Crystal Structures and Spectroscopic Properties of Zinc(II) Ternary Complexes of Vitamin L, H′ and Their Isomer <i>m</i>-Aminobenzoic Acid with Bipyridine

Abstract

The crystal structures of the three Zn(II) complexes, [Zn(bpy)(o-AB)2] (1) (bpy=2,2'-bipyridine, o-AB=o-aminobenzoic acid=Vitamin L), [Zn(bpy)(m-AB)Cl]2 (2) (m-AB=m-aminobenzoic acid), [Zn(bpy)(p-AB)Cl]*p-AB*H2O (3) (p-AB=p-aminobenzoic acid=Vitamin H'), have been determined and the basic coordination geometries and architectures organized by hydrogen-bonds and pi-pi interactions also characterized. The substitute amine group at ortho-, meta-, and para-position of AB plays an important role to produce completely different coordination motif of these complexes, further, in all complexes, aromatic amines are not coordinated to Zn(II) atom. While two different types of coordination modes of the carboxylate O atoms are present in these complexes: one mode consists of the usual Zn-O bond lengths (2.009(2)-2.251(2) A) in complex 1, 2 and 3; another consists of a very long Zn-O bond lengths (2.422(2) A) in complex 1. Each of the complexes has the characteristic UV absorption bands around 250-310 nm region, and the intense fluorescence band at near 325 nm.