Chemical excision of tetrahedral FeSe(2) chains from the superconductor FeSe: synthesis, crystal structure, and magnetism of Fe(3)Se(4)(en)(2)

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.

Controllable Connection of Fe2Se3 Double Chains and Fe(dien)2 Complexes for Organic-Inorganic Hybrid Ferrimagnet with a Large Coercivity

Organic-inorganic hybrid materials built by inorganic and organic building units have attracted intensive interest in the past decades due to unique chemical and physical properties. However, rare organic-inorganic hybrid materials show excellent permanent magnetic properties. Here, we develop a facile chemical solution method to bottom-up synthesize a new hybrid (Fe₂Se₃)₂[Fe(dien)₂]_0.9. This hybrid phase with the space group P2₁/c (14) possesses a rodlike shape with a diameter of 100-2000 nm and a length of 5-50 µm. The hybrid rods are ferrimagnetic with a Curie temperature (T_C) of 11 K. They show a high coercivity (H_C) of 4.67 kOe and a saturation magnetization (M_S) of 13.5 emu/g at 2 K. Compared with orthorhombic (FeSe₂)₂Fe(dien)₂, the excellent magnetic performance of the hybrid rods is ascribed to the monoclinic hybrid structure built by Fe(dien)₂ complexes and Fe₂Se₃ double chains. Our study provides guidance for connecting inorganic fragments of FeSe₂ single chains, Fe₂Se₃ double chains or β-Fe₃Se₄ layers with Fe(dien)₂ complexes for organic-inorganic hybrid phases with varied crystal structures and magnetic properties.

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

A novel mixed-valent hybrid chiral and polar compound, Fe₇As₃Se₁₂(en)₆(H₂O), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [Fe₅Se₉] chains connected via [As₃Se₂]-Se pentagonal linkers and charge-balancing interstitial [Fe(en)₃]²⁺ complexes (en = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing. Magnetic polarizability of the produced compound was confirmed by X-ray magnetic circular dichroism (XMCD) spectroscopy. X-ray absorption spectroscopy (XAS) and ⁵⁷Fe Mössbauer spectroscopy showed the presence of mixed-valent Fe²⁺/Fe³⁺ in the Fe-Se chains. Magnetic susceptibility measurements reveal strong antiferromagnetic nearest neighbor interactions within the chains with no apparent magnetic ordering down to 2 K. Hidden short-range magnetic ordering below 70 K was found by ⁵⁷Fe Mössbauer spectroscopy, showing that a fraction of the Fe³⁺/Fe²⁺ in the chains are magnetically ordered. Nevertheless, complete magnetic ordering is not achieved even at 6 K. Analysis of XAS spectra demonstrates that the fraction of Fe³⁺ in the chain increases with decreasing temperature. Computational analysis points out several competing ferrimagnetic ordered models within a single chain. This competition, together with variation in the Fe oxidation state and additional weak intrachain interactions, is hypothesized to prevent long-range magnetic ordering.

Syntheses and characterization of two new layered ternary chalcogenides NaScQ2 (Q = Se and Te)

Two new metal ternary chalcogenides, NaScSe2 and NaScTe2, have been synthesized via high-temperature reaction.

Intercalated Iron Chalcogenides: Phase Separation Phenomena and Superconducting Properties

