Synthesis, characterization and biological studies of diorganotin(IV) complexes with tris[(hydroxymethyl)aminomethane] Schiff bases

Article abstract of DOI:10.1016/j.ica.2015.01.017

Several Schiff base ligands derived from tris(hydroxymethyl)aminomethane were synthesized and a series of diorganotin(IV) complexes were obtained from the reaction of diorganotin dichlorides or oxides with Schiff base ligands. The ligands and complexes ha

Full text of DOI:10.1016/j.ica.2015.01.017

Accepted Manuscript
Synthesis, characterization and biological studies of diorganotin(iv) complexes
with tris[(hydroxymethyl)aminomethane] schiff bases
See Mun Lee, Kae Shin Sim, Kong Mun Lo
PII:
S0020-1693(15)00019-5
http://dx.doi.org/10.1016/j.ica.2015.01.017
ICA 16366
DOI:
Reference:
Inorganica Chimica Acta
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21 December 2014
9 January 2015
Please cite this article as: S.M. Lee, K.S. Sim, K.M. Lo, Synthesis, characterization and biological studies of
diorganotin(iv) complexes with tris[(hydroxymethyl)aminomethane] schiff bases, Inorganica Chimica Acta (2015),
doi: http://dx.doi.org/10.1016/j.ica.2015.01.017
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SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL STUDIES OF
DIORGANOTIN(IV) COMPLEXES WITH
TRIS[(HYDROXYMETHYL)AMINOMETHANE] SCHIFF BASES
See Mun Leea*, Kae Shin Simb, and Kong Mun Loa
aDepartment of Chemistry, Faculty of Science, University of Malaya,
50603 Kuala Lumpur, Malaysia
bInstitute of Biological Sciences, Faculty of Science, University of Malaya,
50603 Kuala Lumpur, Malaysia
* Corresponding author. Tel.: +603 7967 7022 ext:2141; Fax: +603 7967 4193
E-mail address: smlee@um.edu.my
Abstract
Several Schiff base ligands derived from tris(hydroxymethyl)aminomethane were synthesized and a
series of diorganotin(IV) complexes were obtained from the reaction of diorganotin dichlorides or
oxides with Schiff base ligands. The ligands and complexes have been characterized by elemental
1
analysis, IR, H, 13C and 119Sn NMR spectroscopies. Single-crystal X-ray diffraction analysis
reveals
dimethyltin(IV),
bromophenolato)]dimethyltin(IV), 7 are dimeric structures, in which the central tin atom is rendered
six-coordinate while (2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
that
bis[(2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)]-
1
and bis[(2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
bromophenolato)diphenyltin(IV), 9, (2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
chlorophenolato)dimethyltin(IV), 13, (2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
chlorophenolato)diphenyltin(IV), 15 and (2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-
4-chlorophenolato)dicyclohexyltin(IV), 16 are monomeric structures, whereby the tin atom is in a
distorted trigonal-bipyramidal configuration. The Schiff bases and their corresponding
diorganotin(IV) complexes have been evaluated against three human carcinoma cell lines, namely
1

HT29 (human colon carcinoma cell line), SKOV-3 (human ovarian cancer cell line) and MCF-7
(hormone-dependent breast carcinoma cell line), for its in vitro cytotoxic activities. The dibutyltin
and dicyclohexyltin derivatives of the Schiff base ligands display good cytotoxic activities against
the tested cell lines.
Keywords: organotin, hydrogen-bonding, cytotoxic activity, X-ray structures
1. Introduction
Organotin(IV) compounds have been actively studied due to their medical, industrial and agricultural
applications [1-5]. Among these compounds, the chemistry and applications of organotin(IV)
complexes with monodentate, bidentate, tridentate and multidentate Schiff bases are extensively
studied because of their structural diversity, thermal stability and biological properties such as
antimicrobial [6], antifungal [7,8], antibacterial [7,8], antitumour [7,9-11], antioxidant [11], anti-
insecticidal [12] and anti-inflammatory [11,13]. The biological activities of the organotin(IV)
complexes are largely influenced by the structure of the complexes, coordination number at the tin
atom and by the alkyl/aryl groups in the complexes [14,15].
Schiff bases play an important role as chelating ligands in both main group metal and transition
metal coordination chemistry. This is due to their stability in a variety of oxidative-reductive
condition and their structural versatilities [16]. Tris(hydroxymethyl)aminomethane (TRIS) has been
widely used in biochemistry, physiology and medicine as an inexpensive buffer in the physiological
pH range. From literature, tris(hydroxymethyl)aminomethane (TRIS) and its Schiff base derivatives
are known to have a broad spectrum of biological activities including anti-tumour, antibiotic,
anticancer, antihistamine, antifungal, anti-inflammatory and many others [16-19]. Some metal
complexes with TRIS Schiff base have been reported. For example, TRIS Schiff bases with
2

dioxomolydenum(VI) complexes have been investigated and used as catalysts in epoxidation of
alkenes while its dioxovanadium(IV) complexes have been studied as potential biomimetics [20, 21].
The coordination chemistry of diorganotin(IV) complexes with ONO, ONS and NNO terdentate
ligands is widely discussed for its biological and pharmacological properties. In the current article,
we report the synthesis and structural studies of diorganotin complexes with terdentate ONO Schiff
bases prepared from the condensation reaction of tris(hydroxymethyl)aminomethane with substituted
salicylaldehydes. The prepared diorganotin complexes could be a monomeric or dimeric structure
with coordination geometries which are close to trigonal-bipyramidal, octahedral and pentagonal-
bipyramidal. The in vitro cytotoxicity of the Schiff bases and their diorganotin complexes against
three human carcinoma cell lines (HT29, SKOV-3 and MCF7) is evaluated and discussed.
2. Experimental
2.1 Materials and physical measurements
The reagents used were of reagent grade quality and used as supplied. Dibenzyltin dichloride and
di(p-chlorobenzyl)tin dichloride were prepared according to the literature method [22]. The solvents
used in the reaction were of AR grade and were dried using standard literature procedures [23]. The
melting points of the ligands and complexes were determined using an Electrothermal digital melting
point apparatus and were uncorrected. The IR spectra for the compounds were recorded using KBr
1
13
pellets on a Perkin-Elmer Spectrum RX1 FT-IR spectrophotometer. H and C NMR spectra were
recorded on a JEOL JNM GX-270 FT NMR SYSTEM spectrometer while 119Sn NMR spectra were
recorded on a JEOL ECA-400MHz NMR spectrometer and were referenced against Me4Sn. The
1
chemical shifts were recorded in ppm with reference to Me4Si for H NMR and 13C NMR.
Microanalyses were carried out on an Eager 300 CHNS Elemental Analyzer and a Perkin-Elmer
EA2400 CHNS Elemental Analyzer.
3

