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

Two novel bpy-bridged CoII Schiff base complexes have been synthesized by the hydro(solvo)thermal reactions of corresponding amino-acid-based Schiff bases, bpy and Co(NO3)2·6H2O. The following formulae identify the two complexes: {[Co(napala)(bpy)0.5]·H2O}n (1) and [Co(napgly)(bpy)0.5]n (2) [H2napala = N-(2-hydroxy-1-naphthylmethylidene)-D/L-alanine, H2napgly = 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 CoII4(μ2-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 CoII ions are bridged by μ2-napgly2− to form left- and right-handed [CoII(μ2-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 CoII centers mediated by the syn–anti-COO−-bridges in both complexes.