Synthesis, characterisation and anti-diabetic activities of triorganotin(IV) azo-carboxylates derived from amino benzoic acids and resorcinol: Crystal structure and topological study of a 48 membered macrocyclic-tetrameric trimethyltin(IV) complex

Article abstract of DOI:10.1016/j.ica.2015.10.012

Triorganotin(IV) complexes of azo-carboxylic acids derived from amino benzoic acids and resorcinol were synthesized by the reaction of 2/4-(2,4-dihydroxy-phenylazo)-benzoic acids with appropriate triorganotin(IV) chlorides [R = Me (1 and 3), Ph (2 and 4)

Full text of DOI:10.1016/j.ica.2015.10.012

Accepted Manuscript
Synthesis, characterization and anti-diabetic activities of triorganotin(IV) azo-
carboxylates derived from amino benzoic acids and resorcinol: Crystal structure
and topological study of a 48 membered macrocyclic-tetrameric trimethyl-
tin(IV) complex
Manojit Roy, Subhadip Roy, Keisham Surjit Singh, Janmoni Kalita, S.
Sureshkumar Singh
PII:
S0020-1693(15)00497-1
http://dx.doi.org/10.1016/j.ica.2015.10.012
ICA 16722
DOI:
Reference:
Inorganica Chimica Acta
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Accepted Date:
1 August 2015
23 September 2015
9 October 2015
Please cite this article as: M. Roy, S. Roy, K.S. Singh, J. Kalita, S. Sureshkumar Singh, Synthesis, characterization
and anti-diabetic activities of triorganotin(IV) azo-carboxylates derived from amino benzoic acids and resorcinol:
Crystal structure and topological study of a 48 membered macrocyclic-tetrameric trimethyltin(IV) complex,
Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.10.012
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Synthesis, characterization and anti-diabetic activities of triorganotin(IV) azo-carboxylates
derived from amino benzoic acids and resorcinol: Crystal structure and topological study
of a 48 membered macrocyclic-tetrameric trimethyltin(IV) complex
Manojit Roya, Subhadip Roya, Keisham Surjit Singha,*, Janmoni Kalitab, S. Sureshkumar Singhb
aDepartment of Chemistry, National Institute of Technology Agartala, Jirania, Tripura (west)-
799046, India.
bDepartment of Forestry, North Eastern Regional Institute of Science And Technology, Nirjuli,
Arunachal Pradesh -791009, India.
Abstract
Triorganotin(IV) complexes of azo-carboxylic acids derived from amino benzoic acids and
resorcinol were synthesized by the reaction of 2/4-(2,4-dihydroxy-phenylazo)-benzoic acids
with appropriate triorganotin(IV) chlorides [R= Me (1 and 3), Ph (2 and 4) and Bu (5)] in
presence of triethylamine. The characterization of the complexes was accomplished by elemental
analyses, UV, IR and multinuclear (1H, 13C and 119Sn) NMR spectroscopy. Structure of
compound 3 was established by X-ray crystal structure analysis. X-ray crystal structure of 3
revealed that the compound exhibits a 48 membered macrocyclic-tetrameric structure with
trigonal bipyramidal geometry around the tin atoms in which the three methyl groups occupy the
equatorial positions while the apical positions are being occupied by the oxygen atom of
carboxylate group of one ligand and the phenoxide oxygen atom of another ligand. The
coordination network in 3 has also been analysed from the topological viewpoint. All the
complexes display a sharp singlet 119Sn resonance in the range specified for the four coordinate
structures suggesting that complexes have tetrahedral structures in solution. The five coordinate
structure of the complexes in solid state dissociated into monomeric species with four coordinate
structures in solution. Anti-diabetic activities of the complexes were studied and the results
showed that the compounds 2, 3 and 4 exhibited effective activity even higher than the standard
compound.
Key Words: Azo-carboxylates; triorganotin(IV) complexes; NMR spectroscopy; macrocyclic
tetramer; anti-diabetic activities.
----------------------------------------------------------------------------------------------------------------
*Corresponding author: Tel.: + 913812346630; fax: + 913812346360.
E-mail address: surjitkeisham@yahoo.co.in, singh1971@gmail.com (K. S. Singh).

1. Introduction
Organotin(IV) complexes of carboxylate ligands have been extensively studied because
of their wide range of intriguing structures [1-6] and potential biological activities such as
antitumor, antibacterial, antifungal, cytotoxic, insecticidal, urease inhibition, anti-proliferative
and anti-tuberculosis etc. [5-10]. Organotin(IV) complexes with azo-carboxylates have been also
explored owing to their structural diversity [11-15] and promising biological properties [11-13].
Moreover, organotin(IV) azo-carboxylates derived from amino benzoic acids and
salicylaldehyde have been studied in great details in recent years because of their ability to
exhibit diverse molecular structures [12-15] and larvicidal properties [12-13]. X-ray crystal
structures of tri-n-butyl(IV) complexes with azo-carboxylic acids derived from ortho-amino
benzoic acids exhibited polymeric structures with trans-trigonal bipyramidal geometry around
tin atoms while triphenyltin(IV) complexes showed polymeric or dimeric structures with
distorted trans-trigonal bipyramidal geometry [13-14]. However, triorganotin(IV) complexes
with para-analogues resulted monomeric distorted tetrahedral structures [12]. Recently, we have
also explored structures and antimicrobial activities of triorganotin(IV) complexes [R= methyl,
n-butyl and phenyl] with azo-dicarboxylic acids derived from amino benzoic acids (ortho- and
para-) and salicylic acid [16]. Molecular structure of tri-butyltin(IV) complex with ortho-azo-
carboxylates showed that the complex exhibits polymeric structure in which one of the
carboxylate group in the ligand bonded to tin atoms in bi-dentate bridging mode while the
second carboxylate coordinates to tin atom in mono-dentate fashion. The structure of the
complex is slightly distorted trans-trigonal bipyramidal geometry around tin atoms where
oxygen atoms of carboxylate and hydroxy group bridge the adjacent tin atoms giving rise to a
polymeric structure [16]. The structure of trimethyltin(IV) complex with the same ligand
analogue was also found to be polymeric with trans-trigonal bipyramidal geometry around tin

