Synthesis and spectral studies of organotin(IV) 4-amino-3-alkyl-1,2,4-triazole-5-thionates: In vitro antimicrobial activity

Article abstract of DOI:10.1016/j.saa.2007.09.009

Some di- and triorganotin(IV) triazolates of general formula, R_(4-n)SnL_n (where n = 2; R = Me, n-Bu and Ph; n = 1; R = Me, n-Pr, n-Bu and Ph and HL = 4-amino-3-methyl-1,2,4-triazole-5-thiol (HL-1); and 4-amino-3-ethyl-1,2,4-triazole-5-thiol (HL-2)) were synthesized by the reaction of R_(4-n)SnCl_n with sodium salt of HL-1 and HL-2. The bonding and coordination behavior in these derivatives have been discussed on the basis of IR and ¹¹⁹Sn Moessbauer spectroscopic studies in the solid state. Their coordination behavior in solution is discussed by multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR spectral studies. The IR and ¹¹⁹Sn Moessbauer spectroscopic studies indicate that the ligands, HL-1 and HL-2 act as a monoanionic bidentate ligand, coordinating through S_exo^- and N_ring. The distorted skew trapezoidal-bipyramidal and distorted trigonal bipyramidal geometries have been proposed for R₂SnL₂ and R₃SnL, respectively, in the solid state. In vitro antimicrobial screening of some of the newly synthesized derivatives and of some di- and triorganotin(IV) derivatives of 3-amino-1,2,4-triazole-5-thiol (HL-3) and 5-amino-3H-1,3,4-thiadiazole-2-thiol (HL-4) along with two standard drugs such as fluconazole and ciprofloxacin have been carried out against the bacteria, viz. Staphylococcus aureus and Escherichia coli, and against some fungi, viz. Aspergillus fumigatus, Candida albicans, Candida albicans (ATCC 10231), Candida krusei (GO₃) and Candida glabrata (HO₅) by the filter paper disc method. The studied organotin(IV) compounds show mild antifungal activity as compared to that of fluconazole, however, they show almost insignificant activity against the studied Gram-positive (Staphylococcus aureas) and Gram-negative (Escherichia coli) bacteria as compared to that of standard drug, ciprofloxacin.

Full text of DOI:10.1016/j.saa.2007.09.009

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Spectrochimica Acta Part A 70 (2008) 766–774
Synthesis and spectral studies of organotin(IV)
4-amino-3-alkyl-1,2,4-triazole-5-thionates:
In vitro antimicrobial activity
Mala Natha,∗, Sulaxnaa, Xueqing Songb, George Engb, Ashok Kumarc
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
b Department of Chemistry and Physics, University of The District of Columbia, Washington, DC 20008, USA
c Department of Pharmacology, LLRM Medical College, Meerut 250004, India
Received 16 April 2007; received in revised form 6 September 2007; accepted 17 September 2007
Abstract
Some di- and triorganotin(IV) triazolates of general formula, R(4−n)SnLn (where n = 2; R = Me, n-Bu and Ph; n = 1; R = Me, n-Pr, n-Bu and Ph
and HL = 4-amino-3-methyl-1,2,4-triazole-5-thiol (HL-1); and 4-amino-3-ethyl-1,2,4-triazole-5-thiol (HL-2)) were synthesized by the reaction of
R
(4−n)SnCln with sodium salt of HL-1 and HL-2. The bonding and coordination behavior in these derivatives have been discussed on the basis of
IR and 119Sn Mo¨ssbauer spectroscopic studies in the solid state. Their coordination behavior in solution is discussed by multinuclear (1H, 13C and
119Sn) NMR spectral studies. The IR and 119Sn Mo¨ssbauer spectroscopic studies indicate that the ligands, HL-1 and HL-2 act as a monoanionic
bidentate ligand, coordinating through Se−xo and Nring. The distorted skew trapezoidal-bipyramidal and distorted trigonal bipyramidal geometries
have been proposed for R2SnL2 and R3SnL, respectively, in the solid state. In vitro antimicrobial screening of some of the newly synthesized
derivatives and of some di- and triorganotin(IV) derivatives of 3-amino-1,2,4-triazole-5-thiol (HL-3) and 5-amino-3H-1,3,4-thiadiazole-2-thiol
(HL-4) along with two standard drugs such as fluconazole and ciprofloxacin have been carried out against the bacteria, viz. Staphylococcus
aureus and Escherichia coli, and against some fungi, viz. Aspergillus fumigatus, Candida albicans, Candida albicans (ATCC 10231), Candida
krusei (GO3) and Candida glabrata (HO5) by the filter paper disc method. The studied organotin(IV) compounds show mild antifungal activity as
compared to that of fluconazole, however, they show almost insignificant activity against the studied Gram-positive (Staphylococcus aureas) and
Gram-negative (Escherichia coli) bacteria as compared to that of standard drug, ciprofloxacin.
© 2007 Published by Elsevier B.V.
Keywords: 1,2,4-Triazole; 1,3,4-Thiadiazole; Organotin(IV) compounds; Antifungal activity; Antibacterial activity
1. Introduction
commercially used as antifungal agents [6], therefore, several
studies have been carried out to explore their antimicrobial activ-
ity [7–11]. Many in vitro studies have been performed in order
to explain the mechanism which is responsible for the biological
activity of organotin compounds. Although, the mode of biologi-
cal action of organotin compounds is not completely understood,
but it has been revealed from the literature that the biocidal prop-
erties of organotin(IV) compounds are dependent on both the
organic group and the ligand attached to tin. In this context, the
interaction of organotins has been extensively studied with a
variety of ligands having their biological origin [3,12] and with
other hetero (N/S/O) donor ligands [9–12]. The coordination
of organotins with heterocyclic thionates is of current interest
because thionates can coordinate to the metal ions in different
coordinating modes [13]. Moreover, heterocyclic thionates can
(a) mimic cysteine sulfur coordination in metalloenzymes, (b)
Organotin compounds have emerged as potentially active
compounds among non-platinum chemotherapeutic metal-
lopharmaceuticals in the last two decades. Some organotin(IV)
derivatives have been found to exhibit antitumor activity against
a number of tumor cell lines of human origin [1–4]. Organotin
compounds are formulated as wettable and flowable powders
for use mainly as fungicides to control blights on field crops and
orchard trees, and as molluscicides, acaricides and in marine
antifouling paints [5]. Besides this, the organotin(IV) com-
pounds, viz. Brestan (Ph3SnOAc) and Duter (Ph3SnOH) are
∗
Corresponding author. Tel.: +91 1332 285797; fax: +91 1332 273560.
