Water-soluble Sal2en- and reduced Sal2en-type ligands:: Study of their CuII and NiII complexes in the solid state and in solution

The Cu-II and Ni-II complexes of the Schiff base pyr(2)en [N,N'ethylenebis(pyridoxyliminato)] and reduced Schiff bases RpYr(2)en [N,N'-ethylenebis(pyridoxylaminato)] and R(SO3- sal)(2)en (SO3-sal = salicylaldehyde-5-sulfonate) were prepared and characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy. The structure of Ni(pyr(2)en)(.)3H(2)O was determined by single-crystal X-ray diffraction. The pyr(2)en(2)-ligand is coordinated through two phenolate-O and imine-N atoms, in a distorted square-planar geometry. The complexation of Cu-II and Ni-II with Rpyr(2)en in aqueous solution is studied by pH-potentiometry, UV/Vis spectroscopy, as well as by EPR spectroscopy for the Cull system, and H-1 NMR spectroscopy for the Ni-II system. Complex formation constants were determined and binding modes proposed. While for the Cull system all complexes present a 1:1 stoichiometry with different protonation states, for the Ni-II system the 2:1 (L/M) complexes become important in the basic pH range at a higher ligand excess. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).