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

摘要

A thiocyanate poly(vinyl chloride) (PVC) membrane electrode based on [1,2-bis(diphenylphosphino)ethane]dihalopalladium( II), [(dppe)PdX2, X = Cl (L¹), X = I (L²)] as active sensor has been developed. The diiodopalladium complex, [(dppe)PdI₂](L²) displays an anti-Hofmeister selectivity sequence: SCN^- I^- ClO^4- Sal^- Br^- NO^2- HPO^4- AcO^- NO^3- H₂PO^4- CO₃^2-. The electrode exhibits a Nernstian response (-59.8 mV/decade) over a wide linear concentration range of thiocyanate (1.0 】 10^-1 to 5.0 】 10^-6 M), low detection limit (1.1 】 10^-6 M), fast response (t90% = 24 s), and applicability over a wide pH range (3.5…11). Addition of anionic sites, potassium tetrakis[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.