atoms. However, in this complex both the carboxylate group of the ligand coordinated to the
adjacent tin atoms exclusively in bridging bi-dentate fashion and unlike tributyltin(IV) complex,
the hydroxyl group did not take part in the bonding [16].
On the other hand, diabetes Type 2 (diabetes mellitus) is a metabolic disorder which is
often characterized by hyperglycaemia i.e. blood containing high level of sugar due to insulin
resistance and relatively lack of insulin [17]. Insulin regulates the metabolism of carbohydrates
and fats by promoting the absorption of glucose from the blood to skeletal muscles and fat tissue
and it also inhibits the production of glucose by the liver [18]. Diabetes occurs when the
secretion and activity level of insulin is deteriorated and exogenous insulin is required to treat the
diabetic state [17]. Intestinal α-glucosidase controls postprandial hyperglycaemia by inhibiting
digestion and carbohydrates absorption and it has been reported that by inhibiting α-glucosidase,
diabetes mellitus may be controlled [19]. Triglyceride and postprandial insulin levels can also be
reduced and controlled by α-glucosidase inhibitors [20,21]. In the literature, anti-diabetic
activities of some metal complexes have been reported and have shown effective activities [22-
24]. However, less attention has been paid to the study of anti-diabetic properties of
organotin(IV) complexes even though these class of compounds possess potential biological
properties [5-10].
Therefore, keeping in view the possibility of designing various interesting molecular
structures with potential biological activities that have been exhibited by the organotin(IV) azo-
carboxylates [12-16], we became interested to explore further, the chemistry of organotin(IV)
complexes with azo-carboxylates derived from amino-benzoic acids. Thus, in this present
contribution we have chosen amino benzoic acids and resorcinol for diazo-coupling reaction of
carboxylate ligands and then synthesized a series triorganotin(IV) complexes [R = Me (1 and 3);

Ph (2 and 4) and Bu (5)] using these ligands. The synthesized complexes were fully
characterized by elemental analysis, IR, multinuclear (1H, 13C, 119Sn) NMR spectroscopy.
Structure of a representative trimethyltin(IV) complex 3 was determined by X-ray
crystallography and its topological analysis was also carried out. In addition, we have studied
anti-diabetic activities of the complexes and compared with the standard drug acarbose.
2. Experimental
2.1 Materials and methods
Trimethyltin(IV) choride, Tributyltin(IV) chloride, Triphenyltin(IV) chloride, ortho-
aminobenzoic acid, para-aminobenzoic acid and resorcinol were purchased from Merck as
commercial source and used without further purification. Solvents were purified and dried using
standard procedure. Carbon, hydrogen and nitrogen analyses were performed with a Perkin
Elmer 2400 series II instrument. Electronic spectra for the ligands and compounds were recorded
on UV-1800 Shimadzu spectrophotometer in DMF in the range 200-800 nm while IR spectra
were obtained on Shimadzu FT-IR-8400S spectrophotometer in the range of 4000-400 cm-1
1
13
using KBr discs. The H, C and 119Sn NMR spectra were recorded on a Bruker AMX 400
spectrometer and measured at 400.13, 100.62 and 149.18 MHz respectively. 1H and 13C chemical
shifts were referred to Me4Si set at 0.00 ppm while Me4Sn was employed as external reference
compound for 119Sn chemical shifts set at 0.00 ppm. For anti-diabetic assay, α-glucosidase
(Maltase) (SRL74854), p-nitrophenyl α-D-glucopyranoside (SRL144969) and acarbose (A8980)
were purchased from SRL India and Sigma Aldrich. Na2HPO4, NaH2PO4, Na2CO3, calcium
chloride and other chemicals were of highest purity grade and purchased from Merck, India.
Milli-Q water was used for all the enzymatic assays.