2.2 Preparation of the ligands
2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenol, H2L1
Tris(hydroxymethyl)aminomethane (1.21 g, 0.01 mol) and salicylaldehyde (1.07 mL, 0.01 mol) were
added to 100 mL of ethanol. The solution mixture was refluxed for 2 hours. A yellow solid was
obtained upon cooling to room temperature, and was used without further purification. Yield: 1.90
g (84.5 %) ; m.p. 139-140oC. Anal. Calc for C11H15NO4: C, 58.66: H, 6.71: N, 6.22. Found: C,
58.11: H, 6.33: N, 6.70 IR (cm-1): 3321 ν(O-H), 1636 ν(C=N), 1189 ν(C-O).
The preparation method used for ligand H2L1 was repeated for ligands H2L2 and H2L3 with the
respective substituted salicylaldehydes.
2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenol, H2L2
Yield: 2.13 g (70.1%); m.p. 141-142oC. Anal. Calc for C11H14NO4Br: C, 43.44: H, 4.64: N, 4.61.
Found: C, 43.01: H, 4.60: N, 4.49 IR (cm-1): 3357 ν(O-H), 1637 ν(C=N), 1175 ν(C-O).
2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenol, H2L3
Yield: 1.95 g (75.1%); m.p. 137-138oC. Anal. Calc for C11H14NO4Cl: C, 50.88: H, 5.43: N, 5.39.
Found: C, 51.18: H, 5.42: N, 5.01 IR (cm-1): 3339 ν(O-H), 1639 ν(C=N), 1175 ν(C-O).
2.3 Preparation of the diorganotin complexes, 1-18
The preparation method used for compound 1 was repeated for compounds 3, 4, 7, 9, 10, 13, 15 and
16 with the appropriate diorganotin oxides and Schiff base ligands. The preparation method used for
compound 2 was repeated for compounds 5, 6, 8, 11, 12, 14, 17 and 18 with the appropriate
diorganotin chlorides and Schiff base ligands.
4

Bis[(2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)]dimethyltin(IV), 1
0.23 g (1.0 mmol) of 2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenol, H2L1 in 20 mL
dry toluene was added to a suspension of 0.17 g (1.0 mmol) of dimethyltin oxide in 50 mL of dry
toluene. The mixture was heated under azeotropic removal of water using a Dean-Stark trap. The
solvent was gradually removed by evaporation under vacuum to give a yellow precipitate. The
precipitate was recrystallized from a 1:1 mixture of ethanol:dichloromethane. Yellow crystals
suitable for X-ray crystallographic studies were obtained from the slow evaporation of the filtrate.
Yield: 0.58 g (77.8 %) ; m.p. 196-198oC Anal.Calc for C26H38N2O8Sn2: C, 41.97; H, 5.15; N,
3.77%. Found: C, 42.02 ; H, 5.02 ; N, 3.98%. IR (cm-1): 3495 ν(O-H), 1614 ν(C=N), 1191 ν(C-O),
669 ν(Sn-O), 419 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)dibutyltin(IV), 2
0.23 g (1.0 mmol) of 2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenol, H2L1, and 0.14
mL (1.0 mmol) of triethylamine were added to 50 mL of absolute ethanol and the mixture was
heated under reflux for 2 hours. Dibutyltin dichloride (0.30 g, 1.0 mmol) in 30 mL of absolute
ethanol was added and the mixture was further refluxed for 5 hours and filtered. The filtrate was
evaporated until precipitation was obtained. The precipitation was recrystallized from toluene and
the by-products, triethylammonium chloride, was removed through filtration. The yellow precipitate
was recrystallized from a 1:1 mixture of ethanol:dichloromethane.
Yield: 0.36 g (79.2 %) ; m.p. 126-127oC Anal.Calc for C19H31NO4Sn: C, 50.03; H, 6.85; N, 3.07%.
Found: C, 49.94; H, 7.12; N, 2.79%. IR (cm-1): 3422 ν(O-H), 1611 ν(C=N), 1182 ν(C-O),
678 ν(Sn-O), 422 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)diphenyltin(IV), 3
5

Yield: 0.37 g (74.4 %); m.p. >350oC (dec.) Anal.Calc for C23H23NO4Sn: C, 55.68; H, 4.67; N, 2.82
%. Found: C, 56.00; H, 4.64; N, 2.73 %. IR (cm-1): 3281 ν(O-H), 1611 ν(C=N), 1173 ν(C-O),
699 ν(Sn-O), 436 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)dicyclohexyltin(IV), 4
Yield: 0.38 g (75.5%) ; m.p. 190-191oC Anal.Calc for C23H35NO4Sn: C, 54.35; H, 6.94; N, 2.76%.
Found: C, 53.70; H, 6.87; N, 3.02%. IR (cm-1): 3369 ν(O-H), 1616 ν(C=N), 1149 ν(C-O),
669 ν(Sn-O), 421 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)dibenzyltin(IV), 5
Yield: 0.34 g (65.2%); m.p. >350oC (dec.) Anal.Calc for C25H27NO4Sn: C, 57.28; H, 5.19; N,
2.67%. Found: C, 56.95; H, 5.57; N, 2.43%. IR (cm-1): 3401 ν(O-H), 1612 ν(C=N), 1174 ν(C-O),
698 ν(Sn-O), 458 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)di(p-chlorobenzyltin)(IV), 6
Yield: 0.39 g (65.0 %) ; m.p. > 350oC (dec.) Anal.Calc for C25H25Cl2NO4Sn: C, 50.63; H, 4.25; N,
2.36 %. Found: C, 50.35; H, 3.90; N, 2.20 %. IR (cm-1): 3282 ν(O-H), 1610 ν(C=N), 1172 ν(C-O),
688 ν(Sn-O), 420 ν(Sn-N).
Bis[(2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)]dimethyltin(IV), 7
Yield: 0.71 g (72.1 %) ; m.p. 208-209oC. Anal.Calc for C26H36Br2N2O8Sn2: C, 34.63; H, 4.02; N,
3.11%. Found: C, 34.72; H, 3.83; N, 3.55%. IR (cm-1): 3293 ν(O-H), 1612 ν(C=N), 1169 ν(C-O),
684 ν(Sn-O), 455 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)dibutyltin(IV), 8
6

