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 1 H 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)