E-mail address: malanfcy@iitr.ernet.in (M. Nath).
1386-1425/$ – see front matter © 2007 Published by Elsevier B.V.
doi:10.1016/j.saa.2007.09.009

M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
767
show electronic and structural properties of the active sites in
copper blue proteins involving S, N-coordination, (c) comprise
purine and pyrimidine bases [14,15].
zation of tri- and diorganotin(IV) derivatives of HL-3 and HL-4
have been reported previously in [28,29].
Among N-heterocyclic thionates, thiadiazoles and triazoles,
in particular, are interesting compounds because of their
chemistry and biological activity. The biocidal activities, e.g.,
antifungal [16,17], antibacterial [16,17], antiinflammatory [18],
antituberculosis [19], anticonvulsant [17,20] and anticancer [21]
activities, of thiadiazole derivatives are possibly by virtue of
>N C–S– toxophoric moiety. However, 1,2,4-triazole repre-
sents a hybrid of pyrazole and imidazole with regard to the
arrangement of ring nitrogens [22]. 1,2,4-Triazole and their
derivatives possess a broad range of biological activities includ-
ing antimicrobial and antifungal activities [23,24]. Examples
of such compounds bearing the 1,2,4-triazole moieties are flu-
conazole, a powerful antifungal agent [25] and N-nucleoside
ribavirin, a potent antiviral compound [26]. Several new triazole
derivatives are in various phases of preclinical and clinical trials
[27] and may be available for human use in the near future. In
addition to this, the derivatives of thiadiazoles and triazoles have
been broadly applied in the area of pharmaceutical, agricultural,
industrial, and polymer chemistry [22].
2. Experimental
2.1. Materials and methods
All the syntheses were carried out under an anhydrous nitro-
gen atmosphere and the precautions to avoid the presence of
oxygen were taken at every stage. Solvents were dried and
stored under nitrogen before use. Dimethyltin(IV) dichloride,
di-n-butyltin(IV) dichloride, trimethyltin(IV) chloride, tri-n-
propyltin(IV) chloride, tri-n-butyltin(IV) chloride and triph-
enyltin(IV) chloride (Merck-Schuchardt), tetraphenyltin(IV)
(Sigma–Aldrich), tin tetrachloride (Farmitalia Carlo Erba), thio-
carbohydrazide (Fluka), acetic acid (Merck), propionic acid
(Aldrich), nutrient agar (Qualigen) and sabouraud dextrose agar
(Himedia) were used as received. Diphenyltin(IV) dichloride
was synthesized according to the reported method [5]. The
ligands 4-amino-3-methyl-1,2,4-triazole-2-thiol (HL-1) and 4-
amino-3-ethyl-1,2,4-triazole-2-thiol (HL-2) were synthesized
by the reported method [30].
In the present paper, we report the synthesis and character-
ization of organotin(IV) derivatives of HL-1 and HL-2. The
in vitro antibacterial and antifungal activities of the ligands,
viz. 4-amino-3-methyl-1,2,4-triazole-5-thiol (HL-1), 4-amino-
3-ethyl-1,2,4-triazole-5-thiol (HL-2), 3-amino-1,2,4-triazole-5-
thiol (HL-3) and 5-amino-3H-1,3,4-thiadiazole-2-thiol (HL-4)
(Scheme 1) and some of their organotin(IV) derivatives against
the bacteria, S. aureus and E. coli, and against the fungi, viz.
A. fumigatus, C. Albicans, C. albicans (ATCC 10231), C. krusei
(GO3) and C. glabrata (HO5), carried out by the filter paper disc
method, have also been reported. The synthesis and characteri-
2.1.1. Synthesis by sodium chloride method
A methanolic solution (∼30 ml) of HL-1/HL-2 (4.0 mmol)
was added to sodium methoxide (prepared by dissolving sodium
(4.2 mmol) in dry methanol (∼5 ml)) under dry nitrogen. The
reaction mixture was immediately turned to orange-red color,
which was stirred for another ∼8 h at room temperature. To this,
a methanol (∼30 ml) solution of R2SnCl2 (2.0 mmol)/R3SnL
(4.0 mmol) was added dropwise with constant stirring, and
stirred for 30–35 h at room temperature. The reaction mixture
was centrifuged and filtered in order to remove sodium chloride,
Scheme 1.

768
M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
and the volatiles were removed in vacuo. The solid obtained was
recrystallized from methanol.
in antibacterial activity determination. These Petri dishes were
incubated at 30 1 ◦C for 48 h. The zone of inhibition of growth
was considered as an indicator for the antifungal activity. A con-
trol disc (saturated with solvent) without the test compound was
similarly treated.
2.2. Measurements and antimicrobial studies
All the physico-chemical and spectral measurements were
carried out using the same methods and instruments reported
previously [28,29], except (1H, 13C and 119Sn) NMR spectra of
a few compounds were recorded on a Bruker Avance 500 MHz
NMR spectrometer at the Indian Institute of Technology Roor-
kee, Roorkee.
