Diorganotin(IV) complexes of polyaromatic azo-azomethine ligand derived from salicylaldehyde and ortho-aminophenol: Synthesis, characterization, and molecular structures

Article abstract of DOI:10.1002/hc.21037

The diorganotin(IV) complexes of methyl 2-{4-hydroxy-3-[(2-hydroxy- phenylimino)-methyl]-phenylazo}-benzoate (H2L) were obtained by the reaction of ortho-aminophenol, R₂SnO (R = Me, ⁿBu, or Ph) and methyl 2-[(E)-(3-formyl-4-hydroxy)diazenyl]benzoate (H2PL²) in ethanol, which led to diorganotin(IV) compounds of composition [Me₂SnL] ₂ (1), ⁿBu₂SnL (2), and Ph₂SnL (3) in good yield. The ¹H, ¹³C, and ¹¹⁹Sn NMR, IR, the mass spectrometry along with elemental analyses allowed establishing the structure of ligand (H2L) and compounds 1-3. In all the three cases, ¹¹⁹Sn chemical shifts are indicators of five-coordinated Sn atoms in a solution state. The crystal structures of ligand H2L and complexes 1 and 2 were determined by a single crystal X-ray diffraction study. In the solid state, the ligand H2L exists as a keto-enamine tautomeric form. The molecular structure of complex 1 in the solid state shows a distorted octahedral geometry around a tin atom due to additional coordination with an oxygen atom from a neighboring molecule leading to a four-membered ring with Sn- O···Sn-O intermolecular coordination, leading to a dimeric species. On the other hand, complex 2 is a monomer with trigonal bipyramidal geometry surrounding the tin atom. Copyright

Full text of DOI:10.1002/hc.21037

Heteroatom Chemistry
Volume 00, Number 0, 2012
Diorganotin(IV) Complexes of Polyaromatic
Azo-Azomethine Ligand Derived from
Salicylaldehyde and ortho-Aminophenol:
Synthesis, Characterization, and Molecular
Structures
Smita Basu,1 Cheerfulman Masharing,2 and Babulal Das3
1Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
2Department of Chemistry, Shillong College, Laitumkhrah, Shillong 793 003, India
3Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India
Received 20 March 2012; revised 6 June 2012
The molecular structure of complex 1 in the solid
ABSTRACT: The diorganotin(IV) complexes of
state shows a distorted octahedral geometry around
methyl
2-{4-hydroxy-3-[(2-hydroxy-phenylimino)-
a tin atom due to additional coordination with an
oxygen atom from a neighboring molecule leading to
a four-membered ring with Sn-O· · ·Sn-O intermolec-
ular coordination, leading to a dimeric species. On
the other hand, complex 2 is a monomer with trigonal
bipyramidal geometry surrounding the tin atom.
methyl]-phenylazo}-benzoate (H2L) were obtained
by the reaction of ortho-aminophenol, R2SnO (R =
Me, nBu, or Ph) and methyl 2-[(E)-(3-formyl-4-
hydroxy)diazenyl]benzoate (H2PL2) in ethanol, which
led to diorganotin(IV) compounds of composition
[Me2SnL]2 (1), nBu2SnL (2), and Ph2SnL (3) in
good yield. The 1H, 13C, and 119Sn NMR, IR, the
mass spectrometry along with elemental analyses
allowed establishing the structure of ligand (H2L) and
compounds 1–3. In all the three cases, 119Sn chemical
shifts are indicators of five-coordinated Sn atoms in
a solution state. The crystal structures of ligand H2L
and complexes 1 and 2 were determined by a single
crystal X-ray diffraction study. In the solid state, the
ligand H2L exists as a keto-enamine tautomeric form.
ꢀ
C
2012 Wiley Periodicals, Inc. Heteroatom Chem 00:1–9,
2012; View this article online at wileyonlinelibrary.com.
DOI 10.1002/hc.21037
INTRODUCTION
The ever-increasing interest in the chemistry of
organostannyl complexes has led to elaborate stud-
ies on their reactions with different Schiff base moi-
eties [1–5]. The various applications of organotin(IV)
compounds range from important and economical
industrial catalysts [6] to an extensive array of bio-
logical activities [7] and hence are studied in view of
their structural diversity and their possible biologi-
cal applications [8].
A lot of literature is available on the coordina-
tion chemistry and mode of interaction of the tri-
dentate ONO donor ligands containing amino acids
and amino alcohols [9–18]. But a search of the
Correspondence to: C. Masharing; e-mail: cmasharing@
gmail.com.
Present Address of Smita Basu: Department of Organic Chem-
istry, Jagiellonian University, Ingardena 3, 30-060 Krako´w,
Poland.
Contract grant sponsor: UGC (NERO), Guwahati, India.
Contract grant number: F.5-248/2009-10 (MRP/NERO).
Contract grant sponsor: RFSMS-UGC, New Delhi, India.
Contract grant number: F.42-2/Acad/UGC-SAP/Chem/2007-
1113).
c
ꢀ
2012 Wiley Periodicals, Inc.
1

2
Basu, Masharing, and Das
Cambridge Crystallographic Database (CCDB) [19]
revealed not a single X-ray structure of diorgan-
otin(IV) compounds with methyl, n-butyl, vinyl,
or phenyl substituents attached to the tin atoms
that have been constructed from azo-Schiff base
ligand systems containing aromatic amino alco-
hols. The previously reported diorganotin(IV) com-
pounds of amino alcohol Schiff base ligands were
mainly monomeric [20–23] except the Sn-O· · ·Sn-O
or solvent· · ·Sn coordination modes that were found
in the di-n-butyltin(IV) derivatives [23–25]. These
differences would be important for the biocidal ac-
tivity and toxicity in the new tin prototype, which
can be achieved through chemical substitution with
electron-withdrawing or electron-releasing groups.
