Synthesis, X-ray crystal structures and spectroscopic properties of two Ni(II) complexes of pyridoxal Schiff’s bases with diamines: Importance of steric factor in stabilization of water helices in the lattices of metal complex

Two Ni(II) complexes of the ligands N,N′-dipyridoxylethylenediimine (L1H2) and N,N′-dipyridoxyl-1,3-propanediimine (L2H2) were synthesized and their structures were determined by X-ray crystallography. The complexes are of formula Ni(L1). 3H2O (1·3H2O) and Ni(L2) (2). Both the complexes were found to be luminescent, but the quantum yields are significantly low compared to those of free ligands or their Zn(II) complexes. In 1·3H2O the metallo-organic fragment forms a staircase like network and three water molecules occupy the void space created by the staircase like network. The water molecules are strongly H-bonded between themselves forming a helical chain along ‘b’ axis. Complex 2, in spite of having same number of hydrogen bonding sites as that of 1, can not accommodate water clusters in their lattice. It is argued, that small steric factors, which may affect conformations of the hydrogen donor/acceptor sites, plays an important role in stabilization of water helices in lattices of metal complex.