As-Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe-Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering

Inducing Ferrimagnetic Exchange in 1D-FeSe2 Chains Using Heteroleptic Amine Complexes: [Fe(en)(tren)][FeSe2]2

[Fe(en)(tren)][FeSe2]2 (en = ethylenediamine, C2H8N2, tren = tris(2-aminoethyl)amine, C6H18N4) has been synthesized by a mixed-ligand solvothermal method. Its crystal structure contains heteroleptic [Fe(en)(tren)]2+ complexes with distorted octahedral coordination, incorporated between 1D-FeSe2 chains composed of edge-sharing FeSe4 tetrahedra. The twisted octahedral coordination environment of the Fe-amine complex leads to partial dimerization of Fe-Fe distances in the FeSe2 chains so that the FeSe4 polyhedra deviate strongly from the regular tetrahedral geometry. 57Fe Mössbauer spectroscopy reveals oxidation states of +3 for the Fechain atoms and +2 for the Fecomplex atoms. The close proximity of Fe atoms in the chains promotes ferromagnetic nearest neighbor interactions, as indicated by a positive Weiss constant, θ = +53.8(6) K, derived from the Curie-Weiss fitting. Magnetometry and heat capacity reveal two consecutive magnetic transitions below 10 K. DFT calculations suggest that the ordering observed at 4 K is due to antiferromagnetic intrachain interactions in the 1D-FeSe2 chains. The combination of two different ligands creates an asymmetric coordination environment that induces changes in the structure of the Fe-Se fragments. This synthetic strategy opens new ways to explore the effects of ligand field strength on the structure of both Fe-amine complexes and surrounding Fe-Se chains.

Honeycomb layered topology construction for exceptional long-wave infrared nonlinear optical crystals

Nonlinear optical (NLO) crystals capable of efficient long-wave infrared (8-14 μm) laser output remain scarce, and the exploration of long-wave IR NLO materials with superior comprehensive optical performances is a momentous challenge. Herein, we develop two selenide-halide NLO crystals, Hg3AsSe4Br and Hg3AsSe4I, which are derived from the honeycomb layered topology of prototype GaSe. Remarkably, they exhibit not only strong SHG effects, suitable band gap, large birefringence, broad IR transparency range and low two-photon absorption coefficients but reinforced interlayer interaction and more benign crystal growth habit, compared to those of GaSe, indicating that they are promising long-wave IR NLO materials. Moreover, Hg3AsSe4I achieved better comprehensive optical properties than conventional IR crystals, GaSe, ZnGeP2, CdSe and AgGaSe2. The idea of honeycomb layered topology construction provides a material design heuristic to explore cutting-edge IR NLO materials.

Cobalt-Induced Phase Transformation of Ni3Ga4 Generates Chiral Intermetallic Co3Ni3Ga8

The scientific community has found immense difficulty to focus on the generation of chiral intermetallics compared to the chiral molecular structure, probably due to the technical difficulty in producing them as no general controlled protocol is available. Herein, using a conventional metal flux technique, we have discovered a new ternary intermetallic Co₃Ni₃Ga₈, substituting Co at the Ni sublattice in a highly symmetric Ni₃Ga₄ (Ia3̅d). Co₃Ni₃Ga₈ crystallizes in the I4₁32 space group, a Sohncke type, and can host the chiral structure. To the best of our knowledge, this is the first report of a ternary intermetallic crystallizing in this space group. The chiral structure of Co₃Ni₃Ga₈ is comprehensively mapped by various techniques such as single-crystal X-ray diffraction (XRD), synchrotron powder XRD, X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM) and theoretically studied using density functional theory. The discovery of this chiral compound can inspire the researchers to design hidden ternary chiral intermetallics to study the exotic electrical and magnetic properties.