Thus, the recent interest lies in the molecu-
lar engineering of the substituted azo-Schiff base
systems, which when coupled with diorganotin(IV)
moieties, will result in dimeric aggregates with
the Sn· · ·O interaction, as a study reports very
good in vitro cytotoxic activities with these kinds
of ligand systems [26]. Hence, in this paper,
we report the results of diorganotin(IV) work
to the stable methyl 2-{4-hydroxy-3-[(2-hydroxy-
phenylimino)-methyl]-phenylazo}-benzoate (H2L)
ligand system derived from ortho-aminophenol
(Scheme 1). We also describe the simple synthe-
sis, characterization, and detailed NMR study of
the ligand H2L and its three new diorganotin(IV)
complexes. Crystal and molecular structures of lig-
and H2L and two diorganotin(IV) complexes, i.e.,
(Me2SnL)2and nBu2SnL have also been reported.
MATERIAL AND METHODS
Materials
Me2SnCl2 (Fluka), Ph2SnO (Aldrich), nBu2SnO
(Lancaster), and o-aminophenol (Lobachemie)
were used without further purification. The
solvents used in the reactions were of AR
grade and dried using standard procedures.
Me2SnO was prepared according to the liter-
ature method [27]. Salicylaldehyde (Lancaster)
and the substituted anilines (reagent grade) were
used without further purification. The preligands
2-[(E)-(3-formyl-4-hydroxy-phenyl)-1-diazenyl] be-
nzoic acid (H2PL1) and methyl 2-[(E)-(3-formyl-
4-hydroxy-phenyl)diazenyl]benzoate (H2PL2) were
prepared according to literature methods [28,29].
Physical Measurements
Carbon, hydrogen, and nitrogen analyses were per-
formed with a Perkin–Elmer 2400 series instru-
ment. IR spectra in the range of 4000–400 cm−1
were obtained on a Perkin–Elmer Spectrum BX
series FT-IR spectrophotometer with samples in-
vestigated as KBr disks. The 1H, 13C, and 119Sn
NMR spectra were recorded on a Bruker AMX
400 spectrometer and measured at 400.13, 100.62,
1
and 149.18 MHz. The H, 13C, and 119Sn chemical
shifts were referred to a Me4Si set at 0.00 ppm,
CDCl3 set at 77.0 ppm, and Me4Sn set at 0.00 ppm,
respectively. Mass spectra were obtained from a
SCHEME 1 Synthesis of the preligand H2PL2 and ligand H2L.
Heteroatom Chemistry DOI 10.1002/hc

Diorganotin(IV) Complexes of Polyaromatic Azo-Azomethine Ligand Derived from Salicylaldehyde and ortho-Aminophenol
3
Waters ZQ-4000 mass spectrometer by using the ESI
method.
Syntheses of Diorganotin(IV) Complexes
The general procedure for the preparation of com-
plexes 1 to 3 is described below.
X-Ray Crystallography
Synthesis of 2-(12,12-Dimethyl-11,13-dioxa-5-aza-
12-stanna-dibenzo{a, e}cyclononen-8-ylazo)-benzoic
Methyl Ester [Me2SnL]2 (1). To a reaction vessel,
H2PL2 (0.50 g, 1.75 mmol), ortho-aminophenol
(0.19 g, 1.74 mmol), and di-methyltin(IV) oxide
(0.28 g, 1.69 mmol) were added to 50-mL absolute
ethanol and the resulting solution was maintained
under reflux for 8 h. After the reaction was clear and
completed, the solution was filtered and reduced to
one third of its initial solvent volume. In this case, af-
ter some hours of cooling, orange-red crystals were
obtained to give pure product of 1. Yield: 52%
(0.48 g); mp; 170–172◦C. Anal. Calcd. for
C23H21N3O4Sn: C, 52.91; H, 4.05; N, 8.05. Found:
C, 52.63; H, 3.99; N, 7.98. IR (KBr pellets, cm−1):
1720 (νCOOMe), 1609 (νC N), 1479, 1385, 1267, 1151,
Single crystals of ligand H2L, compounds 1 and 2
suitable for an X-ray crystal structure determina-
tion, were obtained from ethanol for ligand (H2L)
and complex (1) and benzene–hexane mixture (v/v
1:4) for complex 2, respectively, by slow evapora-
tion of the solutions of the respective compounds.
All measurements for the ligand H2L and complexes
1 and 2 were made on a Bruker Nonius SMART CCD
diffractometer [30] with graphite-monochromated
˚
Mo Kα radiation (λ = 0.71073 A) at 296 K. The inten-
sity data were corrected for Lorentz and polarization
effects. The structures were solved by direct meth-
ods using the program SHELXS-97 [31]. Refinement
and all further calculations were carried out using
SHELXS-97 [32]. Smart software was used for data
collection and also for indexing the reflections and
determining the unit cell parameters; the collected
data were integrated using saint software [33].
