CsFe3(SeO3)2F6 with S = 5/2 Cube Tile Lattice

Synthesis, structures, and magnetic properties of alkali metal manganese(III) fluorophosphates containing low-dimensional S = 2 spin structures

Five alkali metal manganese(III) fluorophosphates, K2Mn(PO3F)F3 (I), Rb2Mn(PO3F)F3 (II), Rb2Mn2(PO3F)(PO4)F3 (III), Rb3Mn3(PO3F)2(PO4)F5 (IV), and CsMn(PO3F)F2 (V), were successfully synthesized using a hydrothermal method. The monofluorophosphate anion (PO3F)2- groups work as "chemical scissors" to promote low-dimensional spin structures with the aid of alkali metal cations. I and II had an S = 2 uniform chain structure formed by corner-sharing trans-MnO2F4 octahedra. III contained a quasi one-dimensional S = 2 spin chain composed of trans-MnO4F2 octahedra and trans-MnO2F4 octahedra through vertex-sharing fluorine atoms running along the [1-10] direction, whereas V exhibited a zigzag S = 2 spin chain built from the facial-MnO3F3 octahedron. In contrast, IV constitutes weakly coupled S = 2 spin trimers, where the three-dimensional (3D) framework contains two-dimensional {Mn3O4F4(PO3F)2}2- layers formed by trinuclear Mn-octahedral units via corner-sharing fluorine atoms separated by PO3F tetrahedra. Magnetic measurements confirmed that I and II possess antiferromagnetic (AFM) long-range ordering at low temperature, with intrachain exchange couplings Jintra/kB = -12.1(1) K for I and Jintra/kB = -8.1(2) K for II. The magnetic behaviour of IV was very complex, with three successive magnetic transitions owing to weak AFM coupling among S = 2 spin trimers. V shows an alternating S = 2 one-dimensional (1D) chain with canted AFM ordering at 16.5 K.

Single-Step Synthesis of An Ideal Chain Antiferromagnet [H2(4,4'-bipyridyl)](H3O)2Fe2F10 with Spin S=5/2

One-dimensional (1D) magnets are of great interest owing to their intriguing quantum phenomena and potential application in quantum computing. We successfully synthesized an ideal antiferromagnetic spin S=5/2 chain compound [H2(4,4'-bpy)](H3O)2Fe2F10 (4,4'-bpy=4,4'-bipyridyl) 1, using a single-step low-temperature hydrothermal method under conditions that favors the protonation of the bulky bidentate ligand 4,4'-bpy. Compound 1 consists of well-separated (Fe3+-F-)∞ chains with a large Fe-F-Fe angle of 174.8°. Both magnetic susceptibility and specific heat measurements show that 1 does not undergo a magnetic long-range ordering down to 0.5 K, despite the strong Fe-F-Fe intrachain spin exchange J with J/kB=-16.2(1) K. This indicates a negligibly weak interchain spin exchange J'. The J'/J value estimated for 1 is extremely small (<2.8×10-6), smaller than those reported for all other S=5/2 chain magnets. Our hydrothermal synthesis incorporates both [H2(4,4'-bpy)]2+ and (H3O)+ cations into the crystal lattice with numerous hydrogen bonds, hence effectively separating the (Fe3+-F-)∞ spin chains. This single-step hydrothermal synthesis under conditions favoring the protonation of bulky bidentate ligands offers an effective synthetic strategy to prepare well-separated 1D spin chain systems of magnetic ions with various spin values.

KMB4O6F3 (M = Co, Fe): two-dimensional magnetic fluorooxoborates with triangular lattices directed by triangular BO3 units

