Correlation between spectroscopic characteristics and structure of lanthanide phosphoro-azo derivatives of β-diketones

Abstract

Two types of lanthanide (Nd, Eu, Pr) compounds of formulae: Ln(HX) 3Cl 3 ( 1), Ln(HX) 3(NO 3) 3 ( 2) [where HX=CCl 3CO–NH–PO(NEt 2) 2] with the same ligand type but with different coordination numbers (as a consequence of different site symmetries) were obtained. X-ray data indicate the formation of octahedral complexes of ( 1), strongly distorted into trigonal symmetry, the strongest distortion observed for europium single crystals. On the other hand, the second type of crystals creates intermediate coordination polyhedra with low symmetry; anisotropy of intensities of 4I 9/2→ 4G 5/2, 2G 7/2 transition of Nd crystal well confirms the above structure. High resolution absorption spectra of single crystals of the title compounds were recorded at different temperatures from 293 to 4.2 K. Splitting of levels was determined. Intensities of f–f transitions were calculated and changes of their oscillator strengths, in the region of hypersensitive transitions, for the series Pr, Nd, Eu crystals were related to stronger distortion of the symmetry with a decrease of the ionic radius. Oscillator strength values and Judd–Ofelt parameters were calculated and compared to the respective data reported earlier. Analysis of the electronic components in low temperature spectra point on the D 3 site in ( 1) and most probably C 2 v in ( 2). Electron–phonon coupling was observed in low temperature spectra and its probabilities was analysed for two types of compounds with different symmetries. Vibronic components were related to the internal ligand modes and to the localised Ln–L x modes.