2.2. Synthesis
2.2.1. Synthesis of 2-(2,4-dihydroxy-phenylazo)-benzoic acid (H3L1)
The ligand 2-(2,4-dihydroxy-phenylazo)-benzoic acid (H3L1) was synthesized by
diazotization of amino-benzoic acids and resorcinol following the analogous procedure [16]
described below. To 5.0 g (36.45 mmol) of o- amino benzoic acid, 12 mL conc. HCl and 32 mL
water was added and the mixture was digested on water bath for 1 hour. It was then cooled to
5°C and diazotized with ice cold aqueous NaNO2 solution (2.51 g in 18mL water). A cold
solution of resorcinol (4.03 g, 36.45 mmol) dissolved in 10% NaOH solution (5g, 50 mL) was
added to the cold diazonium salt solution with vigorous stirring at 0 to 2°C. A deep red colour
appeared immediately and the stirring was allowed to continue for an hour. The reaction mixture
was kept overnight in a refrigerator and then kept at room temperature for about 3-4 hours. It was
then acidified with dilute acetic acid to afford red precipitate of the desired product. The
precipitate was filtered, washed thoroughly with water so as to remove excess acetic acid and
water soluble materials, washing was continued till the filtrate became almost neutral and finally
the product was dried on water bath. The solid product was then washed with hexane, dried in
vacuum and recrystallized from methanol to yield the desired crystalline pure ligand (H3L1).
Yield: 75 %; m.p.: 242-245 °C. Anal. Found: C, 60.77; H, 3.83; N, 10.96%. Calc. for
C13H10N2O4: C, 60.46; H, 3.90; N, 10.85%. UV-visible (DMF) λmax(nm): 265, 412. IR (KBr, cm-
1
1): 1681 νasy(COO), 1599, 1486, 1450, 1282 . H NMR (DMSO-d6, 400 MHz) δH: 7.99 [d, 1H,
H-3, J = 7.2 Hz], 7.92 [d, 1H, H-6´, J = 8.4 Hz], 7.69 [m, 2H, H-4 and H-6], 7.53 [t, 1H, H-5, J =
6.8 Hz], 6.57 [d, 1H, H-5´, J = 8.4 Hz], 6.29 [s, 1H, H-3´] ppm; Signals for –OH and –COOH
were not observed due to solvent exchange. 13C NMR (DMSO-d6, 100 MHz) δC: 167.58

[COOH], 164.23 [C-4´], 158.87 [ C-1 and C-2´], 147.78 [C-1´], 134.48 [C-5], 132.90 [C-4],
130.86 [C-3], 128.84 [C-6´], 126.12 [C-6], 115.79 [C-2], 110.70 [C-5´], 103.21 [C-3´] ppm.
2.2.2. Synthesis of 4-(2,4-dihydroxy-phenylazo)-benzoic acid (H3L2)
The above procedure was also followed in case of H3L2 except that p-amino benzoic acid was
used instead of o-amino benzoic acid for the diazo-coupling reaction. Yield: 70%; m.p.: 248-251
°C. Anal. Found: C, 60.71; H, 3.91; N, 10.72%. Calc. for C13H10N2O4: C, 60.46; H, 3.90; N,
10.85%. UV-visible (DMF) λmax(nm): 265, 408. IR (KBr, cm-1): 1686 νasy(COO); 1603, 1506,
1
1456, 1426, 1287. H NMR (DMSO-d6, 400 MHz) δH: 8.10 [d, 2H, H-3 and H-5, J = 7.2 Hz],
7.94 [d, 2H, H-2 and H-6, J = 7.2 Hz], 7.71 [d, 1H, H-6ʹ, J = 8.4 Hz], 6.53 [d, 1H, H-5´, J = 8.4
13
Hz], 6.39 [s, 1H, H-3´] ppm. C NMR (DMSO-d6, 100 MHz) δC: 166.75[COOH], 163.95 [C-
4´], 157.44 [C-1], 153.21 [C-2´], 132.73 [C-4], 131.25 [C-1´], 130.53 [C-3 and C-5], 129.53 [C-
6´], 121.50 [C-2 and C-6], 109.65 [C-5´], 102.97 [C-3´] ppm. The numbering scheme and ligand
skeleton are shown in Scheme 1.
<Scheme 1>
2.2.3. Synthesis of Me3SnH2L1 (1)
2-(2,4-dihydroxy-phenylazo)-benzoic acid (0.5g, 1.93mmol) was dissolved in 50 mL
anhydrous methanol and triethylamine (0.19g, 1.93 mmol) was added. The reaction mixture was
then refluxed for 2 hours. To this mixture, trimethyltin(IV) chloride (0.38 g, 1.93 mmol) was
added as solid with continuous stirring and then again refluxed for 5 hours. The precipitate
containing Et3NHCl was filtered off and the filtrate was evaporated using rotary evaporator. The
solid product was washed with hexane and recrystallized from chloroform which afforded red

