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Synthesis structural characterization biological activity and thermal study of tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole.

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Full Paper
Received: 1 April 2009
Revised: 30 June 2009
Accepted: 30 June 2009
Published online in Wiley Interscience: 18 August 2009
(www.interscience.com) DOI 10.1002/aoc.1537
Synthesis, structural characterization,
biological activity and thermal study of triand diorganotin(IV) complexes of Schiff base
derived from 2-aminomethylbenzimidazole
Mala Natha∗ , Pramendra Kumar Sainia and Ashok Kumarb
This report deals with the synthesis and structural features of tri- and diorganotin(IV) complexes of the general formulae,
Rn Sn(L)m [n = 3, m = 1, R = Me, n-Bu and Ph; n = 2, m = 2, R = Me, n-Bu, n-Oct and Ph; HL = Schiff base derived from the
condensation of 2-aminomethylbenzimidazole (ambmz) and salicylaldehyde (abbreviated as HL or Hsal-ambmz)]. The newly
synthesized complexes were characterized by elemental analysis, molar conductance, electronic, infrared, far-infrared, 1H NMR,
13 C NMR, 119 Sn NMR and 119 Sn Mössbauer spectral studies. Thermal studies of all of the synthesized complexes were also
carried out using thermogravimetry–differential thermal analysis-derivative thermogravimetric (TG-DTA-DTG) techniques.
The residues thus obtained were characterized by infrared and powder X-ray diffraction analysis. The bioassay results of
anti-inflammatory activity (using the carrageenan-induced paw edema bioassay in rats) and acute toxicity (LD50 ) of the
synthesized derivatives indicated that diorganotin(IV) derivatives (19.75–22.23% inhibition) show better activity as compared
c 2009 John Wiley & Sons, Ltd.
with triorganotin(IV) derivatives (10.32–17.86% inhibition). Copyright Keywords: organotins; Schiff base; anti-inflammatory agents; Mössbauer spectra; thermal studies
Introduction
434
The chemistry of organotin(IV) complexes of Schiff bases has
stemmed from their biocidal and antitumour activities, and the
behavior of Schiff bases as model for biological systems.[1] A large
number of Schiff bases have been synthesized and extensively
studied because they have some characteristic properties like
manifestations of novel structures, thermal stability, relevant
biological properties, high synthesis flexibility and medicinal
utility.[2] Schiff bases have been used in the preparation of many
potential drugs and are known to possess a broad spectrum of
biological activities such as antiviral,[3] antifungal,[4] antiparasitic,[5]
antibacterial,[6] anti-inflammatory,[7] antitumor,[8] antiHIV[9] and
anticancer[10] activities. Furthermore, it has also been reported
that Schiff base metal complexes derived from salicylaldehyde
can specially cleave DNA.[1] Salicylaldimines are also a subject
of current interest, not only because they are widely used
as a precursors for a design of various new metal complexes
and as a suitable model for pyridoxal and B6 vitamins, but
also due to their interesting physico-chemical properties, viz.
phenomenon of proton tautomerization, thermochromism and
photochromism as well as because of different aspects of photoand electrochemistry.[11]
Structural modification of organic molecules has considerable
biological relevance. Further, coordination of a biomolecule to the
metal ions significantly alters the effectiveness of the biomolecule.
In the literature vanadium(IV, V) and Cu(II) complexes of Schiff base
derived from salicylaldehyde and 2-aminomethylbenzimidazole
(Hsal-ambmz), have been reported.[12a,b] Hitherto no effort
has been made to synthesize organotin(IV) complexes of this
versatile ligand. Hence this paper reports synthesis, spectral
Appl. Organometal. Chem. 2009 , 23, 434–445
characterization, thermal and biological behavior of organotin(IV)
complexes of Hsal-ambmz in order to investigate the effect of an
organic group on the anti-inflammatory activity of organotin(IV)
complexes of Schiff base derived from salicylaldehyde and 2aminomethylbenzimidazole.
Experimental
Materials and Physical Measurements
All of the syntheses were carried out under an anhydrous nitrogen
atmosphere and precautions to avoid the presence of oxygen were
taken at every stage. Dimethyltin(IV) dichloride (Merk-Schuchardt),
di-n-butyltin(IV) dichloride (Merk-Schuchardt), salicylaldehyde
(Lancaster), glycine (Aldrich) and o-phenylenediamine (Lancaster) were used as received. Diphenyltin(IV) dichloride[13] and
2-aminomethylbenzimidazole hydrochloride (Ambmz.2HCl)[14]
were prepared according to methods reported in the literature.
Solvents such as methanol and cyclohexane (Qualigens) were
dried and distilled, and stored under nitrogen before use.
All the physico-chemical and spectral measurements were
carried out using similar methods and instruments to those
∗
Correspondence to: Mala Nath, Department of Chemistry, Indian Institute of
Technology Roorkee, Roorkee-247667, Uttarakhand, India.
E-mail: malanfcy@iitr.ernet.in
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee247667, Uttarakhand, India
b Department of Pharmacology, LLRM Medical College, Meerut-250004, India
c 2009 John Wiley & Sons, Ltd.
Copyright Tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole
reported previously[15] , except that 1 H, 13 C{1 H} NMR and 119 Sn{1 H}
NMR spectra were recorded at 27 ± 1 ◦ C on a Bruker Avance
(500.133 MHz) FT NMR spectrometer equipped with a Quattro
probe tuned to 500.133 MHz for 1 H, 125.033 MHz for 13 C and
186.50 MHz for 119 Sn nuclei using CD3 OD as solvent, and TMS
(for 1 H and 13 C NMR) and tetraphenyltin (for 119 Sn NMR) as the
internal reference at the Indian Institute of Technology Roorkee,
Roorkee, India. The 119 Sn Mössbauer spectrum of Me3 Sn(L) was
recorded by a standard Mössbauer spectrometer having 1024
channels (procured from Wissel GmbH, Germany) operating in
constant acceleration mode. The detector used was a proportional
counter made by LND, USA. The spectrometer was calibrated by
using a high-purity natural iron foil of thickness 12 µm. The source
used was a 5 mCi Sn − 119 in CaSnO3 matrix. The isomer shifts
were calculated with respect to the center of a pure SnO2 sample
procured commercially. The spectra were recorded at 20 K using a
closed cycle refrigerator (supplied by Janis Research, USA) coupled
to a special anti-vibration stand.
Synthesis
Schiff base (Hsal-ambmz or HL) (1) was prepared according to the
reported method[12a,b] and its tri- and diorganotin(IV) complexes
were synthesized as given in the following sections.
n-Bu3 Sn(L) (3)
Yellowish-brown solid, m.p. 103–105 ◦ C. Yield 79%. Anal. (%)
calcd for C27 H39 N3 OSn (540.34): C, 60.02; H, 7.28; N, 7.78, Sn,
21.97. Found: C, 59.98; H, 7.21; N, 7.73; Sn, 21.89. UV–vis
[CH3 OH, λmax /nm (ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene)
213 (45198), n → π ∗ (C N)azomethine 252 (16010), π →
π ∗ (C N)benzimidazole ring 274 (18282), n → π ∗ (B-band of
benzene) 283 (18370), n → π ∗ (C N)benzimidazole ring 324 (4628);
selected IR (KBr, cm−1 ): ν(N–H)benzimidazole ring 3052m, 2956m,
ν(C N)azomethine 1628vs, νas (C–O)phenolic 1523vs, νs (C–O)phenolic
1307sh, νas (Sn–C)/νs (Sn–C) 633s/606m, ν(Sn–O) 531m, ν(Sn ←
N) 430m.
