Dimeric and monomeric six-coordinate tin(IV) complexes: Synthesis and spectral (IR, NMR (1H, 13C, 119Sn), TOF-MS, and ESI-MS) studies

Article abstract of DOI:10.1080/00958972.2013.800975

Six-coordinate dimeric tin(IV) complexes, [(μ-Cl)2Sn2(?2-sb)2Cl4] {where sb = salicylidene-2- methyl-1-aminobenzene (o-smabH) (1), salicylidene-4- methyl-1-aminobenzene (p-smabH) (2), and salicylidene-2-aminopyridine (sapH) (3)}, have been synthesized by

Full text of DOI:10.1080/00958972.2013.800975

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Dimeric and monomeric six-coordinate
tin(IV) complexes: synthesis and
spectral (IR, NMR (1H, 13C, 119Sn), TOF-
MS, and ESI-MS) studies
Raj Kumar Dubey a & Avadhesh Pratap Singh a
a Synthetic Inorganic and Metallo-organic Research Laboratory,
Department of Chemistry , University of Allahabad , Allahabad ,
India
Published online: 04 Jun 2013.
To cite this article: Raj Kumar Dubey & Avadhesh Pratap Singh (2013) Dimeric and monomeric six-
coordinate tin(IV) complexes: synthesis and spectral (IR, NMR (1H, 13C, 119Sn), TOF-MS, and ESI-MS)
studies, Journal of Coordination Chemistry, 66:12, 2201-2207, DOI: 10.1080/00958972.2013.800975
To link to this article: http://dx.doi.org/10.1080/00958972.2013.800975
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 12, 2201–2207, http://dx.doi.org/10.1080/00958972.2013.800975
Dimeric and monomeric six-coordinate tin(IV) complexes:
synthesis and spectral (IR, NMR (1H, C, 119Sn), TOF-MS,
13
and ESI-MS) studies
RAJ KUMAR DUBEY* and AVADHESH PRATAP SINGH
Synthetic Inorganic and Metallo-organic Research Laboratory, Department of Chemistry,
University of Allahabad, Allahabad, India
(Received 16 July 2012; in final form 8 March 2013)
Six-coordinate dimeric tin(IV) complexes, [(μ-Cl)2Sn2(η2-sb)2Cl4] {where sb = salicylidene-2-
methyl-1-aminobenzene (o-smabH) (1), salicylidene-4-methyl-1-aminobenzene (p-smabH) (2), and
salicylidene-2-aminopyridine (sapH) (3)}, have been synthesized by interactions of tin(IV) chloride
with the appropriate sodium salt of Schiff bases in 1 : 1 M ratio in isopropanol-benzene. These com-
plexes have been characterized by elemental (C, H, N, and Sn) and spectral [IR, NMR (1H, 13C,
119Sn), TOF-MS, and ESI-MS] studies. Complexes 1–3 on treatment with an excess of THF afford
mononuclear six-coordinate tin(IV) complexes, [(sb)SnCl3·THF], 4–6. The biological activities (e.g.
antimicrobial action) of the synthesized Schiff bases and 1–3 were assessed by in vitro testing on
the growth of various strains of bacteria and fungi.
Keywords: Synthesis; Sn(IV) complexes; IR; NMR; MS spectra
1. Introduction
The chemistry of tetravalent metal(loid) complexes derived from N-arylsalicylaldimine
ligands [1, 2] remains of interest from synthetic, physicochemical, and structural points of
view. Our research group has been involved for synthesis and characterization of new
chloro-bridged dimeric and monomeric complexes of Schiff bases with different metals
[3–8]. No such chloro-bridged [Sn(μ-Cl)2Sn] complexes of tin(IV) have been reported
[9–11]. The present investigation assumes additional importance due to established toxico-
logical, biochemical, agricultural, and industrial applications [12–16] of tin(IV) com-
pounds. As part of our continued interest in tin(IV) and organotin(IV) complexes derived
from Schiff base ligands [17–20], we describe herein the synthesis and spectral [IR (1H,
13C, 119Sn) NMR, TOF-MS, and ESI-MS] studies of dimeric [(μ-Cl)2Sn2(η2-sb)2Cl4] (1–3)
and monomeric [(sb)SnCl3·THF] (4–6) complexes of tin(IV).
