X-ray crystal structure and characterization in aqueous solution of {N,N′-ethylenebis(pyridoxylaminato)}zinc(II)

The complexation of Zn-II with H(2)Rpyr(2)en [H(2)Rpyr(2)en = N,N'-ethylenebis(pyridoxylaminato)] in aqueous solution has been studied by pH potentiometry and H-1 NMR spectroscopy. Complex formation constants are determined and binding modes proposed. Complex formation starts at around pH 4, and several species with a 1:1 ligand-to-metal ratio with different protonation states form up to pH 12. Only above pH 10 does a hydrolytic species [ZnLH-1](-) become important. The crystal and molecular structures of [ZnCl(H(2)Rpyr(2)en)]Cl-+(-)-1.5H(2)O (1) have been determined by X-ray diffraction. The coordination of the H(2)Rpyr(2)en ligand involves the two phenolate-O and two amine-N atoms in a distorted square-pyramidal geometry. The two pyridine-N atoms are protonated, and a Cl atom completes the coordination sphere. Upon coordination, both N-amine atoms of H(2)Rpyr(2)en become stereogenic centres, and in both molecules of the unit cell of 1 one of the N-amine donors has an (R)-configuration, and the other an (S)-configuration. (c) Wiley-VCH Verlag GmbH & Co. KGaA.