Ph3 Sn(L) (4)
Brown solid, m.p. 110–112 ◦ C. Yield 73%. Anal. (%) calcd for
C33 H27 N3 OSn (600.31): C, 66.03; H, 4.53; N, 7.00, Sn, 19.78. Found:
C, 66.02; H, 4.56; N, 6.95; Sn, 19.74. UV–vis [CH3 OH, λmax /nm
(ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene) 216 (40380), n → π ∗
(C N)azomethine 257 (10916), π → π ∗ (C N)benzimidazole ring 276
(10202), n → π ∗ (B-band of benzene) 283 (9206), n → π ∗
(C N)benzimidazole ring 325 (2578); selected IR (KBr, cm−1 ): ν(N–H)ring
3064m, 3044m, ν(C N)azomethine 1628vs, νas (C–O)phenolic 1541s,
νs (C–O)phenolic 1307m, νas (Sn–C)/νs (Sn–C) 278vs/223s, ν(Sn–O)
574s, ν(Sn ← N) 449vs.
Me2 Sn(L)2 (5)
Synthesis of Organotin(IV) Complexes of (Hsal-ambmz or HL)
Synthesis of R3 Sn(L) [where R = Me (2), n-Bu (3) and Ph (4)] and
R2 Sn(L)2 [where R = Me (5), n-Bu (6) and Ph (7)] by sodium salt
method
Hsal-ambmz (or HL) (1.0080 g, 4.0 mmol) was dissolved in
the minimum amount (ca 10 ml) of specially dried methanol
and was added to sodium methoxide, prepared by dissolving
sodium (0.0920 g, 4.0 mmol) in specially dried methanol (ca
10 ml). The resulting solution was stirred for 30 min at room
temperature under inert atmosphere of dry nitrogen and then
refluxed for 3 h. It was allowed to cool and a methanol
solution of R3 SnCl (4.0 mmol)/R2 SnCl2 (2.0 mmol) was added
to it with constant stirring. The solution was further stirred
for another 32–35 h at room temperature. It was centrifuged
and filtered in order to remove sodium chloride formed. The
excess of solvent was gradually removed by evaporation under
reduced pressure. The solid thus obtained was recrystallized from
dichloromethane–methanol (2 : 1 v/v) mixture.
Me3 Sn(L) (2)
Appl. Organometal. Chem. 2009, 23, 434–445
n-Bu2 Sn(L)2 (6)
Yellowish-brown solid, m.p. 138–140 ◦ C. Yield 78%. Anal. (%) calcd
for C38 H42 N6 O2 Sn (733.50): C, 62.23; H, 5.77; N, 11.46, Sn, 16.18.
Found: C, 62.29; H, 5.69; N, 11.40; Sn, 16.15. UV–vis [CH3 OH,
λmax /nm (ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene) 208 (26706),
n → π ∗ (C N)azomethine 254 (7780), π → π ∗ (C N)benzimidazole ring
275 (8122), n → π ∗ (B-band of benzene) 284 (7978), n → π ∗
(C N)benzimidazole ring 326 (2220); selected IR (KBr, cm−1 ): ν(N–H)ring
3056w, 2956m, ν(C N)azomethine 1615vs, νas (C–O)phenolic 1539s,
νs (C–O)phenolic 1319w, νas (Sn–C)/νs (Sn–C) 633w/601m, ν(Sn–O)
568w, ν(Sn ← N) 434w.
Ph2 Sn(L)2 (7)
Brown solid, m.p. >300 ◦ C. Yield 71%. Anal. (%) calcd for
C42 H34 N6 O2 Sn (773.48): C, 65.22; H, 4.43; N, 10.87, Sn, 15.35.
Found: C, 65.19; H, 4.45; N, 10.86; Sn, 15.33. UV–vis [CH3 OH,
λmax /nm (ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene) 212
(42084), n → π ∗ (C N)azomethine 241 (18554), π → π ∗
(C N)benzimidazole ring NO, n → π ∗ (B-band of benzene) 282
(15942), n → π ∗ (C N)benzimidazole ring 369 (3682); selected IR (KBr,
cm−1 ): ν(N–H)ring 3060w, ν(C N)azomethine 1624vs, νas (C–O)phenolic
1542vs, νs (C–O)phenolic 1303sh, νas (Sn–C)/νs (Sn–C) 277vs/226w,
ν(Sn–O) 535w, ν(Sn ← N) 448m.
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
435
Brown solid, m.p. 123–125 ◦ C. Yield 82%. Anal. (%) calcd for
C18 H21 N3 OSn (414.09): C, 52.21; H, 5.11; N, 10.15, Sn, 28.67. Found:
C, 52.14; H, 5.03; N, 10.06; Sn, 28.63. UV–vis [CH3 OH, λmax /nm
(ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene) 212 (37742), n → π ∗
(C N)azomethine 254 (13312), π → π ∗ (C N)benzimidazole ring
275 (13522), n → π ∗ (B-band of benzene) 283 (12938),
n → π ∗ (C N)benzimidazole ring 325 (750); selected IR (KBr,
cm−1 ): ν(N–H)benzimidazole ring 3056w, ν(C N)azomethine 1622vs,
νas (C–O)phenolic 1540s, νs (C–O)phenolic 1307sh, νas (Sn–C)/νs (Sn–C)
637w/600w, ν(Sn–O) 548m, ν(Sn ← N) 436w;119m Sn Mössbauer:
QS = 2.8 mm s−1 , IS = 1.3 mm s−1 , ρ (QS/IS) = 2.15, → C–Sn–C
= 122.10◦ .
Brown solid, m.p. 250–252 ◦ C. Yield 81%. Anal. (%) calcd for
C32 H30 N6 O2 Sn (649.34): C, 59.19; H, 4.66; N, 12.94, Sn, 18.28. Found:
C, 59.14; H, 4.60; N, 12.89; Sn, 18.26. UV–vis [CH3 OH, λmax /nm
(ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene) 211 (40164), n → π ∗
(C N)azomethine 252 (14734), π → π ∗ (C N)benzimidazole ring 276
(17106), n → π ∗ (B-band of benzene) 284 (17258), n →
π ∗ (C N)benzimidazole ring 320 (7214); selected IR (KBr, cm−1 ):
ν(N–H)ring 3056w, ν(C N)azomethine 1613vs, νas (C–O)phenolic 1540s,
νs (C–O)phenolic 1306sh, νas (Sn–C)/νs (Sn–C) 637w/566m, ν(Sn–O)
527m, ν(Sn ← N) 433w.
M. Nath, P. K. Saini and A. Kumar
Synthesis of n-Oct2 Sn(L)2 (8) by Azeotropic Removal of Water
Method
Di-n-octyltin(IV) complex of Hsal-ambmz (HL) was prepared by a
dropwise addition of methanolic solution (ca 10 ml) of HL (0.703 g,
3.0 mmol) to a hot methanolic solution of n-Oct2 SnO (0.5415 g,
1.5 mmol) with constant stirring at room temperature under inert
atmosphere of dry nitrogen. The reaction mixture was refluxed
with constant stirring for another ca 45 h at 60–65 ◦ C. The solution
was filtered to remove unreacted reactants, and the excess of
solvent was gradually removed by evaporation under vacuum
until solid product was obtained. The solid was then recrystallized
from dichloromethane–methanol (2 : 1 v/v) mixture.
n-Oct2 Sn(L)2 (8)
Reddish-brown solid, m.p. 128–130 ◦ C. Yield 79%. Anal. (%) calcd
for C46 H58 N6 O2 Sn (845.71): C, 65.33; H, 6.91; N, 9.94, Sn, 14.04.
Found: C, 65.31; H, 6.89; N, 9.96; Sn, 14.01. UV–vis [CH3 OH,
λmax /nm (ε/M−1 cm−1 )]: π → π ∗ (E-band of benzene) 209 (34874),
n → π ∗ (C N)azomethine NO, π → π ∗ (C N)benzimidazole ring 277
(11582), n → π ∗ (B-band of benzene) 283 (11884), n → π ∗
(C N)benzimidazole ring 380 (2862); selected IR (KBr, cm−1 ): ν(N–H)ring
3064m, 2954s, ν(C N)azomethine 1625vs, νas (C–O)phenolic 1539m,
νs (C–O)phenolic 1315w, νas (Sn–C)/νs (Sn–C) 619w/596w, ν(Sn–O)
555w, ν(Sn ← N) 436m.
