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1. Calcium Substitution in Rare‐earth Metal Germanides with the Gd 5 Si 4 Type Structure

   https://doi.org/10.1002/zaac.202200016  

   Suen, Nian‐Tzu ; Bobev, Svilen ( February 2022 , Zeitschrift für anorganische und allgemeine Chemie)

   An extended series of rare‐earth metal calcium germanides have been synthesized and structurally characterized. The compounds have the general formulaRE_5−xCa_xGe₄(1.5<x<3.6;RE=rare‐earth metal; Ce, Nd, Sm, Tb−Lu) and their structures have been established from single‐crystal X‐ray diffraction methods. They crystallize with the Gd₅Si₄‐type in the orthorhombic space groupPnma(No. 62;Z=4; Pearson symboloP36), where the germanium atoms are interconnected into two kinds of Ge₂‐dimers, formally [Ge₂]⁶⁻. These studies show that Ca can be successfully incorporated into the hostRE₅Ge₄structure, whereby trivalent rare‐earth metal atoms can be substituted by divalent calcium atoms. Rare‐earth metal and calcium atoms are arranged in distorted trigonal prisms and cubes, centered by either Ge or Ca atoms. On one of the metal sites, the substitution is preferential and in 9 out of the 10 refined structures, the Wyckoff site 4cis found almost exclusively occupied by Ca. On the other two metal sites the substitution patterns appear to be governed by the mismatch between the size of theRE³⁺and Ca²⁺ions. This work further demonstrates the ability for the Gd₅Si₄structure type to accommodate the substitution of a non‐magnetic element while maintaining the global structural integrity.

    

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2. Quaternary cerium( iv ) containing fluorides exhibiting Ce 3 F 16 sheets and Ce 6 F 30 frameworks

   https://doi.org/10.1039/d0dt00616e  

   Ayer, Gyanendra B. ; Klepov, Vladislav V. ; Pace, Kristen A. ; zur Loye, Hans-Conrad ( May 2020 , Dalton Transactions)

   null (Ed.)

   A series of new Ce( iv ) based fluorides with two different compositions, Cs 2 MCe 3 F 16 (M = Ni 2+ , Co 2+ , Mn 2+ , and Zn 2+ ) and Na 3 MCe 6 F 30 (M = Al 3+ , Ga 3+ , Fe 3+ , and Cr 3+ ) were synthesized as high quality single crystals via a mild hydrothermal route. The compounds with the composition Cs 2 MCe 3 F 16 (M = Ni 2+ , Co 2+ , Mn 2+ , and Zn 2+ ) crystallize in the hexagonal crystal system with space group P 6 3 / mmc and are isotypic with the uranium analogs, whereas the Na 3 MCe 6 F 30 (M = Al 3+ , Ga 3+ , Fe 3+ , and Cr 3+ ) compounds crystallize in the trigonal space group P 3̄ c 1 and are isotypic with the uranium and thorium analogs Na x MM′ 6 F 30 (M′ = Th, U). The Cs 2 MCe 3 F 16 compounds exhibit a complex 3D crystal structure constructed of edge-sharing cerium trimers, in which all three Ce atoms share a common μ 3 -F unit. The Na 3 MCe 6 F 30 compounds are constructed of edge- and vertex-sharing cerium polyhedra connected to each other to form Ce 6 F 30 6− framework, which can accommodate only relatively smaller trivalent cations (M 3+ = Al 3+ , Ga 3+ , Fe 3+ , and Cr 3+ ) as compared to uranium and thorium analogs. Magnetic susceptibility measurements were carried out on the samples of Cs 2 MCe 3 F 16 (M = Ni 2+ and Co 2+ ), which exhibit paramagnetic behavior. 

