Organotin(IV) triazolates: Synthesis and their spectral characterization

Article abstract of DOI:10.1016/j.jorganchem.2005.11.047

Some organotin(IV) triazolates of general formula R_nSn(L) _{4 - n} (where R = Me, n-Bu and Ph for n = 2; R = Me, n-Pr and n-Bu for n = 3 and HL = 3-amino-5-mercapto-1,2,4-triazole) have been synthesized by the reaction of R₂SnCl₂/R₃SnCl with NaL in 1:2/1:1 molar ratio. Whereas, Oct₂SnL₂ has been synthesized azeotropically by the reaction of Oct₂SnO and HL in 1:2 molar ratio. As good single crystals were not obtained, a large number of experimental techniques, viz. UV/Vis, IR, far-IR, multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR and ¹¹⁹Sn M?ssbauer spectroscopic studies, were used to accomplish a definitive characterization and determination of their most probable structures. In these compounds triazole acts as a monoanionic bidentate ligand, coordinating through S_exo and N(4). The IR and ¹¹⁹Sn M?ssbauer spectroscopic studies allow us to deduce a highly distorted cis-trigonal-bipyramidal structure for R₃SnL and a distorted skew trapezoidal-bipyramidal structure for R₂SnL ₂, in the solid state. However, ¹H, ¹³C and ¹¹⁹Sn NMR spectral studies revealed that weak bonding between tin and N(4) is further weakened in the solution leading to pseudo-tetrahedral/ tetrahedral structure.

Full text of DOI:10.1016/j.jorganchem.2005.11.047

Journal of Organometallic Chemistry 691 (2006) 1649–1657
www.elsevier.com/locate/jorganchem
Organotin(IV) triazolates: Synthesis and their spectral characterization
a,
a
b
b
Mala Nath *, Sulaxna , Xueqing Song , George Eng
a
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Department of Chemistry and Physics, University of The District of Columbia, Washington, DC 20008, USA
b
Received 18 November 2005; accepted 21 November 2005
Available online 4 January 2006
Abstract
Some organotin(IV) triazolates of general formula RnSn(L)4 ꢀ n (where R = Me, n-Bu and Ph for n = 2; R = Me, n-Pr and n-Bu for
n = 3 and HL = 3-amino-5-mercapto-1,2,4-triazole) have been synthesized by the reaction of R2SnCl2/R3SnCl with NaL in 1:2/1:1 molar
ratio. Whereas, Oct2SnL2 has been synthesized azeotropically by the reaction of Oct2SnO and HL in 1:2 molar ratio. As good single
crystals were not obtained, a large number of experimental techniques, viz. UV/Vis, IR, far-IR, multinuclear (1H, 13C and 119Sn)
NMR and 119Sn Mo¨ssbauer spectroscopic studies, were used to accomplish a definitive characterization and determination of their most
probable structures. In these compounds triazole acts as a monoanionic bidentate ligand, coordinating through Sexo and N(4). The IR
and 119Sn Mo¨ssbauer spectroscopic studies allow us to deduce a highly distorted cis-trigonal-bipyramidal structure for R3SnL and a dis-
torted skew trapezoidal-bipyramidal structure for R2SnL2, in the solid state. However, 1H, 13C and 119Sn NMR spectral studies revealed
that weak bonding between tin and N(4) is further weakened in the solution leading to pseudo-tetrahedral/tetrahedral structure.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: 1,2,4-Triazole; Organotin(IV) compounds; NMR solution studies; 119Sn Mo¨ssbauer
1. Introduction
particular, its derivatives exhibit a strong property of act-
ing as bridging ligands between two metal centers [1] and
can provide 1,2-bridging as well as 2,4-bridging form in
case of 4-unsubstituted 1,2,4-triazoles. Though, triazoles
have their non-biological origin but their 2,4-bridging form
is similar to 1,3-imidazolate bridging found in enzymes [8],
which has made triazoles and their metal complexes much
sought after compounds to mimic natural processes, and
they are also used to mimic imidazoles in model com-
pounds for such processes [9]. A large number of reports
have been appeared on their metal complexes involving
d-block metals [1,10–17], however, only a few reports have
been cited on tin and organotin derivatives of triazoles
[18–20].
Increasing industrial uses of organotin compounds con-
taining Sn–S bond, especially as stabilizers of polyvinyl
chloride [21], and recognition of the importance of this
bond for the biological properties of organotin compounds
[22], have together spurred to study organotin(IV) thio-
lates. Recently, the organotin complexes of heterocyclic
thioamides, which are interesting owing to their different
1,2,4-Triazole and its derivatives constitute an interest-
ing class of heterocycles, which gained considerable atten-
tion in recent years [1] because 1,2,4-triazole represents a
hybrid of pyrazole and imidazole with regards to the
arrangement of ring nitrogens. They also possess a broad
spectrum of biological activities including antimicrobial
and antifungal activities [2–6], e.g., triazole antifungal
agents, fluconazole and itraconazole, have been extensively
used for the treatment of prophylaxis and a variety of fun-
gal infections since a decade ago [7]. Several new triazole
agents are in various phases of preclinical and clinical trials
[7] and may be available for human use in the near future.
