Eu(III) and Gd(III) complexes with pirazyne-2-carboxylic acid:: luminescence and modelling of the structure and energy transfer process

The synthesis and spectroscopic study of the complexes of Eu(III) and Gd(III) with pyrazine-2-carboxylic acid (pya) are described. The number of water molecules (n) in the first coordination sphere of the Eu(III) ion has been determined through comparison between the experimental and theoretical Stark levels, giving n = 3, where the geometry of Eu(III) complex has been previously optimised using the Sparkle model. Based on this number of water molecules it has been predicted that the excited states for the complex Eu(pya)(3)(.)3H(2)O and the results have been used to carry out an experimental and theoretical analysis of the intensities of the 4f-4f transitions and intramolecular energy transfer processes. Structural data were used to perform theoretical predictions of the Judd-Ofelt intensity parameters (Omega(lambda), lambda = 2, 4). The satisfactory results obtained are an indication that the models used can lead to reliable predictions of the structure and 4f-4f intensities. A complete theoretical model to calculate the luminescent properties of lanthanide compounds has been used to analyze the emission quantum yield of the Eu(pya)(3)(.)3H(2)O compound. This approach has provided an optimum emission quantum yield of 9.2%. (C) 2003 Elsevier B.V. All rights reserved.