Synthesis, Characterization, and Biological Activity of Organotin(IV) Complexes with Schiff Bases

Article abstract of DOI:10.1134/S1070363217120404

The synthesized Schiff base ligands H₂L¹, N,N'-bis(2-hydroxybenzylidene)1,2-diaminobenzene, and H₂L², N,N'-bis(2-hydroxybenzylidene)hydrazine, reacted with Alk₂SnCl₂ to give organotin(IV) complexes 1–10. The products were characterized by elemental analysis, FTIR, ¹H and ¹³C NMR, and mass spectrometry. All organotin(IV) derivatives with [O,N,O] donor ligands retained their 5-coordinated geometry in solid state and solutions. Most of synthesized complexes exhibited significant antibacterial activity. Cytotoxicity was also tested by using the brine shrimp (Artemia salina) lethality bioassay.

Full text of DOI:10.1134/S1070363217120404

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ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 12, pp. 2970–2978. © Pleiades Publishing, Ltd., 2017.
Synthesis, Characterization, and Biological Activity
of Organotin(IV) Complexes with Schiff Bases1
S. Nazneena, S. Alib*, S. Shahzadib,c**, and S. Shujahd
a Department of Chemistry, IMCG (PG), F-7/2, Islamabad, Pakistan
b Department of Chemistry, Quaid-i-Azam University, Islamabad 45320 Pakistan
*e-mail: drsa54@hotmail.com
c Department of Chemistry, University of Sargodha, Lyallpur Campus, Faisalabad, Pakistan
**e-mail: sairashahzadi@hotmail.com
d Department of Chemistry, Kohat University of Science and Technology, Kohat, KPK, 26000 Pakistan
Received October 23, 2017
Abstract―The synthesized Schiff base ligands H2L1, N,N'-bis(2-hydroxybenzylidene)1,2-diaminobenzene,
and H2L2, N,N'-bis(2-hydroxybenzylidene)hydrazine, reacted with Alk2SnCl2 to give organotin(IV) complexes
1–10. The products were characterized by elemental analysis, FTIR, 1H and 13C NMR, and mass spectrometry.
All organotin(IV) derivatives with [O,N,O] donor ligands retained their 5-coordinated geometry in solid state
and solutions. Most of synthesized complexes exhibited significant antibacterial activity. Cytotoxicity was also
tested by using the brine shrimp (Artemia salina) lethality bioassay.
Keywords: Schiff base, organotin(IV), IR, NMR, MS, biological activity
DOI: 10.1134/S1070363217120404
Many organotin compounds of the formula
AlknSnX4–n demonstrate biological activity in which
nature of an alkyl group plays an important role [1, 2].
Activity of those compounds is enhanced by their
coordination with Schiff base ligands [3, 4]. Usually
tin interaction with Schiff base ligands leads to
formation of O–Sn and N–Sn bonds. Such compounds
have some potential as antibacterial and antifungal
agents [5, 6]. In continuation of our previous study on
synthesis of organotin(IV) complexes [7–10], we have
synthesized those with Schiff bases to study the
coordination behavior of the ligand with the Sn(IV)
center. The complexes have been characterized by
Melting points were determined in capillary tubes
on a MPD Mitamura Riken Kogyo (Japan) electro-
thermal melting point apparatus. FT-IR spectra were
recorded (KBr discs) on a Bio-Rad Excaliber FTS
1
Model 3000 MX spectrophotometer. H and 13C NMR
were measured on a Bruker 300 MHz NMR
spectrometer. Elemental analysis was carried out on a
CHNS analyzer 932 LECO, USA.
Synthesis of ligands (general procedure). The
ligands were synthesized according to the developed
earlier methods [12–16] with insignificant modifications.
Synthesis of N,N'-bis(2-hydroxybenzylidene)-
1,2-diaminobenzene (H2L1). A solution of salicyl-
aldehyde (1 mmol, 12.2 g) in 50 mL of ethanol was
slowly added to a solution of o-phenylenediamine
(5 mmol, 5.4 g) dissolved in 50 mL of ethanol. The
reaction mixture was refluxed for 1 h with continuous
stirring. The reaction mixture was cooled down, the
precipitate was filtered off and washed repeatedly by
ethanol and dried in the air (Scheme 1).
1
elemental analysis, IR, H, and 13C NMR and mass
spectra. Antibacterial activity and cytotoxicity of the
complexes was tested.
EXPERIMENTAL
All solvents were obtained from E. Merck
Chemicals (Germany) and BDH (England), and
purified prior to use according to the standard methods
[11]. Most of reagents were purchased from Aldrich
chemicals (USA).
Synthesis of N,N'-bis(2-hydroxybenzylidene)-
hydrazine (H2L2). A solution of hydrazine (5 mmol)
in 50 mL of ethanol was slowly added to a solution of
salicylaldehyde (1 mmol) in 50 mL of ethanol. Stirring
1 The text was submitted by the authors in English.
2970