3. Results and discussion
It has been reported [30] that 4-amino-3-alkyl-1,2,4-triazole-
5-thiones exhibit thione-thiol tautomerism (Scheme 1) and both
forms coexist in the solid-state but thione form is the dom-
inant one in the solid-state and equilibrium shifts to thiol
form in solution. The reactions of diorganotin(IV) dichlo-
rides and triorganotin(IV) chloride with sodium salt of HL
in methanol (where HL = 4-amino-3-methyl-1,2,4-triazole-5-
thiol (HL-1) and 4-amino-3-ethyl-1,2,4-triazole-5-thiol (HL-2))
{formedaccordingtoEq. (1)}in1:2and1:1molarratios, respec-
tively, led to the formation of the compounds according to Eq.
(2). In the resulting organotin(IV) triazolates, HL acts as a mono
deprotonated bidentate ligand with the negative charge residing
on the sulfur atom of the aromatic thiol tautomer.
2.2.1. In vitro antimicrobial activity
The in vitro antibacterial and antifungal activities of the lig-
ands (HL-1 to HL-4) and some of their soluble organotin(IV)
derivatives were performed against the bacteria, viz. Staphyloc-
cus aureus (209p) (Gram-positive) and Escherischia coli (ESS
2231) (Gram-negative), and against the fungi, viz. Aspergillus
fumigatus, Candida albicans, Candida albicans (ATCC 10231),
Candida krusei (GO3) and Candida glabrata (HO5), by filter
paper disc method [31]. The observed screening results of the
test compounds were compared with that of the reference drugs,
viz. ciprofloxacin for antibacterial and fluconazole for antifun-
gal activity. The results of biological screening are mentioned
in mm, showing diameter of inhibition zone (i.z.) and these are
categorized as, 0–6 mm for mild, 7–13 mm for moderate and
14–26 mm for potential efficacy at the tested dose.
HL + NaOMe → NaL + MeOH
nNaL + R(4−n)SnCln → R(4−n)SnLn + nNaCl
(where n = 2, R = Me, n-Bu and Ph; n = 3, R = Me, n-Pr, n-Bu and
Ph;HL = 4-amino-3-methyl-1,2,4-triazole-5-thiol(HL-1)and4-
amino-3-ethyl-1,2,4-triazole-5-thiol (HL-2)).
(1)
(2)
The reactions involved in the synthesis of di- and tri-
organotin(IV) derivatives were found to be quite feasible and
required 30–35 h of stirring at room temperature. All of the
synthesized organotin(IV) derivatives are white powder, except
n-Pr3Sn(L-1/L-2) and n-Bu3Sn(L-1/L-2), which are semisolid.
The diorganotin(IV) derivatives are sparingly soluble in MeOH
and DMSO, whereas triorganotin(IV) derivatives have good
solubility in MeOH and CHCl3, but all of the synthesized
compounds are insoluble in water and other organic solvents.
All of the synthesized compounds are obtained in good yield
(41–63%) and are stable towards atmospheric air and mois-
ture. The analytical data of the synthesized compounds together
with those of HL-1 and HL-2 are given in Table 1, and
correspond to the proposed stoichiometry. The molar conduc-
tances of the studied compounds in methanol (10−3 M) lie
in the range 5.0–70.0 ohm−1 cm2 mol−1, indicating their non-
electrolytic nature.
2.2.1.1. In vitro antibacterial activity. The bacteria were cul-
tured in nutrient agar medium (peptone 10 g, meat extract 10 g,
NaCl 5 g and Agar 10 g in distilled water, at pH 7.5 0.1) and
used as inoculums. The solvent used in control was 10% DMSO
in methanol. Whatmann filter paper discs (diameter 6.5 mm)
weresterilizedbydryheatat140 ◦Cfor1 handsaturatedwiththe
solution of test compound (concentration: 250 ␮g ml−1) or ref-
erence drug, ciprofloxacin (concentration: 50 ␮g ml−1). These
discs were air-dried at room temperature to remove any resid-
ual solvent, which might interfere with the determination. These
discs were then placed on the surface of a sterilized agar nutri-
ent medium that was inoculated with test organism (by using
a sterile swab) and air-dried to remove the surface moisture.
The thickness of the agar medium was kept equal in all Petri
dishes. A control disc (saturated with solvent) without the test
compound was similarly treated. Before incubation, Petri dishes
were placed for 1 h in a cold room (5 ◦C) to allow diffusion of the
compound from the disc into the agar plate. Thereafter, the discs
were incubated at 37 1 ◦C for 20–24 h. The zone of inhibition
of growth was measured, which indicates the inhibitory activity
of the compounds on the growth of the microorganism.
3.1. IR spectral studies
The characteristic infrared absorption frequencies (in cm−1
)
and their assignments for HL-1, HL-2 and their organotin(IV)
derivatives are presented in Table 2. The IR spectra of HL-1
2.2.1.2. In vitro antifungal activity. For antifungal screening,
spore suspension (5 ml) of each test microorganisms (72 h cul-
ture) was added to sterilized sabouraud dextrose agar medium
at 35–40 ◦C with shaking. The Petri dishes were seeded with the
mixture and the filter paper discs of test compound (prepared as
mentioned in Section 2.2.1.1) and reference drug, fluconazole
(concentration 50 ␮g ml−1) were placed in the same manner as
and HL-2 exhibit a weak ν(S–H) band at 2704 and 2671 cm−1
,
respectively, which is not observed in all of the organotin(IV)
derivatives studied, indicating the deprotonation of thiol group
of the ligands and their subsequent coordination to tin. In
the IR spectra of HL-1 and HL-2, there are several medium
intensity bands due to ν(N–H) and ␯(C–H), in the region

M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
769
3272–2946 cm−1, but it is difficult to differentiate between the
N–H and C–H stretching vibrations with certainty. However,
bands at 3270 2 and 3158 20 cm−1 may be assigned to
νas(N–H) and νs(N–H) [20,32], respectively, of NH2 group. In
the IR spectra of most of the organotin(IV) derivatives stud-
ied the (N–H) stretching absorption bands undergo a small
shift to lower wave numbers (νas(N–H): 3289 24 cm−1 and
νs(N–H): 3158 42 cm−1) as compared to that of free ligands,
but a downward shift by 200–300 cm−1 would require for the
coordination of the ligand through the amino group [3,32,33].