Organic molecule-intercalated layered iron-based monochalcogenides are presently the subject of intense research studies due to the linkage of their fascinating magnetic and superconducting properties to the chemical nature of guests present in the structure. Iron chalcogenides have the ability to host various organic species (i.e., solvates of alkali metals and the selected Lewis bases or long-chain alkylammonium cations) between the weakly bound inorganic layers, which opens up the possibility for fine tuning the magnetic and electrical properties of the intercalated phases by controlling both the doping level and the type/shape and orientation of the organic molecules. In recent years, significant progress has been made in the field of intercalation chemistry, expanding the gallery of intercalated superconductors with new hybrid inorganic–organic phases characterized by transition temperatures to a superconducting state as high as 46 K. A typical synthetic approach involves the low-temperature intercalation of layered precursors in the presence of liquid amines, and other methods, such as electrochemical intercalation, intercalant or ion exchange, and direct solvothermal growths from anhydrous amine-based media, are also being developed. Large organic guests, while entering a layered structure on intercalation, push off the inorganic slabs and modify the geometry of their internal building blocks (edge-sharing iron chalcogenide tetrahedrons) through chemical pressure. The chemical nature and orientation of organic molecules between the inorganic layers play an important role in structural modification and may serve as a tool for the alteration of the superconducting properties. A variety of donor species well-matched with the selected alkali metals enables the adjustment of electron doping in a host structure offering a broad range of new materials with tunable electric and magnetic properties. In this review, the main aspects of intercalation chemistry are discussed, involving the influence of the chemical and electrochemical nature of intercalating species on the crystal structure and critical issues related to the superconducting properties of the hybrid inorganic–organic phases. Mutual relations between the host and organic guests lead to a specific ordering of molecular species between the host layers, and their effect on the electronic structure of the host will be also argued. A brief description of a critical assessment of the association of the most effective chemical and electrochemical methods, which lead to the preparation of nanosized/microsized powders and single crystals of molecularly intercalated phases, with the ease of preparation of phase pure materials, crystal sizes, and the morphology of final products is given together with a discussion of the stability of the intercalated materials connected with the volatility of organic solvents and a possible degradation of host materials.

Tuning Fe-Se Tetrahedral Frameworks by a Combination of [Fe(en)3]2+ Cations and Cl- Anions

A one-dimensional (1D) chain compound [Fe(en)3]3(FeSe2)4Cl2 (en = ethylenediamine), featuring tetrahedral FeSe₂ chains separated by [Fe(en)₃]²⁺ cations and Cl^- anions, has been synthesized by a low temperature solvothermal method using simple starting materials. The degree of distortion in the Fe-Se backbone is similar to previously reported compounds with isolated 1D FeSe₂ chains. ⁵⁷Fe Mössbauer spectroscopy reveals the mixed-valent nature of [Fe(en)₃]₃(FeSe₂)₄Cl₂ with Fe³⁺ centers in the [FeSe₂]^- chains and Fe²⁺ centers in the [Fe(en)₃]²⁺ complexes. SQUID magnetometry indicates that [Fe(en)3]3(FeSe2)4Cl2 is paramagnetic with a reduced average effective magnetic moment, μ_eff = 9.51 μ_B per formula unit, and a negative Weiss constant, θ = -10.9(4) K, indicating antiferromagnetic (AFM) nearest neighbor interactions within the [FeSe₂]^- chains. Weak antiferromagnetic coupling between chains, combined with rather strong intrachain AFM coupling, leads to spin-glass behavior at low temperatures, as indicated by a frequency shift of the peak observed at 3 K in AC magnetic measurements. A combination of [Fe(en)₃]²⁺ and Cl^- ions is also capable of stabilizing mixed-valent 2D Fe-Se puckered layers in the crystal structure of [Fe(en)₃]₄(Fe₁₄Se₂₁)Cl₂, where Fe₁₄Se₂₁ layers have a unique topology with large open pores. Property measurements of [Fe(en)₃]₄(Fe₁₄Se₂₁)Cl₂ could not be performed due to the inability to either grow large crystals or synthesize this material in single-phase form.

A Reusable CNT-Supported Single-Atom Iron Catalyst for the Highly Efficient Synthesis of C-N Bonds

C-N bond formation is regarded as a very useful and fundamental reaction for the synthesis of nitrogen-containing molecules in both organic and pharmaceutical chemistry. Noble-metal and homogeneous catalysts have frequently been used for C-N bond formation, however, these catalysts have a number of disadvantages, such as high cost, toxicity, and low atom economy. In this work, a low-toxic and cheap iron complex (iron ethylene-1,2-diamine) has been loaded onto carbon nanotubes (CNTs) to prepare a heterogeneous single-atom catalyst (SAC) named Fe-N_x /CNTs. We employed this SAC in the synthesis of C-N bonds for the first time. It was found that Fe-N_x /CNTs is an efficient catalyst for the synthesis of C-N bonds starting from aromatic amines and ketones. Its catalytic performance was excellent, giving yields of up to 96 %, six-fold higher than the yields obtained with noble-metal catalysts, such as AuCl₃ /CNTs and RhCl₃ /CNTs. The catalyst showed efficacy in the reactions of thirteen aromatic amine substrates, without the need for additives, and seventeen enaminones were obtained. High-angle annular dark-field scanning transmission electron microscopy in combination with X-ray absorption spectroscopy revealed that the iron species were well dispersed in the Fe-N_x /CNTs catalyst as single atoms and that Fe-N_x might be the catalytic active species. This Fe-N_x /CNTs catalyst has potential industrial applications as it could be cycled seven times without any significant loss of activity.