crystalline compound. Yield: 50 %; m.p.: 96-100 °C. Anal. Found: C, 45.87; H, 4.39; N, 6.72%.
Calc. for C16H18N2O4Sn: C, 45.64; H, 4.31; N, 6.65%. UV-visible (DMF) λmax(nm): 265, 412,
479. IR (KBr, cm-1): 1621 νasy(COO); 1340 νsym(COO), 1591, 1483, 1442, 1133, 668 ν(Sn-C),
523 ν(Sn-O).1H NMR (CDCl3, 400 MHz) δH, Ligand skeleton: 13.14 [s, 1H, OH], 8.32 [ d, 1H,
H-3, J= 8.4 Hz] 8.05-7.99 [m, 3H, H-6´, H-4 and H-6], 7.89-7.85 [m, 3H, H-5, H-5´ and H-3´];
Sn-CH3 skeleton: 0.69 [s, 9H, (Sn-CH3)] ppm. 13C NMR (CDCl3, 100 MHz) δC, Ligand skeleton:
168.78 [COO], 164.56 [C-4´], 158.76 [ C-1 and C-2´], 147.01 [C-1´], 134.99 [C-5], 133.60 [C-
4], 131.20 [C-3], 129.04 [C-6´], 126.29 [C-6], 116.21 [C-2], 110.89 [C-5´], 103.52 [C-3´];Sn-
CH3 skeleton: -1.84 [Sn-CH3] ppm.119Sn NMR (CDCl3, 149 MHz): 69.8 ppm. Other triorganotin
(IV) complexes were synthesized by reacting appropriate triorganotin(IV) chlorides and ligands
following the analogous procedure described above.
2.2.4. Synthesis of Ph3SnH2L1 (2)
Yield: 46%; m.p.: 118-120 °C. Anal. Found: C, 61.46; H, 3.91; N, 4.69%. Calc. for
C31H24N2O4Sn: C, 61.31; H, 3.98; N, 4.61%. UV-visible (DMF) λmax(nm): 265, 408, 489. IR
(KBr, cm-1): 1618 νasy(OCO); 1479, 1451, 1427,692 ν(Sn-C), 485ν(Sn-O).1H NMR (CDCl3, 400
MHz) δH, Ligand skeleton: 7.76-7.41 [m, 7H, Ar-H]; Sn-Ph skeleton: 7.67 [m, 6H, H-2*], 7.46
[m, 9H, H-3* and H-4*] ppm.13C NMR (CDCl3, 100 MHz) δC, Ligand skeleton: 170.78 [COO],
164.43 [C-4´], 158.92 [ C-1 and C-2´], 147.80 [C-1´], 135.93 [C-5], 132.97 [C-4], 130.95 [C-3],
128.96 [C-6´], 126.90 [C-6], 115.81 [C-2], 110.78 [C-5´], 103.28 [C-3´]; Sn-Ph skeleton: 137.27
[C-1*], 136.41 [C-2*], 130.50 [C-4*], 128.87 [C-3*] ppm. 119Sn NMR (CDCl3, 149 MHz): - 46.5
ppm.

2.2.5. Synthesis of Me3SnH2L2 (3)
Yield: 56 %; m.p.: 206-209 °C. Anal. Found: C, 45.39; H, 4.37; N, 6.58%. Calc. for
C16H18N2O4Sn: C, 45.64; H, 4.31; N, 6.65%. UV-visible (DMF) λmax(nm): 265, 408, 497. IR
(KBr, cm-1): 1631νasy(COO); 1361 νsym(COO), 1599, 1523, 1502, 1454, 1228, 665 ν(Sn-C), 513
ν(Sn-O).1H NMR (CDCl3, 400 MHz) δH, Ligand skeleton: 13.88 [s, 1H, OH], 8.22 [m, 2H, H-3
and H-5], 7.86-7.79 [m, 3H, H-2, H-6 and H-6´], 6.59 [m, 1H, H-5´], 6.45 [d, 1H, H-3´, J = 2.0
2
13
Hz]; Sn-CH3 skeleton: 0.71 [s, 9H, (Sn-CH3)] J [119Sn-H (58 Hz)] ppm. C NMR (CDCl3, 100
MHz) δC, Ligand skeleton: 174.54 [COO], 164.01 [C-4´], 157.47 [C-1], 152.60 [C-2´], 132.76
[C-3 and C-5], 131.32 [C-4], 130.51 [C-1´], 129.63 [C-6´], 121.57 [C-2 and C-6], 109.74 [C-5´],
102.31 [C-3´]; Sn–CH3 skeleton: -2.76 [Sn-CH3].119Sn NMR (CDCl3,149 MHz): 69.5 ppm
2.2. 6. Synthesis of Ph3SnH2L2 (4)
Yield: 52%; m.p.: 94-96 °C. Anal. Found: C, 61.49; H, 3.89; N, 4.78%. Calc. for C31H24N2O4Sn:
C, 61.31; H, 3.98; N, 4.61%. UV-visible (DMF) λmax(nm): 238, 408, 495. IR (KBr, cm-1): 1635
1
νasy(COO); 1597, 1475, 1418, 685 ν(Sn-C), 575ν(Sn-O). H NMR (CDCl3, 400 MHz) δH,
Ligand skeleton: 7.81[m, 2H, H-3 and H-5] 7.45-7.65 [m, 5H,H-2 and H-6; H-3ʹ, H-5ʹ and H-
6ʹ]; Sn-Ph skeleton: 7.73 [m, 6H, H-2*], 7.46 [m, 9H, H-3* and H-4*] ppm.13C NMR (CDCl3,
100 MHz) δC, Ligand skeleton: 173.24 [COO], 164.04 [C-4´], 157.82 [C-1], 154.10 [C-2´],
131.75 [C-4], 131.27 [C-1´], 129.56 [C-6´], 129.05 [C-3 and C-5], 119.72 [C-2 and C-6], 111.34
[C-5´], 103.01 [C-3´]; Sn-Ph skeleton: 137.88 [C-1*], 136.44 [C-2*], 130.32 [C-4*], 128.74 [C-
3*] ppm.119Sn NMR (CDCl3, 149 MHz): - 44.5 ppm.
2.2.7. Synthesis of Bu3SnH2L2 (5)