Therefore, the observed shift in ν(N–H) vibration mode may
be due to the participation of NH2 group in weak inter-/intra-
molecular hydrogen bonding. In the IR spectrum of HL-1/HL-2,
the thioamide bands I and II (due to ν(C N) vibrations)
have been assigned at 1475/1487 and 1379/1398 cm−1, respec-
tively, whereas the thioamide bands III and IV (due to ν(C S)
vibrations) are observed at 1287/1241 and 1038/1022 cm−1
,
respectively [34]. In the IR spectra of the organotin(IV) deriva-
tives, these thioamide bands shift to lower wave numbers (by
5–78 cm−1), which may be due to the evolution of partial
double bond character in the thioamide group (–N C S–)
after its deprotonation [13] and subsequent coordination to
tin via Sexo and N(1). This mode of coordination of the 4-
amino-3-alkyl-1,2,4-triazole-5-thiols is further confirmed by the
appearance of two medium intensity bands at 452 37 cm−1
and 341 39 cm−1 in the far-IR spectra of the organotin(IV)
compounds which are assigned to the ν(Sn ← N) and ν(Sn–S)
vibrational modes, respectively [3,28,29,32–34]. In all of the
compounds, theνas(Sn–C)andνs(Sn–C)bandsarealsoobserved
in the range 505–604 cm−1 for alkyltin and 220–278 cm−1 for
aryltin compounds [28,29], which suggest a non-planar arrange-
ment of C–Sn–C moiety.
3.2. 119Sn Mo¨ssbauer spectral studies
119
¨
Sn Mossbauer spectral data of the synthesized
The
organotin(IV) derivatives are presented in Table 3. The 119Sn
¨
Mossbauer spectra of the studied organotin(IV) derivatives
exhibit a doublet centered in the isomer shift (I.S.) value range
0.97–1.33 mm s−1. The quadruple splitting (Q.S.) values in the
range 2.25–3.33 mm s−1 for R3SnL/R2SnL2 compounds show
that the electric field gradient around the tin nucleus is pro-
duced by the inequalities in the tin-sulfur/-nitrogen ␴ bonds and
is also due to geometric distortions. The ρ (Q.S./I.S.) values
(2.32–2.94) for these studied compounds indicate a coordina-
tion number superior than four with either a 5- or 6-coordinated
tin.
The point charge calculations for octahedral diorganotin(IV)
derivatives [R2SnX4]2− predict that the Q.S values for the
trans-isomer will be twice (∼4.0 mm s−1) that of the cis-isomer
(2.0 mm s−1), [35]. Further, it has been reported [36] that I.S.
values for cis-[R2SnX4]2− are less than 1.0 mm s−1 while those
for trans-compounds are approximately 1.20–1.30 mm s−1
.
However, the observed Q.S. and I.S. values of the diorgan-
otin(IV) derivatives studied (Table 3) are intermediate between
the two geometries, i.e., the observed values are slightly

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M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
Table 2
IR frequenciesa (in cm−1) of HL-1, HL-2 and their organotin(IV) derivatives
Ligand/compound ν(N–H), ␯(C−H)
ν(S–H) Thioamide bands I, II, III, IV
νas (Sn–C), νs (Sn–C) ν(Sn ← N), ν(Sn–S)
Ligands
HL-1
HL-2
3272vs, 3178vs, 3114vs, 2946s
3268m, 3139sbr, 3054m, 2982w, 2957m
2704w 1475s, 1379vs, 1287m, 1038s
2671w 1487vs, 1398s, 1241vs, 1022s
–
–
–
–
Diorganotin(IV) derivatives
Me2Sn(L-1)2
n-Bu2Sn(L-1)2
Ph2Sn(L-1)2
Me2Sn(L-2)2
n-Bu2Sn(L-2)2
3265m, 3178w, 3113m, 2948m
3269w, 3178w, 3113w, 2956m, 2935m
3274m, 3178m, 3108m, 2952w
3270m, 3139s, 2985s, 2939sh, 2916s, 2804vs
3268m, 3145vs, 3054w 2957s, 2922s, 2870m
–
–
–
–
–
1474m, 1381vs, 1213s, 1039s
1470m, 1379s, 1211s, 1040s
1477m, 1380vs, 1211s, 1039s
1471vs, 1365s, 1257s, 1028m
1487vs, 1381m, 1288s, 1022s
531w, 523w
568s
250s, 220vw
556vs, 520w
547s, 532s
425s 350m
476s 313m
426s 350m
419m 352m
418m 346m
Triorganotin(IV) derivatives
Me3Sn(L-1)
n-Pr3Sn(L-1)
n-Bu3Sn(L-1)
Ph3Sn(L-1)
Me3Sn(L-2)
n-Pr3Sn(L-2)
n-Bu3Sn(L-2)
Ph3Sn(L-2)
3274w, 3117w, 2995m, 2913m
–
–
–
–
–
–
–
–
1474m, 1378s, 1283m, 1046s
1456w, 1383vs, 1256w, 1035m
1460s, 1377vs, 1291w, 1037m
1476s, 1378w, 1263w, 1020m
548vs, 513w
540s, 531m
540s, 533w
275m, 229w
468vs 326w
475s 351m
419s 318w
447s 303s
414m 356w
460m 331w
456w 326m
447m 303s
3265w, 3182w,3117m, 2961s, 2926m, 2865m
3270m, 3178m, 3115m, 2957vs, 2922s, 2855m
3270m, 3178w, 3116m, 3059s
3312s, 3269w, 3200vs, 2985s, 2939m, 2917m
3269w, 3148w, 2956s, 2922m, 2866s
3289m, 3162m, 2956vs, 2917vs, 2859s
3313mbr, 3061s, 3048s, 3017w, 2987m
1480vs, 1396vs, 1254m, 1036vs 543vs, 522s
1486m, 1374s, 1239w, 1023m
1457vs, 1372vs, 1289s, 1018w
1478vs, 1397m 1251m, 1040s
515w, 505w
604m 528m
278m 228m
a
vs, very strong; s, strong; m, medium; w, weak; br, broad; sh, shoulder.
