Hydrolysis of dimethylphenyltin(IV) and triphenyltin(IV) chlorides in different aqueous ethanol solutions

Article abstract of DOI:10.1139/V08-079

The hydrolysis of [(Me)₂(Ph)Sn(IV)]⁺ and [(Ph) ₃Sn(IV)]⁺ has been investigated at 25 °C and different aqueous solutions of ethanol, using a combination of spectrophotometric and potentiometric techniques. The species formed together with their formation constants have been determined using the computer program Squad over a wide pH range of 1 to 11. The hydrolysis constants in different media were analyzed in terms of Kamlet and Taft parameters. Single-parameter correlation of the formation constants, K₁₁ and K₁₂, versus α (hydrogen-bond donor acidity), β (hydrogenbond acceptor basicity), and π* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but multiparameter correlation represents significant improvement with regard to the single-parameter models. In this work, we have also used the normalized polarity parameter, E_T^N, alone and in combination with the Kamlet-Taft parameter to find a better correlation of the formation constants in different aqueous ethanol solutions.

Full text of DOI:10.1139/V08-079

751
Hydrolysis of dimethylphenyltin(IV) and
triphenyltin(IV) chlorides in different aqueous
ethanol solutions
Morteza Jabbari, Farrokh Gharib, Mostafa Mohammadpour Amini, and
Amirreza Azadmehr
Abstract: The hydrolysis of [(Me)2(Ph)Sn(IV)]+ and [(Ph)3Sn(IV)]+ has been investigated at 25 °C and different aque-
ous solutions of ethanol, using a combination of spectrophotometric and potentiometric techniques. The species formed
together with their formation constants have been determined using the computer program Squad over a wide pH range
of 1 to 11. The hydrolysis constants in different media were analyzed in terms of Kamlet and Taft parameters. Single-
parameter correlation of the formation constants, K11 and K12, versus α (hydrogen-bond donor acidity), β (hydrogen-
bond acceptor basicity), and π* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but
multiparameter correlation represents significant improvement with regard to the single-parameter models. In this work,
we have also used the normalized polarity parameter, ETN, alone and in combination with the Kamlet–Taft parameter to
find a better correlation of the formation constants in different aqueous ethanol solutions.
Key words: dimethylphenyltin(IV) chloride, triphenyltin(IV) chloride, hydrolysis constant, aqueous ethanol solutions,
solvent effect.
Résumé : On a étudié l’hydrolyse des cations [(Me)2(Ph)Sn(IV)]+ et [(Ph3)Sh(IV)]+ en faisant appel à une combinaison
de techniques spectrophotométriques et potentiométriques et en opérant à 25 °C, dans diverses solutions aqueuses
d’éthanol. Faisant appel au programme informatique Squad, on a déterminé la nature des espèces qui se forment ainsi
que leurs constantes de formation pour une plage de pH allant de 1 à 11. Les constantes d’hydrolyse dans les divers
milieux ont été analysées en fonction de paramètres de Kamlet et de Taft. Dans les deux cas, les corrélations de para-
mètres uniques des constantes de formation, K11 et K12 en fonction d’α (acidité d’une liaison hydrogène donneur), de β
(basicité d’une liaison hydrogène accepteur) et de π* (caractère dipolaire/polarisabilité) sont relativement mauvaises
pour toutes les solutions; toutefois, les corrélations à plusieurs paramètres présentent des améliorations sensibles par
N
rapport aux modèles à un seul paramètre. Dans ce travail, on a aussi utilisé le paramètre de polarité normalisée, ET
,
seul ou en combinaison avec le paramètre de Kamlet–Taft, pour déterminer une meilleure corrélation des constantes de
formations dans les diverses solutions aqueuses d’éthanol.
Mots-clés : chlorure de diméthylphénylétain(IV), chlorure de triphénylétain(IV), constante d’hydrolyse, solutions
aqueuses d’éthanol, effet de solvant.
[Traduit par la Rédaction] Jabbari et al. 756
Introduction
been the subject of many recent papers. These ions have
rather unusual effects on the structure in water as a solvent.
There should be a particularly pronounced ordering of water
molecules in the equatorial plane of the dialkyltin(IV) ions
because of the strong electrostatic field near the tin atom. In
addition, the hydrophobic nature of the alkyl groups will
tend to force more hydrogen bonding in the solvent around
the axial positions.