2. Experimental
All chemicals and reagents used were of analytical grade. Tin tetrachloride was distilled
prior to use. Salicylaldehyde (Loba), 2-aminopyridine (Merck), o-toludine (BDH), and p-
*Corresponding author. Emails: rajalkoxy@yahoo.com, rajalkoxyau@gmail.com
Ó 2013 Taylor & Francis

2202
R.K. Dubey and A.P. Singh
toludine (Merck) were purified by distillation. Solvents were dried prior to use according
to literature procedures [21]. Elemental (C, H and N) analyses were performed on a Harae-
us Carlo Erba 1108 elemental analyzer. Tin was estimated gravimetrically as SnO2 after
decomposition of complexes with concentrated HNO3. Chlorine was estimated volumetri-
cally by using the Volhard method [22]. Infrared spectra (4000–400 cmÀ1) were recorded
on a Perkin Elmer 100 FT-IR spectrophotometer and Nicole Instrument MAGMA 550 was
used to record spectra from 600 to 50 cmÀ1. NMR (1H, 13C, and 119Sn) spectra were
recorded in a mixture of DMSO-d6 and CDCl3 on a Bruker DRX-300 spectrometer.
Chemical shifts are given in ppm relative to Me4Si (1H, 13C) and Me4Sn (119Sn). Mass
spectra were recorded on WATERS TOF MS/MS and Agilent 6520 Q-Tof LCMS, MS/MS
spectrometers.
2.1. Syntheses
2.1.1. Synthesis of schiff bases. The Schiff bases were synthesized according to the pro-
cedure described in earlier publications [19, 20].
2.1.2. Synthesis of complexes. Similar procedure was used for preparation of 1–3; for
the sake of brevity, general preparative details (scheme 1) are given. To a benzene (20 mL)
solution of SnCl4, equimolar amount of an appropriate sodium salt of Schiff base [pre-
pared by reaction of equimolar amounts of sodium metal and a Schiff base (HL) in isopro-
panol (30 mL)] was added dropwise with constant stirring. The reaction mixture was
refluxed for 5 h and precipitated NaCl was removed by filtration. The solvent was removed
by distillation. The solid products were dried under reduced pressure and recrystallized
from THF-hexane.
2.1.2.1. [(μ-Cl)2Sn2(o-smab)2Cl4] (1). Yield: 69%; dark yellow solid; m.p. 96–98 °C; Anal.
Calcd for C28Cl6H24N2O2Sn2 (%): C, 38.3; H, 2.7; N, 3.2; Cl, 24.4; Sn, 27.2. Found: C,
38.0; H, 2.2; N, 2.9; Cl, 24.2; Sn, 26.2. IR (KBr pellets, cmÀ1): 1598 (νC=N), 1296(νC-O),
537(νSn-O), 460(νSn←N), 324(νSn-Cl terminal), 227(νSn-Cl-Sn bridging). 1H NMR (CDCl3, δH):
8.52(2H, s, CH=N), 6.88–7.37(m, 16H, Ar-H), 2.32(6H, s, Ar-CH3), ppm. 13C NMR
(CDCl3, δC): 161.92 (s, CO), 159.28 (s, CN), 116.68–138.41 (s, Ar-C), 17.75 (s, Ar-CH3),
ppm. 119Sn NMR (DMSO-d6, δSn): - 618.96, ppm. TOF-MS: Found 873.3894, Calcd
870.64.
2.1.2.2. [(μ-Cl)2Sn2(p-smab)2Cl4] (2). Yield: 73%; yellow solid; m.p. 106–108 °C; Anal.
