Ligand field analysis within the framework of the Angular Overlap Model on a series of samarium(III) oxo compounds with supplementary considerations on europium(III) oxo compounds

This work presents the ligand field analysis of samarium(III) and europium(III) oxo compounds, as well as samarium(III) and europium(III) fluoride. The ligand field analyses were carried out within the framework of the Angular Overlap Model (BonnMag software). This is used to develop an understanding of the chemical bonding between lanthanide ions and their chemical environment. The syntheses of a series of samarium(III) and europium(III) oxo compounds form the basis for the bonding analysis. Powders of other compounds of this type were made available for analysis. Chemical gas phase transport provided single crystals of various samarium(III) oxo compounds. Remission measurements on powders, or (high-resolution) absorption measurements on single crystals, as well as temperature-dependent magnetic measurements provided the data basis for the ligand field analyses. By means of absorption measurements at 110 K, hot bands in the spectra of the samarium(III) oxo compounds could be identified. The parameterisation within the framework of the AOM was carried out with only three independent parameters (Slater-Condon-Shortley parameter, spin-orbit coupling constant, AOM binding parameter). The latter is interlinked for the different bonds Ln-O in a chromophore via the correlation with the interatomic distances d(Ln-O). The parameter sets of the samarium(III) and europium(III) compounds each form a consistent series. The plots of the Slater-Condon-Shortley parameter and the AOM bond parameter against the optical basicity of the compounds yield approximately linear curves. The decreasing SCS parameter with optical basicity is consistent with a nephelauxetic effect. Consistent with this, increasing AOM binding parameters with increasing optical basicity are found for samarium(III) and europium(III) oxo compounds. The lack of a nephelauxetic effect with respect to the SCS parameters in the series of europium(III) oxo compounds is all the more surprising. For better modelling of the experimental data in the UV range of the samarium(III) oxo compounds, the parameters F${}_4$ and F${}_6$ were determined independently of F${}_2$ for selected examples. Due to overlaps of absorption bands as well as configuration interactions of the pure 4f${}^5$ states at higher energies with 4f${}^4$5d${}^1$ states, no clear assignment of calculated to observed bands is possible. A chemically meaningful interpretation of the obtained parameters F${}_4$ and F${}_6$ is not possible. It seems likely that the reduced SCS parameters F${}_4$ and F${}_6$ compensate for the configuration interactions. The ligand field analysis on samarium(III) and europium(III) fluoride in the AOM establishes a reference point for non-oxide compounds of the lanthanides. The best fit AOM parameters were chosen similar to those of LnP${}_5$O${}_{14}$ (Ln: Sm, Eu). Due to the similar polarizability of fluoride and oxide in compounds with low optical basicity, this consideration leads to a chemically plausible picture. Eu${}_5$(BO${}_3$)${}_4$ shows a typical transition of europium(III) in the optical absorption spectrum. In connection with the low-lying intervalence charge transfer (from Eu${}^{2+}$ to Eu${}^{3+}$), the compound was classified in category II according to ROBIN and DAY. The ratio Eu${}^{2+}$ : Eu${}^{3+}$ = 3 : 2 was quantitatively determined via the magnetic moment.