Understanding Optical Absorption Spectra and Magnetic Behavior of a Wide Range of Samarium(III) Oxo‐Compounds: Analysis of the Ligand‐Field Effects

Abstract

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.

The weak ligand field in lanthanoid(III) hydrogensulfate‐sulfates

“…We assign these reflections in line with literature to hot bands. [3,32] These are originating from electronic excitation of thermally populated states just above the ground state. This assignment suggests that ligand field (LF) splitting of the 6 H 5/2 ground state on Sm 3 + involves a split-level at 120 cm À 1 .…”

“…The procedure for angular overlap modelling of compounds containing f n ions by using computer program BonnMag has been described in detail in literature several times. [2,3,33] In a recent review historical development and theoretical background of AOM has been covered. [34] We shall therefore restrict the corresponding information provided here to the origin of the numbers and assumptions used in the calculations.…”

“…Only recently, ligand field analyses [1][2][3] on extended series of samarium(III) and europium(III) oxo-compounds have revealed an unexpected correlation between ligand field strength (as it is expressed by the angular overlap parameter e σ (LnÀ O) normalized to d(LnÀ O) = 2.38 Å) and the optical basicity Λ [4] of a compound. Λ is related on one hand to the polarizability of the oxide ion in a solid and on the other to its oxide donor behavior.…”

“…To extend the already studied series of samarium(III) and europium(III) oxocompounds, which ranges from highly basic AEuO 2 and ASmO 2 (A: K, Rb; Λ = 1.18 [3,5] ) to the acidic ultraphosphates LnP 5 O 14 (Λ = 0.41 [2,3] ) we became interested in ligand field analyses of anhydrous lanthanoid(III) sulfates Ln 2 (SO 4 ) 3 and further compounds in the quasi-ternary systems LnO 1.5 -SO 3 -HO 0.5 . Besides hydroxides ( e. g. Dy(OH) 3 [6] ), oxide-hydroxides (e. g. YbO(OH) [7] ), sulfuric acid [8] and disulfuric acid [9] crystal structures for many oxide-sulfates, anhydrous sulfates, sulfate-hydrates and acidic sulfates have already been determined (e. g. La 2 (SO 4 ) 3 • 9 H 2 O, [10] Eu 2 (SO 4 ) 3 • 8 H 2 O, [11] Ce 2 (SO 4 ) 3 • 5 H 2 O, [10] (H 5 O 2 )Er(SO 4 ) 2 , [12] Ho 2 (SO 4 ) 3 • 4 H 2 O, [13] Lu 2 (SO 4 ) 3 • 3 H 2 O, [10] Nd(HSO 4 ) 3 , [14] La 2 (SO 4 ) 3 • H 2 O, [15] Tb(HSO 4 )(SO 4 ), [16] Er 2 (SO 4 ) 3 , [17] La 2 O 2 (SO 4 ) [18] ). Figure S1 gives a graphical survey of all known compositions in systems LnO 1.5 -SO 3 -HO 0.5 .…”

Revisiting the Fundamental Nature of Metal‐Ligand Bonding: An Impartial and Automated Fitting Procedure for Angular Overlap Model Parameters

“…Historically and today, AOM parameter fitting procedures make use of experimental data sensitive to the valence orbitals of predominant d or f orbital character, e. g. UV‐vis spectra or magnetic data. [ 34 , 35 , 36 , 37 , 38 ] Although it has in principle always been within the scope of the AOM to describe complexes with arbitrary or no symmetry, this was almost impossible to achieve, mainly because experimental data provides limited information. For instance, data on optical transitions in transition metal complexes are generally limited to at most four d orbital energy differences.…”