1
834, 748, 613 (νSn C), 510 (νSn O), 473 (νSn N). H
NMR (CDCl3, δH): Ligand skeleton: 8.75 [s, 1H,
H6], 8.01 [dd, (9.2, 2.0 Hz), 1H, H2], 7.93 [s, 1H,
H7], 7.78 [d (8.0 Hz), 1H, H3’], 7.61–7.54 [m, 2H,
H4’, and H10], 7.45 [t, (6.4 Hz), 1H, H11], 7.38
[d (8.0 Hz) 1H, H6’], 7.20 [t, (8.0 Hz) 1H, H5’],
6.84 [dd, (8.8, 3.2 Hz), 2H, H13, and H3], 6.72 [t,
(7.6 Hz), 1H, H12], 3.90 [s, 3H, H8’]; Sn-Me skeleton
(2 J (119Sn–1H) = 78.6 Hz): 0.83 [s, 6H], ppm. 13C
NMR (CDCl3, δC): Ligand skeleton: 170.45 [C7’],
166.57 [C4], 160.10 [C7], 157.32 [C1’], 150.38 [C9],
142.60 [C1], 132.48 [C8], 130.44 [C5’], 129.51 [C11],
129.22 [C4’], 128.21 [C3’], 127.82 [C2] 127.73 [C6],
126.74 [C6’], 122.11 [C12], 117.48 [C10], 117.24
[C5], 115.61 [C2’], 115.45 [C3], 113.54 [C13], 50.91
[C8’]; Sn-Me skeleton (1 J (119Sn–13C) = 632.4 Hz):
−0.001 ppm. 119Sn NMR (CDCl3) δSn : −144.22, ppm.
ESI-MS (m/z): 524.2 [M]+2 (11), 475.6 (100).
Synthesis of Ligand
Preparation of Methyl 2-{4-Hydroxy-3-[(2-
hydroxy-phenylimino)-methyl]-phenyl azo}-benzoate
(H2L). Methyl 2-[(E)-(3-formyl-4-hydroxy-phenyl)
diazenyl]benzoate H2PL2 (0.50 g, 1.75 mmol) was
dissolved in absolute ethanol (35 ml), and ortho-
aminophenol (0.19 g, 1.74 mmol) in ethanol (10 ml)
was added to it. The reaction mixture was refluxed
for 5 h. The clear solution was filtered and reduced
to one third of its initial solvent volume. The slow
evaporation of the solution at room temperature
afforded reddish crystals of H2L in 78% (0.51 g)
yield; mp: 199–200◦C. Anal. Calcd. for C21H17N3O4:
C, 67.19; H, 4.56; N, 11.19. Found: C, 66.79; H,
4.05; N, 10.82. IR (KBr pellets, cm−1): 3431 (νNH),
3052 (νOH), 1716 (νCOOMe), 1620 (νC N). 1H NMR
(d6-DMSO, δH) 13.12 [s, 1H, OH], 10.15 [s, 1H, OH];
9.12 [s, 1H, H6], 7.98 [s, 1H, H7], 7.71 [d, (7.6 Hz)
1H, H2], 7.53 [d, (7.6 Hz), 2H, H3’, and H10], 7.45
[m, 2H, H4’, and H6’], 7.34 [m, 2H, H11, and H13],
6.98 [t, (6.4 Hz), 1H, H5’], 6.80 [d, (6.8 Hz), 1H, H3],
6.72 [t, (7.6 Hz) 1H, H12], 3.67 [s, 3H, H8’], ppm.
13C NMR (d6-DMSO, δC): 169.31 [C7’], 168.25 [C4],
160.15 [C7], 151.14 [C1’], 151.09 [C9], 143.92 [C1],
132.37 [C8], 132.09 [C5’], 131.55 [C11], 130.57 [C4’],
130.07 [C3’], 129.58 [C2] 129.16 [C6], 128.72 [C6’],
126.75 [C12], 120.23 [C10], 120.08 [C5], 119.33
[C2’], 118.42 [C3], 116.95 [C13], 52.75 [C8’] ppm.
ESI-MS (m/z): 376.3 [M]+1(25), 332.2 (20), 331.3
(100).
Synthesis of 2-(12,12-Dibutyl-11,13-dioxa-5-aza-
12-stanna-dibenzo{a, e} cyclononen-8-ylazo)-benzoic
Methyl Ester [nBu2SnL] (2). Metallic brown crystals
of 2 were obtained from a benzene–hexane mixture
(v/v 1:4). Yield: 52%; mp; 96–98◦C. Anal. Calcd. for
C29H33N3O4Sn: C, 57.45; H, 5.49; N, 6.93. Found: C,
57.13; H, 5.12; N, 6.53%. IR (KBr pellets, cm−1): 1724
(νCOOMe), 1608 (νC N), 1479, 1389, 1267, 1152, 834
1
(νSn C), 511 (νSn O), 469 (νSn N). H NMR (CDCl3,
δH): Ligand skeleton: 8.77 [s, 1H, H6], 8.01[dd, (8.8,
2.4 Hz), 1H, H2], 7.93 [s, 1H, H7], 7.79 [d, (7.6 Hz),
1H, H3’], 7.62–7.55 [m, 2H, H4’, and H10], 7.44 [t,
(7.2 Hz), 1H, H11], 7.38 [d, (8.0 Hz) 1H, H6’], 7.20
[t, (8.0 Hz) 1H, H5’], 6.84 [d, (9.6 Hz), 2H, H13, and
H3], 6.71 [t, (7.6 Hz), 1H, H12], 3.91 [s, 3H, H8’];
Sn-nBu skeleton: 2.69 [m, 1*], 1.52 [m, 2*], 1.33 [m,
Heteroatom Chemistry DOI 10.1002/hc

4
Basu, Masharing, and Das
N
H2N
HO
N
O
EtOH
+
R2SnO
+
Reflux
O
O
OH
5'
12
H2PL2
6'
1'
13
4'
3'
11
10
7
6
3
N
5
1
8
N
N
R
2'
9
7'
4
O
2
Sn
O
O
O
R
8'
R2SnL (R = Me(1); nBu(2); Ph(3))
SCHEME 2 Synthesis of diorganotin(IV) complexes (1–3).
