Speciation of Phytate Ion in Aqueous Solution. Trimethyltin(IV) Interactions in Self Medium†

In this paper the results of a potentiometric (ISE-[H⁺] glass electrode) investigation at t = 25 °C on the complexing ability of phytate towards trimethyltin(IV) (tmt) and on the acid-base properties of tmt at high metal concentration (0.050 and 0.075 mol L^-1) are reported. First we determined the hydrolytic constants of tmt in aqueous solution without further addition of background salt (self medium); in these experimental conditions we verified the formation of the following hydrolytic species: tmt(OH)⁰, tmt(OH)₂^- and the binuclear species (tmt)₂(OH)⁺. Successively, we studied the complex formation constants obtained from the interaction of phytate anion with tmt in the same experimental conditions of hydrolytic measurements; the speciation model obtained takes into account several polynuclear species (tmtH₅Phy^6-; tmt₂H₅Phy^5-; tmt₃H₄Phy^5-; tmt₃H₅Phy^4-; tmt₄H₆Phy^2-; tmt₅HPhy^6-). A comparison with literature data is reported too.