Yield: 0.42 g (78.5 %) ; m.p. 110-112oC. Anal.Calc for C19H30BrNO4Sn: C, 42.65; H, 5.65; N, 2.62
%. Found: C, 42.84; H, 5.69; N, 2.42 %. IR (cm-1): 3290 ν(O-H), 1612 ν(C=N), 1169 ν(C-O),
661 ν(Sn-O), 451 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)diphenyltin(IV), 9
Yield: 0.40 g (70.5 %) ; m.p. >350oC. Anal.Calc for C23H22BrNO4Sn: C, 48.04 : H, 3.86 : N, 2.44 %.
Found: C, 48.07; H, 3.79; N, 2.86 %. IR (cm-1): 3380 ν(O-H), 1608 ν(C=N), 1177 ν(C-O),
660 ν(Sn-O), 448 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato) dicyclohexyltin(IV), 10
Yield: 0.40 g (70.5 %) ; m.p. 194-195oC. Anal.Calc for C23H34BrNO4Sn: C, 47.05 : H, 5.84 : N, 2.39
%. Found: C, 47.32; H, 5.27; N, 2.78 %. IR (cm-1): 3369 ν(O-H), 1612 ν(C=N), 1172 ν(C-O), 658
ν(Sn-O), 434 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)dibenzyltin(IV), 11
Yield: 0.40 g (70.5 %) ; m.p. >350oC. Anal.Calc for C25H26BrNO4Sn: C, 49.79 : H, 4.35 : N, 2.32 %.
Found: C, 50.29; H, 4.40; N, 2.55 %. IR (cm-1): 3373 ν(O-H), 1618 ν(C=N), 1172 ν(C-O),
657 ν(Sn-O), 463 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)di(p-chlorobenzyl)-
tin(IV), 12
Yield: 0.40 g (70.5 %) ; m.p.212-213oC. Anal.Calc for C25H24BrCl2NO4Sn: C, 44.68 : H, 3.60: N,
2.08 %. Found: C, 45.02; H, 3.90; N, 2.35 %. IR (cm-1): 3285 ν(O-H), 1611 ν(C=N), 1176 ν(C-O),
653 ν(Sn-O), 420 ν(Sn-N).
7

(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)dimethyltin(IV), 13
Yield: 0.33 g (80.2%); m.p. 220-221oC. Anal.Calc for C13H18ClNO4Sn: C, 38.42; H, 4.46; N, 3.45%.
Found: C, 38.79; H, 4.00; N, 3.80%. IR (cm-1): 3376 ν(O-H), 1618 ν(C=N), 1180 ν(C-O), 702 ν(Sn-
O), 430 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)dibutyltin(IV), 14
Yield: 0.39 g (78.5%); m.p. 133-134oC. Anal.Calc for C19H30ClNO4Sn : C, 46.51; H, 6.16; N,
2.85%. Found: C, 46.34; H, 5.99; N, 3.02%. IR (cm-1): 3372 ν(O-H), 1614 ν(C=N), 1170 ν(C-O),
690 ν(Sn-O), 414 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)diphenyltin(IV), 15
Yield: 0.40 g (75.3%); m.p. >350oC. Anal.Calc for C23H22ClNO4Sn : C, 52.06; H, 4.18; N, 2.64%.
Found: C, 52.27; H, 3.99; N, 2.65%. IR (cm-1): 3380 ν(O-H), 1611 ν(C=N), 1178 ν(C-O),
698 ν(Sn-O), 431 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)dicyclohexyltin(IV), 16
Yield: 0.38 g (70.5%); m.p. 180-181oC. Anal.Calc for C23H34ClNO4Sn: C, 50.90; H, 6.32; N, 2.58%.
Found: C, 50.59; H, 5.89; N, 2.70%. IR (cm-1): 3367 ν(O-H), 1617 ν(C=N), 1172 ν(C-O), 702 ν(Sn-
O), 435 ν(Sn-N).
(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)dibenzyltin(IV), 17
Yield: 0.45 g (81.1%); m.p. >350oC. Anal.Calc for C25H26ClNO4Sn: C, 53.75; H, 4.69; N, 2.51%.
Found: C, 53.38; H, 4.30; N, 2.67%. IR (cm-1): 3399 ν(O-H), 1619 ν(C=N), 1170 ν(C-O),
699 ν(Sn-O), 467 ν(Sn-N).
8

(2-{[1,1-Bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)di(p-chlorobenzyl)-
tin(IV), 18
Yield: 0.42 g (66.2 %); m.p. >350oC. Anal.Calc for C25H24Cl3NO4Sn : C, 47.85; H, 3.86; N, 2.23 %.
Found: C, 47.50; H, 3.47; N, 2.03 %. IR (cm-1): 3283 ν(O-H), 1614 ν(C=N), 1167 ν(C-O),
700 ν(Sn-O), 430 ν(Sn-N).
2.4 X-ray structural studies
The X-ray crystallographic data for compounds 7, 9, 13, and 15 were collected on a Bruker SMART
CCD 1000 diffractometer, while compounds 1 and 16 were collected on a Bruker SMART APEX2
CCD diffractometer. The structures were solved by direct method and refined by the full-matrix
least-squares procedure based on F2 using the SHELXL-97 programme [24]. All data were collected
at 100K or 123 K using graphite-monochromated Mo-Kα (λ= 0.71073Ǻ) radiation. The positions of
hydrogen atoms were calculated, and their contributions in structure factor calculations were
included.
2.5 In vitro cytotoxicity
HT29 (human colon carcinoma cell line), SKOV-3 (human ovarian cancer cell line) and MCF7
(hormone-dependent breast carcinoma cell line) were purchased from the American Type Culture
Collection (ATCC, USA). The HT29 and MCF7 cells were maintained in RPMI 1640 medium
(Sigma) while the SKOV-3 cells in Dulbecco’s Modified Eagle’s Medium (DMEM; Sigma),
supplemented with 10% fetal bovine serum (FBS; PAA Lab, Austria), 100 µg ml-1 penicillin or
streptomycin (PAA Lab, Austria), and 50 µg ml-1 of fungizone (PAA Lab, Austria). The cells were
maintained at 37°C in an atmosphere humidified with 5% CO2. The in vitro cytotoxicity of the
ligands and diorganotin complexes were determined by the Neutral Red cytotoxicity assay with
cisplatin as positive control [25]. All the tests were repeated three times.
9

2.6 Statistical Analysis
Data were presented as mean ± S.E.M. The IC50 values were obtained by non-linear regression using
GraphPad Prism statistical software.
3. Results and discussion
3.1 Synthesis
The Schiff base ligands were synthesized by the condensation process of salicylaldehyde and
substituted salicylaldehydes with tris(hydroxymethyl)aminomethane. Each of the Schiff base
ligands has four potential donor atoms, namely one nitrogen atom and three oxygens from hydroxyl
groups, which enables it to form coordination bonds with metal ions. These ligands are enolized in
solution as shown in Figure 1. The enolized form of the Schiff base ligands provides three acidic
protons which can react with the diorganotin oxides and diorganotin dichlorides as shown in Figure
2. The coordination of one of the oxygen donor atom to the central tin metal further stabilized the
overall structure. The diorganotin complexes are obtained in reasonable yield and they are stable
towards moisture and air. They are soluble in dichloromethane, chloroform and moderately soluble
in polar solvents. The structural features of the diorganotin complexes are characterized using
various spectroscopic techniques.
Figure 1 Enolized form of ligand H2L2
10

