Polarographic study of simple and mixed ligand complexes of Eu(III) with imidazole and succinate

The formation of simple and mixed ligand complexes of Eu(III) with imidazole (Im) and succinate (Succ2-) has been studied polarographically at 25deg C+-0.1deg C, μ=1.0 (NaClO4) and pH=6. The reduction of the complexes at d.m.e. is quasi-reversible and diffusion-controlled. Eu(III) forms six successive complexes with Im, viz. [Eu(Im)]3+, [Eu(Im)2]3+, [Eu(Im)2]3+, [Eu(Im)3]3+, [Eu(Im)4]3+, [Eu(Im)5]3+, and[Eu(Im)6]3+. Their stability constant values are: logβ10=3.6, logβ20=4.6, logβ30=6.5, logβ40=7.8, logβ50=8.4 and logβ60=9.6 respectively. With succ2-, Eu(III) forms four successive complexes; [Eu(Succ)]+, [Eu(Succ)2]-, [Eu(Succ)3]3- and [Eu(Succ)4]5- with the stability constants, logβ01=3.8, logβ02=4.6, logβ03=5.3 and logβ04=6.9 respectively. Eu(III) forms five mixed ligand complexes; [Eu(Im)(Succ)2]-, Eu(Im)2(Succ)2]-, [Eu(Im)3(Succ)2], [Eu(Im)4(Succ)2] and [Eu(Im)5(Succ)]+ with stability constants, logβ12=6.1, logβ22=8.0, logβ32=9.5, logβ42=10.9 and logβ51=10.2 respectively. (author)