3*], 0.85 [t, 4*], ppm. 13C NMR (CDCl3, δC): Lig-
and skeleton: 172.70 [C7’], 168.11 [C4], 161.31 [C7],
159.59 [C1’], 151.96 [C9], 143.97 [C1], 134.10 [C8],
131.94 [C5’], 131.37 [C11], 130.62 [C4’], 129.71 [C3’],
129.20 [C2] 129.15 [C6], 128.20 [C6’], 123.59 [C12],
118.98 [C10], 118.80 [C5], 117.25 [C2’], 116.68 [C3],
114.98 [C13], 52.38 [C8’]; Sn-nBu skeleton: 26.97 [C-
2*], 26.62 [C-3*], 22.42 [C-1*], 13.59 [C-4*], ppm.
119Sn NMR (CDCl3) δSn : −183.40, ppm. ESI-MS
(m/z): 606.3 [M]+1 (18), 475.6 (100).
RESULTS AND DISCUSSION
Synthetic Aspect
The preligand 2-[(E)-(3-formyl-4-hydroxy-phenyl)-
1-diazenyl]benzoic acid (H2PL1) was prepared ac-
cording to the literature method by a diazo-coupling
reaction between the appropriate aniline and salicy-
laldehyde, in alkaline medium under cold conditions
[28]. The preligand H2PL2 was further prepared by
methylation of 2-[(E)-(3-formyl-4-hydroxy-phenyl)-
1-diazenyl] benzoic acid (H2PL1) in the presence
of a catalytic amount of SOCl2 [29]. On the other
hand, H2L was prepared by condensation of H2PL2
with ortho-aminophenol in ethanol at reflux temper-
ature. The preparation of diorganotin(IV) complexes
of type R2SnL followed the procedure involving
1:1:1 stoichiometric addition of ortho-aminophenol,
Synthesis of 2-(12, 12- Diphenyl-11, 13-dioxa-5-
aza-12-stanna-dibenzo{a, e} Cyclononen-8-ylazo)-
benzoic Methyl Ester [Ph2SnL] (3). Dark red crystals
of 3 were obtained from ethanol. Yield: 67%; mp;
186–188◦C. Anal. Calcd. for C33H25N3O4Sn: C, 61.33;
H, 3.90; N, 6.50. Found: C, 60.97; H, 3.66; N, 6.23.
IR (KBr pellets, cm−1): 1718 (νCOOMe), 1608 (νC N),
1477, 1382, 1300, 1150, 837 (νSn C), 523 (νSn O), 449
n
diorganotin(IV) oxides, R2SnO (R = Me, Bu, Ph),
and H2PL2 to ethanol. The details of the synthe-
sis are presented in the Experimental section, and
methods of preparation are described in Scheme 2.
All the complexes 1–3 could be isolated by fractional
crystallization with high purity and moderate yield.
The complexes are crystalline in nature, stable in air,
and soluble in all common organic solvents. 1H, 13C,
119Sn NMR, IR, elemental analyses, mass spectrome-
try, and single crystal X-ray crystallography accom-
plished the structural elucidation of ligand H2L and
complexes 1–3.
1
(νSn N). H NMR (CDCl3, δH): Ligand skeleton: 8.76
[s, 1H, H6], 8.11 [dd, (9.2, 2.0 Hz), 1H, H2], 7.93
[s, 1H, H7], 7.78 [d (7.2 Hz), 1H, H3’], 7.59–7.52
[m, 1H, H4’c, and H10], 7.38 [m, 1H, H11], 7.23 [t,
(8.0 Hz) 1H, H5’], 7.17 [d, (9.2 Hz) 2H, H13, and
H3], 7.13 [d, (8.0 Hz), 1H, H6’], 6.72 [t, (7.6 Hz),
1H, H12], 3.90 [s, 3H, H8’]; Sn-Ph skeleton: 7.94 [m,
4H, H-2*], 7.46–7.34 [m, 6H, H-3*, and H-4*] ppm.
13C NMR (CDCl3, δC): Ligand skeleton: 172.37 [C7’],
168.10 [C4], 161.18 [C7], 158.98 [C1’], 151.90 [C9],
144.36 [C1], 136.53 [C8], 131.98 [C5’], 130.88 [C11],
130.86 [C4’], 130.60 [C3’], 128.25 [C2], 123.89 [C6],
128.25 [C6’], 123.89 [C12], 119.23 [C10], 119.00 [C5],
117.38 [C2’], 117.28 [C3], 114.93 [C13], 52.44 [C8’];
Sn-Ph skeleton: 139.17 [C-1*], 134.11 [C-2*], 128.88
Spectroscopic Characterization
Diagonistically important infrared absorption fre-
quencies for the carboxylate antisymmetric (νCOOMe
stretching vibration of the ligand H2L are given in
the Experimental section. The assignment of the
symmetric (νOCO sym) stretching vibration band could
)
[C-4*], 128.44 [C-3*], ppm. 119Sn NMR (CDCl3) δSn
:
−326.92, ppm. ESI-MS (m/z): 647.4 [M]+1 (9), 475.7
(15) 160.0 (100).