Further, they show a versatile coordinating ability, espe-
cially when the triazole nucleus is substituted with addi-
tional donor groups [1]. In addition, 1,2,4-triazole and, in
*
Corresponding author. Tel.: +91 1332 285797; fax: +91 1332 273560.
E-mail address: malanfcy@iitr.ernet.in (M. Nath).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.11.047

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M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
coordination modes, have attracted great attention. More-
over, they can give a better insight to understand the inter-
action of organotin compounds with sulfur containing
molecules present in biological system [23].
In view of this, here we report the synthesis of seven new
organotin(IV) derivatives of heterocyclic thioamide, viz. 3-
amino-5-mercapto-1,2,4-triazole (HL), and their spectral
characterization by using UV/Vis, IR, far-IR, 1H, 13C
and 119Sn NMR and 119Sn Mo¨ssbauer spectroscopic
techniques.
Ph2SnL2 (4): Pale yellow solid; m.p. 195–199 °C. Anal.
Calc. for C16H16N8S2Sn: C, 38.19; H, 3.20; N, 22.27; S,
12.75; Sn, 23.59. Found: C, 38.15; H, 3.14; N, 22.23; S,
12.69; Sn, 23.55%. UV/Vis: p ! p* at k 208, 216 nm (e:
23983; 28721 lꢀm1olꢀ1 cmꢀ1); n ! p* at k 258 nm (e:
4026 l molꢀ1 cm
) (in MeOH). Molar conductance:
3.0 Xꢀ1 cm2 molꢀ1 (in MeOH).
Me3SnL (5): Pale yellow solid; m.p. 180–184 °C. Anal.
Calc. for C5H12N4SSn: C, 21.53; H, 4.34; N, 20.09; S,
11.50; Sn, 42.56. Found: C, 20.51; H, 4.30; N, 20.01; S,
11.44; Sn, 42.51%. UV/Vis: p ! p* at k 209 nm (e:
2907 l molꢀ1 cmꢀ1); n ! p* at k 260 nm (e: 6726 l molꢀ1
cmꢀ1) (in MeOH). Molar conductance: 4.0 Xꢀ1 cm2 molꢀ1
(in MeOH).
2. Experimental
2.1. Materials
n-Pr3SnL (6): Yellow semi-solid. Anal. Calc. for
C11H24N4SSn: C, 36.39; H, 6.66; N, 15.43; S, 8.83; Sn,
32.70. Found: C, 36.38; H, 6.61; N, 15.41; S, 8.72; Sn,
All the syntheses were carried out under anhydrous
nitrogen atmosphere and the precautions to avoid the pres-
ence of oxygen were taken at every stage. Solvents were
dried and distilled before use. All the di-/triorganotin(IV)
chlorides/oxide (except diphenyltin(IV) dichloride) and 3-
amino-5-mercapto-1,2,4-triazole were purchased from
Merck–Schuchardt and were used as received. Diphenyl-
tin(IV) dichloride was synthesized by the literature method
[24].
32.61%. UV/Vis: p ! p* at
(in MeOH). Molar conductance: 8.0 Xꢀ1 cm2 molꢀ1 (in
MeOH).
k 208 nm (e: 12403 l
molꢀ1 cmꢀ1); n ! p* at k 260 nm (e: 11453 l molꢀ1 cmꢀ1
)
n-Bu3SnL (7): Yellow semi-solid. Anal. Calc. for
C14H30N4SSn: C, 41.51; H, 7.46; N, 13.83; S, 7.91; Sn,
29.30. Found: C, 41.48; H, 7.41; N, 13.75; S, 7.85; Sn,
29.24%. UV/Vis: p ! p* at k 209 nm (e: 8670 l molꢀ1
cmꢀ1); n ! p* at k 261 nm (e: 8356 l molꢀ1 cmꢀ1) (in
MeOH). Molar conductance: 6.0 Xꢀ1 cm2 molꢀ1 (in
MeOH).
2.2. Synthesis of organotin(IV) derivatives of 3-amino-5-
mercapto-1,2,4-triazole (HL)
2.2.1. Synthesis of R2SnL2 (where R = Me (1), n-Bu (2)
and Ph (4)) and R3SnL (where R = Me (5), n-Pr (6)
and n-Bu (7)) by sodium chloride method
2.2.2. Synthesis of dioctyltin(IV) bis(triazolate) (3) by
azeotropic removal of water method
The methanolic solution (ꢁ30 ml) of HL (0.47 g,
4.0 mmol) was added under dry nitrogen to sodium meth-
oxide, prepared by dissolving sodium (0.1 g, 4.2 mmol) in
dry methanol (ꢁ5 ml). The resulting solution was stirred
for ꢁ8 h at room temperature under dry nitrogen. To this
was added a methanolic solution of R3SnCl (4 mmol)/
R2SnCl2 (2 mmol) dropwise with constant stirring, and it
was further stirred for 30–35 h at room temperature. The
reaction mixture was centrifuged and filtered in order to
remove sodium chloride, and the volatiles were removed
in vacuo. The solid obtained was recrystalized from a mix-
ture of methanol and dichloromethane (1:2 v/v).
