Hydride-Reduced Eu2SrFe2O6: A T-to-T' Conversion Enabling Fe2+ in Square-Planar Coordination.

Low-temperature reaction of A-site-ordered layered perovskite Eu2SrFe2O7 (T structure) with CaH2 induces a shift in the Eu2O2 slabs to form Eu2SrFe2O6 with a T' structure (I4/mmm space group) in which only the Fe cation is reduced. Contrary to the previously reported T' structures with Jahn-Teller-active d9 cations (Cu2+ and Ni+), stabilization of Eu2SrFe2O6 with the Fe2+ (d6) cation reflects the stability of the FeO4 square-planar unit. The stability of T'-type Eu2SrFe2O6 over a T-type polymorph is confirmed by density functional theory calculations, revealing the dz2 occupancy for the T' structure. Eu2SrFe2O6 has a bilayer magnetic framework with an Fe-O-Fe superexchange J∥ and an Fe-Fe direct exchange J⊥ (where J∥ > J⊥), which broadly explains the observed TN of 390-404 K. Interestingly, the magnetic moments of Eu2SrFe2O6 lie in the ab plane, in contrast to the structurally similar Sr3Fe2O4Cl2 having an out-of-plane spin alignment.

[Treatment management of sexual offenders]. / Prise en charge thérapeutique des auteurs d'agressions sexuelles.

In France, the Court can issue a medical treatment order only for criminally responsible persons. The nature of the treatment to be administered is at the discretion of the physician in charge of the sexual offender's care. Treatment management of sexual offenders relies essentially on psychotherapy, and preferentially cognitive behavioral therapy. For most severe sexual offenders, drug treatments, including hormonal treatment and selective serotonin reuptake inhibitors, are used to complement psychotherapy. This literature review aims at synthesizing practice changes in the treatment management of sexual offenders.

Ferromagnetically coupled Shastry-Sutherland quantum spin singlets in (CuCl)LaNb2O7.

A thorough crystal structure determination at very low temperature of (CuCl)LaNb2O7, originally proposed as a spin-1/2 square-lattice antiferromagnet, is reported thanks to the use of single-crystal x-ray diffraction and powder neutron diffraction. State-of-the-art calculations (maximum entropy method) reveal that (CuCl)LaNb2O7 is orthorhombic with Pbam symmetry. First-principles calculations demonstrate that the dominant magnetic interactions are antiferromagnetic between fourth nearest neighbors with a Cu-Cl-Cl-Cu exchange path, which lead to the formation of spin singlets. The two strongest interactions between the singlets are ferromagnetic, which makes (CuCl)LaNb2O7 the first system of ferromagnetically coupled Shastry-Sutherland quantum spin singlets.

Spin transition in a four-coordinate iron oxide.

Spin transition has attracted the interest of researchers in various fields since the early 1930s, with thousands of examples now recognized, including those in minerals and biomolecules. However, so far the metal centres in which it has been found to occur are almost always octahedral six-coordinate 3d(4) to 3d(7) metals, such as Fe(II). A five-coordinate centre is only rarely seen. Here we report that under pressure SrFe(II)O(2), which features a four-fold square-planar coordination, exhibits a transition from high spin (S = 2) to intermediate spin (S = 1). This is accompanied by a transition from an antiferromagnetic insulating state to a ferromagnetic so-called half-metallic state: only half of the spin-down (d(xz),d(yz)) states are filled. These results highlight the square-planar coordinated iron oxides as a new class of magnetic and electric materials.

Infinite-layer iron oxide with a square-planar coordination.

Conventional high-temperature reactions limit the control of coordination polyhedra in transition-metal oxides to those obtainable within the bounds of known coordination geometries for a given transition metal. For example, iron atoms are almost exclusively coordinated by three-dimensional polyhedra such as tetrahedra and octahedra. However, recent works have shown that binary metal hydrides act as reducing agents at low temperatures, allowing access to unprecedented structures. Here we show the reaction of a perovskite SrFeO3 with CaH2 to yield SrFeO2, a new compound bearing a square-planar oxygen coordination around Fe2+. SrFeO2 is isostructural with 'infinite layer' cupric oxides, and exhibits a magnetic order far above room temperature in spite of the two-dimensional structure, indicating strong in-layer magnetic interactions due to strong Fe d to O p hybridization. Surprisingly, SrFeO2 remains free from the structural instability that might well be expected at low temperatures owing to twofold orbital degeneracy in the Fe2+ ground state with D(4h) point symmetry. The reduction and the oxidation between SrFeO2 and SrFeO3 proceed via the brownmillerite-type intermediate SrFeO2.5, and start at the relatively low temperature of approximately 400 K, making the material appealing for a variety of applications, including oxygen ion conduction, oxygen gas absorption and catalysis.