Heteroatom Chemistry DOI 10.1002/hc

Diorganotin(IV) Complexes of Polyaromatic Azo-Azomethine Ligand Derived from Salicylaldehyde and ortho-Aminophenol
5
SCHEME 3 Tautomeric equilibrium: enol-imine (I) and Keto-enamine (II) in H2L.
not be made owing to the complex pattern of the
spectra. The solid-state IR spectra of the free lig-
and H2L display a medium intensity band at around
3431 cm−1, which has been assigned to a νNH vibra-
tion. These data are consistent in accordance with
our earlier report [18] and show that the ligand
H2L exists in enol-imine(I) and keto-enamine(II)
tautomeric forms, as shown in Scheme 3. The tau-
tomeric form II was found to be predominant in
the solid state, where the phenolic proton of the
central aromatic ring moved to the nearby imine
N-atom (see Fig. 1 for crystal structure). The assign-
ment of the band is based on comparison with the
spectra of the previously reported free ligand H2PL1
and H2PL2. The antisymmetric (νCOOMe) stretching
vibration for the uncomplexed ligands has been
detected around 1725 and 1716 cm−1 for H2PL2
and H2L, respectively. The IR spectra of the com-
plexes 1–3 showed diagnostically important bands
for the νCOOMe fragment at 1720 cm−1 and νC N asymat
1608 cm−1. The IR band due to νOH around 3000 cm−1
in the free ligand H2L disappears completely upon
complexation in accordance with earlier reports
[34,35].
The mass spectrometry of all compounds was
recorded employing the ESI-MS technique, show-
ing in all cases the expected molecular ions, which
resulted to be the base peak. The main pattern evi-
dences the initial loss of a methyl, butyl, or phenyl
moiety from the respective compounds.
The 1H and 13C NMR data of H2L and com-
plexes 1–3 are given in the Experimental section.
The 1H and 13C NMR signals were assigned by
the use of homonuclear-correlated spectroscopy
(COSY), heteronuclear single-quantum correlation
(HSQC), heteronuclear multiple bond connectivities
(HMBC), and distortionless enhancement by polar-
ization transfer (DEPT) experiments. The conclu-
sions drawn from the ligands (H2PL2 and H2L) as-
signments were then subsequently extrapolated to
complexes, especially 1–3, owing to their data simi-
larity, and it was also possible to detect all protons
and carbon signals for compounds 1–3.
The 1H NMR integration values (see the Experi-
mental section) were consistent with the formulation
of products. The 13C NMR spectra of the ligand and
Sn-R skeletons displayed the expected carbon sig-
nals in all cases; also the assignment of the phenyltin
FIGURE 1 Molecular structure of H2L showing the atom-labeling scheme at the 30% probability level; N–H· · ·O intramolecular
hydrogen bonds are drawn as dashed lines.
Heteroatom Chemistry DOI 10.1002/hc

6
Basu, Masharing, and Das
moiety is straightforward from the multiplicity
patterns, resonance intensities, and also by com-
slow evaporation of the solvent at room tempera-
ture. The results of the X-ray crystallographic studies
were fully consistent with the other spectroscopic ev-
idence presented above. The data collection and re-
finement parameters for ligand H2L and complexes
1 and 2 are given in Table 1. The selected geomet-
ric and H bond parameters for H2L are collected in
Tables 2 and 3, respectively, whereas that of com-
plexes 1 and 2 are given in Table 4. The structures
of ligand H2L and complexes 1 and 2 are discussed
in sequel.
The ligand H2L consist of a three-ring system,
which assumes an extended E-conformation both
around the N N and C N linkage with both
outer ring displaying a slightly twisted conformation
(Fig. 1) with respect to the central aromatic ring.
The twisting around the N N is more promi-
nent compared to the twisting around the C N
linkages. This is also reflected in the dihedral an-
gle between the aromatic rings of 59.61(9)◦ formed
between the C3–C8 and C9–C10 aromatic rings in
N N linkage, which is further reflected in the
N1–N2–C9–C10 and, in particular, the N2–N1–C8–
C3 torsion angles of 158.5(2)◦ and 154.9(2)◦, respec-
tively. Similarly, in the case of C N linkage, a
dihedral angle of 60.18(8)◦ is observed between the
C12–C14 and C16–C17 aromatic rings with torsion
angles of 177.9(2)◦ and 171(2)◦ in C14–C13–C15–
N3 and C15–N3–C16–C17, respectively. The hydro-
gen atom of the hydroxyl group from the central
aromatic ring is found to migrate to the nearby
nitrogen atom of the C N bond which results
in an intramolecular N3–H· · ·O3 hydrogen bond.
1
paring their n J(13C–119/117Sn) values. The H NMR
spectra of the ligand H2L shows two singlets due to
two different hydroxyl groups. However, upon com-
plex formation, the singlet disappears due to Sn-O
bonding.