To the suspension of dioctyltin(IV) oxide (0.72 g,
2.0 mmol, in ꢁ35 ml methanol) a methanol solution of
HL (0.47 g, 4.0 mmol) was added dropwise with constant
stirring at room temperature under dry nitrogen. The
resulting mixture was further stirred for another 40 h at
ꢁ40 °C. The water formed during the reaction was recov-
ered azeotropically and the excess of solvent was removed
in vacuo. The solid obtained was washed with dichloro-
methane and recrystallized from methanol. Pale yellow
solid; m.p. 168–172 °C. Anal. Calc. for C20H40N8S2Sn: C,
41.75; H, 7.00; N, 19.47; S, 11.15; Sn, 20.63. Found: C,
41.68; H, 6.91; N, 19.41; S, 11.10; Sn, 20.60%. UV/Vis:
p ! p* at k 205 nm ꢀ(e1: 9168 l molꢀ1 cmꢀ1); n ! p* at k
260 nm (e: 7097 l mol cmꢀ1) (in MeOH). Molar conduc-
tance: 5.0 Xꢀ1 cm2 molꢀ1 (in MeOH).
Me2SnL2 (1): Pale yellow solid; m.p. 171–174 °C. Anal.
Calc. for C6H12N8S2Sn: C, 19.0; H, 3.19; N, 29.56; S, 16.92;
Sn, 31.77. Found: C, 18.95; H, 3.16; N, 29.49; S, 16.88; Sn,
31.76%. UV/Vis: p ! p* at
(in MeOH). Molar conductance: 3.0 Xꢀ1 cm2 molꢀ1 (in
MeOH).
n-Bu2SnL2 (2): Pale yellow solid; m.p. 221–224 °C. Anal.
Calc. for C12H24N8S2Sn: C, 31.26; H, 5.22; N, 24.19; S,
13.85; Sn, 25.63. Found: C, 31.21; H, 5.19; N, 24.16; S,
13.79; Sn, 25.57%. UV/Vis: p ! p* at k 204 nm (e:
10075 l molꢀ1 cmꢀ1); n ! p* at k 259 nm (e: 2575 l
molꢀ1 cmꢀ1) (in MeOH). Molar conductance: 5.0 Xꢀ1
cm2 molꢀ1 (in MeOH).
k 209 nm (e: 11839 l
molꢀ1 cmꢀ1); n ! p* at k 258 nm (e: 13842 l molꢀ1 cmꢀ1
)
2.2.3. Attempted synthesis of triphenyltin(IV) triazolate
Triphenyltin(IV) chloride (1.16 g, 3.0 mmol) was dis-
solved in ꢁ30 ml of methanol. It was added slowly, with
constant stirring, to the performed sodium salt of HL in
methanol (as described in Section 2.2.1) in a 1:1 molar
ratio. The resulting reaction mixture was further stirred
for ꢁ40 h at room temperature/at 40 °C, but the unreacted
reactants were recovered in each case. Another attempt to
synthesize this compound was made by adding a methanol
solution of triphenyltin hydroxide (1.10 g, 3.0 mmol) to a

M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
1651
methanol solution of HL (0.35 g, 3.0 mmol) with constant
stirring and the mixture was heated at 40 °C for ꢁ40 h, but
no complexation took place.
All of the synthesized compounds are light yellow pow-
der and soluble in DMSO and MeOH, but insoluble in
CHCl3, except n-Pr3SnL and n-Bu3SnL. Me2SnL2 and
Ph2SnL2 are hygroscopic in nature and decomposed on
exposure in air. The analytical data of the complexes are
in agreement with the proposed stoichiometry. The com-
pounds are non-electrolytes as suggested by the low molar
conductance values (3.0–8.0 Xꢀ1 cm2 molꢀ1) of 10ꢀ3 M
solution in MeOH.
2.3. Measurements
The melting points of the synthesized compounds were
determined on a Toshniwal capillary melting point appara-
tus and were uncorrected. Carbon, hydrogen, nitrogen, sul-
fur and tin were determined as reported previously [25].
UV–Vis spectra and molar conductance measurements of
the compounds were recorded in MeOH on the same
instruments as reported previously [25]. IR and far-IR
spectra of the solid compounds were recorded on a Per-
kin–Elmer 1600 series FT-IR in the range 4000–200 cmꢀ1
3.1. Electronic spectral studies in solution
The ultraviolet spectrum of HL exhibits two strong
bands at 207 and 260 nm, which have been assigned to
p ! p* and n ! p* transitions of (C@N) chromophore
[27], respectively. For organotin(IV) triazolates a corre-
sponding shift is observed in these bands.
