226
C. De Stefano . C. Foti . A. Gianguzza . S. Sammartano
mation of the anion species [(CH3Sn}zA(OHhro. ll7 (curve 5) considerably lowers the
formation percentage of the corresponding simple hydrolytic species, [(CH 3 Snh(OHhl+'
and becomes predominant by achieving a formation percentage of over 70%, in the
pH range 6-7. Association with the anion components of sea water does not influence
the formation of the other important species [CH 3 Sn(OHhlo formed at higher pH
values. On the contrary, the interaction with the cation component (B) of sea water
leads to the formation of the very strong species [CH 3 SnB(OH)41+o. 117 which becomes
the only present at pH > 10. In conclusion, at seawater pH value, hydrolytic species of
monomethyltin(IV) are [(CH 3 Snh(OHhl+' [CH 3 Sn(OHhlo and [(CH 3 Sn}zA(OH)sro. ll7
with formation percentages achieving 10%, 20% and 75%, respectively.
11.7
Conclusions
The most important feature of the solution chemistry of organotin(IV) compounds
lies in their very strong hydrolysis. No study of the speciation of these cations can be
made without deep knowledge of their hydrolysis thermodynamic parameters. In the
absence of interacting anions, in the pH range of interest for natural fluids, (CH3)xSn(4-X)
is fully hydrolyzed. The interaction of chloride and sulfate complexes is significant,
but no very strong species are formed. However, owing to the high concentration of
these anions in sea water, the speciation of (CH3)xSn(4-X) cations is altered, as shown
in Fig. 11.7-11.9. Note that at pH > 10 the cation of sea salt also interacts with the anionic species of dimethyltin(IV). Other major anionic components of sea water were
not considered in this report, i.e. F- and CO~- (or HC0 3 ). As regards carbonate, recent
measurements from these laboratories showed that it forms strong complexes which
may have great importance in the speciation of alkyltin(IV) cations.
The final remarks must deal with the scarceness of data we can found in literature.
In particular we need:
a. hydrolysis constants of other alkyltin(IV) cations (in particular unsimmetrical);
b. dependence on medium in large ionic strength range;
c. more calorimetric measurements to obtain reliable thermodynamic parameters;
d. formation constants for inorganic complexes, in particular with fluoride and carbonate.
References
Aizawa S, Natsume T, Hatano K, Funahaschi S (1996) Complexation equilibria and structure of
dimethyltin(IV) complexes with N -methyliminodiacetate, pyridine-2,6-dicarboxylate, ethylenediamine-N-N'-diacetate and ethylenediamine-N,N,N',N'-tetracetate. Inorg Chim Acta 248:215-224
Arakawa Y, Wada 0 (1993) Biological properties of alkyltin compounds. In: Siegel H, Siegel A (eds)
Metal ions in biological systems, vol XXIX. Marcel Dekker, Inc., New York, Basel, p 101-136
Arena G, Gianguzza A, Pellerito L, Purrello R, Rizzarelli E (1989) Thermodynamics of hydroxo complex formation of dialkyltin{IV) ions in aqueous solution. J Chern Soc Dalton Trans 773-777
Asso M, Carpeni G (1968) Recherches sur Ie point isohydrique et les equilibres acido-basique de condensation ou association en chimie. XXVII. Les hydroxocomplexes des sels organostanniques
(CH3hSnCI et (C2HshSnCI, en solutions aqueuses, 11 25°C et 11 differentes forces ioniques. Can J of
Chern 46:1795-1802
Barbieri R, Silvestri A (1991) The hydrolysis of Me2Sn{IV) and Me3Sn{IV) moieties monitored through
119Sn Mossbauer spectroscopy. Inorganica Chimica Acta 188:95-98
C. De Stefano . C. Foti . A. Gianguzza . S. Sammartano
mation of the anion species [(CH3Sn}zA(OHhro. ll7 (curve 5) considerably lowers the
formation percentage of the corresponding simple hydrolytic species, [(CH 3 Snh(OHhl+'
and becomes predominant by achieving a formation percentage of over 70%, in the
pH range 6-7. Association with the anion components of sea water does not influence
the formation of the other important species [CH 3 Sn(OHhlo formed at higher pH
values. On the contrary, the interaction with the cation component (B) of sea water
leads to the formation of the very strong species [CH 3 SnB(OH)41+o. 117 which becomes
the only present at pH > 10. In conclusion, at seawater pH value, hydrolytic species of
monomethyltin(IV) are [(CH 3 Snh(OHhl+' [CH 3 Sn(OHhlo and [(CH 3 Sn}zA(OH)sro. ll7
with formation percentages achieving 10%, 20% and 75%, respectively.
11.7
Conclusions
The most important feature of the solution chemistry of organotin(IV) compounds
lies in their very strong hydrolysis. No study of the speciation of these cations can be
made without deep knowledge of their hydrolysis thermodynamic parameters. In the
absence of interacting anions, in the pH range of interest for natural fluids, (CH3)xSn(4-X)
is fully hydrolyzed. The interaction of chloride and sulfate complexes is significant,
but no very strong species are formed. However, owing to the high concentration of
these anions in sea water, the speciation of (CH3)xSn(4-X) cations is altered, as shown
in Fig. 11.7-11.9. Note that at pH > 10 the cation of sea salt also interacts with the anionic species of dimethyltin(IV). Other major anionic components of sea water were
not considered in this report, i.e. F- and CO~- (or HC0 3 ). As regards carbonate, recent
measurements from these laboratories showed that it forms strong complexes which
may have great importance in the speciation of alkyltin(IV) cations.
The final remarks must deal with the scarceness of data we can found in literature.
In particular we need:
a. hydrolysis constants of other alkyltin(IV) cations (in particular unsimmetrical);
b. dependence on medium in large ionic strength range;
c. more calorimetric measurements to obtain reliable thermodynamic parameters;
d. formation constants for inorganic complexes, in particular with fluoride and carbonate.
References
Aizawa S, Natsume T, Hatano K, Funahaschi S (1996) Complexation equilibria and structure of
dimethyltin(IV) complexes with N -methyliminodiacetate, pyridine-2,6-dicarboxylate, ethylenediamine-N-N'-diacetate and ethylenediamine-N,N,N',N'-tetracetate. Inorg Chim Acta 248:215-224
Arakawa Y, Wada 0 (1993) Biological properties of alkyltin compounds. In: Siegel H, Siegel A (eds)
Metal ions in biological systems, vol XXIX. Marcel Dekker, Inc., New York, Basel, p 101-136
Arena G, Gianguzza A, Pellerito L, Purrello R, Rizzarelli E (1989) Thermodynamics of hydroxo complex formation of dialkyltin{IV) ions in aqueous solution. J Chern Soc Dalton Trans 773-777
Asso M, Carpeni G (1968) Recherches sur Ie point isohydrique et les equilibres acido-basique de condensation ou association en chimie. XXVII. Les hydroxocomplexes des sels organostanniques
(CH3hSnCI et (C2HshSnCI, en solutions aqueuses, 11 25°C et 11 differentes forces ioniques. Can J of
Chern 46:1795-1802
Barbieri R, Silvestri A (1991) The hydrolysis of Me2Sn{IV) and Me3Sn{IV) moieties monitored through
119Sn Mossbauer spectroscopy. Inorganica Chimica Acta 188:95-98