Yield: 58%; m.p.: 133-138 °C. Anal. Found: C, 55.27; H, 6.50; N, 5.26%. Calc. for
C25H36N2O4Sn: C, 54.86; H, 6.63; N, 5.12%. UV-visible (DMF) λmax(nm): 239, 411,497. IR
(KBr, cm-1): 1635 νasy(COO); 1392νsym(COO), 1537, 1418, 659ν(Sn-C), 530 ν(Sn-O). 1H NMR
(CDCl3, 400 MHz) δH, Ligand skeleton: 8.17 [d, 2H, H-3 and H-5, J = 7.6 Hz], 7.63 [m, 1H, H-
6´], 7.76 [d, 2H, H-2 and H-6, J =8.4 Hz], 6.55 [d, 1H, H-5´, J = 10.4 Hz], 6.31 [s, 1H, H-3´];
Sn-nBu skeleton: 1.69 [m, 6H, H-1*], 1.37 [m, 12H, H-2* and H-3*], 0.94 [t, 9H, H-4*] ppm.
13C NMR (CDCl3, 100 MHz) δC, Ligand skeleton: 173.93 [COO], 164.12 [C-4´], 157.96 [C-1],
154.02 [C-2´], 133.97 [C-3 and C-5], 132.49 [C-4], 131.29 [C-1´], 129.56 [C-6´], 119.92 [C-2
and C-6], 114.04 [C-5´], 103.98 [C-3´]; Sn-nBu skeleton: 29.68 [C-2*], 27.82 [C-3*], 17.85[C-
1*], 13.69 [C-4*] ppm.119Sn NMR (CDCl3, 149 MHz): 114.8 ppm. The numbering scheme for
Sn-Bu and Sn-Ph in the complexes is given below:
Sn
1*
2*
3*
*4CH3-*3CH2-*2CH2-*1CH2-Sn
4*
2.3. X-ray crystallography and Topological analysis
For complex 3, data collection was made using Bruker SMART APEX II CCD area
detector area detector equipped with graphite monochromatedMo Kαradiation (λ = 0.71073 Å)
at 293(2) K. The unit cell parameters were calculated and refined from the full data set. Crystal
cell refinement and data reduction were carried out using Bruker SAINT [25]. The absorption
correction was applied using SADABS [26]. The structure was solved with SIR-92 [27] and
refined with the full-matrix least-squares procedure on F2 by SHELXL-97 [28]. All non-
hydrogen atoms were refined anisotropically. Hydrogen positions were calculated geometrically

and refined using the riding model. The crystallographic data and structure refinement parameter
for compound 3 is given in Table 1.
<Table 1>
Topological analysis was performed with the ToposPro program package and the TTD
collection of periodic network topologies [29]. The RCSR three-letter codes [30] were used to
designate the network topologies. Those nets that are absent in the RCSR are designated with the
TOPOS NDn nomenclature [31], where N is a sequence of coordination numbers of all non-
equivalent nodes of the net, D is periodicity of the net (D= M, C, L, T for 0-,1-, 2-, 3-periodic
nets), and n is the ordinal number of the net in the set of all non-isomorphic nets with the given
ND sequence.
2.4. Anti-diabetic activity
Anti-diabetic properties of the compounds 1-5 were screened by α-glucosidase inhibitory
assay and performed according to Kumar et al. [32]. In brief, 25 µL of sample solution in ethanol
(1 mg/mL) and 25 µL of the enzyme were added in the well and the solution was mixed gently
and incubated at 37oC±1oC for 10 min. Then, 25 µL of the substrate (p-nitrophenyl α-D
glucopyranoside in 0.5 mM concentration in the buffer, pH 6.8) was added in the mixture and
incubated again at 37o C for 30 min. The reaction was terminated by adding 100 µL of 0.2M
sodium carbonate solution. Amount of p-nitrophenol released from the substrate was quantified
on a UV-Vis spectrophotometer at 405 nm (Multiskan™ GO Spectrophotometer, Thermo-Fisher,
Finland). Inhibition concentration (IC50) of enzyme activity was also calculated by following the
same enzyme assay. A gradient concentration of 33.3, 66.6 and 99.9 µg/mL was used for each of
the synthesized compounds analyzed along with the drug, acarbose as the standard inhibitor of α-

glucosidase (positive control). Appropriate controls were used for each sample and all the
analysis were done in triplicate. Percentage enzyme inhibition was calculated by using the
following formula: Enzyme inhibition (%): [Control OD-Sample OD/Control OD] x100;
[Where, Sample OD = (Sample OD- Sample Blank OD) and Control OD= (OD of the control
reaction without inhibitor-blank OD)]
3. Results and discussion
3.1. Synthesis
Triorganotin (IV) complexes, 1-5 were synthesized by reacting 2-(2,4-dihydroxy-
phenylazo)-benzoic acid (H3L1) for compounds [1 and 2] or 4-(2,4-dihydroxy-phenylazo)-
benzoic acid (H3L2) for compounds [3-5] with appropriate triorganotin(IV) chorides [R= Me (1
and 3), Ph (2 and 4) and Bu (5)] in presence of triethlylamine in methanol. The reaction scheme
for the synthesis of complex 1 as one of the representative complex is shown in Scheme 2 along
with the line diagram of the structure. Reaction produces moderate to good yield and complexes
are soluble in all common organic solvents.
<Scheme 2>
3.2. X-ray crystal structure description and topological study of compound 3
The free azo-carboxylic acid ligand contains two hydroxyl groups (2, 4 disposition).
Upon complexation, the hydroxyl group at 2-position loses its proton, so the phenoxide O-atom
acquires negative charge and the imino N-atom becomes protonated, leading to a zwitterionic
ligand. In related systems, existence of such zwitterionic form is a common occurrence [33-37].
The zwitterionic azo-carboxylate ligand bridges the Sn-atoms via a carboxylate O-atom and the
phenoxide O-atom. The molecular structure and packing diagram of complex 3 is shown in Fig.