higher than the values for cis-octahedral configuration, but
substantially lower than the values for trans-octahedral config-
uration. Indeed, where the other donor groups of the ligands
have higher electronegativity, the Q.S. is mainly governed by
C–Sn–C bond angle [37], and the distortion from the regu-
lar six coordination can give values similar to those reported
[38] for highly distorted square-bipyramidal/ skew trapezoidal-
bipyramidal structure. Therefore, a distorted skew-trapezoidal
bipyramidal structure is proposed for R2SnL2 compounds,
which is also supported by the calculated values of the angle
∠C–Sn–C (105–137◦) as given in Table 3, which are close to the
average of the two extremes, in which the organic substituents
do not adopt either cis- or trans-geometries about the tin center
[38].
Fig. 1. Proposed structure for R2SnL2 (where R = Me, n-Bu and Ph).
organic groups occupy the axial positions. The solution NMR
spectral studies suggest that in R2SnL2 compounds, the primary
bonding occurs through (Sexo)−, however, Sn ← N(1) interac-
tions are very weak and may easily be disrupted in solution
(discussed later in NMR).
119
¨
Sn Mossbauer spectra of R3SnL exhibit Q.S. in the
The
The most probable structure for R2SnL2, which is in agree-
ment with all the spectral observations and the observed
Goldanskii-Karyagin effect [39] is shown in Fig. 1, in which the
ligands, HL-1/HL-2, act as monoanionic bidentate coordinat-
ing through (Sexo) and N(1) in the equatorial positions and two
range 2.74–3.33 mm s−1 and in the range I.S. 1.09–1.33 mm s−1
.
It has been reported [40] that the three conceivable (Fig. 2)
five coordinate isomers of R3SnXY (where X or Y = N/O/S;
XY are the donor sites of the bidentate ligand) have different
Table 3
119Sn Mo¨ssbauer spectral data (80 K) of synthesized compoundsa
Compound
I.S. (mm s−1
)
Q.S. (mm s−1
)
ρ (Q.S./I.S.)
τ1 (L)
τ2 (R)
∠C–Sn–Cb
Diorganotin(IV) derivatives
Me2Sn(L-1)2
n-Bu2Sn(L-1)2
Me2Sn(L-2)2
n-Bu2Sn(L-2)2
1.03
0.97
1.05
1.16
3.03
2.25
2.81
2.89
2.94
2.32
2.68
2.48
–
–
129
105
122
125
1.12
1.36
1.27
1.14
1.47
1.54
Triorganotin(IV) derivatives
Me3Sn(L-1)
Ph3Sn(L-1)
Me3Sn(L-2)
Ph3Sn(L-2)
1.26
1.14
1.33
1.09
3.33
2.98
3.19
2.74
2.63
2.61
2.40
2.52
1.07
1.24
1.44
1.72
1.22
1.09
1.52
1.93
137
127
133
120
a
Q.S.: quadruple splitting; I.S.: isomer shift relative to BaSnO3 and tin foil (splitting: 2.52 mm s−1); τ1 (L): half line-width left doublet component; τ2 (R): half
line-width right doublet component.
b
Calculated by using Parish’s relationship [37]: Q.S. = 4[R][1 − 3/4sin22θ]1/2; ∠C–Sn–C = 180–2θ◦.

M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
771
Fig. 2. Three possible isomers of R3Sn(XY) [40].
Q.S. value ranges; for isomer (a) 1.70–2.40 mm s−1; for (b)
Fig. 3. Proposed structure for R3SnL (where, R = Me, n-Pr, n-Bu and Ph;
R’ = Me or Et).
3.0–4.0 mm s−1; and for (c) 3.50–4.10 mm s−1
.
The observed Q.S. values (2.74–3.33 mm s−1) of R3Sn(L-1/
L-2) (R = Me and Ph) are higher than that for isomer (a) as shown
in Fig. 2, and considered to be compatible with trans-structure,
i.e., isomer (b) as shown in Fig. 2. But the observed νas(Sn–C)
and νs(Sn–C) stretching vibrations in the IR spectra of the tri-
organotin(IV) derivatives studied indicate a non-planar SnC3
fragment and rule out the possibility of trans-isomer as shown
in Fig. 2b. Therefore, a highly distorted cis-trigonal-bipyramidal
structure (Fig. 3), which is intermediate between fac (Fig. 2a)
and mer (Fig. 2c) cis-trigonal bipyramidal structures is proposed
for these triorganotin(IV) derivatives, in the solid state. On the
basis of IR spectral interpretations, a similar structure (as shown
in Fig. 3) has been tentatively proposed for n-Pr3SnL and n-
119
¨
Sn Mossbauer spectra could not be
Bu3SnL because their
recorded as they are semisolid.
3.3. Multinuclear (1H, 13C and 119Sn) NMR spectral
studies in solution
1Hand13CNMRspectraldataofHL-1, HL-2andtheirorgan-
otin(IV) derivatives (except those, which do not have enough
solubility) are given in Table 4 and 5, respectively. In the H
NMR spectra of HL-1 and HL-2, the –SH resonance is observed
at δ ∼1.30 ppm, which is absent in all of the studied organ-
otin(IV) derivatives, indicating deprotonation of thiol group of
1
Table 4
1H NMR spectral data of HL-1, HL-2 and their organotin(IV) derivatives (recorded in CD3OD unless otherwise reported)
Ligand/compound (solvent)
∠C–Sn–Ca (◦)
δb (ppm)
Ligands
HL-1c
HL-2c
–
–
1.30 (s, 1H, SH); 2.35 (s, 3H, H-1ꢀ); 5.40 (s, 2H, NH2).