Calcd for C28Cl6H24N2O2Sn2 (%): C, 38.3; H, 2.7; N, 3.2; Cl, 24.4; Sn, 27.2. Found:
C, 38.1; H, 2.3; N, 2.9; Cl, 24.1; Sn, 26.6. IR (KBr pellets, cmÀ1): 1607(νC=N), 1287
(νC-O), 543(νSn-O), 454(νSn←N), 327(νSn-Cl terminal), 230(νSn-Cl-Sn bridging). 1H NMR
(CDCl3, δH): 8.60(2H, s, CH=N), 6.58–7.89(m, 16H, Ar-H), 2.27(6H, s, Ar-CH3), ppm.
13C NMR (CDCl3, δC): 161.15 (s, CO), 159.46 (s, CN), 115.33–140.64 (s, Ar-C), 16.61
(s, Ar-CH3), ppm. 119Sn NMR (DMSO-d6, δSn): À621.87, ppm. ESI-MS: Found 875.1,
Calcd 870.64.
2.1.2.3. [(μ-Cl)2Sn2(sap)2Cl4] (3). Yield: 73%; dark brown solid; m.p. 126–127 °C; Anal.
Calcd for C24Cl6H18N4O2Sn2 (%): C, 34.1; H, 2.1; Cl, 25.1; N, 6.6; Sn, 28.1. Found: C,

Six-coordinate tin(IV)
2203
SnCl4
HC N Ar
ONa
C6H6-PriOH
reflux∼5h
C
H
N Ar
O
Sn Cl
Cl
Cl
NaCl
Cl
Cl Sn Cl
O
Ar
N
C
H
excessTHF
stirring ∼ 48h
C
N
Ar
H
O
Cl
Sn Cl
Cl
O
Complex
Ar-
(1), (4)
(2), (5)
(3), (6)
CH3
N
H3C
Scheme 1. Synthesis of 1–6.
33.9; H, 1.9; Cl, 24.8; N, 6.4; Sn, 26.4. IR (KBr pellets, cmÀ1): 1612(νC=N), 1504 (νC=N
1
pyridine), 1286(νC-O), 542(νSn-O), 440(νSn←N), 303(νSn-Cl terminal), 228(νSn-Cl-Sn bridging). H
NMR (CDCl3, δH): 9.93(2H, s, CH=N), 6.65–8.44(m, 14H, Ar-H), ppm. 13C NMR
(CDCl3, δC): 163.81 (s, CO), 160.33 (s, CN), 117.90–148.00 (s, Ar-C, Py-C), ppm. 119Sn
NMR (DMSO-d6, δSn): À621.02, ppm. ESI-MS: Found 847.5, Calcd 844.57.
Mononuclear 4–6 were prepared by treating 1–3 with an excess of THF followed by
stirring 48 h.
2.1.2.4. [(o-smab)SnCl3·THF] (4). Yield: 83%; dirty green solid; m.p. 89–91 °C; Anal.
Calcd for C18Cl3H20NO2Sn (%): C, 42.6; H, 3.9; Cl, 20.9; N, 2.7; Sn, 23.3. Found: C,
42.3; H, 3.7; Cl, 20.4; N, 2.6; Sn, 22.9. IR (KBr pellets, cmÀ1): 1602(νC=N), 1279(νC-O),
1
1076 (νC-O-C THF), 539(νSn-O), 445(νSn←N), 445(νSn←O THF), 328(νSn-Cl terminal). H NMR
(CDCl3, δH): 8.51(H, s, CH=N), 6.64–7.29(m, 8H, Ar-H), 3.15–3.55(m, 2Ha, THF), 2.28
(s, Ar-CH3), 1.07–1.87(m, 2Hb, THF), ppm. 13C NMR (CDCl3, δC): 163.81 (s, CO),
160.33 (s, CN), 117.90–148.00 (s, Ar-C), 66.93 (s, Ca-THF), 24.71 (s, Cb-THF), 17.35(s,

2204
R.K. Dubey and A.P. Singh
Ar-CH3), ppm. 119Sn NMR (DMSO-d6, δSn): - 631.06, ppm. ESI-MS: Found 510.3, Calcd
507.4.