1 and 2; selected bond lengths and bond angles are listed in Table 2. In the molecular structure
of complex 1, Me3Sn and the ligand alternately link into a cyclotetrameric 48 membered
Sn4C28O8N8 ring. Each tin atom is trigonal bipyramidal (3C, 2O) with two oxygen atoms from
the two ligands occupying the axial positions and the equatorial positions occupied by the methyl
groups. The tin oxygen distances are in the range 2.095(2)–2.790(4) Å. The distances of
Sn(1)...O(7)1 and O(7)...Sn(1)1 [1:12-x,1-y, 2-z], 2.790(4) Å, is greater than the sum of the
covalent radii of Sn and O (2.56 Å), but is considerably less than the sum of the van der Waals
radii (3.68 Å) and are considered as part of the primary coordination environment. Sn⋯O
interactions in the range 3.274 (4) to 3.420 (3) Å [Sn(1)⋯O(2) and Sn(2)⋯O(6)], although, are
well inside of the sum of the van der Waals radii of the Sn and O atoms, these Sn...O distances
are too long to be considered bonding.
<Fig. 1>
<Fig. 2>
<Table 2>
The width of the cavity of the macrocyclic derivative can be evaluated by the
transannular Sn...Sn distances, which is 16.81 x 15.27 Å2. Analogous triorganotin(IV) tetrameric
macrocycles have been found in triphenyltin[((E)-1-{2-hydroxy-5-[(E)-2-phenyl-1-
diazenyl]phenyl}methylidene)-amino]acetate [36], tributyltin(IV) 2,6-difluorobenzoate [38] and
tributyltin(IV) (Z)-3-(4-nitrophenyl)-2-phenyl-2-propenoate [39]. Both intramolecular and
intermolecular hydrogen bonds are foreseen in the structure. The N+–H group is involved in
intramolecular hydrogen bonding with the phenoxide O-atom. Intermolecular O–H...O hydrogen
bond between two adjacent hydroxyl/carboxylate groups also occurs.

To provide further insight into the H-bonding and coordination network, we have
performed topological analysis. In compound 3, in addition to intramolecular H-bonding
interactions that occur within a molecule, each molecule is engaged in eight intermolecular
hydrogen bonds which connect four neighbouring molecules, resulting in a layer structure. The
H-bonded layer structure can be topologically classified as sql (Figs. 3, 4), the most frequent
underlying topology observed for H-bonded layers (see Supporting Information for further
details). The layers stack along [100] as (AB) (Fig. 5).
<Fig. 3>
<Fig. 4>
<Fig. 5>
A more detailed topological description where Sn atoms are considered as the nodes of
the underlying net while both coordination and hydrogen bonds are taken into account leads to a
2-periodic three-dimensional 63Ia topology (also known as sphere-packing graph for layer
groups) [40] (Fig. 6, 7). We have found 41 molecular structures with the same 63Ia topology in
the standard representation (in the Supporting Information) [41].
<Fig. 6>
<Fig. 7>
3.3. Spectroscopic characterization
3.3.1. UV-visible spectroscopy
The electronic spectra for compounds 1–5 were recorded in DMF solution (10–4 M) at room
temperature. The electronic spectra of the ligands H3L1and H3L2 show UV absorptions near 265
nm as a result of π→π* of the aromatic ring [42]. UV-Visible spectra of the compounds 1-5

exhibited three absorption bands near 265-275, 408-412 and 475-497 nm, respectively. The new
band observed at 475-479 nm indicates ligand to metal charge transfer [43].
3.3.2. IR spectroscopy
IR spectroscopy is a useful tool to ascertain the mode of coordination of the ligands to the metal
atom in complexes in solid state. In the complexes 1-5, the IR absorption bands for -COO-
stretching frequencies were observed at lower frequencies as compared to the corresponding
ligands indicating the carboxylate coordination of the ligand to the tin atom [13]. The
asymmetric [νasym(OCO)] stretching vibration for the free ligands were detected near 1681 cm-1;
in the complexes, these bands were observed at 1618-1635 cm-1. The value of ∆ν [νasy(OCO) -
νsym(OCO)] also provides useful information to determine the mode of coordination of
carboxylate to tin(IV) atom in organotin(IV) complexes [44]. In general, ∆ν below 200 cm-1
indicates bi-dentate mode and greater than 200 cm-1 is the indication of the mono-dentate mode
of coordination of the carboxylate ligands to the tin in the complexes [16,44]. In case of the
triphenyltin(IV) complexes 2 and 4, IR absorption band for νsym(OCO) could not be assigned due
to the complex pattern of the spectra. The magnitude of ∆ν [∆ν =νasy(OCO) - νsym(OCO)] for the
complexes 1 and 3 were found to be in the range 270-278 cm-1 indicating mono-dentate mode of
coordination of the carboxylate ligands in these complexes [45]. Strong bands observed at 650-
690 cm-1 and 485-575 cm-1 in all the complexes may be assigned to ν(Sn-C-Sn) and ν(Sn-O-Sn)
mode of vibration [42].
3.3.3 Multinuclear (1H, 13C and 119Sn) NMR spectroscopy