I
from CsI discs. H NMR spectra were recorded on a Bru-
ker Avance 500 MHz (at 296.3 K) at the Indian Institute of
1
Technology Roorkee, Roorkee. H (of HL) and 13C NMR
(at 300.0 K) spectra were recorded at the Central Drug
Research Institute, Lucknow, India and 119Sn NMR spec-
tra were recorded at the Regional Sophisticated Instrumen-
tation Center, Indian Institute of Technology Bombay,
India using the same instruments as reported previously
[25]. 119Sn Mo¨ssbauer spectra were recorded on a Mo¨ss-
bauer spectrometer model MS-900 according to the proce-
dure reported previously [25], at the Department of
Chemistry and Physics, University of the District of
Columbia, Washington, DC.
3.2. Infrared spectral studies
The characteristic IR bands of HL and its organotin(IV)
derivatives assigned with the help of the following general
references [28,29] and of other related molecules
[14,18,30,31] are presented in Table 1. In the spectrum of
HL, several medium intensity bands are observed in the
region 3382–2704 cmꢀ1, mainly due to NH stretching
vibrations [31,32]. The bands, particularly, at 3382 and
3299 cmꢀ1 are assigned to mas(N–H) and ms(N–H), respec-
tively, of NH2 group [31]. The remaining bands in the
region 3382–2704 cmꢀ1 are assigned to m(N–H) of Nring
–
3. Results and discussion
H [31] as HL exhibits thione-thiol tautomerism (Fig. 1) in
the solid state [14]. In the complexes the coordination via
NH2 group would require a downward shift in the sensitive
NH stretching frequencies by 200–300 cmꢀ1 [32]. On the
contrary, the studied organotin(IV) triazolates reveal an
upward shift by 10–70 cmꢀ1 relative to the frequencies of
HL. The upward shift as well as the position and character
of the m(NH) bands is indicative of the weakening of exten-
sive H-bonding that was originally present in the crystal
lattice of HL, upon complexation.
The reactions of di-/triorganotin(IV) chloride with
sodium salt of 3-amino-5-mercapto-1,2,4-triazole (HL)
{formed according to Eq. (1)} led to the formation of the
compounds according to Eq. (2). In these compounds HL
acts as a mono deprotonated bidentate ligand with the
negative charge residing on the sulfur atom of the resulting
aromatic tautomer [26]. The reaction of dioctyltin(IV)
oxide with HL in
a 1:2 molar ratio yielded the
product under azeotropic removal of water according to
Eq. (3).
A medium intensity band at 2618 cmꢀ1 attributable to
m(SH) of HL [32] disappears in all the studied complexes
and confirms the deprotonation of thiol group. The bands
at 1485 and 1399 cmꢀ1 are assigned to m(CN) vibrations
(i.e., thioamide bands I and II, respectively) of the thioam-
ide group, whereas the bands at 1141 and 1030 cmꢀ1 are
assigned to m(CS) vibrations (i.e., thioamide bands III
and IV, respectively) of the thioamide group of HL [23].
In the studied organotin(IV) triazolates, these bands shift
to lower wave numbers indicating the coordination of Lꢀ
through Sexo and Nring. The observed shifts in these
thioamide bands might be due to the evolution of partial
double bond character in the (AN'C'SA) group after
its deprotonation [26] and subsequent coordination to
tin. In addition to this, the bands observed in the region
1650–800 cmꢀ1 in the spectra of the organotin(IV) triazo-
lates, show a shift in their position, some of them shift to
HL + NaOMe ! NaL + MeOH
mNaL + RnSnClð4 ꢀ nÞ ! RnSn(L)m + mNaCl
ð1Þ
ð2Þ
(where m = 1, n = 3, R = Me, n-Pr and n-Bu; m = 2, n = 2,
R = Me, n-Bu and Ph; HL = 3-amino-5-mercapto-1,2,4-
triazole)
2HL + Oct2SnO ! Oct2SnL2 + H2O
ð3Þ
The reactions involved in the synthesis of di- and triorg-
anotin(IV) triazolates were found to be quite feasible and
required 30–35 h of stirring at room temperature except
Oct2SnL2 which requires 40 h stirring at 40 °C. However,
even prolonged stirring for ꢁ40 h at 40 °C of the mixture
of Ph3SnCl/Ph3SnOH with NaL/HL in methanol did not
result in complexation.