2.1.2.5. [(p-smab)SnCl3·THF] (5). Yield: 88%; green solid; m.p. 87–88 °C; Anal. Calcd
for C18Cl3H20NO2Sn (%): C, 42.6; H, 3.9; Cl, 20.9; N, 2.7; Sn, 23.3. Found: C, 42.4; H,
3.8; Cl, 20.5; N, 2.5; Sn, 22.9. IR (KBr pellets, cmÀ1): 1598(νC=N), 1284(νC-O), 1068 (νC-
1
O-C THF), 532(νSn-O), 435(νSn←N), 440(νSn←O THF), 328(νSn-Cl terminal). H NMR (CDCl3,
δH): 8.32(H, s, CH=N), 6.40–7.97(m, 8H, Ar-H), 3.57–4.00(m, 2Ha, THF), 2.22(s, Ar-
CH3), 1.22–1.58(m, 2Hb, THF), ppm. 13C NMR (CDCl3, δC): 161.81 (s, CO), 160.57 (s,
CN), 116.67–138.32 (s, Ar-C), 68.01 (s, Ca-THF), 21.66 (s, Ar-CH3), 27.28 (s, Cb-THF),
ppm. 119Sn NMR (DMSO-d6, δSn): À623.14, ppm. ESI-MS: Found 509.6, Calcd 507.4.
2.1.2.6. [(sap)SnCl3·THF] (6). Yield: 78%; brown solid; m.p. 110–113 °C Anal. Calcd for
C16Cl3H17N2O2Sn (%): C, 38.8; H, 3.4; Cl, 21.5; N, 5.6; Sn, 24.0. Found: C, 38.6; H,
3.2; Cl, 21.3; N, 5.2; Sn, 23.8. IR (KBr pellets, cmÀ1): 1615(νC=N), 1500 (νC=N pyridine),
1281(νC-O), 1058 (νC-O-C THF), 536(νSn-O), 443(νSn←N), 424(νSn←O THF), 301(νSn-Cl terminal).
1H NMR (CDCl3, δH): 9.93(H, s, CH=N), 6.86–8.57(m, 7H, Ar-H, Py-H), 3.38–3.65(m,
2Ha, THF), 1.00–1.81(m, 2Hb, THF), ppm. 13C NMR (CDCl3, δC): 162.24 (s, CO),
158.90 (s, CN), 110.70–142.16(s, Ar-C, Py-C), 66.85 (s, Ca-THF), 26.40 (s, Cb-THF),
ppm. 119Sn NMR (DMSO-d6, δSn): À639.34, ppm. ESI-MS: Found 493.4, Calcd
494.39.
3. Results and discussion
Equimolar reactions of tin(IV) chloride with sodium salts of Schiff bases afford chloride-
bridged 1–3, which on treatment with an excess of THF followed by stirring for 48 h yield
mononuclear 4–6 (scheme 1). All these complexes are yellow-brown solids, soluble in
methanol, ethanol, isopropanol, chloroform, DMSO, or DMF.
3.1. Infrared spectra
Salient features of IR spectra are the disappearance of stretch due to phenolic (O–H) at
3484–3430 cmÀ1, assigned to deprotonation of phenolic hydrogen on complexation [23].