1
13
The H, C and 119Sn NMR spectral data of the complexes 1-5 were recorded in CDCl3
and the data are given in the experimental section and spectra for few representative complexes
have been provided in the Supporting Information. The complete assignment of the ligands was
achieved by examining their chemical shift values, integration values and multiplicity patterns
and also by careful comparison of proton NMR data with the similar type of azo-ligands derived
from either amino benzoic acid or resorcinol reported earlier [13,46]. In case of the complexes,
assignments of the chemical shifts of the protons was done by extrapolating the conclusions
drawn from the ligand assignments to the spectra of the corresponding complexes owing to the
similarity of the spectra. In complex 1 and 3, the singlet peaks appeared at 0.69 and 0.71 ppm are
assigned to methyl tin protons. In case of the triphenyl tin(IV) complexes 2 and 4, the two
distinct multiplicities due to phenyl tin protons were observed at around 7.41-7.69 ppm while
three multiplets appeared in compound 5 in the range 0.93 to 1.69 ppm are assigned to butyl tin
2
protons. J (119Sn-H) coupling constant value for complex 3 was found to be 58 Hz which is in
consistent with four coordinate structure [37,47]. Further, the angle between C-Sn-C in 3 was
also calculated using Lockhart and Mander’s equation [48]{θ(C-Sn-C) = 0.0161 |2J(Sn-H)|2 -1.32
|2J(Sn-H)| + 133.4} and the angle was found to be 111.3° thereby supporting 4-coordinate
tetrahedral geometry around tin atom in solution [45]. In 13C NMR spectra of all the complexes,
the δ(COO) signals were found to be shifted to the downfield region (174.5-168.7 ppm) as
compared to the free acid ligands (167.5-166.7 ppm) indicating that the carboxylate anions are
13
coordinated to tin atom [16,47]. In all complexes, the expected C signals were able to detect
and the number of carbon signals are completely in consistent with the formulation of expected
products. All the complexes were subjected to 119Sn NMR study to determine geometry around
tin atom. The complexes displayed a sharp singlet 119Sn resonance peak near + 69.8 and + 69.5

ppm for 1 and 3; - 46.5 and - 44.5 ppm for 2 and 4 while +115 ppm was observed for 5. 119Sn
resonances of the complexes 1-5 suggest four coordinate tetrahedral structures in solution state
[47,49-51]. From the above discussion it is evident that the five coordinate structures of the
complexes in solid state are dissociated into four coordinate structures in solution state.
3.4. Anti-diabetic activities
The screening of the anti-diabetic activities of the synthetic complexes and ligands using
α-glucosidase enzyme revealed that compounds 2, 3 and 4 have shown significant results by
inhibition of more than 50% of α-glucosidase activity. These compounds were further analysed
for calculation of IC50 as compared to the standard drug, acarbose. The ligands and other
compounds 1 and 5 have shown lower activities than the standard drugs in the preliminary
screening, so we have determined IC50 values for only those complexes which showed
significant activities. The pictorial representation in terms of percentage of enzyme activity
inhibition and IC50 (µg/mL) values for the complexes 2, 3 and 4 along with the standard
compound acarbose are given in Fig. 8 and Table 3 respectively. As can be seen from the
diagram, with the change in concentration from 33.33µg/mL, to 66.66 and 99.99 µg/mL, the
activity for compounds 2 and 3 increased while for the standard drug acarbose the activity was
found to be almost same.From the table, it is also clear that compound 2showed lowest IC50
values at 6.43 µg/mL followed by compound 3 and 4 at 9.70 and 11.19 µg/mL respectively
against the standard compound, acarbose with IC50 value at 12.15 µg/mL. This promising result
of the test is important finding for consideration of in-vivo test in near future. These compounds
could be better candidate for anti-diabetic studies provided the complexes show permissible
toxicities level and increased solubility in water.

<Fig. 8>
<Table 3>
4. Conclusions
A new series of triorganitin(IV) complexes with azo-caboxylic acids derived from amino
benzoic acids and resorcinol were synthesized and complete characterization of the complexes
were accomplished by elemental analysis, UV, IR and multinuclear NMR spectroscopy. IR
spectral study indicates the presence of mono-dentate mode of coordination of carboxylate
ligands in trimethyl and tri-n-butyltin(IV) complexes. Complexes display a single sharp 119Sn
NMR resonance in the range specified for the four coordinate structures thus suggesting that
complexes have four coordinate tetrahedral geometry around tin atoms in solution. Molecular
structure of trimethyltin(IV) complex 3 was determined by X-ray crystallography. Crystal
structure of the complex reveals a 48 membered macrocyclic tetrameric structure in which tin
atoms show trans-trigonal bipramidal geometry with the three methyl groups occupying the
equatorial plane while the apical positions are being occupied by the oxygen atom of carboxylate
and phenoxide oxygen atom of another ligand. The complex also exhibits zwitterionic form
where a hydrogen atom of one of the hydroxyl groups is shifted to the nearby nitrogen atom of
the azo-group. In 3, H-bonding results in a layer structure with sql topology. A more detailed
analysis reveals an overall 2-periodic three-dimensional 63Ia topology. Anti-diabetic activities of
the complexes were also studied on α-glucosidase enzyme and showed better results than the
standard drug acarbose. Since the compounds exhibited effective anti-diabetic activity than the
standard compound, these compounds could be further studied to explore the possibility of anti-

