Potentiometric study of tungsten(VI) complex formation with tartrate

Complexation of tungstate with tartrate has been investigated by potentiome try in the pH range 2.5-7.5 in 1 M-KNO3 at 25 degreesC. The experimental da ta were evaluated with ESAB (for the calculation of protonation constants o f tartrate) and OPIUM (for the calculation of formation constants of comple xes) computer programs. A high number of chemical models including polynucl ear complexes were considered and tested on a computer. The final model com prises five complexes that have a tungsten(VI) : tartrate ratio of 2 : 2 an d 1 : 2. The following formation constants (beta (p,q,r)) were calculated: log beta (212) = 16.6 +/- 0.1, log beta (312) = 20.4 +/- 0.2, log beta (412 ) = 23.9 +/- 0.1, log beta (322) = 26.68 +/- 0.08, and log beta (422) = 30. 7 +/- 0.1, where p, q, r refer to stoichiometric coefficients in general fo rmula (H)(p)(WO4)(q)(C4H4O6)(r)(p-2q-2r). Structures of the complexes were proposed.