2.80–2.73 (q, 2H, 7.5 Hz, H-1ꢀ); 1.30 (t, 3H, 7.5 Hz, H-2ꢀ + SH); 5.40 (s, 2H, NH2).
Diorganotin(IV) derivatives
d
Me2Sn(L-1)2
n-Bu2Sn(L-1)2
–
–
2.35 (s, 6H, H-1ꢀ); 5.33 (s, 4H, NH2); 0.92 (s, 6H, H-␣).
2.35 (s, 6H, H-1ꢀ); 5.28 (s, 4H, NH2); 1.59 (br, 4H, H-␣); 1.70 (brm, 4H, H-␤); 1.44–1.36 (m, 4H, H-␥); 0.93 (t,
6H, 7.0 Hz, H-␦).
d
d
Ph2Sn(L-1)2
–
–
2.30 (s, 6H, H-1ꢀ); 5.29 (s, 4H, NH2); 7.81 (m, 4H, 7.5 Hz, H-␤); 7.45 (m, 6H, H-␥, H-␦).
2.65–2.61 (q, 4H, 7.5 Hz, H-1ꢀ); 1.18 (t, 6H, 7.5 Hz, H-2ꢀ); 5.53 (s, 4H, NH2); 2.51 (s, 6H, H-␣).
d
Me2Sn(L-2)2
Triorganotin(IV) derivatives
Me3Sn(L-1)c
115.62
–
2.33 (s, 3H, H-1ꢀ); 5.40 (s, 2H, NH2); 0.51 (s, 9H, H-␣) [2J(1H-119Sn) = 65 Hz].
2.33 (s, 3H, H-1ꢀ); 5.40 (s, 2H, NH2); 1.31 (t, 6H, 7.5 Hz, H-␣); 1.76–1.63 (m, 6H, H-␤); 0.98 (t, 9H, 7.5 Hz,
H-␥).
n-Pr3Sn(L-1)c
n-Bu3Sn(L-1)c
–
2.34 (s, 3H, H-1ꢀ); 5.40 (s, 2H, NH2); 1.43–1.30 (m, 12H, H-␣, H-␥)e; 1.70–1.60 (m, 6H, H-␤); 0.92 (t, 9H,
7.2 Hz, H-␦).
Ph3Sn(L-1)d
–
111.56
–
2.26 (s, 3H, H-1ꢀ); 7.78 (d, 6H, 6.6 Hz, H-␤) [3J(1H-119/117Sn) = 61/58 Hz]; 7.51–7.41 (m, 9H, H-␥, H-␦)e.
2.76–2.69 (q, 2H, 7.5 Hz, H-1ꢀ); 1.28 (t, 3H, 7.5 Hz, H-2ꢀ); 0.75 (s, 9H, H-␣) [2J(1H-119Sn) = 59 Hz].
2.80–2.72 (q, 2H, 7.5 Hz, H-1ꢀ); 1.33–1.23 (m, 9H, H-2ꢀ + H-␣); 1.76–1.66 (m, 6H, H-␤); 1.02 (t, 9H, 7.2 Hz,
H-␥).
2.73–2.66 (q, 2H, 7.5 Hz, H-1ꢀ); 1.25 (t, 3H, 7.5 Hz, H-2ꢀ); 4.62 (s, 2H, NH2); 1.40–1.30 (m, 12H, H-␣, H-␥)e;
1.68–1.58 (m, 6H, H-␤); 0.90 (t, 9H, 7.2 Hz, H-␦).
2.76–2.62 (q, 2H, 7.5 Hz, H-1ꢀ); 1.28 (t, 3H, 7.5 Hz, H-2ꢀ); 7.82 (d, 6H, 6.0 Hz, H-␤))
[3J(1H-119/117Sn) = 61/58 Hz]; 7.51–7.44 (m, 9H, H-␥, H-␦).
Me3Sn(L-2)c (CDCl3)
n-Pr3Sn(L-2)c
n-Bu3Sn(L-2)c (CDCl3)
Ph3Sn(L-2)c
–
–
a
Ref. [41]
b
s, singlet; d: doublet; dd: double doublet; t: triplet; q: quartet; m: multiplet; br: broad; the signal of NH2 group is weak and broad and sometimes not observed.
Spectrum recorded on a Bruker DRX 300 MHz, FTNMR spectrometer.
Spectrum recorded on a Bruker Avance 500 MHz, FTNMR spectrometer.
c
d
e
Strongly overlapping multiplets.

772
M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
Table 5
13C NMR spectral data of HL-1, HL-2 and their organotin(IV) derivatives (recorded in CD3OD unless otherwise reported)
Ligand/compound (solvent)
∠C–Sn–Ca
␦ (ppm)
Ligands
HL-1b
HL-2b
–
–
C-1ꢀ: 10.55; C-3: 151.0; C-5: 163.0.
C-1ꢀ: 19.30; C-2ꢀ: 10.70; C-3: 155.70; C-5: 167.70.
Diorganotin(IV) derivatives
c
Me2Sn(L-1)2
–
–
C-1ꢀ: 9.25; C-3: 149.83; C-5: 165.0; C-␣: 1.61.
Ph2Sn(L-1)2
C-1ꢀ: 9.21; C-3: 150.39; C-5: 165.50; C-␣: 139.50; C-␤: 136.26 [2J(13C-119Sn) = 43 Hz]; C-␥: 128.38
[3J(13C-119Sn) = 64 Hz]; C-␦: 129.23 [4J(13C-119Sn) = 13 Hz].
C-1ꢀ: 17.95; C-2ꢀ: 9.36; C-3: 154.29; C-5: 167.80; C-␣: 3.78.
c
c
Me2Sn(L-2)2
–
Triorganotin(IV) derivatives
Me3Sn(L-1)b
119.12
113.07
C-1ꢀ: 10.60; C-3: 151.70; C-5: 168.50; C-␣: −3.40 [1J(13C-119/117Sn) = 483/468 Hz].