diabetic therapeutic uses. This promising result will also open a new avenue to the researcher to
investigate organotin (IV) azo-carboxylates for their anti-diabetic activities.
Acknowledgements
Authors thank to SAIF, IIT Madras for providing X-ray crystal data for compound 3 and IISc,
Bangalore for NMR spectra.
Supplementary materials
CCDC 1415981 contains the supplementary crystallographic data for complex 3. These data can
be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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3'
HO
O
HO
N
OH
2'
4'
5'
1'
2
N
1
3
4
6'
6
5
2-(2,4-dihydroxy-phenylazo)-benzoic acid (H3L1)
3'
HO
OH
2'
4'
1'
2
5
N
1
5'
3
N
6'
HO
6
O
4-(2,4-dihydroxy-phenylazo)-benzoic acid (H3L2)
Scheme 1. Ligand skeleton and numbering scheme for H3L1 and H3L2.

OH
HO
N
H
O
O
Sn
O
_
+
N
N
+
HO
O
N
_
O
H
Sn
O
O
Et3N,Me3SnCl
N
Methanol
N
O
O
Reflux, 7 hrs
OH
Sn
O
_
+
O
N
H
+
H
OH
N
N
_
OH
N
O
Sn O
OH
Scheme 2. Reaction scheme for the synthesis of macro-cyclic tetrameric trimethyltin(IV)
complex 3.

Table 1. Crystallographic and structure refinement data for compound 3.
Empirical formula
C64H72N8O16Sn4
Formula weight
1684.06
Temperature/K
293(2)
Crystal system
Triclinic
Space group
P-1
a/Å
9.852(5)
b/Å
13.975(5)
c/Å
14.530(5)
α/°
110.354(5)
β/°
107.778(5)
γ/°
98.906(5)
Volume/Å3
1708.0(12)
Z
1
ρcalcg/cm3
1.637
µ/mm-1
1.516
F(000)
840
Crystal size/mm3
0.30 x 0.20 x 0.20
MoKα (λ = 0.71073)
1.63 to 26.00
Radiation
Theta range for data collection/°
Index ranges
-12 ≤ h ≤ 12, -17 ≤ k ≤ 17, -17 ≤ l ≤ 17
35400
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
Largest diff. peak/hole / e Å-3
6714 [Rint = 0.0266]
6714/1/ 429
1.114
R1 = 0.0268, wR2 = 0.0660
R1 = 0.0369, wR2 = 0.0752
0.845 and -0.592

Table 2. Selected bond distances and angles of compound 3.
Atom Atom Length/Å
C(1) Sn(1) 2.110(4)
C(2) Sn(1) 2.107(4)
C(3) O(2) 1.219(4)
C(4) Sn(1) 2.095(4)
C(12) O(3) 1.289(3)
C(14) O(4) 1.322(4)
N(3) N(4) 1.287(4)
Sn(1) O(7)1 2.790(4)
O(3) Sn(2) 2.364(2)
O(5) Sn(2) 2.149(2)
12-x,1-y,2-z
Atom Atom Length/Å
C(20) O(6) 1.227(4)
C(20) O(5) 1.271(4)
C(3) O(1) 1.280(4)
C(28) O(7) 1.290(4)
C(30) O(8) 1.336(4)
N(1) N(2) 1.298(3)
O(1) Sn(1) 2.095(2)
C(17) Sn(2) 2.109(3)
C(18) Sn(2) 2.109(4)
C(19) Sn(2) 2.108(3)
Atom Atom Atom Angle/°
O(1) Sn(1) C(2) 98.37(15)
C(2) Sn(1) C(1) 116.7(2)
C(4) Sn(1) C(2) 119.40(18)
C(17) Sn(2) O(3) 83.71(11)
C(18) Sn(2) C(17) 114.86(16)
C(19) Sn(2) C(17) 119.08(15)
C(18) Sn(2) O(5) 95.00(13)
O(5) Sn(2) O(3) 173.61(8)
12-x,1-y,2-z
Atom Atom Atom Angle/°
O(1) Sn(1) C(1) 92.52(13)
C(4) Sn(1) C(1) 118.49(18)
O(1) Sn(1) O(7)1 177.96(10)
C(18) Sn(2) O(3) 88.75(12)
C(19) Sn(2) C(18) 125.52(15)
C(17) Sn(2) O(5) 90.01(12)
C(19) Sn(2) O(5) 92.14(13)
O(2) C(3) O(1) 125.1(3)

Table 3. IC50 values for triorganotin(IV) complexes 2, 3, 4 and standard drug acarbose.
Sl. No.
Complexes/reference IC50 value (µg/mL)
SD
1
2
3
4
Ph3SnH2L1 (2)
Me3SnH2L1 (3)
Ph3SnH2L2 (4)
Acarbose
6.43
3.12
1.18
2.70
1.94
9.70
11.19
12.15

Fig. 1. Molecular structure of compound 3 showing trigonal bipyramidal geometry around tin
atoms in the tetrameric macrocycle (50% probability ellipsoids).
Fig. 2. Packing diagram of complex 3.

Fig. 3. Underlying net 2-periodic sql in the standard representation.
Fig. 4. Underlying net sql in the standard representation merged with initial molecular network.

Fig. 5. Stacking (AB) of the H-bonded layers. Layers A and B are differently highlighted.
Fig. 6. Underlying net 2-periodic 63Ia in the standard representation (left); Ideal net 2-periodic
63Ia (right).