تعيين ثابتهاي اسيدي و پايداري كمپلكسهاي پارا - نيتروفنيل دي فسفات با فلزات دو ظرفيتي

Determination of The Acidity and Stability Constants of P-Nitrophenyl diphosphate Complexes with Divalent Metal Ions

The stability constants of 1:1 complexes formed between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ , or Cd2+ and the nitrophenyl-diphosphate NPhDP3ʹ were determined by potentiometric pH titration in aqueous solution (1= 0.1 M, NaNO3; 25°C). For comparison, the same values were measured for the corresponding complexes with the simple diphosphates monoesters (R-DP3ʹ ). The acidity constants for NPhDP3ʹ were measured also via potentiometric pH titration and various comparisons with related constants are made. By constraction of log KM(R_DP) versus p KHR_DP) plots for the complexes by a careful evaluation of the various data pairs from the straight-line correlation, the expectation is confirmed that in the M(NPhDP)ʹ- complexes the metal ion is only diphosphate-coordinated. The straight line equations, which result from the mentioned correlations, in adition with the pKa value of a given monoprotonated diphosphate monoester allow now to predict the stability constants of M(R-DP)ʹ-complexes.