Spectroscopic study of lanthanide(III) complexes with aliphatic dicarboxylic acids

The complexation of trivalent lanthanides with aliphatic dicarboxylic acids (malonic, succinic, glutaric and adipic) were studied at 25°C and 0.1 M (NaClO4) ionic strength by luminescence and absorption spectroscopy and luminescence lifetime measurements. The luminescence spectra and decay constants indicate that ML and ML2 complexes were formed. The stability constants of Eu(III) complexes with the dicarboxylic acids were calculated from the changes of the 5D0←7F0 excitation spectra of Eu(III). For the four dicarboxylic acids studied, both the stability constant and the number of water molecules released from the inner sphere of Eu(III) upon complexation decrease from malonate to adipate for both the ML and ML2 complexes. The results are interpreted as reflecting an increasing tendency from chelation to monodentation as the carbon chain length increases between carboxylate groups. The trend in the oscillator strength in the hypersensitive transition of the Nd(III)and Ho(III) complexes is the same as that in the ligand basicity.