Frustrated magnetic systems are of great interest owing to their spin liquid state for application in quantum computing. However, experimentally, spin liquid has not been realized. Thus, experimental explorations of frustrated magnetic systems including triangular lattices are still urgent, particularly for directed synthesis compared to random exploration. Herein, for the first time, directed by the use of a triangular unit of the BO3 anion group, two novel layered magnetic fluorooxoborates KMB4O6F3 (M = Co 1, Fe 2) with triangular lattices have been hydrothermally synthesized and characterized. Compounds 1 and 2 are isostructural and crystallize in the P21/c space group with layered magnetic triangular lattices, which are further separated by K+ ions. Magnetic susceptibility curves of both 1 and 2 show no λ-anomaly peak down to a low temperature of 2 K in the absence of a magnetic long-range ordering transition, which are further confirmed by the heat capacity results. The magnetic-field dependence of magnetization at 2 K shows saturation of 2.20μB for 1 and 4.24μB for 2, respectively, at 7 T, after roughly subtracting the Van Vleck paramagnetic contribution. Further in-depth investigation of the underlying physics at a lower temperature below 2 K would be subsequently performed. Moreover, thermal stability and FT-IR and UV-vis-NIR spectroscopy with optical bandgap properties are also reported. Most importantly, our work provides a promising method to experimentally realize specific magnetic lattices (e.g. triangular lattices) directed by the use of triangular groups (e.g. BO3) as the functional unit.

Investigation of Charge-Ordered Barium Iron Fluorides with One-Dimensional Structural Diversity and Complex Magnetic Interactions

Three mixed-valence barium iron fluorides, Ba7Fe7F34, Ba2Fe2F9, and BaFe2F7, were prepared through hydrothermal redox reactions. The characteristic structures of these compounds feature diverse distributions of FeIIF6 octahedra and FeIIIF6 groups. Ba7Fe7F34 contained one-dimensional infinite ∞[FeIIFeIII6F34]14- double chains, comprising cis corner-sharing octahedra along the b direction; Ba2Fe2F9 contained one-dimensional ∞[Fe2F9]4- double chains, consisting of cis corner-sharing octahedra along the chain (a-axis direction) and trans corner-sharing octahedra vertical to the chain, while BaFe2F7 revealed three-dimensional (3D) frameworks that consist of isolated edge-sharing dinuclear FeII2F10 units linked via corners by FeIIIF6 octahedra. Magnetization and Mössbauer spectroscopy measurements revealed that Ba7Fe7F34 exhibits an antiferromagnetic phase transition at ∼11 K, where ferrimagnetic ∞[FeIIFeIII6F34]14- double chains are arranged in a paralleling manner, while Ba2Fe2F9 shows canted antiferromagnetic ordering at ∼32.5 K, leading to noncollinear spin ordering.

Open-Framework Iron Fluoride Phosphates Based on Chain, Trinuclear, and Tetranuclear Chain FeIII Building Units: Crystal Structures and Magnetic Properties

We report the synthesis and characterization of a series of new open-framework iron fluoride-fluorophosphates based on linear, trinuclear, and tetranuclear chain Fe^III building units. KFe₂(PO₃F)₂F₃ (I) consists of {Fe₂(O₃F)₂F₂}^10- zigzag chains interconnected by P(O/F)₄ tetrahedra forming a three-dimensional (3D) open framework. K₂Fe(PO_2.5F_1.5)₂F₂ (II) is built up by {Fe(PO_2.5F_1.5)₂F₂}^2- chains separated by K⁺ cation layers. The framework for K₃Fe₃(PO₄)(PO₃F)₂F₅ (III) contains two-dimensional {Fe₃O₄F₄(PO₃F)₂}^2- sheets, which are built from trimeric Fe-octahedra insulated by PO₃F tetrahedra. The macroanionic framework of K₃Fe₄(PO₄)₂F₉ (IV) comprises linear {Fe₄O₈F₉}^10- chains consisting of tetranuclear magnetic clusters of [Fe₄O₈F_9]^10- formed via corner-sharing fluorine atoms decorated with PO₄ groups. The magnetic characterization of three iron fluorophosphates reveals diversified magnetism: S = 5/2 spin chains for I, antiferromagnetically coupled triangular Fe units for III, and coupled tetrahedral S = 5/2 spin chains for IV. IV shows strong geometric frustration thanks to its spin motifs of corner-shared tetrahedral clusters.

Lone pair electron effect induced differences in linear and nonlinear optical properties of bismuth borates

We analyzed systematically each phase of BIBO, and we found that the synergistic effect between bismuth oxygen polyhedra and boron–oxygen groups codetermines the optical properties of BIBO.

PbFePO4F2 with a 1/6th bond depleted triangular lattice

A 1/6th bond depleted triangular lattice has been experimentally realized in the novel compound PbFePO₄F₂ with moderately strong frustration.