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SYNTHESIS, CHARACTERIZATION, AND BIOLOGICAL ACTIVITY
2971
Scheme 1.
O
+ 2H2O
CH
N
N
Ethanol
+
2
1 h, reflux
OH HO
OH
H2N
NH2
N,N'-Bis(2-hydroxybenzylidene)-1,2-diaminobenzene
o-Phenylenediammine Salicylaldehyde
H2L1
Scheme 2.
O
C
H
N N
Ethanol
1−2 h, stirring
H2N NH2
Hydrazine
+
2
+ 2H2O
OH
HO
OH
Salicylaldehyde
N,N'-Bis(2-hydroxybenzylidene)hydrazine
H2L2
of the reaction mixture lasted for 1–2 h. The cor-
responding light yellow precipitate was filtered off and
washed repeatedly by distilled water, then with
ethanol, and dried in the air (Scheme 2).
evaporated under reduced pressure. The product
obtained was washed, dried and recrystallized from
chloroform : n-hexane mixture (4 : 1).
R2SnCl2 + H2L + Et3N
Synthesis of organotin(IV) complexes 1–10 (general
procedure). Diorganotin(IV) complexes 1–10 were
prepared by treating the corresponding the ligands with
organotin oxides/hydroxides or chlorides [17].
Toluene
R2SnL1,2 + 2Et3N HCl,
.
6−7 h, reflux
R = Ph, Me.
Procedure 1 [based on organotin(IV) chlorides].
A mixture of a Schiff base H2L1,2 with R2SnCl2 (R =
Me, Ph) and Et3N (ratio 1 : 1 : 2) was refluxed in dry
toluene for 6–7 h. After cooling to room temperature,
Et3N.HCl formed was filtered off and toluene was
Procedure 2 [based on organotin(IV) oxide/
hydroxide]. A mixture of a Schiff base H2L1,2 with
R2SnO (R = Bu, Oct) was refluxed (ratio 1 : 1) in dry
toluene using a Dean-Stark apparatus for 6–7 h with
Table 1. Physical properties of ligands and their organotin(IV) derivatives
Found, %
H
Calculated, %
Comp. no
Formula
Mw
mp, °C
C
N
C
H
N
H2L1
H2L2
C20H16N2O2
C14H12N2O2
316
240
140–142 75.90
215–216 70.04
180–181 57.05
165–166 61.46
110–112 65.51
5.02
8.82
75.94
5.06
5.00
8.86
11.66
5.04 11.62 70.00
1
2
3
4
5
C22H20N2O2Sn
C28H32N2O2Sn
C36H48N2O2Sn
C32H24N2O2Sn
C24H23N2O2ClSn
463
547
659
587
525
4.35
5.89
7.24
6.00
5.15
4.20
4.81
5.37
57.01
61.42
65.55
65.41
54.85
4.31
5.85
7.28
4.08
4.38
6.04
5.11
4.24
4.77
5.33
80–82
65.45 4.04
4.34
240–241 54.81
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 12 2017

