The europium-oxygen interaction in nine different europium(III) oxo-compounds (including C-type EuO) was investigated on the basis of powder reflectance spectra (near-IR/vis/UV) and temperature-dependent magnetic measurements. Computation of the transition energies and of the effective Bohr magneton numbers for Eu in the different ligand fields were performed within the framework of the angular overlap model (AOM) using the computer program BonnMag. These calculations show that all electronic transition energies in the optical spectra, the magnetic susceptibilities as well as their temperature dependence, are very well-accounted for by AOM. BonnMag provides a facile way to perform these calculations. Analysis of the obtained "best fit" AOM parameters e(Eu-O) shows that these are significantly influenced by the further bonding partners of oxygen ("second-sphere ligand-field effect"). An increase of e(Eu-O) from 404 cm (EuPO) to 687 cm (EuSbO), both normalized to d(Eu-O) = 2.38 Å, is found. Correlation of this variation to oxide polarizability and optical basicity of the oxo-compounds is discussed.

Optical spectra (powder reflectance, UV/Vis/NIR region), and temperature dependent magnetic behavior (χ, μ/μB) were recorded for the series of anhydrous europium(III) phosphates EuIII3O3(PO4), EuIIIPO4, EuIII2P4O13, lt‐ and ht‐EuIII(PO3)3, and EuIIIP5O14. By modeling within the AOM framework, the experimental data can be related to the ligand‐field splitting experienced by the Eu3+ ions in the various mainly low‐symmetry coordination environments. Our study confirms the well‐established relation eσ(Eu3+–O2–) ~ d(Eu3+–O2–)–7.0 between the AOM parameter and the interatomic distance. In addition it is shown that eσ(Eu3+–O2–) depends strongly on the highly variable polarizability of the oxygen ligator atoms. This polarizability can be related to the optical basicity Λ of the various phosphates.

In this study powder reflectance spectra as well as temperature dependent magnetic susceptibilities of eight different samarium(III) oxo‐compounds (SmP5O14, SmPO4, SmVO4, SmNbO4, SmTaO4, Sm2Ti2O7, SmAsO4, B‐type Sm2O3 and C‐type Sm2O3) have been measured. In addition, high‐resolution electronic absorption spectra in the near infrared of single crystals of seven of these compounds are reported. Comparing our experimental data to the results of ligand field analyses (angular overlap model AOM allowing for decomposition of the global ligand field into the contributions of the individual ligands; computer program BonnMag) shows reasonable agreement of electronic transition energies in optical spectra and a good fit of the temperature dependent Bohr magneton numbers μeff/μB. Analysis of the ‘best fit’ AOM parameters reveals a significant variation in the nephelauxetic effect with F2=379 cm−1 for SmP5O14 and F2=356 cm−1 for KSmO2. A trend in the variation of the AOM parameter eσ with the optical basicity Λ is discussed. The values for eσ(Sm−O), normalized to d(Sm−O)=2.38 Å, range from 337 cm−1 for SmP5O14 to 573 cm−1 for KSmO2. For the ratio eπ/eσ only a negligible influence on the match between calculated and experimental data is observed. For the relation of eσ(Sm−O) to the interatomic distance d(Sm−O) the correlation eσ(Sm−O) ∼1/d7(Sm−O) was found to reproduce in AOM the observed ligand field splitting well. For SmPO4 a high resolution, low temperature (110 K) spectrum allows the assignment of hot bands.

In memory of Professor Rudolf Hoppe on his 100 th anniversaryThe hydrogensulfate-sulfates Ln(HSO 4 )(SO 4 ) (Ln: Sm, Eu, Gd, Tb, Dy) have been crystallized from sulfuric acid and their thermal decomposition behavior has been studied. The crystal structures for all members of the series were refined from X-ray single-crystal diffraction data (for all: Tb(HSO 4 )(SO 4 ) structure type, P2 1 , Z = 2, a � 6.66 Å, b � 6.63 Å, c � 6.82 Å, β � 104.6°). Optical spectra (Sm-Dy) and magnetic susceptibilities (Eu-Dy) have been measured. For comparison the octahydrates Ln 2 (SO 4 ) 3 • 8 H 2 O (Sm, Eu) and the anhydrous sulfates Ln 2 (SO 4 ) 3 (Sm, Eu) have also been characterized by optical spectroscopy and magnetic measurements. Ligand field analyses (angular overlap model) based on these data suggest for the squareantiprismatic [Ln III O 8 ] chromophores in the hydrogensulfatesulfates a rather weak ligand field, which is comparable only to that in ultraphosphates LnP 5 O 14 and in contrast to the much stronger field observed for most other lanthanoid(III) oxocompounds studied so far. Results and DiscussionSynthesis. The well-known lanthanoid(III) sulfate octahydrates Ln 2 (SO 4 ) 3 • 8 H 2 O (Ln: Sm, Eu) [11,19] were crystallized from approx. 40 %wt. sulfuric acid at room temperature (for details see [a

The mixed‐valent, europium borate Eu5(BO3)4 was synthesized from Eu2B2O5 and EuB2O4. Its structure was refined by Rietveld analysis. Eu5(BO3)4 crystallizes in space group Pnma (a=2229.77(2) pm, b=1599.91(2) pm, and c=877.75(1) pm) and was found to be isostructural with Eu5(BO2.51N0.49)4. Powder reflectance spectra (UV/vis/NIR) and magnetic susceptibility data of Eu5(BO3)4 and of the reference compounds EuIIB4O7 and EuIIIBO3 were measured. The spectrum of the mixed‐valent europium(II, III) borate shows the 7F0→7F6 transition of the Eu3+ ion and the intervalence charge transfer Eu2+→Eu3+. The experimental Bohr magneton number of Eu5(BO3)4, μobs/μB=14.90, agrees well to μcalc/μB for a combination of three Eu2+ and two Eu3+ per formula.