The 119Sn NMR chemical shifts of the diorgan-
otin(IV) complexes (1–3) obtained in a noncoor-
dinating (CDCl3) solvent are listed in the Experi-
mental section. The dimethyltin(IV) complex (1) in
CDCl3 exhibits a single sharp 119Sn resonance at
−144.22 ppm; the dibutyltin(IV) complex (2) at
−183.4 ppm, whereas, in the diphenyltin(IV) com-
plexes (3) at −326.9 ppm. The chemical shift data for
complexes 1–3 in CDCl3 suggest that in noncoordi-
nating solvents all species are monomeric, with pen-
tacoordinated tin atoms bound to two oxygen atoms,
one nitrogen atom, and two alkyl or aryl groups,
since all chemical shifts appear in the typical range
for a trigonal bipyramidal (TBP) geometry [36]. Thus
119Sn NMR shift for complex 1 indicates that the
dimer, revealed in the crystal structure (Fig. 2), is
not retained in solution state.
X-Ray Crystallography
Crystals of methyl 2-{4-hydroxy-3-[(2-hydroxy-
phenylimino)-methyl]-phenyl azo}-benzoate (H2L)
and diorganotin(IV) complexes 1 and 2 suitable for
X-ray crystal structure determination were obtained
from ethanol for ligand H2L and complex 1, and
benzene–hexane mixture (v/v 1:4) for complex 2 by
FIGURE 2 Molecular structure of [Me2SnL]2 (1) at the 30% probability level.
Heteroatom Chemistry DOI 10.1002/hc

Diorganotin(IV) Complexes of Polyaromatic Azo-Azomethine Ligand Derived from Salicylaldehyde and ortho-Aminophenol
TABLE 1 Crystallographic Data and Structure Refinement Parameters for H2L and Complexes 1 and 2
7
H2L
1
2
Empirical formula
Formula weight
Crystal size (mm)
Crystal shape
C21H17N3O4
375.38
C23H21N3O4Sn
522.12
C29H33N3O4Sn
606.27
0.32 × 0.20 × 0.12
0.45 × 0.24 × 0.15
0.35 × 0.25 × 0.14
Block
Tablet
Prism
Temperature (K)
Crystal system
Space group
296(2)
Monoclinic
P2(1)/n
296(2)
Monoclinic
P2(1)/c
296(2)
Monoclinic
¯
P21/c
´
˚
a (A)
12.7560(6)
8.5812(4)
17.2319(9)
7.5305(3)
15.5979(9)
´
˚
b (A)
19.6927(11)
´
˚
c (A)
20.5720(10)
90
125.499(3)
90
18.1171(9)
90
105.181(3)
90
9.0285(5)
90
91.359(3)
90
α (◦)
β (◦)
γ (◦)
´
3
˚
V (A )
Z
1833.29(15)
2268.92(19)
2772.5(3)
4
4
4
Dx (g cm−3
)
1.360
0.096
1.96 < θ < 28.33
21125
4492; 0.0741
263
1.528
1.159
2.90 < θ < 28.36
15201
5434; 0.0675
284
1.452
0.960
1.31 < θ < 28.54
42279
6802; 0.1081
338
μ (mm−1
)
Scan range (◦)
Reflections measured
Independent reflections; Rint
Number of parameters
Number of restraints
R(F) (I > 2σ(I ) reflns.)
R indices [I > 2σ(I )]
GOF (F2)
0
0
0
0.0422, wR2 0.1022
0.1134, wR2 0.1305
0.964
0.0384,wR2 0.0907
0.0471,wR20.0949
0.985
0.0367,wR2 0.0711
0.0784,wR20.0772
0.968
´
−3
˚
max, min ꢀρ (e/A
)
0.132, −0.161
1.429, −1.312
0.678, −0.599
TABLE 2 Selected Bond Lengths and Angles for H2L
The molecule of 1 consists of centrosymmetric
dimers of the basic Me2SnL moiety (Fig. 2), where
the two Sn atoms are linked by two asymmetric Sn–
O· · ·Sn–O bridges involving hydroxyl O atom of the
aminophenol ligand. It has a distorted octahedral
(DOC) geometry around the tin atoms [20–22]. The
O,N,O-tridentate ligand is in a mer orientation to the
tin octahedron. The methyl substituents are trans to
each other, allowing the intramolecular coordina-
tion of the O1 with tin to build a dimeric species.
The dimeric assembly occurs via the formation of
a Sn2O2 four-membered ring [24, 25]. The O· · ·Sn
bonding occurs with the oxygen atom at the five-
membered ring. The crystal structure of 2 (Fig. 3)
reveals a TBP geometry surrounding the tin atom.
The O,N,O-tridentate ligand places its two oxygen
donating atoms in the axial positions, and the nitro-
gen atom occupies one equatorial position.
˚
Bond Lengths (A)
Bond Angles (◦)
O(3)–C(12)
1.292(2)
1.357(2)
0.8200
1.429(2)
1.413(2)
1.301(2)
0.929(19)
N(2)–N(1)–C(8)
N(1)–N(2)–C(9)
C(15)–N(3)–C(16) 126.90(16)
N(3)–C(15)–C(13) 123.04(17)
C(15)–N(3)–H(3)
C(16)–N(3)–H(3)
113.61(15)
114.62(15)
O(4)–C(17)
O(4)–H(4)
N(1)–C(8)
N(2)–C(9)
N(3)–C(15)
N(3)–H(3N)
115.9(12)
117.2(12)
◦
˚
TABLE 3 Hydrogen Bond Parameter (A and ) for H2L
˚
Bond Lengths (A)
Bond Angles (◦)
D–H· · ·A
D–H D–H· · ·A
D· · ·A
< D–H· · ··A,
N3-H· · ·O3 0.82
1.85(18) 2.60(2)
134
Compound [Me2SnL]2 (1) and nBu2SnL (2) crys-
tallizes in the monoclinic P2(1)/c space group. The
˚
Figure 1 clearly indicates that the keto-enamine form
predominates in the solid state. The hydroxyl group
of the phenolic aromatic ring forms the intermolec-
ular interaction O4-H· · ·O3 with a centrosymmetric
mate.