Owing to antitumour activity, we have recently begun to
investigate several reaction equilibria of organotin(IV) spe-
cies with some ligands, particularly those of biological inter-
est, such as amino acids, peptides, and nucleotides. The
main objectives of the research are to establish the stoichio-
metries, structures, and stability constants of the reactions of
organotin ions with a range of ligands having a variety of
donor atoms. The effect of varying reaction media, such as
ionic strength, ionic media, and using different aqueous–
organic solvents on the stability, hydrolysis, and protonation
constants are also investigated.
Organotin(IV) complexes have been found to exhibit rela-
tively high antitumour activity (1–15). Several authors have
tried to elucidate many aspects of these complexes, such as
their structures, stability constants, binding sites, chelating
donor atoms of a ligand, and so forth (1–15). The structures
adopted by the di- and tri-alkyltin(IV) ions in aqueous solu-
tions appear to have linear C-Sn-C and planar skeletons, re-
spectively (16–17). Information pertaining to the structure
and behavior of these ions in solution at different pHs has
Received 5 December 2007. Accepted 11 April 2008.
Published on the NRC Research Press Web site at
canjchem.nrc.ca on 9 June 2008.
M. Jabbari, F. Gharib,1 M.M. Amini, and A. Azadmehr.
Chemistry Department, Shahid Beheshti University, Tehran,
Evin, Iran.
1Corresponding author (e-mail: f-gharib@cc.sbu.ac.ir).
Can. J. Chem. 86: 751–756 (2008)
doi:10.1139/V08-079
© 2008 NRC Canada

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Can. J. Chem. Vol. 86, 2008
Now we have extended our work to triorganotin(IV) with
Measurements
mixed alkyl and aryl substitution bonded to tin for
complexation framework study. Accepting the hypothesis
that R2Sn2+ and R3Sn+ are the usual active species for
antitumour action of organotins (18), a good antitumour
agent should be easily dissociable following administration.
This requires weak bonds between tin and the donor atom of
the coordinated ligands, which are readily hydrolysable. If
the compound is hydrolytically unstable, the R2Sn2+ and
R3Sn+ moieties will be released too soon, and if it is too sta-
ble it may be released too slowly and consequently lower ac-
tivity will be observed. Therefore, there is a relationship
between the stability of the organotin compounds and their
antitumour activity.
Organotin cations are considered to be acids, in the Lewis
scale, of different hardness, depending on the groups bonded
to the tin(IV). Consequently, they show a strong tendency to
hydrolysis in aqueous solution, as demonstrated by several
authors (5–9). Other studies on the interactions of organotin
cations with O-donor ligands have been recently reported,
confirming the results obtained previously in the hydrolysis
investigations (19–21).
All measurements were carried out at 25 °C. The ionic
strength was maintained with sodium perchlorate, 0.1 mol dm–3,
as supporting electrolyte. The pH-meter was calibrated for
the relevant H+ concentration with a solution of 0.01 mol dm–3
of HClO4 solution containing 0.09 mol dm–3 sodium per-
chlorate (for adjusting the ionic strength to 0.1 mol dm–3).
We set –log[H+] = 2.0 (22). Junction potential corrections
have been calculated from eq. [1]
[1]
–log[H+]real = –log[H+]measured + a + b[H+]measured
where a and b were determined by measuringthe hydrogen
ion concentration for two different solutions of perchloric
acid with sufficient sodium perchlorate to adjust the ionic
strength.
Procedure
Acidic solution (50 mL) of dimethylphenyltin(IV) or
triphenyltin(IV) chlorides, (1.0–2.0 × 10–3 mol dm–3), was
titrated with an alkali solution, 0.1 mol dm–3 NaOH with the
same ionic strength and mole fraction of ethanol. Due to in-
solubility of triorganotin(IV) in water, aqueous ethanol solu-
tion has been used. The –log[H+] and absorbance were
measured after addition of a few drops of titrant, and this
procedure was extended up to the required –log[H+]. To ex-
clude carbon dioxide from the system, a stream of purified
nitrogen was passed through a sodium chloride solution and
then bubbled slowly through the reaction solution. In all
cases, the procedure was repeated at least three times and
the resulting average values and corresponding standard de-
viation are shown in the text and tables.
This work deals with the study of hydrolysis of
(CH3)2C6H5Sn(IV) and (C6H5)3Sn(IV) to investigate the ef-
fect of a changing dielectric constant on the hydrolysis of
triorganotin(IV).