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M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
Table 1
IR spectral bandsa of 3-amino-5-mercapto-1,2,4-triazole and its organotin(IV) compounds
HL
Me2SnL (1)
n-Bu2SnL2 (2)
Oct2SnL2 (3)
Ph2SnL2 (4)
Me3SnL (5)
n-Pr3SnL (6)
n-Bu3SnL (7)
Assignments
3382s
3330brs
3144w
2852w
3456brw
3330brw
3213w
2869s
3439w
3382w
3213w
3182w
3095w
2853s
3430wsh
3384wsh
3013w
2952w
2923m
2858m
3419m
3375m
3301m
3213w
3104m
2767m
2708m
3386mbr
3300mbr
3170mbr
2866s
3425m
3317m
3230w
3182w
3113w
3299m
3267m
3216m
3170m
3107m
3019m
2909m
2858m
2761w
2704w
2787vw
2857s
m(N–H)
2765vw
2704vw
2922s
2958s
2925s
–
1624s
1529s
2965s
2923s
–
3064s
3043s
–
2982m
2907m
–
1623s
1549s
2957s
2926s
–
1652s
1578s
2957s
2922s
–
1633s
1578m
m(C–H)
m(S–H)
d(N–H)
2618m
1646vs
1586s
1544s
1485s
1399m
1141s
1030s
–
–
1669s
1638s
1541s
1430m
1364m
1096m
1023s
574m
557shw
474m
325w
1645s
1593m
1543m
1466m
1364m
1108m
1056s
608m
574m
466s
1643s
1587wsh
1539w
1429vs
1301m
1077vs
1024m
275s
1466s
1377s
1078s
1024m
596m
570m
474m
302m
1440s
1327s
1101s
1024s
552m
543s
1461m
1332m
1109m
1023m
615w
600w
470m
386m
1464s
1377s
1077s
1022s
543wsh
507s
Thioamide band (I)
Thioamide band (II)
Thioamide band (III)
Thioamide band (IV)
mas(Sn–C)
–
–
–
228m
449s
376s
ms(Sn–C)
445s
392s
465m
353m
m(Sn N)
324m
m(Sn–S)
a
s: strong; m: medium; w: weak; vw: very weak; brs: broad strong; sh: shoulder.
3.3. 119Sn Mo¨ssbauer spectral studies
a
NH
b
NH
2
2
4
3
4
HN
3
N
The 119Sn Mo¨ssbauer spectra of the organotin(IV) triaz-
olates are shown in Fig. 2 and the spectral data are pre-
sented in Table 2. The spectral data show a small
lowering in the isomer shift (I.S.) values as compared to
the corresponding organotin(IV) chlorides because the 5s
orbital electron density of tin atom is reduced upon com-
plexation. The quadrupole splitting (Q.S.) values in the
range 2.02–2.93 mm sꢀ1 show that the electric field gradient
around the tin nucleus is produced by the inequalities in the
tin-sulfur/nitrogen bonds and is also due to geometric dis-
tortions. The q (Q.S./I.S.) values in the range 1.96–2.72 for
these studied derivatives indicate a coordination number
greater than four with either a five- or six-coordinated tin.
Octahedral cationic [36], neutral [36,37] and anionic [38]
tin(IV) complexes containing two organic residues and four
electronegative ligands possess a mutually trans-geometry
for the tin-carbon bonds (with a few exceptions). In this
context, the magnitude of the 119Sn Mo¨ssbauer Q.S. is a
useful parameter. The point charge calculations [39] for
octahedral diorganotin(IV) derivatives predict that the
Q.S. for the trans-isomer will be twice (ꢁ4.0 mm sꢀ1) that
of the cis-isomer (ꢁ2.0 mm sꢀ1). However, the observed
Q.S. values (2.02–2.93 mm sꢀ1) of the studied diorgano-
tin(IV) bis(triazolate) lie in the intermediate range i.e.,
higher than that of cis-octahedral, but substantially lower
than that of trans-octahedral arrangement. Indeed, where
the other ligands have higher electronegativity, the Q.S. is
2
2
5
5
N
N
1
N
H
1
N
H
HS
S
Fig. 1. Thiol (a) and thione (b) tautomer of 3-amino-5-mercapto-1,2,4-
triazole.
higher wave numbers while others to lower wave numbers
as compared to those of the non-coordinated HL. But
assignment of these bands in terms of localized vibrations
could not possible because the ring atoms are involved in
several vibrational modes.
In the region 600–200 cmꢀ1, a few new bands are
observed due to mas(Sn–C) and ms(Sn–C), which suggest a
non-planar arrangement of C–Sn–C moiety. All of the com-
plexes display new bands of medium intensity in the region
470–400 cmꢀ1 and 390–310 cmꢀ1, which are assigned to
m(Sn N) and m(Sn–S) modes [23,32], respectively. These
new bands further confirm the complexation of tin via Sexo
and Nring. For the triazole ring Johnson et al. [33] and Vas-
nin et al. [19] reported that N(4) is the potential donor site
among the ring nitrogens. These spectral investigations
along with the literature data reveal that the coordination
of triazolate anion (Lꢀ) occurs through Sexo and ring
N(4), whereas N(1)H and NH2 groups participate in inter-
molecular H-bonding of NHꢂ ꢂ ꢂN type [17,18].