N(1)–Sn(1) bond distance for 1 is 2.20 and 2.22 A for
2. The Sn(1)–O(1) bond distance for 1 and 2 are 2.12
˚
and 2.11 A, whereas, Sn(1)–O(2) bond distance for
˚
1 and 2 are 2.19 and 2.16 A, respectively. The bond
angles between carbon and tin atoms (C–Sn–C) are
Heteroatom Chemistry DOI 10.1002/hc

8
Basu, Masharing, and Das
TABLE 4 Selected Bond Lengths and Angles for Complexes 1 and 2
Complex 1
Complex 2
˚
Bond lengths (A)
O(1)–Sn(1)
O(2)–Sn(1)
N(1)–Sn(1)
C(22)–Sn(1)
C(23)–Sn(1)
C(9)–O(2)
2.1227(19)
2.191(2)
2.209(2)
2.093(3)
2.096(3)
1.289(3)
1.337(3)
O(1)–Sn(1)
O(2)–Sn(1)
N(1)–Sn(1)
C(22)–Sn(1)
C(26)–Sn(1)
C(1)–O(1)
2.1126(18)
2.1652(19)
2.222(2)
2.121(3)
2.104(3)
1.337(3)
1.298(3)
C(1)–O(1)
C(9)–O(2)
Bond angles (◦)
O(1)–Sn(1)–C(22)
O(1)–Sn(1)–C(23)
C(22)–Sn(1)–C(23)
O(1)–Sn(1)–O(2)
C(22)–Sn(1)–O(2)
C(23)–Sn(1)–O(2)
O(1)–Sn(1)–N(1)
C(22)–Sn(1)–N(1)
C(23)–Sn(1)–N(1)
O(2)–Sn(1)–N(1)
97.85(12)
99.91(12)
145.65(15)
155.02(8)
85.02(12)
90.92(13)
75.47(7)
110.05(13)
102.78(11)
80.22(8)
O(1)–Sn(1)–C(26)
O(1)–Sn(1)–C(22)
C(26)–Sn(1)–C(22)
O(1)–Sn(1)–O(2)
C(26)–Sn(1)–O(2)
C(22)–Sn(1)–O(2)
O(1)–Sn(1)–N(1)
O(2)–Sn(1)–N(1)
C(26)–Sn(1)–N(1)
C(22)–Sn(1)–N(1)
94.56(10)
101.42(11)
142.65(13)
156.41(8)
87.09(10)
91.11(11)
76.13(8)
81.76(8)
114.48(10)
102.11(11)
FIGURE 3 Molecular structure of nBu2SnL(2) at the 30% probability level.
145.65◦ for 1 and 142.65◦ for 2, indicating DOC ge-
ometry around 1 and TBP geometry surrounding tin
atom around 2.
phenylimino)-methyl]-phenylazo}-benzoate), which
were carried out through a one-step procedure lead-
ing to crystalline pure substances in good yield. This
is also the first reported diorganotin(IV) complexes
containing azo-Schiff ligand systems obtained by the
condensation of methyl 2-[(E)-(3-formyl-4-hydroxy-
phenyl)diazenyl]benzoate with ortho-aminophenol.
It is intended to employ this new ligand system
to other diorganotin(IV) starting material. This will
open a prospective gateway in application of these
CONCLUSIONS
This article reports the preparation and crystal struc-
tures of three novel diorganotin(IV) complexes of
n
composition R2SnL (where R = Me (1), Bu (2), or
Ph (3) and L = methyl 2-{4-hydroxy-3-[(2-hydroxy-
Heteroatom Chemistry DOI 10.1002/hc

Diorganotin(IV) Complexes of Polyaromatic Azo-Azomethine Ligand Derived from Salicylaldehyde and ortho-Aminophenol
9
[15] Reyes, H.; Santillan, R.; Ochoa, M. E.; Romero, M.;
Farfa´n, N. J Mexican Chem Soc 2007, 51, 39–44.
[16] Zamudio-Rivera, L. S.; George-Tellez, R.; Lopez-
Mendoza, G.; Morales-Pacheco, A.; Flores, E.; Ho¨pfl,
H.; Barba, V.; Fernandez, F. J.; Cabirol, N.; Beltra´n,
H. I. Inorg Chem 2005, 44, 5370–5378.
complexes in cancer chemotherapy as both diorgan-
otin(IV) complexes, and amino alcohols were found
to be as potential candidates as anti-cancer drugs.
SUPPLEMENTARY MATERIAL
[17] Gomez, E.; Ordon˘ez, G. C.; Apan, T. R. Chem Pharma
Bull 2006, 54, 54–57.
CCDC-864863 (H2L), 864864 (1), and 864865 (2)
contain the supplementary crystallographic data for
this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data request/cif, by
e-mailing data request@ccdc.cam.ac.uk, or by con-
tacting The Cambridge Crystallographic Data Cen-
tre, 12, Union Road, Cambridge CB2 1EZ, UK; fax:
+44 1223 336033.
[18] Basu, S.; Gupta, G.; Das, B.; Rao, K. M. J Organomet
Chem 2010, 695, 2098–2104.
[19] http://www.ccdc.cam.ac.uk.