Figure 2. Reaction scheme for the reaction of the ligands with diorganotin dichlorides and
diorganotin oxides
3.2 IR Spectral
The infrared spectra data of the ligands and the complexes are given in the Experimental section.
From the infrared spectra, the hydroxyl stretching frequencies of the free ligands, H2L1, H2L2 and
H2L3 are located at 3321, 3357 and 3339 cm-1, respectively. However, no visible N-H stretching is
observed in the ligands’ infrared spectra. This might be due to the overlapping of the N-H stretching
frequency with the O-H stretching frequency. In the diorganotin complexes, a characteristic
absorption is clearly observed in the 3200-3400 cm-1 region [26] suggesting that not all the hydroxy
oxygens participated in the coordination to the central metal atom.
The Schiff base ligands exhibit a C=N stretching frequencies in the region of 1630-1640 cm-1 for the
azomethine group, which is within the range reported for the similar group of Schiff base ligands
[27-30]. Meanwhile, the C=N stretching frequencies for the diorganotin complexes are found in the
11

region between 1610-1620 cm-1 which is about 20 cm-1 lower than those reported for the ligands.
This confirms the involvement of the azomethine nitrogen in the coordination with the central tin
atom for the complexes. The C-O stretching frequencies for both ligands and complexes are within
the 1150-1200 cm-1 region [31].
Two new bands are observed in the 400-750 cm-1 region. The medium band in the region of 650-710
cm-1 is assigned to the Sn-O stretching frequency while the weak absorption band in the region of
410-470 cm-1 to the Sn-N stretching frequency. Both the Sn-O and Sn-N stretching frequencies are
in the range reported for diorganotin derivatives [32-34].
3.3 Multinuclear (1H, 13C and 119Sn) NMR Spectra
1
13
The H, C and 119Sn NMR spectral data of the Schiff base ligands and its diorganotin complexes
are presented in Tables 1, 2 and 3. Overall, the chemical shifts for the ligands and the complexes are
1
found within the expected range. In the H NMR spectral, the signals at 6.60-7.40 are assigned to
the aromatic protons of the ligands and diorganotin complexes. The signal for the methylene protons
is found as a group of multiplets in the range of 3.39-4.00 ppm. The 1H NMR chemical shifts of the
hydroxyl protons in the ligands are found around 4.80 ppm, while for the complexes, the chemical
shifts are slightly downfield, in the 5.00-5.45 ppm region. In the diorganotin complexes, the
decrease in the integration value of the hydroxy protons signal suggests the bonding of the tin atom
to one of the oxygen atom of the Schiff base ligand through the replacement of one of the phenolic
protons. Meanwhile, a singlet peak around 8.39-8.60 is assigned to the methine protons of the
azomethine carbon [35].
The 13C NMR spectra for the complexes show a significant downfield shift for the carbon resonances
in comparison to the free ligands. The signals of the azomethine carbons (C-7) for the Schiff base
12

ligands and the diorganotin complexes appear in the 164-173 ppm region [28, 30]. Meanwhile, the
signals for the quarternary carbon (C-8) are observed between 66-68 ppm. The chemical shift values
for the methylene carbons, (C-9), (C-10) and (C-11) can be found in the region of 61-62 ppm for the
ligands while for the diorganotin complexes, its chemical shift value range is slightly wider, between
60-70 ppm due to the influence of the interaction between the methylene oxygen and the tin atom.
The heteronuclear coupling constant is used to predict the geometry and the coordinating
environment of the tin atom in the complexes. In most of the diorganotin complexes, the satellite
signals due to hydrogen-tin coupling and carbon-tin coupling are observed and the coupling
constants are reported. However, for the diphenyltin, dibenzyltin and di(p-chlorobenzyl)tin, the
spin-spin coupling peak between the tin nucleus and its neighbouring carbons is not well resolved.
The geometry of the diorganotin complexes is predicted from the C-Sn-C angle which is calculated
based on the Lockhart and Manders equation: θ(C-Sn-C) = 0.0161|2J(119Sn-1H)|2 -1.32 |2J(119Sn-1H)|
2
+ 133.4 [36, 37]. The observed coupling constants J(119Sn-1H) values for the diorganotin
complexes are in the range 72-88 Hz, which suggests a five- and six-coordinated geometry.
1
Similarly, the C-Sn-C angle of the diorganotin complexes can also be estimated from J(119Sn-13C)
13
coupling constants obtained from the C NMR spectra using the Lockhart’s equation; θ(C-Sn-C) =
[|1J(119Sn-13C)| + 875]/11.4. The calculation of the C-Sn-C angle values based on the coupling
constant obtained from the NMR spectra show a slight deviation from the C-Sn-C angles obtained by
X-ray diffractometry studies. The calculated C-Sn-C angles lies in the range 120-137o, which
correspond to five- and six-coordination of the tin atom in the complexes [38].
The presence of a single peak in the 119Sn NMR spectral of the complexes confirms the formation of
a single species. The 119Sn NMR chemical shifts of the dimethyltin complexes, 1 and 7 are found
around -174 ppm while for compound 13, it is found at -117 ppm. The 119Sn NMR chemical shifts
13

of the dibutyltin complexes, 2, 8 and 14 are found around -187 ppm, while the dicyclohexyltin
complexes, 4, 10 and 16, are found around -244 ppm. The 119Sn NMR chemical shifts for the
dibenzyltin and substituted dibenzyltin complexes are found between -217 to -296 ppm while the
119Sn NMR chemical shifts for the diphenyltin complexes, 3, 9, and 15, are found between -344 to -
1
1
355 ppm. The 119Sn NMR chemical shifts, J(119Sn-1H) and J(119Sn-13C) coupling values are in
accordance with five-coordination tin centre [39-43]. Also, these 119Sn NMR chemical shift values
are found to be in the similar range as those reported for the respective diorganotin complexes [44-
46], indicating most of the diorganotin complexes are in a five-coordinated tin geometry except for
compounds 1 and 7.
3.4 X-ray structural studies
The molecular structures of the molecules are depicted in Figure 3, 4, 5, 6, 7 and 8 respectively. The
crystallographic data and refinement details for compounds are given in Table 4 while selected bond
lengths and angles are given in Table 5.
The molecular structures revealed that the ligands, 2-{[1,1-bis(hydroxymethyl)-2-
oxidoethyl]iminomethyl}phenol, H2L1, 2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
bromophenol, H2L2 and 2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenol,
H2L3 act as dianionic ligands and is coordinated to the tin atom via the phenoxy oxygen, one
methoxy oxygen, and an imino nitrogen forming five- and six-membered chelate rings with the
corresponding bite angles of 76.8o and 82.1o, respectively. The six-membered cyclic rings are
relatively planar with root mean square (RMS) deviations from planarity in the range of 0.01-0.12 Å.
On the other hand, the five-membered ring is slightly pluckered with a RMS deviation of 0.15-0.18
Å from planarity. The dihedral angles between these chelate rings are in the range of 6.7-12.5o, and
this clearly indicates the non-planarity of the ligand plane around the tin atom.
14

