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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. Structures of Three Alkaline-Earth Metal Germanides Refined from Single-Crystal X-ray Diffraction Data

   https://doi.org/10.3390/chemistry4040094  

   Suen, Nian-Tzu ; Bobev, Svilen ( December 2022 , Chemistry)

   The calcium- and strontium- alumo-germanides SrxCa1–xAl2Ge2 (x ≈ 0.4) and SrAl2Ge2 have been synthesized and structurally characterized. Additionally, a binary calcium germanide CaGe has also been identified as a byproduct. All three crystal structures have been established from single-crystal X-ray diffraction methods and refined with high accuracy and precision. The binary CaGe crystallizes with a CrB-type structure in the orthorhombic space group Cmcm (no. 63; Z = 4; Pearson symbol oC8), where the germanium atoms are interconnected into infinite zigzag chains, formally [Ge]2−. The calcium atoms are arranged in monocapped trigonal prisms, centered by Ge atoms. SrxCa1−xAl2Ge2 (x ≈ 0.4) and SrAl2Ge2 have been confirmed to crystallize with a CaAl2Si2-type structure in the trigonal space group P3¯m1 (no. 164; Z = 1; Pearson symbol hP5), where the germanium and aluminum atoms form puckered double-layers, formally [Al2Ge2]2−. The calcium atoms are located between the layers and reside inside distorted octahedra of Ge atoms. All presented structures have a valence electron count satisfying the octet rules (e.g., Ca2+Ge2− and Ca2+[Al2Ge2]2−) and can be regarded as Zintl phases. 

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3. Experimental and Theoretical Study on the Substitution Patterns in Lithium Germanides: The Case of Li 15 Ge 4 vs Li 14 ZnGe 4

   https://doi.org/10.1002/ejic.202100901  

   Osman, Hussien H. ; Bobev, Svilen ( December 2021 , European Journal of Inorganic Chemistry)

   A new ternary lithium zinc germanide, Li_13.83Zn_1.17(2)Ge₄, was synthesized by a high‐temperature solid state reaction of the respective elements. The crystal structure was determined by single‐crystal X‐ray diffraction methods. The new phase crystallizes in the body‐centered cubic space groupI3d(no. 220) with unit cell parameter of 10.695(1) Å. The crystal structure refinements show that the parent Li₁₅Ge₄structure is stabilized as Li_15−xZn_xGe₄(x≈1) via random substitution of Li atoms by the one‐electron‐richer atoms of the element Zn, by virtue of which the number of valence electrons increases, leading to a more electronically stable system. The substitution effects in the parent Li₁₅Ge₄structure were investigated through both theory and experiment, which confirm that the Zn atoms in this structure prefer to occupy only one of the two available crystallographic sites for Li. The preferred substitution pattern established from experimental results is supported by DFT electronic structure calculations, which also explore the subtleties of the chemical bonding and the electronic properties of the title compounds.

    

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4. Yet Another Case of Lithium Metal Atoms and Germanium Atoms Sharing Chemistry in the Solid State: Synthesis and Structural Characterization of Ba 2 LiGe 3

   https://doi.org/10.1002/chem.202302385  

   Ghosh, Kowsik ; Bobev, Svilen ( October 2023 , Chemistry – A European Journal)

   Several Ba−Li−Ge ternary phases are known and structurally characterized, including the title compound Ba₂LiGe₃. Its structure is reported to contain [Ge₆]¹⁰⁻anions that exhibit delocalized bonding with a Hückel‐like aromatic character. The Ge atoms are in the same plane with the Li atoms, and if both types of atoms are considered as covalently bonded, [LiGe₃]⁴⁻honeycomb‐like layers will result. The latter are separated by slabs of Ba²⁺cations. However, based on the systematic work detailed herein, it is necessary to re‐evaluate the phase as Ba₂Li_1−xGe_3+x(x<0.05). Although small, the homogeneity range is clearly demonstrated in the gradual change of the unit cell for four independent samples. Subsequent characterization by single‐crystal X‐ray diffraction methods shows that the Ba₂Li_1−xGe_3+xstructure, responds to the varied number of valence electrons and the changes are most pronounced for the refined lengths of the Li−Ge and Ge−Ge bonds. Indirectly, the changes in the Ge−Li/Ge distances within layers affect the stacking too, and these changes can be correlated to the variation of thec‐cell parameter. Chemical bonding analysis based on TB‐LMTO‐ASA level calculations affirms the notion for covalent character of the Ge−Ge bonds; the Ba−Ge and Li−Ge interactions also show some degree of covalency.

    

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5. Fantastic n = 4: Ce5Co4+xGe13-ySny of the An+1MnX3n+1 Series

   Weiland, A. ; Wei, K. ; Graf, D. ; McCandless, G.T. ; Baumbach, R.E. ; Chan, J.Y. ( March 2021 , The Journal of chemical physics)

   null (Ed.)

   ABSTRACT Ce-based intermetallics are of interest due to the potential to study the interplay of localized magnetic moments and conduction electrons. Our work on Ce-based germanides led to the identification of a new homologous series An+1MnX3n+1 (A = rare earth, M = transition metal, X = tetrels, and n = 1–6). This work presents the single-crystal growth, structure determination, and anisotropic magnetic properties of the n = 4 member of the Cen+1ConGe3n+1 homologous series. Ce5Co4+xGe13−ySny consists of three Ce sites, three Co sites, seven Ge sites, and two Sn sites, and the crystal structure is best modeled in the orthorhombic space group Cmmm where a = 4.3031(8) Å, b = 45.608(13) Å, and c = 4.3264(8) Å, which is in close agreement with the previously reported Sn-free analog where a = 4.265(1) Å, b = 45.175(9) Å, and c = 4.293(3) Å. Anisotropic magnetic measurements show Kondo-like behavior and three magnetic transitions at 6, 4.9, and 2.4 K for Ce5Co4+xGe13−ySn 

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