Experimental section
Chemicals
Sodium perchlorate was obtained from Merck as an ana-
lytical reagent grade material and was dried under vacuum at
room temperature for at least 72 h before use. The NaOH
solution was prepared from a titrisol solution (Merck) and
its concentration was determined by several titrations with
standard HCl solution. Perchloric acid, ethanol (absolute),
and triphenyltin(IV) were obtained from Merck and Fluka,
respectively, as analytical reagent grade materials and were
used as supplied. Dilute acid solution was standardized
against standard NaOH solution. Dimethylphenyltin(IV)
chloride was synthesized following the procedure described
before (18). All dilute solutions were prepared from double-
distilled water with specific conductance equal to 1.3 0.1 µ
Calibration of the glass electrode
The glass electrode potential in an aqueous solution
differs from that in a solution of mixed solvents, and a
liquid-junction potential of uncertain magnitude may affect
the results. To overcome this difficulty, it was necessary to
calibrate the glass electrode in different solvent mixtures.
The experimental method outlined by Van Uitert and Hass
(23) and the proposed eq. [2] were employed for this pur-
pose.
[2]
–log[H+] = B + logµH° + logγ
Where B is the actual pH-meter reading, γ the mean activ-
ity coefficient of perchloric acid in the solvent mixture at the
same temperature and ionic strength, and µH° is the correc-
tion factor. Values of B (pH-meter readings) were recorded
in various aqueous solvent mixtures ranging from 50% to
80% (v/v) ethanol containing a known concentration of
perchloric acid and sufficient sodium perchlorate to give a
constant ionic strength of 0.1 mol dm–3. The difference be-
tween the logarithm of the known hydrogen ion concentra-
tion and the corresponding values of B was used to calculate
values of the correction term, logµH°.
Ω–1 cm–1
.
Apparatus
A Jenway research pH-meter, model 3520 (with a preci-
sion of 0.001 units), was used for pH measurements. The hy-
drogen ion concentration was measured with a combination
electrode (Jenway). Spectrophotometric titrations were per-
formed on a UV–vis Shimadzu 2100 spectrophotometer
(with a precision of 0.0002 units) combined to a Pentium 4
computer and using thermostated matched 10 mm quartz
cells. The measurement cell was of flow type. A Masterflex
pump allowed circulation of the solution under study from
the potentiometric cell to the spectrophotometric cell. So,
the absorbance and pH of the solution could be measured si-
multaneously.
Results and discussion
Organotin(IV) generally hydrolyzes to form a series of
mono- and poly-nuclear hydroxo complexes. The hydrolysis
reaction, in general, could be as
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Jabbari et al.
753
Table 1. Average values of hydrolysis constants for Me2PhSn(IV)
(np–q)+
[3]
pMn+ + q(OH)– ꢀ Mp(OH)q
and Ph3Sn(IV) species in different aqueous solutions of ethanol
at 25 °C and an ionic strength of 0.1 mol dm–3 (NaClO4).
with the hydrolysis constant, Kpq,
[4]
Kpq = [Mp(OH)q(np–q)+] / [Mn+]p[OH–]q
Ethanol
pK11
pK12
pK11
pK12
(% v/v)
(Me2PhSn)
(Me2PhSn)
(Ph3Sn)
(Ph3Sn)
In the case of dimethyltin(IV), as reported earlier (1), the
following mono- and di-nuclear complex species were con-
sidered [M(OH)]+, [M(OH)2], [M(OH)3]–, [M2(OH)2]2+, and
[M2(OH)3]+, where M represents (CH3)2Sn2+. The investiga-
tion was performed in the pH range of 1 to 11 employing a
nonlinear curve fitting method, with this notation that the
dinuclear hydroxo species never exceeded 6% of the total
dimethyltin(IV) (1).
50
55
60
65
70
80
0.86 0.02
0.65 0.01
0.48 0.03
0.50 0.02
0.56 0.03
—
6.41 0.05
6.35 0.04
6.32 0.06
6.33 0.05
6.4 0.06
—
0.84 0.02
0.68 0.03
0.57 0.03
0.73 0.02
0.98 0.04
1.10 0.03
5.53 0.04
5.25 0.05
5.07 0.05
5.20 0.06
5.49 0.05
5.95 0.04
To the best of our knowledge there have been no reports
on determination of the hydrolysis constant of dimethyl-
phenyltin(IV) species. Using again eq. [3], the hydroxo com-
plex species of the triorganotin ions were studied. The
hydrolysis constant values, Kpq, were determined spectro-
photometrically on the basis of the relation A = f(pH).
