radi, Chem.
Res. Toxicol., 12, 442 (1998).
[
16] A. Volbeda, M. H. Charon, C. Piras, E. C. Hatchikian, M. Frey, and J. C. Fontecilla
Camps, Nature (London), 373, 580 (1995).
[
17] C. A. Marganisn, H. Vizar, N. Baidya, M. M. Olmostead, and P. K. Mascharak,
J. Am. Chem. Soc., 117, 1584 (1995).
[
18] S. Brooker and T. C. Davidson, Chem. Commun., 2007 (1997).
[
19] S. Brooker, P. D. Croucher, and F. M. Roxborgh, J. Chem. Soc. Dalton, Trans, 3031
(1996).
[
[
20] F. M. Menger and K. K. Catlin, Angew, Chem. Ed. Engl., 34, 2147 (1998).
21] M. M. G. Antonisse and D. N. Reinhoudt, Chem. Commun., 443 (1998).

6
26
A. Chaudhary and R. V. Singh
[
22] A. Bencini, A. Bianchi, C. Giorgi, P. Paoletti, B. Votancoli, V. Fusi, E. Garcia-Espana,
J. M. Llinar, and J. A. Ramirez, Inorg. Chem., 35, 1114 (1995).
[
[
23] Z. A. Siddiqi and V. J. Mathew, Polyhedron, 13, 799 (1994).
24] S. Matsuoka, K. Yamamoto, T. Ogato, M., Kusaba, N. Nakashima, E. Fujita, and
S. Yanafida, J. Am. Chem. Soc., 115, 601 (1993).
[
25] N. B. Colthup, L. H. Dally, and S. E. Wiberley, Introduction of Infrared and Raman
Spectroscopy (Acadmic Pres, New Delhi, 1964).
[
[
[
[
[
[
26] D. K. Dey, M. K. Saha, and L. Dahlenburg, Indian J. Chem., 39A, 1177 (2000).
27] T. C. Woon and D. P. Fairilie, Inorg. Chem., 31, 4069 (1992).
28] M. Shakir and S. P. Varkey, Trans. Met. Chem., 19, 606 (1994).
29] D. Singh, R. B. Goyal, and R. V. Singh, Appl. Organomet. Chem., 5, 45 (1991).
30] N. Fahmi and R. V. Singh, Bol. Chil, Quim., 41, 65 (1996).
31] A. Kumari, R. V. Singh, and J. P. Tandon, Phosphorus, Sulphur, and Silicon, 66, 195
(1992).