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Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely, chimie douce approaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11 (x = 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space group P6322 (#182), a = 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2 at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site 2d (~94%; Eu1) versus 2b (~6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2d site. Tantalum vacancies of ~1% occur within the layer of Eu cations and TaO6 octahedra, and ~20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations. 151Eu M¨ossbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal of Γ = 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff = 6.2 μB and θCW = 10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11 was found to be ~1.5 eV (indirect), significantly redshifted as compared to ~4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu 4f7 states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing ox- ides for tunable magnetic and optical properties. 

The quinary members in the solid solution Hf₂Fe_1−δRu_5−xIr_x+δB₂(x=1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness forx=1 and 3 and the highest forx=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (T_N=55–70 K) found at low magnetic fields changed to ferromagnetic (T_C=150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf₂FeRu₃Ir₂B₂has the highest intrinsic coercivity (H_c=74 kA/m) reported to date for Ti₃Co₅B₂‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf₂FeIr₅B₂, indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials.

 

The removal of lead from commercialized perovskite‐oxide‐based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)‐perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO₃in space groupPbam, is shown to react with SnClF at a low temperature of 300 °C, and resulting in the first complete Sn(II)‐for‐Pb(II) substitution, i.e. SnHfO₃. During this topotactic transformation, a high purity and crystallinity is conserved withPbamsymmetry, as confirmed by X‐ray and electron diffraction, elemental analysis, and¹¹⁹Sn Mössbauer spectroscopy. In situ diffraction shows SnHfO₃also possesses reversible phase transformations and is potentially polar between ≈130–200 °C. This so‐called ‘de‐leadification’ is thus shown to represent a highly useful strategy to fully remove lead from perovskite‐oxide‐based piezoceramics and opening the door to new explorations of polar and antipolar Sn(II)‐oxide materials.

 

The removal of lead from commercialized perovskite‐oxide‐based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)‐perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO₃in space groupPbam, is shown to react with SnClF at a low temperature of 300 °C, and resulting in the first complete Sn(II)‐for‐Pb(II) substitution, i.e. SnHfO₃. During this topotactic transformation, a high purity and crystallinity is conserved withPbamsymmetry, as confirmed by X‐ray and electron diffraction, elemental analysis, and¹¹⁹Sn Mössbauer spectroscopy. In situ diffraction shows SnHfO₃also possesses reversible phase transformations and is potentially polar between ≈130–200 °C. This so‐called ‘de‐leadification’ is thus shown to represent a highly useful strategy to fully remove lead from perovskite‐oxide‐based piezoceramics and opening the door to new explorations of polar and antipolar Sn(II)‐oxide materials.

 

The synthesis and characterization of a series of Sn( ii ) and Sn( iv ) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pin F ) ligand are reported herein. Three analogs of [Sn IV (pin F ) 3 ] 2− with NEt 3 H + ( 1 ), K + ( 2 ), and {K(18C6)} + ( 3 ) counter cations and two analogs of [Sn II (pin F ) 2 ] 2− with K + ( 4 ) and {K(15C5) 2 } + ( 5 ) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119 Sn Mössbauer and NMR spectroscopies. The six-coordinate Sn IV (pin F ) complexes display 119 Sn NMR resonances and 119 Sn Mössbauer spectra similar to SnO 2 (cassiterite). In contrast, the four-coordinate Sn II (pin F ) complexes, featuring a stereochemically-active lone pair, possess low 119 Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn( ii ) complexes are unreactive towards both Lewis bases (pyridine, NEt 3 ) and acids (BX 3 , Et 3 NH + ). Calculations confirm that the Sn( ii ) lone pair is localized within the 5s orbital and reveal that the Sn 5p x LUMO is energetically inaccessible, which effectively abates reactivity. 

Transition‐metal borides (TMBs) containing B_n‐fragment (n>3) have recently gained interest for their ability to enable exciting magnetic materials. Herein, we show that the B₄‐containing TiFe_0.64(1)Os_2.36(1)B₂is a new ferromagnetic TMB with a Curie temperature of 523(2) K and a Weiss constant of 554(3) K, originating from the chain ofM₃‐triangles (M=64 %Fe+36 %Os). The new phase was synthesized from the elements by arc‐melting, and its structure was elucidated by single‐crystal X‐ray diffraction. It belongs to the Ti_1+xOs_2−xRuB₂‐type structure (space groupP2 m, no. 189) and contains trigonal‐planar B₄boron fragments [B−B distance of 1.87(4) Å] interacting withM₃‐triangles [M–Mdistances of 2.637(8) Å and 3.0199(2) Å]. The experimental results were supported by computational calculations based on the ideal TiFeOs₂B₂composition, which revealed strong ferromagnetic interactions within and between the Fe₃‐triangles. This discovery represents the first magnetically ordered Os‐rich TMB, thus it will help expand our knowledge of the role of Os in low‐dimensional magnetism of intermetallics and enable the design of such materials in the future.