Such interaction is also supported by shift of νC-O 16–24 cm À1 to higher frequency, with
respect to parent Schiff bases. The appearance of new bands at 543–532 cmÀ1 are assign-
able [24] to νSn-O. Coordination through azomethine nitrogen was supported by shift of
νC=N (1615–1598 cmÀ1) to lower frequencies from 1634–1616 cmÀ1 in free Schiff bases
[19, 20]. Coordination of azomethine nitrogen was further supported by a band at 460–
440 cmÀ1 due to Sn←N stretch [25]. In 4–6 C–O–C stretches of coordinated THF were
observed at 1076–1058 cmÀ1 consistent with coordination [26] of THF, further supported
by mass and 119Sn NMR studies. In 1–3 a band assignable to νSn-Cl was observed at 230–
227 cmÀ1, characteristic of bridging chloride [27, 28] and supporting the dimeric nature of
these complexes. Dimeric 1–3 and monomeric 4–6 are supported by mass and 119Sn NMR
spectral studies. The noninvolvement of pyridine nitrogen in complex formation [29] is
supported by the unaltered position of the pyridinic νC=N (1502 2 cmÀ1).

Six-coordinate tin(IV)
2205
3.2. 1H, 13C, 119Sn NMR spectra
1H NMR spectra of 1–6 exhibit no signal due to OH at 13.25–12.76 ppm, indicating metal-
lation of OH [23]. Azomethine hydrogens at 9.93–8.32 ppm compared to parent Schiff
bases (9.23–8.23 ppm) supports coordination of azomethine nitrogen to tin [30, 31].
13C NMR spectra of 1–6 exhibit signals due to azomethine carbon at 160.5–158.9 ppm,
shifted compared to that of parent Schiff bases (158.3–156.5 ppm), indicating coordination
of azomethine nitrogen to tin [25, 32]. Signals at 163.8–161.1 ppm support formation of
Sn–O–C bond. Complexes 4–6 show additional 13C NMR signals at δ 67.06, 65.46,
64.74, and δ 26.77, 25.40, and 24.27 from THF.
The 119Sn NMR chemical shifts for 1–6 are at À639.3 to À619.0 ppm, indicating six-
coordinate tin [33–35].
3.3. Mass spectra
The mass spectra [4, 7, 36] exhibited molecular ion peaks (see experimental section) (m/z),
characteristic of dimeric (1–3) and monomeric (4–6) complexes, respectively. Most of the
fragments were observed as groups of peaks due to various isotopes of tin and chlorine.
Mass spectra, their fragmentation pattern, and calculated isotopic distribution for the
molecular ion peaks at m/z 873.3894, 847.5, 510.3, and 493.4, respectively, for 1, 3, 4,
and 6 are given (see Supplementary material.doc). These observations are in agreement
with the molecular composition of the complexes. In mass spectra of 1 and 3 the molecu-
lar ion peak at m/z 873.38 [calculated mass for (C28Cl6H24N2O2Sn2); = 870.69], 847.5
[calculated mass for (C24Cl6H18N4O2Sn2); = 844.57] corresponds to the molecular mass
supporting dimeric complexes. Important peaks were also observed at m/z 781.17, 731.49,
665.25, 569.17, 542.15, 493.31, 472.05, 438.08 (monomer), 436.08, 367.17, 322.20,
303.16, 263.16, 211.12, and 161.02 due to formation of various radicals C14H12Cl3NOSnÅ,
C7H7Å , HCN, CH3Å , ClÅ, C7H6NÅ, C6H5OÅ, SnClÅ, and SnClÅ2 in 1, whereas 3 showed promi-
nent peaks at m/z 768.6, 745.5, 665.3, 660.3, 568.2, 543.2, 477.3, 425.2 (monomer),
380.1, 355.1, 321.2, 285.1, 248.2, 212.1, 186.1, and 138.0 due to formation of various
radicals C12H9Cl3NOSnÅ, C5H4NÅ, HCN, ClÅ, C6H5OÅ, SnClÅ, and SnClÅ2. Mass spectra of
4 and 6 showed molecular ion peak at m/z 510.3 [calculated mass for (C18Cl3H20NO2Sn);
= 506.96] and m/z 493.4 [calculated mass for (C16Cl3H17N2O2Sn); = 494.3996], which
corresponds to molecular mass of the monomeric complexes. Important peaks were also
observed at m/z 459.4, 431.1, 429.2, 391.3, 371.2, 355.1, 318.2, 297.2, 281.2, 246.2,
Table 1. Antibacterial activitya of Schiff bases and 1–3.