Except for compounds 1 and 7, the tin atom in the other diorganotin complexes (compounds 9, 13,
15 and 16) adopts a distorted trigonal-bipyramidal geometry in which the trigonal plane consists of
the imine nitrogen and two alkyl/aryl groups. The axial positions are occupied by the phenoxy
oxygen and ethoxy oxygen.
The distortion from the ideal trigonal-bipyramidal geometry are
evidenced from their O(1)-Sn-O(2) angles of 159.33o, 159.03o, 156.46o and 158.29o for compounds
9, 13, 15 and 16, respectively. This is also reflected in the indices of the trigonality of the plane
which could be determined from the τ-value, defined as τ = (β-α)/60, whereby α and β are the two
largest donor-metal-donor angles in the five-coordinated environment.
For an ideal trigonal-
bipyramid, the τ-value will be close to 1, while for an ideal tetragonal-pyramid, the τ-value should be
close to zero. In this case, the determined τ-values for compounds 9, 13, 15 and 16 are in the range
of 0.42 - 0.57, indicative of a distorted trigonal-bipyramidal geometry [45].
In contrast, compounds 1 and 7 form dimers via the coordination of the methoxy oxygen to the tin
atom of an adjacent molecules forming a central planar Sn2O2 four-membered ring [Sn(1)-O(2); 1:
2.079(2), 2.379(2) Å; 7: 2.075(2), 2.090(3) 2.329(2), 2.348(3) Å]. This has resulted in the formation
of a six-coordinate tin species in these two compounds. In addition, the C-Sn-C angles are also
found to have opened up to 144.4(1)o for 1 and 147.9(2), 150.9(2)o for compound 7 as compared to
those of the five-coordinate compounds [120.8-126.6o]. The crystal structures of compounds 1 and
7 also revealed that the two terminal hydroxyl groups are involved in intermolecular hydrogen-
bonding with the terminal hydroxyl group and the coordinated phenoxy oxygen of a neighbouring
molecule (Figure 9) [1: O-H..O 2.724(3), 2.829(3) Å; 7: O-H..O 3.117(5), 2.697(4), 2.705(4) and
2.703(4) Å]. On the other hand, the two terminal hydroxyl groups in compounds 9, 13, 15 and 16
are intermolecular hydrogen-bonded to the methoxy oxygen and terminal hydroxy oxygen of the
neighbouring molecules [9: O-H..O 2.623(3) and 2.666(3) Å; 13: O-H..O 2.620(2) and 2.707(2) Å;
15

15: O-H..O 2.639(2) and 2.695(3) Å; 16: O-H..O 2.747(6) and 2.548(6) Å] [47-51] and prevent the
formation of dimeric tin structures in compounds 9, 13, 15 and 16 (Figure 10).
Apart from the dative Sn(1)-O(2) and Sn(2)-O(6) bond distances in compounds 1 and 7 which are
are slightly longer (2.333 – 2.349 Å ), the rest of the covalent Sn-O bond distances are shorter and
within the values of those reported for five-coordinated diorganotin complexes [9: 2.083(2) Å and
2.073(2) Å, 13: 2.125(2) Å and 2.075(2) Å, 15: 2.092(2) Å and 2.082(2) Å, 16: 2.076(5) Å, 2.093(4)
Å, 2.131(4) Å and 2.107(4) Å respectively]. The dative Sn(1)-N(1) bond distances [2.19-2.22 Å] for
all the complexes are also well within those reported in the literature for similar complexes [30, 45,
47].
3.5 In vitro cytotoxicity
The efficiency of the diorganotin compounds as anticancer drug has been tested in vitro on three cell
lines, HT29 (human colon carcinoma cell line), SKOV3 (human ovarian cancer cell line), and MCF-
7 (hormone-dependent breast carcinoma cell line). The results of the IC50 values of the Schiff base
ligands and the diorganotin complexes are summarized in Table 6.
Cisplatin as the positive control in the present study is found to exhibit remarkable growth inhibitory
activities with mean IC50 values ranging from 1.4-5.0 g ml-1 on the studied cancer cell lines.
Overall, the Schiff base ligands are found to be not cytotoxic against all the tested human cell lines.
The dimethyltin derivative of H2L1, 1 is only active against the MCF-7 cell line. The dibutyltin and
dicyclohexyltin derivatives [compounds 2 and 4] show prominent cytotoxicity activities for all the
tested cell lines. However, the dibenzyltin and di(p-chlorobenzyl)tin derivatives are found to be
inactive in all the tested cell lines.
16

Among the H2L2 complexes, the dicyclohexyltin derivative, 10 displays good cytotoxic activities in
all the tested cell lines. The dibutyltin derivative, 8 is found to be active against the MCF-7 and
SKOV-3 cell lines while, the diphenyltin derivative, 9 is only active against the SKOV-3 cell lines.
Similarly, the dibenzyltin and di(p-chlorobenzyl)tin derivatives are found to be inactive in all the
tested cell lines.
Among the H2L3 complexes, the dibutyltin and dicyclohexyltin derivatives [compounds 14 and 16]
show good cytotoxic activities in all the tested cell lines. While, the diphenyltin derivative, 15 is only
active against the MCF7 and SKOV3 cell lines.
In general, the dibutyltin and dicyclohexyltin derivatives show good cytotoxic activities with IC50
values ranging between 2-9 g ml-1. The dimethyltin, diphenyltin, dibenzyltin and
di(p-chlorobenzyl)tin derivatives are relatively less cytotoxic against most of the tested cell lines.
4. Conclusion
Several diorganotin complexes have been synthesized and characterized by various spectroscopic
techniques. The diorganotin complexes are five or six-coordinated, as shown by the spectroscopic
data and X-ray crystallographic diffraction. Compound 1 and 7 show a dimeric structure whereas
compounds 9, 13,15 and 16 are monomeric structures. The results of the cytotoxic activities of the
complexes are promising, whereby compounds 2 and 4 are most active among the diorganotin
complexes of H2L1 ligand. For the diorganotin complexes of H2L2 ligand, compound 10 shows
good cytotoxic activities against all the tested cell lines. Meanwhile, for the diorganotin complexes
of H2L3 ligand, compounds 14 and 16 show good cytotoxic activities against all the tested cell lines.
Thus, the above complexes can be considered as agents with potential anticancer activities.
17