Toxicity and Anti-inflammatory Activity
Toxicity (LD50 : average lethal dose at 50% survival) of the
studied complexes was determined in albino mice of either
gender (body weight 20–25 g). The test compound was injected
intraperitoneally at different dose levels in groups of 10 animals
and percentage mortality in each group was observed after 24 h of
drug administration. The LD50 value (mg/kg) was calculated from
the data according to the procedure reported previously.[15b,c]
The anti-inflammatory activity (percentage inhibition) of the
synthesized complexes was determined out in vivo using the
carrageenan-induced paw edema bioassay in rats and on either
adult mongrel dogs (body weight 10–20 kg) or on cats (body
weight 3–4 kg) of either gender, respectively, according to the
procedures reported recently.[15b,c]
Results and Discussion
436
The interaction of R3 SnCl and R2 SnCl2 with sodium salt of Schiff
base [HL or Hsal-ambmz; formed according to reactions (1) and (2)]
in a 1 : 1 and 1 : 2 molar ratio, respectively, led to the formation of
the compounds according to reactions (3) and (4), respectively, as
shown in Scheme 1. The reaction (5) of di-n-octyltin(IV) oxide with
HL in a 1 : 2 molar ratio resulted in a product with an azeotropic
removal of water.
All of the synthesized organotin(IV) complexes were yellow to
brown powders. The synthesized complexes were obtained in
good yield (71–82%) and are stable towards air and moisture.
Triorganotin(IV) derivatives of Hsal-ambmz (or HL) were soluble
in methanol, ethanol, dichloromethane and dimethylsulfoxide,
whereas diorganotin(IV) derivatives were soluble in methanol
and dimethylsulfoxide. The analytical data of the synthesized
complexes are given in the Experimental section. The molar
conductance values (at room temperature) of 10−3 M solutions
(in methanol) of the synthesized organotin(IV) complexes were
in the range ca 7.0–15.0 ohm−1 cm2 mol−1 , suggesting their
non-electrolytic nature.
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Electronic spectra
The electronic spectral bands (in nm) together with their ε
(molar extinction coefficient) values of Hsal-ambmz (or HL) and
of its tri- and diorganotin(IV) complexes recorded in absolute
methanol are given in the Experimental section. The ultraviolet
spectrum of HL shows five sharp absorption maxima.[12a] A weak
shoulder due to hydrogen bonding appears along with these
bands. A band observed at 227 nm in HL may be assigned to
the E band (π → π ∗ ) of the phenyl ring of salicylaldimine.
This band blue shifts upon complexation and is observed at
212 ± 4 nm in the complexes. Similarly, the ligand chromophore
(<C N–) (azomethine) absorbs at 256 nm, and shifts to a shorter
wavelength (blue shift) upon complexation (249±8 nm) indicating
the coordination of azomethine (<C N–) group.[16 – 18] A band
in the spectra of Schiff base and its organotin(IV) complexes in
the region 274–277 nm is likely due to the (π → π ∗ ) transition
of (<C N–) group of benzimidazole moiety or (n → π ∗ ) of
benzene ring. The band at 282 ± 2 nm in all of the complexes was
due to the B band (n → π ∗ ) of the benzene ring of benzimidazole.
Further, a band in the spectrum of the Schiff base at 319 nm was
probably due to (n → π ∗ ) transition arising from the (<C N–)
group of benzimidazole moiety. This band shifts to 350 ± 30 nm
in the complexes, possibly owing to the polarization of C N
bond caused by metal–ligand interaction and intramolecular
charge transfer. Moreover, there were a few sharp bands observed
in the region 240–270 nm in the spectra of complexes, which
could be assigned to charge transfer bands.[16,18 – 21] It has been
reported[16,20] that a metal/metalloid is capable of forming dπ –pπ
bonds with ligands containing nitrogen as donor atom. The tin
atom has its 5d orbitals completely vacant and hence L → M
bonding can take place by the acceptance of pair of electron from
nitrogen or oxygen donor atom of the ligands.
IR and far-IR Spectral
The characteristic frequencies of HL and its organotin(IV) complexes are given in the Experimental section. The IR spectrum
of HL shows a very strong and broad band with a shoulder
at 3415 cm−1 . Since, the band is broad; it is more likely to be
due to intramolecular hydrogen bonding between the hydroxyl
hydrogen and nitrogen of azomethine group forming a stable sixmembered ring (as shown in Scheme 1). Absence of ν(OH) mode in
all of the studied complexes suggests the deprotonation of phenolic –OH of Hsal-ambmz and its subsequent coordination through
the oxygen atom.[16,19,20,22,23] Two strong bands around 1530 ± 10
and 1313 ± 6 cm−1 in the complexes were observed at lower wave
numbers as compared with uncoordinated Hsal-ambmz (1561
and 1320 cm−1 ), indicating the participation of phenolic oxygen
in bonding with tin.[20]
Further, the IR spectrum of Hsal-ambmz showed a very sharp and
strong band due to the ν(–C N–) of azomethine at 1638 cm−1 .
Since the imidazole ring has an aromatic character, a shoulder
at 1615 cm−1 may be assigned to ν(C N) of the imidazole
ring.[16,19,20,22,24] In the IR spectra of the studied complexes, a
single sharp band at 1621 ± 8 cm−1 was observed because
the azomethine ν(C N) merges with ν(C N) of imidazole
ring, indicating the coordination of azomethine nitrogen to tin.
Moreover, the presence of two medium intensity bands in the
regions 3052–3064 and 2954–3044 cm−1 in Hsal-ambmz as well
as in most of the complexes indicates that the N–H of imidazole
ring does not participate in the coordination.
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 434–445
Tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole
Scheme 1. Reaction pathways for R3 Sn(L) and R2 Sn(L)2 .
Figure 2. Probable structures (fac/mer) of R3 Sn(L) (R = Me, n-Bu and Ph).
Figure 1. Possible isomers for MR3 XY[27] .
Appl. Organometal. Chem. 2009, 23, 434–445
of monofunctional bidentate Schiff base (HL) with ON donor site
exhibit trigonal–bipyramidal geometry with either fac or mer
configuration (Fig. 2).
The IR and far-IR spectra of the six-coordinated diorganotin(IV)
complexes of the type R2 Sn(L)2 (R = Me, n-Bu, n-Oct and Ph) also
depict two Sn–C stretching frequencies at 628 ± 9 and 584 ± 18
cm−1 for R = Me, n-Bu and n-Oct, and 277and 226 cm−1 for R =
Ph. This suggests the existence of cis-R2 Sn(IV) moiety in a distorted
octahedral arrangement around tin atom[25] as shown in Fig. 3. The
ν(Sn–O) band in the region 527–574 cm−1[20,26] is also observed
in the spectra of all of the synthesized complexes.
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
437
The conclusions drawn above are further supported by the
presence of new band in the far-IR spectra of the studied
complexes, at ca 439 ± 10 cm−1 , which may be assigned to ν(Sn ←
N).[16,18 – 20,22] Five coordinate complexes of the type MX3 Y2 may
assume either of the three trigonal-bipyramidal arrangements, (A),
(B) and (C) of C4 , D3h and C2v symmetry, respectively (Fig. 1).
The IR and far-IR spectra of Me3 Sn(L), n-Bu3 Sn(L) and Ph3 Sn(L)
depict two Sn–C stretching frequencies at 637, 600; 633, 606; and
278, 223 cm−1 , respectively. This indicates that the three organic
groups are not in equatorial position and that the two donor
atoms, viz. oxygen and nitrogen in (sal-ambmz)−1 , are not in
axial positions, as one would expect from the steric properties
of the bidentate ligand.[16,20] Hence the triorganotin(IV) chelates
M. Nath, P. K. Saini and A. Kumar
Figure 3. Probable cis-octahedral structure of diorganotin(IV) complexes
of the type R2 Sn(L)2 (R = Me, n-Bu, n-Oct and Ph).
