Cadmium-halide and mixed cadmium-halide-dicyanamide polymers mediated by ancillary 2-aminoalkyl-pyridine ligands: Synthesis, X-ray single crystal structures and luminescence property

A series of mixed halide-dicyanamide and halide complexes of cadmium(II) mediated by 2-aminoalkyl-pyridine ligands [2-aminomethylpyridine (ampy) and 2-aminoethylpyridine (aepy)] have been synthesized. Five of them, [CdCl(dca)(aepy)](n) (1), [CdBr(dca)(ampy)](n) (2), [CdCl(dca)(ampy)](n) (3) (dca = dicyanamide); (Cdl(2)(aepy)](n) (4), and (Cdl(2)(ampy)](n) (S), (dca = dicyanamide) have been characterized by X-ray single crystal structure analysis. The structural determination shows that the compounds are 1 D coordination polymers, with the exception of 3 that gives origin to a 2D sheet-like network. The ampy and aepy ligands (also with the occurrence of dca anions in 1-3) reveal to be useful ancillary fragments for the construction of unprecedented Cd-halide polymeric species. The crystal packing shows that the dimensionality of all compounds is enlarged to 2D, and 3D in the case of complex 3, through pi-pi interactions occurring between the pyridine rings. All the species exhibit interesting luminescence property in solution as well in solid state which is originated from ligand-centered pi-pi transitions. The fluorescence band maxima and fluorescence efficiency (in methanol) are found to be dependent not only on the pyridine ligand but also on the type of halide, and the co-ligand. Solid state luminescent study implies that pi-pi interactions occurring between pyridine rings are also important in controlling the fluorescence intensity. Amongst the synthesized complexes reported, complex S exhibits the highest fluorescence efficiency in methanol. (C) 2008 Elsevier Ltd. All rights reserved.