Rational design of two bpy-bridged 3D and 2D Co-II open frameworks with similar amino-acid-based Schiff bases

Two novel bpy-bridged Co-II Schiff base complexes have been synthesized by the hydro(solvo)thermal reactions of corresponding amino-acid-based Schiff bases, bpy and Co(NO3)(2)center dot 6H(2)O. The following formulae identify the two complexes: {[Co(napala)(bpy)(0.5)]center dot H2O}(n) (1) and [Co(napgly)(bpy)(0.5)](n) (2) [H(2)napala = N-(2-hydroxy-1-naphthylmethylidene)-D/L-alanine, H(2)napgly = N-(2-hydroxy-1-naphthylmethylidene)-glycine and bpy = 4,4'-bipyridine]. These two compounds have been characterized using single-crystal X-ray diffraction, infrared, powder X-ray diffraction, thermogravimetric analysis, optical spectra analysis, and magnetic measurement. Complex 1 features an unprecedented threefold interpenetrated diamond network based on the fan-shaped Co-4(II)(mu(2)-napala)(4) molecular square node and bpy linker, which represents the first example of 3D framework among the amino-acid-based Schiff base complexes with salicylaldehyde or its derivatives. In 2, adjacent Co-II ions are bridged by mu(2)-napgly(2-) to form left-and right-handed [Co-II(mu(2)-napgly)](n) helical chains. These two types of helical chains are sustained alternately by a symmetrical bpy co-ligand into a 2D grid-based layer. The solid-state fluorescence of complexes 1 and 2 are quenched almost completely compared with free mixed-ligands at room temperature. Moreover, magnetic studies show the dominant antiferromagnetic coupling between the Co-II centers mediated by the syn-anti-COO--bridges in both complexes.