119 Sn Mössbauer Spectra
The 119 Sn Mössbauer spectrum of Me3 Sn(L) (2) could be taken
as representative for the assignment of structure of the studied
triorganotin(IV) complexes of Hsal-ambmz. The 119 Sn Mössbauer
spectrum of Me3 Sn(L) exhibits isomer shift (IS) at 1.30 mm s−1
and quadrupole splitting (QS) at 2.80 mm s−1 , showing that the
electric field gradient around tin nucleus is produced by the
inequalities in the tin–oxygen and tin–nitrogen bonds and is also
due to geometric distortions. The ρ (QS/IS) value of 2.15 clearly
indicates a coordination number greater than four in the solid
state. It has been reported[27] that the three conceivable (Fig. 1)
five-coordinate isomers of R3 SnXY (where X or Y = N/O/S; XY are
the donor sites of the bidentate ligand) have different QS value
ranges, for isomer (A) 1.70–2.30 mm s−1 ; for (B) 3.0–3.90 mm s−1 ;
and for (C) 3.50–4.10 mm s−1 . The observed value of QS (2.80 mm
s−1 ) in Me3 Sn(L) is higher than that for isomer (A) and considered
to be compatible with trans-structure, which is the conventional
one (following Bent’s rule) found in organotin chemistry. However,
the observed νas (Sn–C) and νs (Sn–C) stretching vibrations in the
IR spectra of all of the studied triorganotin(IV) complexes as well
as diorganotin(IV) complexes indicate a non-planar SnC3 /SnC2
fragment and rule out the possibility of trans-isomer 1(B).
Therefore, the most plausible structure for Me3 Sn(L) (2) is a highly
distorted cis-trigonal-bipyramidal as shown in Scheme 1, which
is intermediate between 1(A) (fac) and 1(C) (mer) cis-trigonalbipyramidal structures. A similar structure has been reported
for the closely related compound Me3 SnL (where HL = Schiff
base),[20] which was considered to have a cis-trigonal-bipyramidal
arrangement having Sn–O–C–N ring. Furthermore, a similar
structure as shown in Scheme 1 has also been suggested for
n-Bu3 Sn(L) and Ph3 Sn(L).
Multinuclear (1 H, 13 C and 119 Sn) NMR Spectra
1 H NMR Spectra
1
438
H NMR spectral data of Hsal-ambmz (or HL) and of its organotin(IV)
complexes are presented in Table 1. The monobasic bidentate
Schiff base (HL) exhibits hydrogen-bonded OH (phenolic) proton
signal at δ 12.83 ppm in DMSO-d6 . The absence of such a signal
in all of the organotin(IV) complexes suggests the deprotonation
of the phenolic OH of Schiff base on complexation.[16,20,28] In
the 1 H NMR spectra of the complexes, a signal at δ 8.63 ± 0.04
ppm for triorganotin(IV) complexes and δ 8.72 ± 0.09 ppm for
diorganotin(IV) complexes has been assigned to the azomethine
proton (–CH N–). It appears at low frequency in all of the
studied complexes as compared with the corresponding signal
of uncoordinated Schiff base (8.69 ppm in CD3 OD/8.96 ppm in
DMSO-d6 ), indicating thereby the coordination of the ligand
to the tin via azomethine nitrogen (Sn ← N).[20] Two signals
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due to both azomethine protons appear in the spectra of nBu2 Sn(L)2 , n-Oct2 Sn(L)2 and Ph2 Sn(L)2 , except Me2 Sn(L)2 , where
a broad unresolved signal is obtained, indicating the presence
of non-equivalent magnetic field around two ligand molecules.
The signals due to the NH group could not be located in the
δ = 0–15 ppm region, neither in the spectra of Schiff base nor in
the complexes.[12] The signal due to –CH2 –protons appears at δ
5.05/5.06 ppm as a sharp singlet in Schiff base while this signal
in complexes is overlapped with those of solvent and appears
as a broad singlet in range of δ 4.82–5.00 ppm. It is difficult to
distinguish between the aromatic protons attached to the tin atom
and those of Schiff base. The Sn–CH3 protons in the spectra of
Me3 Sn(L) appear as two singlets at δ 0.41 and δ 0.07 ppm. This also
indicates that all the three methyl groups are not equivalent.[20]
The intensity of the signal centered at δ 0.41 is approximately
twice the second signal at δ 0.07 ppm. In the same way all the nonequivalent alkyl/phenyl protons of the organic groups attached to
tin are also successfully identified and are given in Table 1.
The n J(1 H– 119 Sn) coupling constant, which gives important information about the coordination environment, is also determined
and are given in Table 1. The 2 J(1 H– 119 Sn) and 3 J(1 H– 119 Sn) values are 64.0, 54.7 Hz for Me3 Sn(L), 70.9, 56.5 Hz for n-Bu3 Sn(L)
and 63.6, 83.3 Hz for Ph3 Sn(L), respectively. Except 83.3 Hz for
Ph3 Sn(L), the 2 J(1 H– 119 Sn) coupling constant values correspond
to a penta-coordinated, trigonal–bipyramidal geometry[28 – 30] in
accordance with the conclusion drawn from the far-IR results
in the previous section. Among diorganotin(IV) complexes, the
2 J(1 H– 119 Sn) value has been determined only for Me Sn(L)
2
2
(76.2 Hz), which corresponds to the octahedral geometry.[29,30]
The ∠ C–Sn–C calculated by using Lockhart and Manders[29,30]
equation (θ = 0.0161 | 2 J | 2 − 1.32 | 2 J | + 133.4) is in the range
109.38–120.79◦ (as given in Table 1) for triorganotin(IV) complexes, indicating also a distorted trigonal–bipyramidal geometry.
The n J(1 H– 119 Sn) values of Ph3 Sn(L) (83.3 Hz) and Me2 Sn(L)2
(76.2 Hz) correspond to ∠ C–Sn–C of 135.13 and 126.36◦ , respectively, which clearly indicate a distorted cis-octahedral arrangement. The number of protons of various groups calculated
from the integration curves and those calculated for the expected
molecular formula agrees with each other.
