Effect of ligand radicals on vibrational IR, Raman and vibronic spectra of europium β-diketonates

Abstract

Vibrational IR, Raman spectra and vibronic sidebands of Eu 3+ electronic transitions of europium tris-β-diketonates Eu(β) 3·Ph (β-dipyvaloylmethane (DPM), acetylacetone (AA), benzoylacetone (BA), thenoyltrifluoroacetone (TTFA) and other β-diketones; Ph-methyl-, phenyl-, and nitro-derivatives of 1,10-phenanthroline (Phen)) as well as Eu(β) 3·Bpy and Eu(β) 3·D-Bpy (Bpy- and D-Bpy–H- and D-2,2′-bipyridine) were studied. Effect of ligand radical properties on spectra and manifestation of the reciprocal influence of non-equivalent ligands in spectra are discussed. Dependence of the spectra on electronic density distribution in both ligands as well as on the strength of MO and MN bonds at the variation of radicals of one of the ligands, β or Ph, was examined. Shape of vibronic sidebands was analysed. Behaviour of bands in the middle and far regions of IR spectra of the series Eu(β) 3·Phen and Eu(TTFA) 3·Ph was investigated. Increase of the polarising influence of Eu 3+ ions on Phen and Bpy molecules and strengthening the EuN bonds in TTFA compounds in comparison with DPM compounds were disclosed from the Raman spectra of Eu(β) 3·Phen and Eu(β) 3·Bpy, that is in accordance with properties of β-diketone radicals. Conclusion about weaker EuN bonds in europium β-diketonates with heterocyclic diimines in comparison with corresponding nitrates was derived from the spectra. Spectral data concerning the relative strength of Euligand bonds are in agreement with available X-ray data.