Absorbance, A, and –log[H+] were measured for a solution
containing (CH3)2C6H5Sn+ or (C6H5)3Sn(IV)+ with sufficient
NaOH solution, as described before. Treatment of the spec-
trophotometric data in the range of 230 to 280 nm (with an
interval of 1 nm) was obtained during the titrations as a
function of H+ concentration analyzed by the computer pro-
gram Squad (24). The final selection of the species resulting
from the computer program was based on graphical fitting.
In addition, the various statistical criteria, i.e., sums of the
squared residuals and the difference of total concentration of
the metal ion existing experimentally in solution from the
calculated ones, were considered.
Fig. 1. The equilibrium distribution of the hydrolyzed species of
(a) dimethylphenyltin(IV) and (b) triphenyltin(IV) in 70% etha-
nol (by volume) as a function of –log[H+] at 25 °C and ionic
strength 0.1 mol dm–3 (NaClO4).
The program allows calculation of the hydrolysis constant
for different stoichiometry models. Different models includ-
ing [M(OH)], [M(OH)2]–, and several polynuclear species
with various hydroxyl groups were tested by the program,
where M is (CH3)2C6H5Sn+ or (C6H5)3Sn+. As expected,
polynuclear species were rejected by the program, as were
M2(OH), M(OH)3, M2(OH)2, and M2O (charges are omitted
for simplicity). Values of these parameters for M2(OH) were
also calculated for both systems, but the species was not
considered further because the estimated error in its forma-
tion constant was unacceptable and its inclusion does not
improve the goodness of the fit. The species finally chosen
–
were M(OH) and M(OH)2 , resulting in a satisfactory graph-
ical fitting. The average values of the computed hydrolysis
constant of the metal ions for the wavelengths range used in
this study and different runs at various media are listed in
Table 1 and their mole fractions are plotted in Fig. 1 versus
–log[H+].
The hydrolysis of triphenyltin(IV) ion in dioxane–water
solution was previously investigated (25) and only one
hydrolytic species had been characterized. For clarification,
we applied the computer program in two ways: first calculat-
ing only one hydrolysis and second calculating two hydroly-
sis equilibria of triphenyltin(IV). The estimated error
resulting from the computer program for the first assumption
is about 100 times more than that for the second one. It is
also interesting to note that log K11 obtained from the first
method (in the solution of ethanol–water 70:30 by volume)
resulted in the value of 5.43, which is very close to the value
reported before in 75% dioxane–water solution, 5.71.
The hydrolysis of the organotins(IV) were studied care-
fully to determine whether any singly-bridged dimers analo-
gous to those observed with trialkyltin(IV) were formed.
Some association might be expected because the hydroxide
itself has been reported to be somewhat associated with or-
ganic solvents (26). While two bridging hydroxo groups are
more probable with coordination compounds, single OH
bridges are observed rarely. However, no appreciable con-
centration of such a dimer was found to exist in the range of
© 2008 NRC Canada

754
Can. J. Chem. Vol. 86, 2008
Table 2. The solvatochromic and normalized polarity parameters
of different aqueous solutions.
concentrations used in this work, which is in agreement with
results of other homologous triorganotin(IV) systems re-
ported before (27).
Ethanol
(% v/v)
Dielectric
constant
N
ET
β
α
π*
Solvent effect
50
55
60
65
70
80
65.67
63.63
61.34
58.76
55.84
48.64
1.097
1.085
1.072
1.057
1.040
0.999
0.536
0.547
0.559
0.572
0.587
0.625
0.960
0.939
0.916
0.890
0.860
0.786
0.918
0.905
0.891
0.874
0.855
0.809
To obtain a quantitative method for determination of the
solvent effect on physical properties, many empirical solvent
scales have been devised during the last two decades (28–
29). Among these scales (more than 40), the most compre-
hensive are the solvatochromic ones, but only a few of them
have found a wider application in the correlation analysis of
solvent effects. A quantitative measurement of the solvent
polarity has been introduced by Kamlet, Abboud, Abraham,
and Taft (KAT) (30–31). The KAT equation contains non-
specific as well as specific solute–solvent interactions sepa-
rately, and the latter should be subdivided into solvent
Lewis-acidity interactions (hydrogen-bond accepter, HBA,
solute and hydrogen-bond donor, HBD, solvent) and solvent
Lewis-basicity interactions (HBD solute–HBA solvent). This
approach has been widely and successfully applied in the
correlation analysis of many solvent-dependent processes
(28). Using the solvatochromic solvent parameters, α, β, and
π*, which have been introduced in previous reports (32–35),
the multiparametric equation, eq. [5], has been proposed for
use in the so-called linear solvation energy relationship.