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2972
NAZNEEN et al.
Table 2. IR characteristic bands (cm–1) for ligands and their organotin(IV) derivatives
Comp.
no.
ν(O–H)
H-bonded
Comp.
no.
ν(O–H)
H-bonded
ν(C=N) ν(C–O) ν(C=C)
ν(Sn–O) ν(Sn–N)
ν(C=N) ν(C–O)ν(C=C)
ν(Sn–O) ν(Sn–N)
H2L1 1618 1277 1561
H2L2 1624 1267 1574
3419
–
–
5
6
1607 1258 1531
1610 1240 1580
1614 1244 1573
1609 1250 1572
1612 1253 1575
1615 1248 1574
–
–
–
–
–
–
538
565
558
562
548
555
447
461
456
439
450
445
3200
–
–
1
2
3
4
1605 1250 1578
1600 1256 1525
1609 1245 1532
1610 1253 1576
–
–
–
–
540
531
551
546
450
484
463
480
7
8
9
10
Table 3. 1H NMR data for N,N-bis(2-hydroxybenzylidene)-1,2-diaminobenzene and its organotin(IV) derivatives
10
9
8
7
N
N
3
2
1
4
HO
OH
5
6
γ
β
H2
H2
H2
H2
H2
H2
α
δ
δ
β'
β
δ'
CH3
β
α
C
C
C
C
C
C
Sn⎯CH3
γ
α
γ
δ
α
Sn
C
CH3
Sn
C
C
α'
C
γ'
Sn
H2
H2
H2
H2
Proton
H2L1
13.1 s
1
2
3
4
5
OH
2
–
–
–
–
–
7.39 d (3.9)
6.84 t
7.45 d (3.6)
6.64 t
7.33 d (3.5)
6.59 t
7.41 d (3.2)
6.59 t
7.51 d (3.5)
6.50 t
7.26 d (3.8)
6.64 t
3
4
7.23–7.27 m
7.07 d (6.9)
8.64 s
7.41 t
7.36 t
7.36 t
7.49 t
7.9 t
5
7.05 d (7.0)
8.88 s
6.70 d (6.7)
8.73 s
6.77 d (6.5)
8.83 s
6.75 d (6.8)
8.77 s
6.98 d (6.4)
8.89 s
6
7
7.34 d (3.6)
7.23–7.27 m
7.55 d (3.5)
7.25–7.35 m
0.74 s
7.33 d (3.2)
7.37–7.39 m
1.37–1.43 m
1.27 t
7.37 d (3.3)
7.20–7.23 m
1.36–1.40 m
1.21–1.29 m
1.17–1.24 m
1.17–1.24 m
1.17–1.24 m
1.17–1.24 m
1.04–1.06 m
0.83 t
7.39 d (3.4)
7.42–7.46 m
7.24 d (3.1)
6.63–6.69 m
1.77 t
8
9
10
α
7.39 d
1.30–1.32 m
0.79–0.84 m
0.56–0.60 m
1.08–1.15 m
0.64 t
7.25 t
β
7.02–7.13 m
γ
δ
α'
β'
γ'
δ'
26.5
22.7
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SYNTHESIS, CHARACTERIZATION, AND BIOLOGICAL ACTIVITY
Table 4. 1H NMR data for N,N-bis(2-hydroxybenzylidene)hydrazine and its organotin(IV) derivatives
2973
4
3
H
H
C7 N N C7'
2
5
1
6
OH
HO
Proton
H2L2
11.41 s
6
7
8
9
10
OH
3
–
–
–
–
–
7.39–7.41 m
6.99 t (7.2)
7.44–7.48 m
7.05 d (6.5)
8.73 s
7.35–7.44 m
6.96 t
7.36–7.44 m
6.99 t
7.36–7.44 m
6.99 t
7.47–7.5 m
6.99 t
7.36–7.44 m
6.98 t
4
5
7.35–7.44 m
7.05 d (6.8)
7.36–7.44 m
7.05 d (6.2)
8.89 s, 8.70 s
1.38–1.36 m
1.13 t
7.36–7.44 m
7.05 d (6.9)
8.93 s, 8.73 s
1.30–1.62 m
1.30–1.62 m
1.30–1.62 m
1.30–1.62 m
1.30–1.62 m
1.30–1.62 m
1.30–1.62 m
1.30–1.62 m
1.04–1.06 m
0.83 t
7.68–7.7 m
7.02 d (6.7)
8.88 s, 8.71 s
–
7.36–7.44 m
7.05 d (6.3)
8.79 s, 8.72 s
1.82 t
6
7
8.91 s, 8.74 s
0.8 s
9
10
α
7.39 d
1.37–1.49 m
0.90–1.00 m
1.0–0.90 m
0.96–0.92 m
0.96–0.92 m
7.42 t
β
7.47–7.5 m
γ
δ
α'
β'
γ'
δ'
continuous removal of water formed. After cooling to
room temperature, the solvent was evaporated under
reduced pressure. The solid product obtained was air
dried and recrystallized from dry chloroform and
n-hexane mixture (4 : 1).
IR spectra. The characteristic IR absorption bands
for the ligands and their organotin(IV) complexes are
presented in Table 2.
Complexation of tin atom with the ligands was
confirmed by the absence of the broad bands, ν(OH),
at 3419 and 3200 cm-1 [18]. Stretching vibrations of
(C=N) shifted to lower values indicating coordination
of tin to nitrogen of a Schiff base in all complexes
[19]. Appearance of new bands in the range 565–531
and 484–450 cm–1 indicated the presence of Sn–O and
Sn–N stretching vibrations, respectively, confirming
coordination of tin with N and O atoms [20]. Both
ligands bands at 1277 and 1267 cm–1 (C–O) were shifted
towards lower values in the spectra of complexes due
to attachment of tin to oxygen [21]. The shift of C=N
band of complexes to lower frequencies indicated
donation of nitrogen lone pair of electrons of the
azomethine group towards Sn atom [22].
Toluene
R2SnL1,2 + H2O,
R2SnO + H2L1,2
6−7 h, reflux
R = Bu, Oct.
Toluene
BuSnClL1,2 + 2H2O.
BuSn(OH)2Cl + H2L1,2
6−7 h, reflux
RESULTS AND DISCUSSION
Physical data for the ligands H2L1, H2L2 and the
synthesized complexes are presented in Table 1. The
ligands and the complexes were stable compounds
soluble in common organic solvents.
1H NMR spectra. The signals of aromatic protons
of ligands did not show any significant shift for tin
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 12 2017