Organopalladium(II) Complexes as Ionophores for Thiocyanate Ion-Selective Electrodes

Abstract

A thiocyanate poly(vinyl chloride) (PVC) membrane electrode based on [1,2-bis(diphenyl phosphiho)ethane]dihalo-palladium(II), [(dppe)PdX2, X = Cl (L-1), X = 1(L-2)] as active sensor has been developed. The duodopalladium complex, [(dppe)PdI2](L-2) displays an anti-Hofmeister selectivity sequence SCN- > I- > ClO4 > Sal(-) > Br- > NO2- > HPO4- > AcO- > NO3- > H2PO4- > CO32-. The electrode exhibits a Nernstian response (-59 9 mV/decade) over a wide linear concentration range of thiocyanate (1.0 x 10(-1) 5.0 x 10(-6) M), low detection limit (1.1 x 10(-6) M), fast response (t(90%)=24 s), and applicability over a wide pH range (35 similar to 11) Addition of anionic sites, potassium letrakis[p-chlorophenyl]borate (KTpClPB) is shown to Improve potentiometric anion selectivity, suggesting that the palladium complex may operate as a partially charged carrier-type ionophore within the polymer membrane phase. The reaction mechanism is discussed with respect to UV-Vis and IR Spectroscopy Application of the electrode to the potentiometric titration of thiocyanate ion with silver nitrate is reported.