solvent properties by means of single and multiple linear re-
gression analysis by a suitable computer program (37). We
used the Gauss–Newton linear least-squares method in the
computer program to refine the pK by minimizing the error
squares sum from eq. [7]. Single-parameter correlations of
log K11 and log K12 in terms of individually with α, β, or π*
did not give a good result for both cases.
2
[7]
S = ∑ (pKexp – pKcal)
So, we thought it would be interesting to correlate log K
versus a multiparametric equation involving α, β, and π*.
However, the results from eq. [5], multiparametric equation,
indicate significant improvement with regard to the single-
parameter models, eqs. [8] and [9] for dimethylphenyltin(IV)
and triphenyltin(IV), respectively.
[5]
pK = A0 + aα + bβ + pπ*
where A0 represents the regression value and π* is the index
of the solvent dipolarity/polarizability, which is a measure of
the ability of a solvent to stabilize a charge or a dipole by its
own dielectric effects. The π* scale was selected to run from
0.0 for cyclohexanone to 1.0 for dimethylsulfoxide. The α
coefficient represents the solvent hydrogen-bond donor
(HBD) acidity, in other words it describes the ability of a
solvent to donate a proton in a solvent to a solute hydrogen
bond. The α scale extends from 0.0 for nonHBD solvents to
about 1.0 for methanol. The β coefficient is a measure of a
solvent hydrogen-bond acceptor (HBA) basicity and de-
scribes the ability of a solvent to accept a proton in a solute
to solvent hydrogen bond. The β scale was selected to extend
from 0.0 for nonHBA solvents to about 1.0 for
hexamethylphosphoric triamide. The empirical values of the
solvatochromic solvent parameters (α, β, and π*) for pure
ethanol and water were found in the literature (28). How-
ever, the solvatochromic parameters for the different binary
aqueous mixtures of ethanol were calculated with the proce-
dure proposed by Blanco et al. (36) (eq. [6]),
[8a] pK11 = 353.79 + 219.86α – 464.73β – 359.40π*
[8b] pK12 = 78.37 + 207.05α – 181.24β – 210.36π*
(n = 5, r2 = 0.9983 and 0.9994, respectively)
[9a] pK11 = 551.80 + 154.92α – 618.97β – 405.36π*
[9b] pK12 = 560.77 + 592.52α – 859.30β – 775.68π*
(n = 6, r2 = 0.9997 and 0.9994, respectively)
The coefficients of π*, α, and β in eqs. [8]–[9] are very
different from each other and are almost in the order of β >
π* > α. This indicates the hydrogen-bond acceptor basicity
parameter of the solvent is the most important, the polarity
parameter plays a relatively small role, and finally, the hy-
drogen-bond donor acidity parameter has less significance in
changing the hydrolysis constant of tin(IV) systems in the
proposed various aqueous solutions of ethanol.
The solvent polarity parameter of the media, π*, increases
with increasing the mole fraction of water in aqueous solu-
tions of ethanol. If the π* of the media was the only factor
for the solvent effect on the complexation, it may be ex-
pected that the log K in a solution with a higher dielectric
constant should be greater than those of all the other aque-
ous solutions of ethanol. However, the hydrolysis constants
increase with increasing the solvent hydrogen-bond acceptor
basicity parameter, β, and decreases with increasing the sol-
vent polarity, π*, and the hydrogen-bond donor acidity pa-
rameter of the solvents, α, for different ethanol–water
mixtures, Table 1.
[6]
Pmixture = PEtOHXEtOH + PH O XH O
2 2
where P is the property of interest and X is the mole fraction
of the component in the solution. The calculated values of
solvatochromic parameters used for different aqueous mix-
tures of ethanol are listed in Table 2.