M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
1653
Fig. 2. 119Sn Mo¨ssbauer spectra of compounds 1–5.
mainly governed by C–Sn–C bond angle [40], and the
distortion from regular six coordination can give values
similar to those reported [41] for highly distorted square
N(4) atoms, whereas the two organic groups occupy the
axial positions (Fig. 3). The proposed structure is similar
to the structures reported for Bu2SnL2 (where L = merca-
ptobenzoxazole [43] and 2-thio-5-nitro-pyridine [44]). The
distortion in these studied compounds is significant due
to the formation of four membered (Sn–S–C–N) chelate
rings as shown in Fig. 3. Further, the pronounced line
asymmetry (Goldanskii–Karyagin effect) observed in the
119Sn Mo¨ssbauer spectra (Fig. 2, spectra (1)–(4)) of these
compounds suggests the intermolecularly associated crystal
lattice [45] and also explains the low solubility of these
compounds.
bipyramidal/skew
trapezoidal-bipyramidal
structure.
Further, it has been reported [42] that I.S. value for cis-
[R2SnX4]2ꢀ arelessthan1.00 mm sꢀ1 whiletrans-compounds
have I.S. values approximately 1.20–1.30 mm sꢀ1. In the
studied diorganotin(IV) bis(triazolate) the I.S. value are
observed in the range 1.03–1.21 mm sꢀ1 and the angle
\C–Sn–C lies in the range 121.91–124.84° (Table 2), which
are close to the average of the two extremes, in which the
organic substituents do not adopt either cis- or trans-geom-
etry about the tin center [41]. Therefore, the observed 119Sn
Mo¨ssbauer parameters of the studied diorganotin(IV)
bis(triazolate) are best interpreted in terms of a highly dis-
torted skew trapezoidal-bipyramidal geometry in which
equatorial positions are occupied by two sulfur and two
The 119Sn Mo¨ssbauer spectrum of Me3SnL could be
taken as representative for the assignment of structure of
the studied triorganotin(IV) triazolates. The spectra of
n-Pr3SnL and n-Bu3SnL could not be recorded because
of their semi-solid nature. The 119Sn Mo¨ssbauer spectrum

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M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
Table 2
119Sn Mo¨ssbauer spectral dataa of organotin(IV) derivatives of 3-amino-5-mercapto-1,2,4-triazole
Compound
I.S. (mm sꢀ1
)
Q.S. (mm sꢀ1
)
q (Q.S./I.S.)
s (L)
s (R)
\C–Sn–Cb
c
Me2SnCl2
1.66
1.75
1.45
1.07
1.20
1.21
1.03
1.40
3.56
3.50
2.76
2.90
2.81
2.93
2.02
2.79
c
n-Bu2SnCl2
c
Ph2SnCl2
1
2
3
4
5
a
2.72
2.34
2.42
1.96
1.99
1.386
1.166
1.127
1.683
1.103
1.988
1.346
1.488
1.991
1.120
124.84
122.36
121.91
–
125.79
Compound numbers according to Table 1; Q.S. quadrupole splitting; I.S. isomeric shift; s (L) half line-width left doublet component; s (R) half line-
width right doublet component.
b
Ref. [34].
Ref. [35].
c
NH2
H2N
R
H2N
R
N
N
N
Sn
R
N
N
Sn
N
N
N
H
N
S
S
S
H
H
R
R
Fig. 5. Proposed structure for R3SnL (where R = Me, n-Pr and n-Bu).
Fig. 3. Proposed structure for R2SnL2 (where R = Me, n-Bu, Oct and Ph).
of Me3SnL exhibits Q.S. at 2.79 mm sꢀ1 and I.S. at
1.40 mm sꢀ1. It has been reported [46] that the three con-
ceivable (Fig. 4) five coordinate isomers of R3SnXY (where
X or Y = N/O/S; XY are the donor sites of the bidentate
ligand) have different Q.S. value ranges, for isomer (a)
1.70–2.30 mm sꢀ1; for (b) 3.0–3.90 mm sꢀ1; and for (c)
closely related compound Me3SnL (where L = pyridine-
2-thiolate) [47], which was considered to have a cis-
trigonal-bipyramidal arrangement having Sn–S–C–N ring.
Furthermore, a similar structure as shown in Fig. 5 has also
been suggested for n-Pr3SnL and n-Bu3SnL.
3.50–4.10 mm sꢀ1
.