[20] Narula, S. P.; Bharadwaj, S. K.; Sharda, Y.; Day, R.
O.; Howe, L.; Holmes, R. R. Organometallics 1992,
11, 2206–2211.
[21] Dakternieks, D.; Jurkschat, K.; van Dreumel, S.;
Tiekink, E. R. T. Inorg Chem 1997, 36, 2023–2029.
[22] Dakternieks, D.; Basu Baul, T. S.; Dutta, S.; Tiekink,
E. R. T. Organometallics 1998, 17, 3058–3062.
[23] Narula, S. P.; Kaur, S.; Shankar, R.; Verma, S.;
Venugopalan, P.; Sharma, S. K.; Chada, R. K. Inorg
Chem 1999, 38, 4777–4783.
ACKNOWLEDGMENT
We thank the NMR facility at Indian Institute of Sci-
ence, Bangalore, India, for providing NMR spectra.
[24] (a) Reyes, H.; Garcia, C.; Farfan, N.; Santillan, R.;
Lacroix, P. G.; Lepetit, C.; Nakatani, K. J Oragnomet
Chem 2004, 689, 2303–2310; (b) Farfa´n, N.; Mancilla,
T.; Santillan, R.; Gutierrez, A.; Zamudio-Rivera, L. S.;
Beltra´n, H. I. J Organomet Chem 2004, 689, 3481–
3491.
REFERENCES
[25] Beltra´n, H. I.; Zamudio-Rivera, L. S.; Mancilla, T.;
Santillan, R.; Farfan, N. Chem Eur J 2003, 9, 2291–
2306.
[26] Basu Baul T. S. (2008). Patent under process.
[27] (a) Ingham, R. K.; Rosenberg, S. O.; Gilman, H. Chem
Rev 1960, 60, 459–539; (b) Rochow, E. G.; Seyferth,
D. J Am Chem Soc 1953, 75, 2877–2878.
[1] Gielen, M. Coord Chem Rev 1996, 151, 41–51.
[2] Yamada, S. Coord Chem Rev 1966, 1, 415–437.
[3] Sacconi, L. Coord Chem Rev 1966, 1, 126–132.
[4] Collinson, S. R.; Fenton, D. E. Coord Chem Rev 1996,
148, 19–40.
[5] Nath, M.; Saini, P. K. Dalton Trans. 2011, 40, 7077–
7121 and the references therein.
[28] Basu Baul, T. S.; Pyke, S. M.; Sharma, K. K.; Tiekink,
E. R. T. Main Group Met Chem 1996, 19, 807–814.
[29] Basu Baul,.S.; Basu, S.; Tiekink, E. R. T. Acta Cryst
E 2007, 63, o3358.
[30] SMART-NT, Data Reduction Software, version 5.0.
Bruker Analytical X-ray Instruments Inc.: Madison,
WI, 1999.
[31] G M SHELXL 97, Program for the solution of crys-
tal structure; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
[32] 12 G M SHELXL 97, Program for the refinement of
crystal structure; University of Go¨ttingen, Germany,
1997.
[33] SAINT-NT, Data Reduction Software, version 5.0,
Bruker Analytical X-ray Instruments Inc., Madison,
Wisconsin, USA, 1999.
[34] Basu Baul, T. S.; Dhar, S.; Kharbani, N.; Pyke, S.
M.; Butcher, R.; Smith, F. E. Main Group Met Chem
1999, 22, 413–421.
[35] Basu Baul, T. S.; Dhar, S.; Pyke, S. M.; Tiekink,
E. R. T.; Rivarola, E.; Butcher, R.; Smith, F. E. J
Organomet Chem 2001, 633, 7–17.
[36] Holecˇek, J.; Na´dvornik, M.; Handlirˇ, K.; Lycˇka, A. J
Organomet Chem 1986, 315, 299–308.
[6] Davies, A. G.; Gielen, M.; Pannell, K. H,; Tiekink,
E. R. T. (Eds.). Tin Chemistry Fundamentals, Fron-
tiers and Applications; Wiley, Chichester, UK, 2008;
ch. 4, pp. 413–719.
[7] Rossen, K.; Steven, A.; Sager, J.; Reamer, R. A.; Askin,
D.; Volante, R. P.; Reider, P. J. Tetrahedron Lett 1995,
36, 6419–6422.
[8] Manju, Kishore, D.; Kumar, D. J. Coord Chem 2011,
12, 2130–2156.
[9] Cashion, J. D.; Bomazetis, G.; James, B. D. J
Organomet Chem 1980, 185, 433–441.
[10] Hynes, M. J.; O’Dowd, M. J Chem Soc, Dalton Trans
1987, 563–566.
[11] Arena, G.; Gianguzza, A.; Pellerito, L.; Musumeci, S,;
Purello, R.; Rizzarelli, E. J Chem Soc, Dalton Trans
1990, 2603–2608.
[12] Buzas, N. N.; Gajda, T.; Kuzmann, E.; Vertes, A.;
Burger, K. Main Group Met Chem 1995, 11, 641–649.
[13] Arena, G.; Cali, R.; Contino, A.; Musumeci, A.;
Musumeci, S.; Purello, R. Inorg Chim Acta 1995, 237,
187–191.
[14] Beltra´n, H. I.; Damian-Zea, C.; Ortega, S. H.;
Camacho, A. N.; Apan, M. T. R. J. Inorg Biochem
2007, 101, 1070–1085.
Heteroatom Chemistry DOI 10.1002/hc