Zone of inhibition (in mm)
Compounds
E. coli
S. aureus
P. aeruginosa
S. epidermis
o-smabH
p-smabH
sapH
[(μ-Cl)2Sn2(o-smab)2Cl4] (1)
[(μ-Cl)2Sn2(p-smab)2Cl4] (2)
[(μ-Cl)2Sn2(sap)2Cl4] (3)
Tetracyclin
6
8
6
7
7
9
12
13
9
12
14
12
22
14
19
12
17
22
17
11
11
19
20
13
16
12
18
22
aIn vitro, agar well diffusion method, conc. 1 mg/mL in DMSO.

2206
R.K. Dubey and A.P. Singh
Table 2. Antifungal activitya of Schiff bases and 1–3.
Zone of inhibition (in mm)
Compounds
A. niger
C. albicans
T. rubrum
Microsporum
o-smabH
p-smabH
sapH
[(μ-Cl)2Sn2(o-smab)2Cl4] (1)
[(μ-Cl)2Sn2(p-smab)2Cl4] (2)
[(μ-Cl)2Sn2(sap)2Cl4] (3)
Fluconazole
12
13
11
19
19
13
23
9
6
12
8
7
14
16
12
22
11
14
9
13
16
14
23
13
16
14
11
23
aIn vitro, agar well diffusion method, conc. 100 μg/mL in DMSO.
214.1, 177.1, and 147.0 due to formation of various small molecules and radicals C6HÅ5,
C4H8O, CHÅ3, ClÅ, HCN, and SnÅ in 4, whereas 6 showed important peaks at m/z 462.3,
424.3, 380.0, 367.2, 355.2, 322.2, 289.1, 279.1, 263.1, 241.1, 211.1, 153.0, and 122 due
to formation of various small molecules and radicals C4H8O, ClÅ, C5H4NÅ HCN, and SnÅ.
3.4. Biological activity
The Schiff bases o-smabH, p-smabH, sapH, and their complexes (1–3) were tested for
inhibitory effect on growth of different bacteria, E. coli, S. aureus, P. aeruginosa,
S. epidermidis, and fungi, A. niger, C. albicans, T. rubrum, and Microsporum using the
agar well diffusion method. The antibacterial and antifungal activities obtained for the
Schiff bases and 1–3 are listed in tables 1 and 2, respectively. The complexes (1–3)
displayed more activity against the same micro-organisms compared to the parent Schiff
bases under identical experimental condition.
4. Conclusion
Six-coordinate chloride-bridged Sn(μ-Cl)2Sn dimeric and mononuclear complexes, [(μ-
Cl)2Sn2(η2-sb)2Cl4] and [(sb)SnCl3·THF], have been synthesized and their structural fea-
119
tures elucidated by IR, (1H, 13C, and
Sn) NMR, and mass spectral studies. The ligands
and 1–3 were screened against bacteria and fungi as size of inhibition diameter. The Schiff
bases show moderate activity and tin(IV) complexes (1–3) show appreciable activity.
Acknowledgments
A.P.S. gratefully acknowledges the CSIR, New Delhi, for Senior Research Fellowship and
Chemistry Department for laboratory facilities. Special thanks to Mr Suman Gupta,
Department of Chemistry, University of Rajasthan, Jaipur, for recording 1H, 13C, 119Sn
NMR, and TOF-MS spectra and Dr Chandan Prasad for IR spectra of the complexes. The
authors are also grateful to CDRI, Lucknow, for providing the analytical and ESI-MS data
and IIT Bombay for FAR-IR spectral facilities. The authors are also grateful to RND
division, MRD Life Sciences, Lucknow, for biological activity studies.

Six-coordinate tin(IV)
2207
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