C-1ꢀ: 10.75; C-3: 151.40; C-5: 166.20; C-␣: 19.90 [1J(13C-119/117Sn) = 414/ 396 Hz]; C-␤: 20.51
[2J(13C-119Sn) = 25 Hz]; C-␥: 19.06 [3J(13C-119Sn) = 73 Hz].
n-Pr3Sn(L-1)b
n-Bu3Sn(L-1)b
Ph3Sn(L-1)c
112.81
–
C-1ꢀ: 10.72; C-3: 151.90; C-5: 167.30; C-␣: 17.0 [1J(13C-119/117Sn) = 411/393 Hz]; C-␤: 29.24
[2J(13C-119Sn) = 25 Hz]; C-␥: 28.08 [3J(13C-119Sn) = 72 Hz]; C-␦: 14.04.
C-1ꢀ: 9.21; C-3: 160.49; C-5: 165.50; C-␣: 139.55; C-␤: 136.26 [2J(13C-119Sn) = 43 Hz]; C-␥: 128.38
[3J(13C-119Sn) = 64 Hz]; C-␦: 129.23 [4J(13C-119Sn) = 50 Hz].
Me3Sn(L-2)b (CDCl3)
n-Pr3Sn(L-2)b
116.49
113.25
C-1ꢀ: 18.70; C-2ꢀ: 10.90; C-3: 155.10; C-5: 167.0; C-␣: −3.70 [1J(13C-119Sn) = 453 Hz].
C-1ꢀ: 18.51; C-2ꢀ: 11.07; C-3: 155.20; C-5: 167.50; C-␣: 19.42 [1J(13C-119Sn) = 416 Hz]; C-␤: 20.50
[2J(13C-119Sn) = 26 Hz]; C-␥: 18.99 [3J(13C-119Sn) = 69 Hz].
n-Bu3Sn(L-2) b(CDCl3)
Ph3Sn(L-2)b
–
–
C-1ꢀ: 18.69; C-2ꢀ: 10.75; C-3: 154.90; C-5: 171.60; C-␣: 15.68; C-␤: 27.82 [2J(13C-119Sn) = 20 Hz]; C-␥: 26.85
[3J(13C-119Sn) = 65 Hz]; C-␦: 13.46.
C-1ꢀ: 19.50; C-2ꢀ:11.90; C-3: 155.30; C-5: 164.60; C-␣: 140.90; C-␤: 137.60 [2J(13C-119Sn) = 38 Hz]; C-␥:
129.70 [3J(13C-119Sn) = 60 Hz]; C-␦: 130.60.
a
Ref. [41].
b
Spectrum recorded on a Bruker DRX 300 MHz, FTNMR spectrometer.
Spectrum recorded on a Bruker Avance 500 MHz, FTNMR spectrometer.
c
the ligands, and its subsequent coordination to tin. The absence
of an appreciable shift in NH2 proton resonance indicates its
non-involvement in coordination to the organotin(IV) moiety.
In the 13C NMR spectra of HL-1 and HL-2, the C-5 resonance
is observed at δ 163.0 and 167.70 ppm, respectively, which is
shifted downfield in all of the organotin(IV) derivatives studied
(see Table 5), indicating the coordination of the deprotonated
chemical shifts are very sensitive to coordination number of tin
and are generally shifted upfield on bonding to Lewis base. It has
been reported [42] that the 119Sn chemical shifts in the ranges
200 to −60, −90 to −190 and −210 to −400 ppm are associated
with four-, five- and six-coordinated alkyltin(IV) compounds
and these 119Sn shifts are higher with aryltin(IV) compounds.
In the 119Sn NMR spectra of Me3Sn(L-1), n-Pr3Sn(L-2) and
ligands to tin via (Sexo)
− attached to C-5 carbon. The heteronu-
clear coupling constants, viz. 2J(1H–119Sn) and 1J(13C–119Sn)
are very useful as they provide important information about
the coordinating environment of tin. In a few compounds
studied, the satellites are resolved and the observed coupling
Table 6
119Sn NMR spectral data of synthesized compounds
Compound
Solvent
δ (ppm)
2
1
constants, J(1H–119Sn) and J(13C–119/117Sn) are 62 3 Hz
and 447 36/429 36 Hz (Table 4 and 5), respectively, indi-
cating pseudotetrahedral or distorted tetrahedral arrangement
around tin. The angle, ∠C–Sn–C calculated by the Lockhart and
Diorganotin(IV) derivatives
a
Me2Sn(L-1)2
Ph2Sn(L-1)2
Me2Sn(L-2)2
CD3OD
CD3OD
DMSO-d6
−264.25
−383.40
−30.84
a
b
Triorganotin(IV) derivatives
Me3Sn(L-1)a
Manders equation [41] using the observed J(1H–119Sn) and
2
CDCl3
CD3OD
CD3OD
CDCl3 + CD3ODc
CDCl3
105.37
−174.63
−384.94
−0.50
1J(13C–119Sn) values, is 115.34 3.78◦, which also suggests
a distorted tetrahedral/pseudotetrahedral environment around
tin [41] in solution. However, in other compounds studied, the
n-Pr3Sn(L-1)a
Ph3Sn(L-1)a
Me3Sn(L-2)b
n-Pr3Sn(L-2)b
n-Bu3Sn(L-2)b
Ph3Sn(L-2)b
86.29
2J(1H–119Sn) and J(13C–119Sn) coupling constants could not
1
CDCl3
CD3OD
90.46
−175.28
be resolved successfully. The resonances of the magnetically
non-equivalent protons and carbons of alkyl/phenyl groups of
the organotin moiety and of ligands have also been given in
Tables 4 and 5.
a
NMR spectrum recorded on Mercury Varian 300 MHz, FTNMR spectrom-
eter.
b
NMR spectrum recorded on a Bruker Avance 500 MHz, FTNMR spectrom-
eter.