1
3.4. H, 13C and 119Sn NMR solution spectral studies
The observed value of Q.S. (2.79 mm sꢀ1) in Me3SnL is
higher than that for isomer (a) and considered to be com-
patible with trans-structure which is the conventional one
(follows BentÕs rule) found in organotin chemistry. But
the observed mas(Sn–C) and ms(Sn–C) stretching vibrations
in the IR spectra of the studied triorganotin(IV) triazolates
indicate a non-planar SnC3 fragment and rule out the pos-
sibility of trans-isomer 4(b). Therefore, the most plausible
structure for Me3SnL is a highly distorted cis-trigonal-
bipyramidal as shown in Fig. 5, which is intermediate
between 4(a) (fac) and 4(c) (mer) cis-trigonal-bipyramidal
structures. A similar structure has been reported for the
1
The H NMR spectral data of the ligand (HL) and its
1
organotin complexes are given in Table 3. The H NMR
Table 3
1H NMR spectral dataa of organotin(IV) compoundsb of 3-amino-5-
mercapto-1,2,4-triazole
Compound
(d/ppm)
HL (DMSO-d6 +
CDCl3)
SH: 2.58; N(1)–H: 12.19; N(4)–H: 11.79; NH2: 5.31
1 (CD3OD)
3 (DMSO-d6)
4 (CD3OD)
5 (CD3OD)
6 (CDCl3)
NH2: 5.14; Ha: 2.18 s
NH2: 5.14; Ha
2.99–1.83 m;c Hx: 0.85 t
to
l
NH2: 5.14; Ho: 7.74;d Hm + p: 7.44d
NH2: 5.36; Ha: 0.47 [64.20/61.55]e
NH2: 4.30; Ha: 1.29; Hb: 1.69–1.64 m;
Hc: 0.97 t (10 Hz)f
a
c
b
Y
R
Sn
R
Y
7 (CDCl3)
NH2: 4.59; Ha + c: 1.34–1.28 m; Hb:
1.65–1.57 m; Hd: 0.87 t (10 Hz)f
X
Y
R
a
R
Sn
R
R
Sn
R
Compound numbers according to Table 1.
For N(1)–H: broad and weak signals is observed; s: singlet; t: triplet;
b
R
R
X
m: multiplet.
c
X
Unassigned due to overlapping patterns.
d
e
f
Broad peaks.
2J(1H–119/117Sn).
3J(1H–1H).
Fig. 4. Three possible isomers of R3Sn(XY) [46].

M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
1655
spectrum of HL exhibits two signals at d 12.19 and
11.79 ppm which may be assigned to N(1)–H and N(4)–
H, respectively, whereas a signal of less than half intensity
at d 2.58 ppm has been assigned to –SH. Therefore, it is
concluded that thiol–thione equilibrium is fast on the
NMR timescale and predominant species may be thione
form of HL in solution. A signal observed at d 5.31 ppm
is also assigned to –NH2 group. In the organotin(IV) triaz-
olates the signal due to N(1)–H is observed as a broad
singlet centered at d ꢁ12 ppm, whereas –SH/N(4)–H
resonances are absent in the organotin(IV) triazolates, indi-
cating the deprotonation of the ligand and its coordination
to tin. The signal of NH2 is observed in the range d 5.36–
4.30 ppm. The characteristic signals for all the magnetically
non-equivalent alkyl- or phenyl-protons of the organotin
moieties have also been assigned, which are in good
agreement with reported values [17]. The observed
2J(1H–119/117Sn) for Me3SnL is 64.20/61.55 Hz (Fig. 6a).
The angle \Me–Sn–Me calculated by using Lockhart and
Manders [48] equation (h = 0.0161|2J|2 ꢀ 1.32|2J| + 133.4)
is 114.83°, which indicates pseudotetraheral arrangement.
The 13C and 119Sn NMR spectral data are presented in
Table 4. In the 13C NMR spectrum of HL, three signals
are observed at d 173.62, 161.72 and 151.14 ppm; as the
ligand exists in thiol–thione tautomeric forms (Fig. 1),
these signals are assigned to C(5) of thione form, C(3) thi-
one/thiol form and C(5) of thiol form, respectively, on the
basis of the literature values reported for the related mole-
cules [19,31,49,50]. In the 13C NMR spectra of organo-
tin(IV) triazolates, C(3) and C(5) are observed in the
range d 158.11–159.0 and 160.70–164.15 ppm, respectively.
A small shift to lower d value of C(3) signals may be due to
the weakening of hydrogen bonding that occurs via NH2
group, while a shift in d value of C(5) signal is because of
the evolution of thiolate ion on deprotonation of HL which
participates in bond formation with organotin moiety [49].
The characteristic signals for all the magnetically non-
equivalent alkyl- or phenyl-carbons of the organotin moie-
ties have also been assigned, which are in good agreement
with reported values [17]. For triorganotin(IV) derivatives
viz. Me3SnL, n-Pr3SnL (Fig. 6b) and n-Bu3SnL, the
1
observed J(13C–119/117Sn) values (ꢁ353–397 Hz) lie in the
range of pseudotetrahedral arrangement as reported for
other R3Sn(XY) (where X or Y = O/N/S; XY are the
donor sites of the bidentate ligand) [48,51]. For n-Bu2SnL2
1
the value of J(13C–119Sn) is 397.13 Hz, which indicates a
tetracoordinated tin. Moreover, the calculated values of
1
\C–Sn–C using the observed J(13C–119Sn) values in the
equation given by Lockhart and Manders [48]
(|1J| = 11.4h ꢀ 875) are in the range of 108.0–111.6° (Table
3) indicating a distorted tetrahedral/pseudotetrahedral
geometry for R2Sn(Sexo)2/R3SnSexo
.