13 C NMR Spectra
13
C NMR spectral data along with the assignment of characteristic
peaks of Schiff base (HL) and all of its synthesized organotin(IV)
complexes are presented in Table 2. In the 13 C NMR spectrum
of Schiff base in CD3 OD/DMSO-d6 the signals corresponding
to carbon atom attached to the phenolic oxygen (C-1) and
azomethine nitrogen (C-7) are observed at δ 168.5/164.5 and
160.9/160.7 ppm, respectively, which are shifted either toward
high or low frequency (downfield or upfield) in all of the studied
organotin(IV) complexes (Table 2), indicating the coordination of
deprotonated Schiff base to tin via (O)phenolic attached to C-1 and
(N)azomethine attached to C-7. These chemical shifts are slightly
shifted in organotin(IV) complexes as compared to uncoordinated
ligand because the extent of O–H· · ·N hydrogen bonding is greatly
reduced[31] upon complexation. The alkyl carbon of Schiff base
is shifted towards higher field, δ = (7.6–7.7 ppm), which also
supports the coordination of azomethine nitrogen to tin. The
aromatic carbons of the ligand as well as complexes appear well
within the expected range and are given in Table 2. All magnetically
non-equivalent carbons of alkyl or phenyl groups attached to tin
have also been identified and their chemical shift values are in
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 434–445
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
8.73, s(1H); 8.51, s
(1H)
(7) (CD3 OD + 2–3 drops
of DMSO-d6 )
7.58–7.56, m (2H); 7.42, d (1H, 7.0 Hz); 7.34–7.31, t
(1H); 7.25–7.23, m (2H); 6.92–6.88, m (2H)
7.57–7.55, m (3H); 7.23–7.22, 7.31–7.25, m (3H);
6.89–6.87, m (2H)
7.71, dbr (2H, 3.5 Hz); 7.60–7.56, m (4H); 7.39–7.37,
mbr (2H); 7.23–7.20, mbr (4H); 6.84–6.77, m (2H);
6.73–6.67, m (2H)
4.95, sbr (2H)d
4.95, sbr (2H)d
4.84, s (4H)d
4.91, s (4H)d
4.82, s (4H)d
7.72–7.68, m (2H); 7.46–7.34, mbr (3H); 7.27–7.17, m
(3H); 7.04, (1H, 3 Hz); 7.02–6.98, m (2H); 6.92–6.83,
mbr (4H); 6.65–6.62, tbr (1H);
7.71, sbr (1H); 7.63, dbr (1H, 6.0 Hz); 7.28–7.27, mbr
(2H); 7.17, dbr (1H, 9.0 Hz); 7.14, dbr 1H, 10.5 Hz);
6.98, d (1H, 7.5 Hz); 6.83–6.77, m (2H); 6.72–6.67,
mbr (2H); 6.65–6.60, mbr (2H); 6.49–6.44, mbr (2H);
6.31, d (1H, 8.0 Hz)
7.70, dbr (2H, 3.5 Hz); 7.61, sbr (4H); 7.36–7.34, mbr
(3H); 7.25–7.20, mbr (4H); 6.85, d (1H, 7.5 Hz); 6.78, d
(1H, 7.5 Hz); 6.70, d (1H, 9 Hz,)
7.57–7.51, m (3H); 7.25–7.19, m (3H); 6.89–6.86, m
(2H)
5.00, sbr (2H)d
4.84, s (4H)d
7.67, d (2H, 7.0 Hz); 7.52, d (2H, 8.5 Hz); 7.46–7.42, m
(2H); 7.01–6.98, m (2H)
7.57, sbr (2H); 7.44, d (1H, 8.0 Hz); 7.37–7.34, t (1H, 8.0,
7.5 Hz); 7.25–7.23, q (2H); 6.95–6.90, q (2H, 7.5, 10.0,
8.5 Hz)
H-2, H-3, H-4, H-5, H-11, H-12,
H-13, H-14 (phenyl protons)
5.06, s (2H)
5.05, s (2H)
H-8 (-CH2 )
H-α to H-µ, 1.42–1.20, me (10H),
1.21–1.10, me (8H), 0.97–0.85, me (10 H);
H-ω, 0.85–0.75, me (6H).
H-β, 7.97, 7.91 dd (4H, 6.5, 7.5 Hz); H-γ ,
7.51–7.43 mbr (4H);
H-δ, 7.38–7.36 mbr (2H)
H-α, 1.26–1.23, t (4H);
H-β, 1.61–1.59, m (4H);
H-γ ,1.52, sbr (4H);
H-δ, 0.76–0.73, t (6H)
H-α, 0.64, 0.61,s (6H)
H-β, H-δ, 7.44, dbr (9H, 7.0 Hz); H-γ ,
7.79, sbr (6H)
H-α, 1.5–1.18, t (6H, 8.0 Hz);
H-β,1.64, sbr (6H); H-γ , 1.40–1.35, m (6H);
H-δ, 0.95–0.92, t (9H, 7.0 Hz)
H-α, 0.41, s (6H), 0.07, s (3H)
–
–
Sn–H-α/H-β/
H-γ /H-δ/upto H-ω
n J(1 H–
–
–
–
76.2
63.6, 83.3
56.5, 70.9
64.0, 54.7
–
–
119 Sn) (Hz)
–
–
–
126.36
114.50, 135.13
115.50, 120.79
114.87, 109.38
–
–
∠ C–Sn–
Cc (deg)
s: singlet; d: doublet; dd: double doublet; t: triplet; m: multiplet; br: broad; sbr, singlet broad, dbr, doublet broad, mbr, multiplet broad. a Sl. No. as indicated in Experimental; b m.p. 160 ◦ C, phenolic proton
peak is observed at: 12.83, s (1H); c calculated using the equation θ = 0.0161 | 2 J | 2 − 1.32 | 2 J | + 133.4; d overlapped with solvent; e strongly overlapping multiplets.
8.73, s (1H); 8.65, s
(1H)
8.81, s (1H); 8.70, s
(1H)
(6) (CD3 OD + 2–3 drops
of DMSO-d6 )
(8) (CD3 OD + 2–3 drops
of CDCl3 )
8.64, sbr (2H)
(5) (CD3 OD)
8.66, s (1H)
(3) (CD3 OD)
8.59, s (1H)
8.61, s (1H,)
(2) (CD3 OD)
439
Appl. Organometal. Chem. 2009, 23, 434–445
(4) (CD3 OD)
8.96, s (1H)
(1)b (DMSO-d6 )
H-7 (azomethine proton)
H NMR chemical shifts (δ, ppm) of HL and its tri- and diorganotin(IV) complexes
8.69, s (1H)
1
(1) (CD3 OD)
Sl. no.a
(solvent)
Table 1.
Tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole
440
www.interscience.wiley.com/journal/aoc
c 2009 John Wiley & Sons, Ltd.
Copyright 128.4, 122.3
128.9, 127.1
168.4
168.5
165.6
166.2
165.0
(4) CD3 OD
(5) CD3 OD
(6) CD3 OD + 2–3 drops
of DMSO-d6
(7) CD3 OD + 2–3 drops
of DMSO-d6
(8) CD3 OD + 2–3 drops
of CDCl3
128.0, 122.4
131.0
136.2
132.5
131.0
131.8
131.8
131.6
131.8
132.5
C-6
160.7
160.8
161.0
161.1
160.7
160.9
160.7
160.6
160.7
C-7
48.5
48.6
48.6
48.6
48.6
56.3
58.4
48.5
48.5
C-8
153.8
151.3
148.7
151.2
151.4
151.5
147.6
152.5
151.7
C-9
C-11,
C-14
132.3
140.5
142.0
140.9
132.5
117.1, 112.6
118.2, 117.6
117.4, 115.3
116.8, 114.9
116.4
140.9, 132 116.3
134.0, 133 117.1
138.5
116.4, 114.4
145.7
116.4, 114.3
C-10,
C-15
121.4, 125.4
118.7, 121.9
119.6, 120.0
121.9, 122.3
118.7
118.7
119.7, 119.7
118.6, 119.0
118.6, 119.1
C-12,
C-13
141.4c , 139.7,
136.3, 128.4,
129.2
02.0
23.3, 27.0, 26.1,
12.6
136.5, 129.2,
127.7, 128.7
24.9, 32.9, 28.8,
31.8, 28.9, 26.4,
22.2, 13.1
−4.7
15.8, 27.8, 26.8,
12.7
–
–
Sn-(C-α
to C-ω)
679.0d
718.7,d 34.1,e
54.8,f 37.9g
749.6,d 54.9,e
79.8,f 44.9g
–
465.1d
486.1,d 25.1,e
70.9f ,–
469.6,d 42.5,e
66.0,f 56.7g
–
–
n J(13 C– 119/117 Sn)
–
142.51
136.31
139.80
117.94
–
–
117.55
119.39
→ C–Sn–Cb
Carbon no. as indicated in Scheme 1 for HL (1) and Sl. no. as indicated in Experimental; b calculated using the equatio | 2 J | = 11.4θ − 875); c very weak resonance; d 1 J(13 C– 119/117 Sn); e 2 J(13 C– 119/117 Sn);
f 3 J(13 C– 119/117 Sn); g 4 J(13 C– 119/117 Sn);
a
131.0, 123.0
130.1, 124.0
168.5
164.5
168.4
168.5
(1) CD3 OD
(1) DMSO-d6
(2) CD3 OD
(3) D3 OD
126.0, 122.4
129.8, 123.7
132.5, 122.3, 122.1
131.8, 122.3
C-1
C-2, C-3,
C-4, C-5
13 C NMR chemical shifts (δ, ppm) of HL and its tri- and diorganotin(IV) complexes
Sl. no.
(solvent)
a
Table 2.
