Luminescence properties of palladium(II) phenanthroline derivative coordination compounds

A series of [ PdCl2(L)] and [PdCl2(PPh3)(L)] coordination compounds, where L= 4,7-dichloro-5-fluoro-2,9-dimethyl-1,10-phenanthroline, 4,7-dichloro-2,5,9-trimethyl-1,10-phenanthroline and 4,7-dichloro-2,9-dimethyl-1,10-phenanthroline, were synthesized and characterized by spectroscopic methods. The molecular structures of the coordination compounds were determined by X-ray crystallography. The ligands and the coordination compounds exhibit photoluminescence in the solutions. At 77 K both phenanthroline compounds and their palladium( II) coordination compounds reveal phosphorescence. The emissive active excitations have mixed intraligand/ ligand-to-ligand charge transfer with admixture of metal-to-ligand charge transfer character. Furthermore, in the case of the chloride coordination compounds of the [PdCl2(L)] formula, the halide-to-metal charge transfer transitions plays role in the excitation processes. The role of PPh3 ligand in the coordination sphere depends on the phenanthroline ligand. The excitations in the case of the [PdCl2(PPh3)(L)] compounds have the interligand (pi(phen)-> pi*(PPh3)) character.