Acknowledgements
The authors are grateful to University of Malaya for the financial support [Grant: BK029-2012,
RG080-09AFR, RP017B-14AFR] in supporting this research work.
Appendix
Crystallographic data for the compounds 1, 7, 9, 13, 15 and 16 have been deposited at the Cambridge
Crystallographic Data Center as supplementary publication numbers CCDC 1017649, CCDC
1017650, CCDC 1017651, CCDC 1017652, CCDC 1017653, CCDC 1022850. Copies of available
material may be obtained on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
+44 1223 336 033; or email: deposit@ccdc.cam.ac.uk).
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21

Table 1: 1H NMR chemical shifts (δ, ppm) of the Schiff base ligands and their diorganotin(IV) complexes
Compound H-3, H-4, H-6 (aromatic protons)
No.
-CH=N-
-OH
-CH2-
Sn-R
-
H2L1
6.63, d (1H, J = 8.3 Hz),
7.13-7.26, m (4H)
6.67, d (1H, J = 8.1 Hz),
7.25-7.35, m (4H)
6.62, d (1H, J = 8.1 Hz),
7.26-7.37, m (4H)
8.47, s (1H) 4.76, s (3H) 3.47-3.59, m (6H)
8.39, s (1H) 5.21, s (2H) 3.47-3.60, m (6H) 0.43, s (6H, Hα, 2J(119Sn-1H) = 88 Hz)
1a
8.94, s (1H) 5.24, s (2H) 3.55-3.65, m (6H) 1.64, t (4H, Hα, J = 6.3 Hz, 2J(119Sn-1H) = 75 Hz),
1.59, sbr (4H, Hβ, 3J(119Sn-1H) = 27 Hz),
2a
1.34, sbr (4H, Hγ, 4J(119Sn-1H) = 50 Hz),
0.86, t (6H, Hδ, J = 6.9 Hz, 5J(119Sn-1H) = 10 Hz)
3b
6.67, d (1H, J = 8.5 Hz),
8.58, s (1H) 5.27, s (2H) 3.48-3.63, m (6H) 7.28-7.38, m (4H), 7.40-7.52, m (6H)
7.15-7.26, m (4H)
6.60, d (1H, J = 8.2 Hz),
7.10-7.22, m (4H)
6.92, d (1H, J = 8.3 Hz),
7.10-7.21, m (4H)
6.74, d (1H, J = 8.3 Hz),
7.12-7.28, m (4H)
8.39, s (1H) 5.02, s (2H) 3.57-3.70, m (6H) 2.25, t (2H, Hα, J = 6.5 Hz, 2J(119Sn-1H) = 72 Hz),
1.24-1.76 (m, 20H, Hβ, Hγ, Hδ)
4a
5c
8.40, s (1H) 5.04, s (2H) 3.56-3.70, m (6H) 1.60, t (4H, Hα, J = 6.6 Hz, 2J(119Sn-1H) = 78 Hz),
7.51-7.75, m (10H)
8.56, s (1H) 5.20, s (2H) 3.60-3.77, m (6H) 1.20, t (4H, Hα, J = 6.5 Hz, 2J(119Sn-1H) = 78 Hz),
7.50-7.66, m (8H)
6c
H2L2
7a
6.67, d (1H, J = 8.4 Hz),
7.34-7.50, m (4H)
6.60, d (1H, J = 8.1 Hz),
7.23-7.40, m (4H)
6.60, d (1H, J = 8.2 Hz),
7.20-7.38, m (4H)
8.50, s (1H) 4.85, s (3H) 3.47-3.59, m (6H)
-
8.85, s (1H) 5.30, s (2H) 3.69-3.80, m (6H) 0.63, s (6H, Hα, 2J(119Sn-1H) = 88 Hz)
8.94, s (1H) 5.45, s (2H) 3.50-3.75, m (6H) 1.67, t (4H, Hα, J = 6.4 Hz, 2J(119Sn-1H) = 78 Hz),
1.62, sbr (4H, Hβ, 3J(119Sn-1H) = 28 Hz),
8a
1.42, sbr (4H, Hγ, 4J(119Sn-1H) = 52 Hz),
0.86, t (6H, Hδ, J = 6.9 Hz, 5J(119Sn-1H) = 10 Hz)
9b
6.90, d (1H, J = 8.4 Hz),
7.15-7.28, m (4H)
6.52, d (1H, J = 8.3 Hz),
7.10-7.34, m (4H)
6.60, d (1H, J = 8.2 Hz),
7.12-7.40, m (4H)
8.52, s (1H) 5.04, s (2H) 3.56-3.82, m (6H) 7.37-7.47, m (4H), 7.50-7.76, m (6H)
8.59, s (1H) 5.10, s (2H) 3.50-3.62, m (6H) 2.25, t (2H, Hα, J = 6.6 Hz, 2J(119Sn-1H) = 74 Hz),
1.24-1.76, m (20H, Hβ, Hγ, Hδ)
10a
11c
8.58, s (1H) 5.21, s (2H) 3.50-3.68, m (6H) 1.30, t (4H, Hα, J = 6.6 Hz, 2J(119Sn-1H) = 77 Hz),
7.45-7.68, m (10H)
22