M. Nath, P. K. Saini and A. Kumar
Appl. Organometal. Chem. 2009, 23, 434–445
Tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole
Table 3. 119 Sn NMR spectral data of the synthesized organotin(IV)
complexes of HL
Complex
Solvent
δ (ppm)
Me3 Sn(L) (2)
CD3 OD
n-Bu3 Sn(L) (3)
Ph3 Sn(L) (4)
CD3 OD
CD3 OD
−10.65a ,
−103.57a
−167.41
−122.51b ,
−471.63b
−129.07b,c ,
−392.99b,d
−228.15
−252.78
CD2 Cl2
Me2 Sn(L)2 (5)
n-Bu2 Sn(L)2 (6)
Ph2 Sn(L)2 (7)
n-Oct2 Sn(L)2 (8)
CD3 OD
CD3 OD + 2–3
drops of DMSO-d6
CD3 OD + 2–3
drops of DMSO-d6
CD3 OD + 2–3
drops of CDCl3
−549.80,
−552.76
−215.02
a Intensity ratio of two peaks is 1 : 1 together with a very weak signal
at 0.56 ppm; b intensity ratio of two peaks is 2 : 1; c width of signal at
half height, ±405 Hz; d width of signal at half height, ± 120 Hz; internal
standard is tetraphenyltin.
close agreement with the reported values.[25] The heteronuclear
coupling constant, viz. 1 J(13 C– 119 Sn) is very useful in providing
information about the coordinating environment and geometry
of the organotin complexes. In the most of the studied
organotin(IV) complexes, the satellites are resolved and the
observed coupling constants 1 J(13 C– 119 Sn) are 476 ± 10 and
715 ± 36 Hz (Table 2) for triorganotin(IV) and diorganotin(IV)
complexes, respectively. These values lie in the range of
penta-coordinated (trigonal–bipyramidal) and hexa-coordinated
(octahedral) arrangement as reported for other complexes of
types, R3 Sn(XY) and R2 Sn(XY)2 (where X and Y = O/N/S, the
donor site of bidentate ligand).[29,30,32] Moreover, the calculated
values of ∠ C–Sn–C using observed 1 J(13 C– 119 Sn) values in the
equation given by Lockhart and Manders[29,30] (| 2 J | = 11.4θ −875)
are in the range of 117.55–119.39◦ (as given in Table 2) for
triorganotin(IV) complexes and 136.31–142.51◦ (as given in
Table 2) for diorganotin(IV) complexes indicating a distortion in
their trigonal–bipyramidal and octahedral geometry, respectively.
119 Sn NMR Spectra
Appl. Organometal. Chem. 2009, 23, 434–445
2Me3 Sn(L)
CD3 OD
Me4 Sn + Me2 SnL · solvent
(6)
The possible geometries around tin in tri- and diorganotin(IV)
complexes of Schiff base are distorted trigonal–bipyramidal and
octahedral, respectively, in which Schiff base acts as a bidentate
ligand and coordinates through the phenolic oxygen (O) and
azomethine nitrogen (N). Thus, the structure of R3 Sn(L) is best
described by a distorted cis-trigonal-bipyramidal configuration, as
shown in Scheme 1. The possible structures of Ph3 Sn(L) are shown
in Fig. 4. For R2 Sn(L)2 , structure is best described by a distorted
cis-octahedral configuration, as shown in Scheme 1.
Biological Studies
The studies on structure–activity correlation of organotin(IV)
compounds reveal that the active compounds are characterized
by the following structural features:[25] (i) the availability of
coordination position at tin; (ii) the occurrence of ligand–Sn
bonds, viz. Sn–N and Sn–S/O bonds; and (iii) low hydrolytic
decomposition of these bonds.
Further, it has been stated that the inactive species are associated with stable compounds having Sn–N bond lengths of
<2.39 Å,[34] and the activity is due to dissociation of nitrogen
containing ligands as part of the mechanism for inhibition.[35]
Furthermore, it has been proposed for R2 Sn(IV)–glycylglycinates
(R = Me, n-Bu, n-Oct and Ph) on the basis of solution studies using several spectroscopic techniques,[36,37] that solvated species in
aqueous solution or mixture of H2 O and organic solvent and unsolvated species (mainly organic solvent) are present in equilibrium
and contribute to the passage of alkyltin(IV) complexes across
the cell membrane.[36,37] A quantitative structure–activity relation (QSAR) for a series of triaryltin(IV)/diorganotin(IV) complexes,
Ph3 SnXY/R2 SnXY,[38,39] indicated that R3 Sn+ and R2 Sn+2 are the
causative agents and the XY group influences only the readiness
of delivery of the active part, R3 Sn+ /R2 Sn+2 into the cell.[40] Thus
an attempt is being made to formulate the structure–activity correlation of the synthesized tri- and diorganotin(IV) complexes of
Hsal-ambmz.
Anti-inflammatory Activity
The anti-inflammatory activities (percentage inhibition) of Schiff
base and its tri- and diorganotin(IV) complexes are presented in
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
441
The 119 Sn NMR spectral data of organotin(IV) complexes of Schiff
base (HL) are given in Table 3. The 119 Sn NMR chemical shift is
very sensitive to complexation and is usually shifted high or low
frequency on bonding to a Lewis base. The tin shielding in 119 Sn
NMR spectra increases markedly with increase in coordination
number, δ 50 to −60 ppm for four-coordinate, −100 to −200 ppm
for five-coordinate and −200 to −330 ppm for six-coordinate
alkyltin(IV) compounds, and these 119 Sn shifts are higher with
phenyl compared with alkyl substituents.[33] The observed 119 Sn
chemical shifts of the studied triorganotin(IV) complexes are in
the range of five-coordinated tin compounds, whereas for the
diorganotin(IV) complexes, the observed 119 Sn chemical shifts
are in the range of six-coordinated tin compounds. The 119 Sn
NMR spectrum of Ph3 Sn(L) shows two signals at δ −122.51 and
−471.63 ppm in CD3 OD and at −129.07 and −392.99 ppm in
CD2 Cl2 , which correspond to the presence of five-coordinate
and six-coordinate tin moieties, respectively, in 2 : 1 ratio as
indicated by their intensities.[33] Therefore, the weak interaction
between central tin and (N)imidazole may occur, leading to an
octahedral species in the solution. The broadness (±405 Hz) of
119
Sn resonance at room temperature in CD2 Cl2 suggests the
existence of an equilibrium mixture of different species (Fig. 4),
which is also observed in 1 H [3 J(1 H– 119 Sn) = 63.6, 83.3 Hz] and
13 C NMR (C-α = 139.7 ppm, a weak resonance at 141.4 ppm,
which becomes slightly intense at 285 K). In Me3 Sn(L), two
resonances at δ −10.65 and −103.57 ppm together with a very
weak signal at 0.56 ppm were observed in approximately intensity
ratio of 40/40/5. The two-dimensional 1 H– 119 Sn HMQC spectrum
displays 2 J(1 H– 119 Sn) coupling correlation between methyl proton
resonances and 119 Sn resonances at 0.56 ppm (54.7 Hz) owing to
(CH3 )4 Sn and at −10.65 ppm (64.0 Hz) owing to Me3 Sn(L). The tin
resonance at −103.57 ppm also correlates with methyl resonances
with approximately 2 J(1 H– 119 Sn) value of 76.0 ± 0.8 Hz. These
results suggest the dissociation of Me3 Sn(L) in nucleophilic solvent
CD3 OD according to the following equation [eqn (6)]:
M. Nath, P. K. Saini and A. Kumar
Figure 4. (a) cis-Trigonal-bipyramidal (distorted) structure of Ph3 Sn(L) and (b) octahedral (distorted) structure of Ph3 Sn(L) involving weak interaction
between tin and (N)imidazole .
Table 4. The activity of the standard drug phenylbutazone has
been used for comparison. As revealed from the data presented
in Table 4, the organotin(IV) complexes of HL (10.32–22.23%
inhibition) at a dose of 40 mg kg−1 are found to be more
active than Schiff base (HL) (2.67% inhibition) and organotin(IV)
chlorides/oxides (2.97–9.89% inhibition) at the same dose level.