The119SnNMRspectraldataforallofthestudiedcompounds
except n-Bu2Sn(L-1/L-2)2 are given in Table 6. The 119Sn NMR
c
A drop of solvent was added.

M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
773
Table 7
Results of antimicrobial (antibacterial and antifungal) activity of ligands and their organotin(IV) derivativesa
Compound
Zone of inhibition (z.i.) in mm
Bacteria
Fungi
S. aureus (209p)
E. coli (ESS 2231)
A. fumigatus
C. albicans
C. albicans
C. krusei
C. glabrata
(ATCC 10231)
(GO3)
(HO5)
HL-1
HL-2
HL-3
HL-4
7
1
7
6
3
3
3
7
3
6
6
5
1
18
5
6
7
6
5
6
6
25
20
23
24
23
21
20
10
11
12
13
14
22
18
20
18
20
21
19
18
17
18
–
26
22
24
25
20
22
21
12
13
13
14
15
18
19
18
21
21
22
20
19
18
19
–
24
26
25
26
21
23
22
14
15
14
15
16
21
20
19
22
22
23
21
20
19
20
–
21
20
23
22
18
20
23
23
25
18
19
21
21
18
22
20
21
24
23
20
19
21
–
22
21
24
23
19
21
19
24
22
19
22
23
20
22
19
22
21
25
20
22
20
22
–
5
Me2Sn(L-1)2
n-Bu2Sn(L-1)2
n-Bu3Sn(L-1)
Me2Sn(L-2)2
n-Bu2Sn(L-2)2
Me3Sn(L-2)
n-Bu3Sn(L-2)
Ph3Sn(L-2)
n-Oct2Sn(L-3)2
Ph2Sn(L-3)2
Me3Sn(L-3)
Me2Sn(L-4)2
n-Bu2Sn(L-4)2
n-Oct2Sn(L-4)2
Ph2Sn(L-4)2
Me3Sn(L-4)
n-Bu3Sn(L-4)
Ph3Sn(L-4)
Ciprofloxacinb
Fluconazoleb
10% DMSO in Methanol
11
12
10
8
9
1
15
5
9
7
8
8
7
6
7
7
7
6
20
–
6
7
6
7
20
–
0
29
0
29
0
25
0
19
0
15
0
0
a
Concentration used: test compounds = 250 ␮g ml−1; standard drugs = 50 ␮g ml−1
Standard drugs.
.
b
n-Bu3Sn(L-2) recorded in CDCl3, the 119Sn chemical shifts
are observed at δ 105.37, 86.29 and 90.46 ppm, respectively,
which lie in the range of four-coordinated tin [42]. This indi-
cates that the six-coordinated and five-coordinated structure of
di-/ and triorganotin(IV) derivatives, respectively, found in the
solid-state, do not exist in solution. It seems that the weak coor-
dination between Sn and N(1) as found in the solid-state, is
easily disrupted in the solution giving rise to the distorted tetra-
hedral R2SnL2/R3SnL monomeric unit in solution. However,
for all other compounds (recorded in MeOH-d6/DMSO-d6) the
119Sn chemical shifts are observed in the range: δ −0.50 to
−384.94 ppm, which suggest a five-coordinated tin [42]. The
119Sn NMR is more sensitive to structural changes as compared
results suggest that the ligands as well as their organotin(IV)
derivatives(exceptn-Bu3Sn(L-2))(concentration:250 ␮g ml−1
)
show almost insignificant activity against the bacteria, viz.
Staphylococcus aureus and Escherichia coli, as compared to
ciprofloxacin (concentration: 50 ␮g ml−1) used as standard
drug. However, n-Bu3Sn(L-2) shows mild antibacterial activ-
ity (Table 7). The screening results of the ligands (HL-1 to
HL-4) and their organotin(IV) derivatives against the fungi,
viz. A. fumigatus, C. albicans, C. albicans (ATCC 10231), C.
krusei (GO3) and C. glabrata (HO5) (Table 7) suggest that
the ligands and their organotin(IV) derivatives (concentration:
250 ␮g ml−1) (except for the organotin(IV) derivatives of HL-
2, which show mild activity) show moderate antifungal activity
as compared to the reference drug, fluconazole (concentration:
50 ␮g ml−1). However, no significant difference is observed in
the di- and triorganotin(IV) derivatives of a given ligand. The
ligands are more active than the corresponding organotin(IV)
derivatives.
1
to H and 13C NMR. The observed 119Sn chemical shifts of
these compounds suggest that the nature of the solvent plays an
important role in these compounds, and it is proposed that one
molecule of coordinating solvent (DMSO or MeOH) is coor-
dinated to tin in these compounds in the solution, yielding a
distorted trigonal-bipyramidal geometry around tin.
Acknowledgements
3.4. Antimicrobial studies
The authors are thankful to the Head, Regional Sophisti-
cated Instrumentation Centre, Central Drug Research Institute,
The antimicrobial activities of the ligands (HL-1 to HL-
4) and some of their organotin(IV) derivatives having good
solubility are presented in Table 7. The observed screening
1
Lucknow, India for providing H and 13C NMR spectra and
to the Head, IIC, IIT Roorkee, Roorkee, India for provid-

774
M. Nath et al. / Spectrochimica Acta Part A 70 (2008) 766–774
ing 119Sn NMR spectral facilities. One of the authors (Ms.
Sulaxna) is thankful to the Council of Scientific and Indus-
trial Research, New Delhi, India, for awarding Senior Research
[19] A. Foroumadi, Z. Kiani, F. Soltani, Farmaco 58 (2003) 1073.
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¨
the National Institute of Biomedical Research Support Pro-
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Thanks are also extended to the Microbiology Department,
L.L.R.M. Medical College, Meerut for biological studies.
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