12c
H2L3
13a
6.70, d (1H, J = 8.2 Hz),
7.10-7.35, m (4H)
6.73, d (1H, J = 8.4 Hz),
7.13-7.25, m (4H)
6.73, d (1H, J = 8.1 Hz),
7.13-7.38, m (4H)
6.64, d (1H, J = 8.2 Hz),
7.05-7.34, m (4H)
8.60, s (1H) 5.20, s (2H) 3.69-3.80, m (6H) 1.20, t (4H, Hα, J = 6.5 Hz, 2J(119Sn-1H) = 77 Hz),
7.40-7.65, m (8H)
8.51, s (1H) 4.83, s (2H) 3.50-3.65, m (6H)
-
8.40, s (1H) 5.02, s (2H) 3.40-3.62, m (6H) 0.42, s (6H, 2J(119Sn-1H) =76 Hz)
8.91, s (1H) 5.27, s (2H) 3.50-3.68, m (6H) 1.64, t (4H, Hα, J = 6.4 Hz, 2J(119Sn-1H) = 78 Hz),
1.60, sbr (4H, Hβ, 3J(119Sn-1H) = 28 Hz),
14a
1.42, sbr (4H, Hγ, 4J(119Sn-1H) = 52 Hz),
0.86, t (6H, Hδ, J = 6.9 Hz, 5J(119Sn-1H) = 10 Hz)
15b
16a
17c
18c
6.86, d (1H, J = 8.4 Hz),
7.10-7.25, m (4H)
6.71, d (1H, J = 8.3 Hz),
7.12-7.34, m (4H)
6.65, d (1H, J = 8.2 Hz),
7.12-7.35, m (4H)
8.53, s (1H) 5.05, s (2H) 3.66-3.80, m (6H) 7.31-7.42, m (4H), 7.45-7.58, m (6H)
8.56, s (1H) 5.05, s (2H) 3.39-3.73, m (6H) 2.25, t (2H, Hα, J = 6.6 Hz, 2J(119Sn-1H) = 74 Hz),
1.24-1.76, m (20H, Hβ, Hγ, Hδ)
8.55, s (1H) 5.08, s (2H) 3.40-3.73, m (6H) 1.70, t (4H, Hα, J = 6.6 Hz, 2J(119Sn-1H) = 77 Hz),
7.45-7.70, m (10H)
6.65, d (1H, J = 8.2 Hz),
7.10-7.35, m (4H)
8.54, s (1H) 5.10, s (1H) 3.40-3.70, m (6H) 2.80, t (4H, Hα, J = 6.5 Hz, 2J(119Sn-1H) = 77 Hz),
7.40-7.65, m (8H)
[s: singlet; sbr: singlet broad; d: doublet; t: triplet; m: complex pattern ]
a spectra recorded in CDCl3
b spectra recorded in DMSO-d6
c spectra recorded in 1,4-dioxane + 2-3 drops of CDCl3
23

Table 2: 13C NMR chemical shifts (δ, ppm) of the Schiff base ligands and their corresponding diorganotin(IV) complexes
Compound No. C-1, C-2, C-3, C-4, C-5, C-6
C-8
67.2
C-7
164.6
C-9, C-10, C-11
61.2
Sn-(Cα to Cδ)
-
118.6, 163.7, 117.7,
132.6, 117.3, 132.4
121.9, 168.4,18.5,
136.5, 117.8, 133.5
122.3, 169.7, 117.6,
135.9, 116.1, 133.9
H2L1
1a
67.3
66.9
173.3
173.6
61.5, 62.4
63.7, 64.2
1.1 (Cα, 1J(119Sn-13C) = 710 Hz)
21.2 (Cα, 1J(119Sn-13C) = 565 Hz),
27.3 (Cβ, 2J(119Sn-13C) = 28 Hz),
26.8 (Cγ, 3J(119Sn-13C) = 77 Hz),
13.6 (Cδ)
2b
122.0, 168.8, 117.7,
136.7, 116.6, 132.9
67.9
67.5
173.7
173.4
61.5, 60.4
60.4, 61.8
137.5 (Cα, 1J(119Sn-13C) = 510 Hz),
130.0 (Cβ, 2J(119Sn-13C) = 22 Hz),
127.8 (Cγ, 3J(119Sn-13C) = 56 Hz),
131.8 (Cδ)
3b
4a
122.0, 170.1, 118.0,
136.9, 116.8, 133.0
41.0 (Cα, 1J(119Sn-13C) = 574 Hz),
30.4 (Cβ, 2J(119Sn-13C) = 22 Hz),
28.8 (Cγ, 3J(119Sn-13C) = 76 Hz),
26.4 (Cδ)
122.0, 168.9, 118.2,
136.4, 116.8, 132.6
67.0
66.3
67.2
67.3
67.3
172.3
172.2
163.8
172.0
172.9
61.4, 63.2
61.7, 62.5
61.2
10.8 (Cα, 1J(119Sn-13C) = 602 Hz),
135.7, 125.3, 124.2, 128.2
5c
6c
122.9, 167.9, 118.3,
135.9, 117.3, 133.6
8.9 (Cα, 1J(119Sn-13C) = 596 Hz),
133.3, 127.6, 124.9, 131.0
120.4, 163.8, 119.6,
132.7, 118.8, 131.3
-
H2L2
7a
124.3, 158.8, 114.9,
136.9, 106.6, 132.0
63.8, 64.4
62.4, 63.6
12.2 (Cα, 1J(119Sn-13C) = 690 Hz)
124.4, 168.5, 118.8,
139.1, 106.8, 137.2
21.3 (Cα, 1J(119Sn-13C) = 565 Hz),
27.3 (Cβ, 2J(119Sn-13C) = 31 Hz),
26.8 (Cγ, 3J(119Sn-13C) = 78 Hz),
13.6 (Cδ)
8a
124.5, 167.7, 119.3,
138.4, 106.4, 134.4
68.3
172.7
61.1, 64.0
136.3 (Cα, 1J(119Sn-13C) = 498 Hz),
130.2 (Cβ, 2J(119Sn-13C) = 24 Hz),
129.6 (Cγ, 3J(119Sn-13C) = 56 Hz),
9b
24

135.0 (Cδ)
10a
124.4, 168.6, 119.1,
137.4, 106.5, 135.2
67.0
172.1
61.0, 61.2
43.9 (Cα, 1J(119Sn-13C) = 530 Hz),
29.9 (Cβ, 2J(119Sn-13C) = 22 Hz),
28.1 (Cγ, 3J(119Sn-13C) = 78 Hz),
26.4 (Cδ)
124.0, 165.8, 119.7,
137.5, 106.9, 130.5
67.5
66.4
67.2
171.5
169.7
165.1
60.8, 61.9
59.3, 61.0
61.2
9.3 (Cα, 1J(119Sn-13C) = 587 Hz),
135.0, 128.2, 124.5, 129.9
11c
12c
124.5, 165.8, 120.0,
137.6, 109.5, 131.1
9.4 (Cα, 1J(119Sn-13C) = 590 Hz),
138.2, 128.4, 127.3, 129.8
121.1, 163.8, 119.4,
135.5, 106.6, 134.4
-
H2L3
123.8, 167.1, 118.5,
135.6, 118.1, 134.5
68.0
67.3
171.9
172.9
61.0, 61.2
61.1, 63.8
8.7 (Cα, 1J(119Sn-13C) = 590 Hz)
13a
14a
124.1, 168.1, 120.3,
136.6, 118.9, 134.1
21.4 (Cα, 1J(119Sn-13C) = 560 Hz),
27.4 (Cβ, 2J(119Sn-13C) = 31 Hz),
26.9 (Cγ, 3J(119Sn-13C) = 78 Hz),
13.6 (Cδ)
123.9, 167.3, 119.2,
136.4, 118.3, 129.0
68.1
68.0
172.6
171.8
61.1, 64.3
60.7, 61.5
136.9 (Cα, 1J(119Sn-13C) = 498 Hz),
130.2 (Cβ, 2J(119Sn-13C) = 24 Hz),
128.7 (Cγ, 3J(119Sn-13C) = 56 Hz),
131.2 (Cδ)
15b
16a
123.8, 168.6, 119.5,
136.5, 118.5, 134.6.
40.4 (Cα, 1J(119Sn-13C) = 530 Hz),
30.2 (Cβ, 2J(119Sn-13C) = 22 Hz),
28.8 (Cγ, 3J(119Sn-13C) = 78 Hz),
24.2 (Cδ)
123.8, 167.7, 119.6,
135.6, 118.9, 133.4
67.4
67.6
171.7
171.7
61.4, 63.4
61.3, 62.2
9.0 (Cα, 1J(119Sn-13C) = 587 Hz),
135.0, 128.2, 124.3, 129.1
17c
18c
124.0, 168.5, 120.1,
135.2, 118.1, 134.0
8.6 (Cα, 1J(119Sn-13C) = 590 Hz),
138.2, 128.4, 127.3, 129.8
a spectra recorded in CDCl3
b spectra recorded in DMSO-d6
c spectra recorded in 1,4-dioxane + 2-3 drops of CDCl3
25