Further, it has been observed that the diorganotin(IV) complexes
(19.75–22.23% inhibition) show better activity as compared
with triorganotin(IV) complexes (10.32–17.86% inhibition). nOct2 Sn(L)2 showed good anti-inflammatory activity (22.23%
inhibition), which is higher than that of Me2 Sn(L)2 (19.75%
inhibition), n-Bu2 Sn(L)2 (21.23% inhibition) and Ph2 Sn(L)2 (20.16%
inhibition), but is lower than that of the standard drug,
phenylbutazone (31.89% inhibition). Among the triorganotin(IV)
complexes, the order of their percentage inhibition is Me3 Sn(L)
< n-Bu3 Sn(L) < Ph3 Sn(L) (Table 4). Furthermore, it has also been
observed that activity of diorganotin(IV) complexes increases on
increase in dose level. The analysis of data in Table 4 indicates
that the anti-inflammatory activity of the studied complexes is
influenced by the number and nature of the organic groups
attached to tin.
Toxicity Studies
The LD50 (mg kg−1 ) values of Schiff base (HL), organotin(IV)
chlorides/oxides and tri- and diorganotin(IV) complexes of Schiff
base are given in Table 4. The tested organotin(IV) complexes of
Schiff base (HL) have LD50 values (>800 mg kg−1 ) greater than
that of HL (>400 mg kg−1 ) and organotin(IV) chlorides/oxides
(>400 mg kg−1 ), suggesting the greater safety margin of these
derivatives because of their lower toxicity. It has been observed
that the studied organotin(IV) complexes of Schiff base (HL) are
much less toxic than the organotin(IV) complexes of simple αamino acids[41] (>50 mg kg−1 ) and peptides[42,43] (>500 mg kg−1 ),
indicating that Schiff base Hsal-ambmz (HL) upon complexation
lowers the toxicity and enhances the activity of the resulting
organotin(IV) complexes.
Thermal Studies
442
Thermal decomposition of all of the studied complexes was carried
out using TG, DTG and DTA techniques. TG and DTA curves of the
complexes are presented in Figs 5 and 6, respectively. All of the
complexes decompose gradually with the formation of SnO2 .
Thermal decomposition data are presented in Table 5. The main
diffraction lines along with their relative d values reported[44] for
Sn, SnO, SnO2 , and of residues thus obtained, are given in Table 6.
www.interscience.wiley.com/journal/aoc
Table 4. Anti-inflammatory activity and acute toxicity data of Schiff
base, organotin(IV) chlorides/oxides, organotin(IV) complexes of Schiff
base and standard drug
Complex/starting
materials/
reference drug
HL (1)
Me3 Sn(L) (2)
n-Bu3 Sn(L) (3)
Ph3 Sn(L) (4)
Me2 Sn(L)2 (5)
n-Bu2 Sn(L)2 (6)
Ph2 Sn(L)2 (7)
n-Oct2 Sn(L)2 (8)
Me2 SnCl2
n-Bu2 SnCl2
Ph2 SnCl2
n-(Oct)2 SnO
Me3 SnCl
n-Bu3 SnCl
Ph3 SnCl
Phenylbutazone
Anti-inflammatory activity
Edema
Dose
inhibition
(mg kg−1 p.o.)
(%)
40
40
40
40
40
20
40
80
20
40
80
20
40
80
40
40
40
40
40
40
40
20
40
80
2.67
10.32
14.66
17.86
19.75
11.57
21.23
37.39
10.02
20.16
36.15
12.12
22.23
39.36
2.97
5.35
4.65
6.39
9.89
4.89
7.29
12.67
31.89
48.26
Acute
toxicity LD50
(mg kg−1 p.o.)
>400
>800
>800
>800
>800
>800
>800
>800
>400
>400
>400
>400
>400
>400
>400
–
Me3 Sn(L) and n-Bu3 Sn(L) decompose in three steps whereas
Ph3 Sn(L) decomposes in two steps. The mass loss observed in
the first step of decomposition of all triorganotin(IV) complexes
corresponds to the loss of organic groups attached to tin, viz. in
Me3 Sn(L), loss of 3Me (C3 H9 ; weight loss observed: 10.20%; calcd:
10.89%); in n-Bu3 Sn(L), loss of 3Bu (C12 H27 ; weight loss observed:
32.22%; calcd 31.71%); in Ph3 Sn(L), loss of 3Ph (C18 H15 ; weight
loss observed 37.69%; calcd: 38.53%). The second weight loss
step occurs in the temperature range 125–543 ◦ C for Me3 Sn(L),
301–510 ◦ C for n-Bu3 Sn(L) and 434–800 ◦ C for Ph3 Sn(L), and
the observed mass losses are 57.16% (calcd: 57.58%), 37.00%
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 434–445
Tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole
Figure 5. TG profiles of (a) R3 Sn(L) (R = Me, n-Bu and Ph) and (b) R2 Sn(L)2
(R = Me, n-Bu, n-Oct and Ph).
Appl. Organometal. Chem. 2009, 23, 434–445
the end product, which is confirmed by the XRD data (Table 6) and
the presence of ν(Sn–O) at 615 cm−1[25] in the IR spectrum.
Similarly, the mass loss observed in the first step of decomposition of n-Bu2 Sn(L)2 (C8 H18 ; weight loss observed: 17.30%; calcd:
15.57%) and Ph2 Sn(L)2 (C12 H10 ; weight loss observed: 19.84%;
calcd: 19.94%) corresponds to the loss of organic groups attached
to tin. The second (loss of C28 H22 N4 ) and third (loss of C2 H2 N2 )
steps in n-Bu2 Sn(L)2 are similar to those of Me2 Sn(L)2 as shown
in Table 5, and the residue obtained is 20.28% at 840 ◦ C (calcd
for SnO2 20.55%). This was further confirmed by the presence of
ν(Sn–O) at 619 cm−1 in the IR spectrum of the residue and by XRD
(Table 6). The second step in case of Ph2 Sn(L)2 corresponds to the
loss of a part of ligand moiety (C26 H16 N4 ; weight loss observed:
44.85%; calcd: 49.70%) with exothermic peak observed at 447 ◦ C
in DTA curve. In the third step, remaining ligand moiety is lost
with the complete oxidation of tin to SnO2 (observed: 17.83%;
calcd: 19.48%). The end product obtained by the decomposition
of Ph2 Sn(L)2 has been analyzed by IR and XRD. The d values in XRD
spectrum are in good agreement with the reported[44] values for
SnO2 (Table 6). Further, the ν(Sn–O) at 620 cm−1 is observed in
the IR spectrum of the residue.[25]
n-Oct2 Sn(L)2 shows a two-step TG profile. In the first step the
mass loss observed corresponds to the loss of two octyl groups
(C16 H34 ; observed: 26.72%; calcd: 26.78%) in the temperature
range 25–280 ◦ C. The mass loss observed in the second step
is 61.97% (calcd: 55.41%) and the residue left is 11.29% (for
SnO2 calcd: 17.82%). On the basis of experimental TG weight
losses the decomposition pathways for Me2 Sn(L)2 , Ph2 Sn(L)2
and n-Oct2 Sn(L)2 are tentatively proposed and are given in
Scheme 2.