Crystal and Magnetic Structures of the Chain Antiferromagnet CaFe4Al8

The crystal structure of CaFe₄Al₈ was studied by X-ray single crystal and powder diffraction as well as high-resolution neutron powder diffraction. CaFe₄Al₈ crystallizes with a tetragonal CeMn₄Al₈-type structure, an ordered variant of the ThMn₁₂-type (Pearson symbol tI26, space group I4/ mmm, a = 8.777(1), c = 5.077(1) Å). Similarly to the well-known A15-type superconductors, the structure of CaFe₄Al₈ contains one-dimensional chains of d-metal atoms, which are parallel to the crystallographic fourfold axis. CaFe₄Al₈ is paramagnetic at room temperature and exhibits long-range antiferromagnetic ordering at about 180 K, combined with a short-range ordered spin arrangement. The magnetic structure, determined by powder neutron diffraction at 4 K, shows that the magnetic moments on the Fe atoms form mirror-inverted chains along the c-direction and are slightly canted from the axis.

Systematic dimensional reduction of the layered β-FeSe structure by solvothermal synthesis

Dimensional reduction of superconducting anti PbO-type iron selenide has been achieved by terminating the tetragonal square layers of FeSe_4/4 tetrahedra by ethylenediamine (en) ligands. We obtained three new structures in the Fe-Se-en system. Fe₃Se₄(en)₃ contains FeSe₂ single chains bridged via Fe(en)₃ complexes. Fe₁₀Se₁₂(en)₇ has Fe₂Se₃ double strands separated by Fe(en)₃ complexes and free en molecules. Fe_0.85Se(en)_0.3 conserves the tetragonal layers of bulk FeSe which are now widely separated by en molecules. Through systematic dilution of the solvent we were able to introduce an additional parameter in solvothermal synthesis and thus have control over the connectivity of the tetrahedra. Additionally, a phase diagram of the Fe-Se-en system is generated by variation of the reaction temperature. The magnetic properties of the FeSe derivatives range from superconductivity and antiferromagnetism to paramagnetism.

High-Tc superconducting phases in organic molecular intercalated iron selenides: synthesis and crystal structures

Phase pure hybrid iron-based superconductors with various structural types can be obtained by sonochemical insertion of organic molecules into FeSe-layers.

Control over connectivity and magnetism of tetrahedral FeSe2 chains through coordination Fe–amine complexes

Magnetic interactions in compounds containing tetrahedral _∞¹(FeSe₂) chains separated by Fe–amine complexes are controlled by the denticity of the amine.

[Mn(dien)2]MnSnS4, [Mn(1,2-dap)]2Sn2S6 and [Mn(en)2]MnGeS4: from 1D anionic and neutral chains to 3D neutral frameworks

Three new organic–inorganic hybrid manganese thiogermanates and thiostannates with 1D anionic or neutral chains and 3D neutral frameworks have been synthesized and feature interesting antiferromagnetic or ferromagnetic properties.

Assembly and structural transformation of organic-decorated manganese selenidostannates

Presented here are three organic-decorated manganese selenidostannates with various structural dimensionalities (D), namely, 1D – SnSe3Mn(en)2 (en = ethylenediamine) (1), 2D – SnSe3Mn(en) (2) and 3D – MnSnSe4Mn(en)2 (3). 2 and 3 represent the first 2D and 3D organic-decorated Mn–Sn–Se compounds, respectively. A structural transformation was observed between 1 and 2.