Table 3: 119Sn NMR spectral data of the diorganotin(IV) complexes
Compound No.
1a
δ (ppm)
-164.4
2a
3b
-189.2
-324.7
4a
5c
6c
7c
8a
-244.5
-174.4
-174.9
-174.8
-186.9
26

9a
-325.5
-243.1
-174.7
-179.1
-163.4
-186.6
-325.3
-244.2
-190.1
-188.9
10b
11a
12c
13c
14c
15a
16a
17b
18a
a spectra recorded in CDCl3
b spectra recorded in DMSO-d6
c spectra recorded in 1,4-dioxane + 2-3 drops of CDCl3
27

Table 4
Crystallographic data of bis[(2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)[dimethyltin(IV), 1, bis[(2-{[1,1-
bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)]dimethyltin(IV), 7, (2-{[1,1-bis(hydroxymethyl)-2-
oxidoethyl]iminomethyl}-4-bromophenolato)diphenyltin(IV), 9, 2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
chlorophenolato)dimethyltin(IV), 13, (2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)diphenyltin(IV), 15 and (2-
{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)dicyclohexyltin(IV), 16
Compound
1
7
9
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Empirical formula
Formula weight
Crystal system, space group
a (Å)
C13H19NO4Sn
371.98
Triclinic, Pī
8.5456(2)
8.8357(2)
10.5779(2)
65.470(1)
C26H36Br2N2O8Sn2
901.77
Monoclinic, P21/n
18.9301(4)
C23H22BrNO4Sn
575.02
Triclinic, Pī
8.0138(1)
11.6732(1)
29.5049(3)
104.680(1)
94.759(1)
113.230(1)
1123.57(5)
2
b (Å)
8.8951(2)
19.8873(4)
c (Å)
α (o)
90
β (o)
71.212(1)
89.592(1)
680.42(3)
114.075(1)
γ (o)
90
Volume (Å3)
3057.43(11)
4
1.959
Z
2
Calculated density (mg m-3)
1.816
1.887
372
1.700
µ (mm-1)
4.297
1760
2.944
568
F(000)
θ range (o) for data collection
Reflections collected / unique
Max. and min. transmission
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Δρmax/Δρmin (e Å-3)
2.26 to 27.50
6470 / 3089 [R(int) = 0.020]
0.746and 0.600
3089 / 0 / 176
1.13
R1 = 0.024, wR2 = 0.076
R1 = 0.025, wR2 = 0.077
1.51 and -0.95
1.25 to 27.49
21362 / 7016 [R(int) = 0.0279]
0.390 and 0.0.278
7016 / 0 / 365
1.16
R1 = 0.029, wR2 = 0.085
R1 = 0.039, wR2 = 0.105
1.60 and -1.09
1.45 to 27.50
8208 / 5038 [R(int) = 0.018]
0.417 and 0.364
5038 / 0 / 274
1.16
R1 = 0.024, wR2 = 0.071
R1 = 0.029, wR2 = 0.009
0.75 and -0.79
28

Table 4 (continued)
Crystallographic data of bis[(2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}phenolato)[dimethyltin(IV), 1, bis[(2-{[1,1-
bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-bromophenolato)]dimethyltin(IV), 7, (2-{[1,1-bis(hydroxymethyl)-2-
oxidoethyl]iminomethyl}-4-bromophenolato)diphenyltin(IV), 9, 2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-
chlorophenolato)dimethyltin(IV), 13, (2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)diphenyltin(IV), 15 and (2-
{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-4-chlorophenolato)dicyclohexyltin(IV), 16
Compound
13
15
16
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Empirical formula
Formula weight
Crystal system, space group
a (Å)
C13H18ClNO4Sn
406.42
C23H22ClNO4Sn
530.56
C23H34ClNO4Sn
542.65
Monoclinic, C2/c
14.8956(6)
13.8128(5)
16.7610(6)
90
Triclinic, Pī
8.6518(3)
9.9622(4)
15.0439(6)
100.951(2)
102.843(2)
113.111(1)
1105.8(7)
Monoclinic, P21/n
17.0081(4)
12.6893(4)
22.1755(6)
90
b (Å)
c (Å)
α (o)
β (o)
114.299(2)
90
3143.1(2)
97.778(2)
90
4764.2(2)
γ (o)
Volume (Å3)
Z
8
2
8
Calculated density (mg m-3)
1.718
1.807
1.593
1.305
1.513
µ (mm-1)
1.213
F(000)
1616
532
2224
θ range (o) for data collection
Reflections collected / unique
Max. and min. transmission
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Δρmax/Δρmin (e Å-3)
2.14 to 31.56
16984 / 3594 [R(int) = 0.027]
0.899 and 0.497
3594 / 2 / 191
1.24
R1 = 0.018, wR2 = 0.054
R1 = 0.021, wR2 = 0.068
0.75 and -0.46
2.13 to 31.55
9422 / 4953 [R(int) = 0.016]
0.926 and 0.591
4973 / 0 / 273
1.34
R1 = 0.020, wR2 = 0.060
R1 = 0.026, wR2 = 0.097
0.66 and -1.17
2.28 to 19.84
37000 / 8392 [R(int) = 0.137]
0.942 and 0.839
8392 / 0 / 545
1.00
R1 = 0.053, wR2 = 0.086
R1 = 0.110, wR2 = 0.105
0.68 and -0.68
29