The 119Sn NMR chemical shifts are very sensitive to
coordination number of tin and are greatly shifted upfield
Fig. 6. (a) 1H NMR spectrum of Me3SnL; (b) 13C NMR spectrum of n-Pr3SnL; and (c) 119Sn NMR spectrum of Me2SnL2.

1656
M. Nath et al. / Journal of Organometallic Chemistry 691 (2006) 1649–1657
Table 4
13C and 119Sn NMR spectral dataa of organotin(IV) compounds of 3-amino-5-mercapto-1,2,4-triazole (in CD3OD, if not indicated otherwise)
Ligand/compound (solvent)
d
119Sn (ppm)
d
13C (ppm)
\C–Sn–C (°)
HL (DMSO-d6 + CDCl3)
1
C(3): 161.72; C(5): 173.62 (thione); C(5): 151.14 (thiol)
C(3): 158.26; C(5): 164.15; Ca: 1.94
–
–
96.0
–
–
2
C(3) + C(5): 160.0; Ca: 24.27 [397.13];b Cb: 28.92 [28.69];c Cc: 28.10 [46.06];d Cd: 14.11
C(3): 158.47; C(5): 163.27; Ca: 23.44; Cb: 34.97; Cc: 26.15; Cd:
32.78, 32.73; Ch: 30.13; Ck: 24.91; Cl: 21.33; Cx: 14.43
C(3): 159.0; C(5): 163.0; Ca: 139.90; Cb: 137.70; Cc: 129.70; Cd: 130.60
C(3): 158.72; C(5): 160.70; Ca: ꢀ3.26 [353.0]b
111.60e
–
3 (CD3OD + CDCl3)
4
–
–
–
5
108.0e
6 (CDCl3)f
7 (CDCl3)f
92.18
94.36
C(3): 158.71; C(5): 162.49; Ca: 19.86 [397.0/379.0];b Cb: 20.62 [24.16];c Cc: 19.07 [70.22]d 111.50e
C(3): 158.54; C(5): 162.86; Ca: 16.85 [379.0/365.0];b Cb:
29.40 [23.41];c Cc: 28.10 [66.44];d Cd: 14.06
110.0e
β
γ
α
α
β
γ
α
β
γ
δ
α
β
γ
δ
θ
λ
µ
ω
:
α
Sn-CH3; Sn-CH2CH2CH3; Sn-CH2CH2CH2CH3; Sn-CH2CH2CH2CH2CH2CH2CH2CH3;
δ
Sn
a
Compound numbers according to Table 1.
b
1J(13C–119/117Sn).
c
2J(13C–119Sn).
d
3J(13C–119Sn).
e
For 1J(13C–119Sn).
f
For 119Sn NMR.
on bonding to Lewis base. The 119Sn NMR spectra of suf-
ficiently soluble compounds, viz. Me2SnL2, n-Pr3SnL and
n-Bu3SnL were recorded in CD3OD or CDCl3 in order to
obtain additional support for the conclusions drawn by
1H and 13C NMR. The 119Sn NMR spectrum of Me2SnL2
is shown in Fig. 6c. For Me2SnL2, n-Pr3SnL and n-Bu3SnL,
the 119Sn chemical shifts are observed at d 96.0, 92.18 and
94.36 ppm, respectively. As reported in the literature [52],
the values of 119Sn chemical shifts in the ranges 200 to
ꢀ60, ꢀ90 to ꢀ190 and ꢀ210 to ꢀ400 ppm have been asso-
ciated with four-, five- and six-coordinate tin centers,
respectively. The observed 119Sn chemical shifts of the stud-
ied compounds are in the range of four-coordinate tin com-
pounds and show an upward shift as compared to the
reactants Me2SnCl2 (d = 137 ppm) and n-Bu3SnCl
(d = 154 ppm) [53].
the solution the bonding between tin and N(4), becomes
weaker leading to the distorted tetrahedral/pseudo-tetrahe-
dral geometry.
Acknowledgements
The authors are thankful to the Head, Regional Sophis-
ticated Instrumentation Centre, Central Drug Research
Institute, Lucknow, India for providing 1H and 13C
NMR spectral studies, and to the Head, Sophisticated
Instrumentation Centre, Indian Institute of Technology
Bombay, Mumbai, India for providing 119Sn NMR spec-
tral studies. One of the author (Ms. Sulaxna) is thankful
to the Council of Scientific and Industrial Research, New
Delhi, India, for awarding Junior Research Fellowship.
Financial support for 119Sn Mo¨ssbauer work from the Na-
tional Institute of Biomedical Research Support Program
(MBRS/SCORE, GM08005) is gratefully acknowledged.
1
Therefore, 119Sn, H and 13C NMR spectral data reveal
that the weak interaction between central tin and N(4) (as
existing in the solid state supported by IR and 119Sn
Mo¨ssbauer) weakens further in the solution, leading to
the distorted tetrahedral R2Sn(Sexo)2/pseudo-tetrahedral
R3SnSexo moiety.
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