In eq. [5], the discontinuous polarizability correction term
is omitted because of the solvent used in this work contain-
ing no chlorine atoms. The regression coefficients, a, b, and
p, measure the relative susceptibilities of the solvent-
dependent log K to the indicated solvent parameters.
To explain the obtained log K values through the KAT sol-
vent parameter, the formation constants were correlated with
We have also tried to use the polarity scale proposed by
Reichardt (28, 38), ET, based on the solvatochromic behavior
of pyridinium N-phenoxide betaine dye. This dye is the most
solvatochromic compound reported to date. This scale has
© 2008 NRC Canada

Jabbari et al.
755
Table 3. The percentage contribution of KAT and normalized polarity parameters on the effect of dif-
ferent media on hydrolysis of the species at 25 °C and an ionic strength of 0.1 mol dm–3 (NaClO4).
In terms of eqs. [10] and [11]
In terms of eqs. [8] and [9]
N
Different species
ET
α
β
π*
α
β
π*
(CH3)2C6H5Sn(OH)
(CH3)2C6H5Sn(OH)2
(C6H5)3Sn(OH)
0.2
0.4
2.8
3.3
18.9
32.7
11.0
28.4
46.6
31.9
51.7
35.9
34.3
35.1
34.5
32.4
21.1
34.6
13.1
26.6
44.5
30.3
52.5
38.6
34.4
35.1
34.4
34.8
–
–
(C6H5)3Sn(OH)2
now been revised and normalized to ETN, known as normal-
Fig. 2. The plots of the experimental values of pK vs the calcu-
lated ones for triphenyltin(IV) for (a) pK11 and (b) pK12.
ized polarity parameter, due to the introduction of SI units.
N
ET has the value of zero for tetramethylsilane, the least po-
lar solvent, and 1.0 for water, the most polar solvent. The
N
ET value is related to the ability of a solvent to stabilize
N
charge separation in the dye, a correlation between the ET
and dielectric constant might be expected (28).
The hydrolysis constants again were correlated with ET
N
as a single linear regression analysis and then with the multi-
ple regression one with Kamlet and Taft’s (33) parameters
besides ETN. Single parameter correlation of pK in terms of
N
ET did not again give good results. However, the
multiparametric equation involving ETN, α, β, and π* showed
very significant improvement with regard to the single-
parameter model, eqs. [10]–[11] for dimethylphenyltin(IV)
and triphenyltin(IV), respectively.
N
[10a] pK11 = 375.83 + 1.99ET + 191.19α
– 471.46β – 347.74π*
N
[10b] pK12 = 89.70 + 2.01ET + 186.83α
– 182.08β – 200.52π*
(n = 5, r2 = 0.9989 and 1.0, respectively)
N
[11a] pK11 = 583.89 + 34.91ET + 139.21α
– 652.46β– 435.51π*
N
[11b] pK12 = 491.68 – 73.27ET + 622.31α
– 785.57β – 708.84π*
(n = 6, r2 = 1.0 and 0.9999, respectively)
To show the efficiency of the suggested multiparameter
correlations, experimental values of log K are plotted versus
their calculated ones from eqs. [10–11], for the different
aqueous ethanol solutions. It can be seen, Fig. 2, that the ex-
perimental and calculated values of log K are in good agree-
ment with each other, with r2 > 0.99 in both cases. From the
values of the regression coefficients, the contribution of each
parameter on a percentage basis was calculated and is listed
in Table 3.
hydrolytic species at pH ≅ 3 and 8, respectively. The
determined hydrolysis constants in different aqueous ethanol
solutions are analyzed in terms of Kamlet and Taft parame-
ters (33). Single-parameter correlation of the formation con-
stants in both cases are poor, but multiparameter correlation
represents significant improvement with regard to the single-
parameter models. Using the normalized polarity parameter
in combination with Kamlet–Taft parameters results in a
better correlation of the formation constants in the different
medias used.
Conclusions
The combined potentiometric and spectrophotometric
measurements were used to characterize the hydrolytic spe-
cies formed in dimethylphenyltin(IV) and triphenyltin(IV)
chlorides in various aqueous ethanol solutions. Our data re-
veal that the two coordinated water molecules on
triorganotin(IV) are able to release two protons to form two
Acknowledgement
One of us (MJ) gratefully acknowledges a research grant
from the Research Council of Shahid Beheshti University.
© 2008 NRC Canada

756
Can. J. Chem. Vol. 86, 2008
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