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
443
(calcd: 43.36%) and 32.35% (calcd: 39.02%), respectively, which
correspond to the loss of ligand moiety along with oxidation of tin,
which is evidenced by the exothermic peaks observed in their DTA
curves (Table 5 and Fig. 6). The residue left 29.96% at 800 ◦ C in case
of Ph3 Sn(L) was SnO2 (calcd: 24.45%), which is confirmed by the
XRD data (Table 6) and the presence of ν(Sn–O) at 622 cm−1[25]
in the IR spectrum. Whereas partial oxidation of tin in the second
step takes place in Me3 Sn(L) and n-Bu3 Sn(L), thereafter, a very slow
decomposition is continued up to 692 and 510 ◦ C, respectively,
followed by slow sublimation. Hence, the weight of residues
observed is less than that of calculated. The same residue was also
analyzed by XRD. The d values of the first five high intensity peaks
observed in the residue are in good agreement with the reported
values for SnO2 [44] (Table 6). The IR spectra of the residues thus
obtained from Me3 Sn(L) at 692 ◦ C and n-Bu3 Sn(L) at 510 ◦ C exhibit
ν(Sn–O) at 618 and 617 cm−1 , respectively.[25]
Me2 Sn(L)2 decomposes in three steps. The first step of
decomposition corresponds to the loss of two methyl groups
(C2 H6 ; weight loss observed: 6.5%; calcd: 4.63%) in the temperature
range 100–210 ◦ C. The mass loss observed in the second step of
decomposition corresponds to the loss of the part of the ligand
moiety (C28 H22 N4 ; weight loss observed: 59.67%; calcd: 63.84%).
The mass loss observed in the second step is less than the
calculated value. This may be due to the partial oxidation of tin,
which is supported by the broad exothermic peak observed at
446 ◦ C in its DTA and 429 ◦ C in DTG curves, and this is followed
by the loss of remaining part of ligand moiety (C2 H2 N2 ; weight
loss observed: 8.32%; calcd: 10.20%) in the third step. The mass
remaining of 23.63% at 955 ◦ C suggests SnO2 (calcd: 23.21%) as
Figure 6. DTA curves of (a) R3 Sn(L) (R = Me, n-Bu and Ph) and (b) R2 Sn(L)2
(R = Me, n-Bu, n-Oct and Ph).
M. Nath, P. K. Saini and A. Kumar
Table 5. Thermal analysis data of organotin(IV) complexes of HL in air
Loss of mass (%)
Observed
(calcd)
Species lost
–
−3062
−138
10.20 (10.89)
57.16 (57.58)
4.37
C3 H9 (3Me)
C15 H12 N3
Sublimation
–
−224
−4117
−73.6
32.22 (31.71)
37.00 (43.36)
C12 H27 (3Bu)
C15 H12 N3
776
–
355 (exothermic)
463 (exothermic)
776 (exothermic)
4.03
Sublimation
153
180, 291
440
449, 455
80 (endothermic)
285 (endothermic)
452 (exothermic)
469 (exothermic)
33.4
101
−2018.58
−2761.42
37.69 (38.53)
C18 H15 (3Ph)
32.35 (39.02)
C15 H12 N3
100–210
210–521
521–955
207
429
952
185 (exothermic)
446 (exothermic)
792 (endothermic)
−117
−8693
16.1
6.50 (4.63)
59.67 (63.84)
8.32 (10.20)
C2 H6 (2Me)
C28 H22 N4
C2 H2 N2
I
II
25–270
270–700
260
482
262 (exothermic)
486 (exothermic)
667 (exothermic)
–
−14.2
−3115
−58.2
–
17.30 (15.57)
54.22 (56.51)
C8 H18 (2Bu)
C28 H22 N4
8.20 (7.36)
C2 H2 N2
−167
−7086
−260.74
−179.26
22.5
19.84 (19.94)
44.85 (49.70)
17.48 (10.87)
C12 H10 (2Ph)
C26 H16 N4
C4 H8 N2
–
−5807
26.72 (26.72)
61.97 (55.41)
C16 H34 (2Oct)
C30 H24 N6
Step
no.
Temperature
range in TG (◦ C)
Peak temperature
in DTG (◦ C)
Peak temp.
in DTA (◦ C)
Me3 Sn(L) (2)
I
II
III
100–125
125–543
543–692
114, 120
488
–
No sharp peak
490 (exothermic)
681 (exothermic)
n-Bu3 Sn(L) (3)
I
II
90–310
301–510
260
455
III
670–850
I
100–434
II
434–800
Me2 Sn(L)2 (5)
I
II
III
n-Bu2 Sn(L)2 (6)
Compound
Ph3 Sn(L) (4)
III
700–950
–
Ph2 Sn(L)2 (7)
I
II
III
100–325
325–626
626–960
234
444
706
949
258 (exothermic)
447 (exothermic)
663 (exothermic)
704 (exothermic)
789 (endothermic)
n-Oct2 Sn(L)2 (8)
I
II
25–280
280–528
259
486
–
498 (exothermic
Table 6. The main diffraction lines (intensity) for the residue obtained
Tin
compound/
residue of
complex
Sn
a
Main diffraction lines d (Å) (intensity, %) (h k l)
1
2
2.92 (100) 2.79 (90)
(2 0 0)
(1 0 1)
SnOa
3.39 (100) 3.00 (50)
SnO2 a
3.35 (100) 2.64 (80)
(1 1 0)
(1 0 1)
Me3 Sn(L) (2)
3.35 (100) 2.64 (98)
n-Bu3 Sn(L) (3) 3.34 (100) 2.64 (97)
Ph3 Sn(L) (4)
3.34 (100) 2.64 (95)
Me2 Sn(L)2 (5)
3.35 (95) 2.64 (100)
n-Bu2 Sn(L)2 (6) 3.34 (100) 2.64 (95)
Ph2 Sn(L)2 (7)
3.35 (95) 2.64 (100)
a
3
4
5
2.06 (34)
(2 2 0)
2.89 (90)
2.37 (25)
(2 0 0)
2.37 (25)
2.36 (32)
2.36 (25)
2.36 (35)
2.36 (31)
2.37 (25)
2.02 (74)
(2 1 1)
2.67 (90)
1.77 (65)
(2 1 1)
1.77 (90)
1.76 (83)
1.76 (65)
1.76 (81)
1.76 (79)
1.76 (98)
1.48 (23)
(1 1 2)
1.77 (80)
1.68 (18)
(2 2 0)
1.68 (18)
1.67 (23)
1.67 (24)
1.68 (24)
1.67 (24)
1.68 (25)
Reference.[44]
Conclusions
444
Organotin(IV) complexes of Schiff base ligand (Hsal-ambmz) have
been synthesized through the sodium salt method as well as
azeotropical removal of water. The spectral studies of all the
synthesized triorganotin(IV) complexes, except Ph3 SnL, suggest
a cis-trigonal–bipyramidal structure. For Ph3 SnL, an equilibrium
www.interscience.wiley.com/journal/aoc
Enthalpy (mJ
mg−1 )
between distorted cis-trigonal–bipyramidal and octahedral environments around tin has been tentatively proposed in solution,
whereas a distorted cis-octahedral structure has been proposed
for diorganotin(IV) complexes. The anti-inflammatory activity of
the studied complexes revealed that the activity increases upon
complexation and it has been observed that diorganotin(IV)
complexes (19.75–22.23% inhibition) show better activity as
compared with triorganotin(IV) analogs (10.32–17.86% inhibition). The order of their percentage inhibition for diorganotin(IV)
complexes is n-Oct2 SnL2 > n-Bu2 SnL2 > Ph2 SnL2 > Me2 SnL2
and for triorganotin(IV) complexes is Me3 SnL < n-Bu3 SnL<
Ph3 SnL. The thermal decomposition of the studied complexes
yielded SnO2 as end product, which is confirmed by X-ray
diffraction.
Acknowledgments
The authors are thankful to the Head, Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee, India, for providing facilities to carry out (1 H, 13 C and
119
Sn) NMR measurements, thermal studies and X-ray diffraction analysis. The authors are also grateful to Dr Dipankar
Das, for recording and providing 119 Sn Mössbauer spectrum
of one complex. One of the authors (Mr Pramendra Kumar
Saini) is thankful to the Council of Scientific and Industrial
Research, New Delhi, India, for awarding a Senior Research Fellowship.
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 434–445
Tri- and diorganotin(IV) complexes of Schiff base derived from 2-aminomethylbenzimidazole
Scheme 2. Thermal decomposition routes of Me2 Sn(L)2 , Ph2 Sn(L)2 and n-Oct2 Sn(L)2 .
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