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3. Field tunable magnetic transitions of CsCo 2 (MoO 4 ) 2 (OH): a triangular chain structure with a frustrated geometry

   https://doi.org/10.1039/d2qm01272c  

   Sanjeewa, Liurukara D. ; Garlea, V. Ovidiu ; Fishman, Randy S. ; Foroughian, Mahsa ; Yin, Li ; Xing, Jie ; Parker, David S. ; Smith Pellizzeri, Tiffany M. ; Sefat, Athena S. ; Kolis, Joseph W. ( March 2023 , Materials Chemistry Frontiers)

   The sawtooth chain compound CsCo 2 (MoO 4 ) 2 (OH) is a complex magnetic system and here, we present a comprehensive series of magnetic and neutron scattering measurements to determine its magnetic phase diagram. The magnetic properties of CsCo 2 (MoO 4 ) 2 (OH) exhibit a strong coupling to the crystal lattice and its magnetic ground state can be easily manipulated by applied magnetic fields. There are two unique Co 2+ ions, base and vertex, with J bb and J bv magnetic exchange. The magnetism is highly anisotropic with the b -axis (chain) along the easy axis and the material orders antiferromagnetically at T N = 5 K. There are two successive metamagnetic transitions, the first at H c 1 = 0.2 kOe into a ferrimagnetic structure, and the other at H c 2 = 20 kOe to a ferromagnetic phase. Heat capacity measurements in various fields support the metamagnetic phase transformations, and the magnetic entropy value is intermediate between S = 3/2 and 1/2 states. The zero field antiferromagnetic phase contains vertex magnetic vectors (Co(1)) aligned parallel to the b -axis, while the base vectors (Co(2)) are canted by 34° and aligned in an opposite direction to the vertex vectors. The spins in parallel adjacent chains align in opposite directions, creating an overall antiferromagnetic structure. At a 3 kOe applied magnetic field, adjacent chains flip by 180° to generate a ferrimagnetic phase. An increase in field gradually induces the Co(1) moment to rotate along the b -axis and align in the same direction with Co(2) generating a ferromagnetic structure. The antiferromagnetic exchange parameters are calculated to be J bb = 0.028 meV and J bv = 0.13 meV, while the interchain exchange parameter is considerably weaker at J ch = (0.0047/ N ch ) meV. Our results demonstrate that the CsCo 2 (MoO 4 ) 2 (OH) is a promising candidate to study new physics associated with sawtooth chain magnetism and it encourages further theoretical studies as well as the synthesis of other sawtooth chain structures with different magnetic ions. 

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4. Triangular Arrangement of Ferromagnetic Iron Chains in the High‐ T C Ferromagnet TiFe 1−x Os 2+x B 2

   https://doi.org/10.1002/chem.202201058  

   Scheifers, Jan P. ; Flores, Justin H. ; Janka, Oliver ; Pöttgen, Rainer ; Fokwa, Boniface P. T. ( June 2022 , Chemistry – A European Journal)

   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.

    

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5. Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure

   https://doi.org/10.1111/ijag.16611  

   Alderman, Oliver L. G. ; Benmore, Chris J. ; Reynolds, Bryce ; Royle, Brock ; Feller, Steve ; Weber, Rick J. K. ( September 2022 , International Journal of Applied Glass Science)

   The structure of liquid lithium pyroborate, Li₄B₂O₅(J= Li/B = 2), has been measured over a wide temperature range by high‐energy X‐ray diffraction, and compared to that of its glass and borate liquids of other compositions. The results indicate a gradual increase in tetrahedral boron fraction from 3(1)% to 6(1)% during cooling fromT= 1271(15) to 721(8) K, consistent with the largerN₄ = 10(1)% found for the glass, and literature¹¹B nuclear magnetic resonance measurements. van't Hoff analysis based on a simple boron isomerization reaction BØ₃O^2–⇌ BØO₂^2–yields ΔH= 13(1) kJ mol^–1and ΔS= 40(1) J mol^–1 K^–1for the boron coordination change from 4 to 3, which are, respectively, smaller and larger than found for singly charged isomers forJ ≤ 1. With these, we extend our model forN₄(J,T), nonbridging oxygen fractionf_nbr(J,T), configurational heat capacity , and entropyS^conf(J,T) contributions up toJ= 3. A maximum is revealed in atJ= 1, and shown semi‐quantitatively to lead to a corresponding maximum in fragility contribution, akin to that observed in the total fragilities by temperature‐modulated differential scanning calorimetry. Lithium is bound to 4.6(2) oxygen in the pyroborate liquid, with 2.7(1) bonds centered around 1.946(8) Å and 1.9(1) around 2.42(1) Å. In the glass,n_LiO= 5.4(4), the increase being due to an increase in the number of short Li–O bonds.

    

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