Eu7Ga6Sb8: A Zintl phase with Ga–Ga bonds and polymeric gallium antimonide chains

From Three-Dimensional Clathrates to Two-Dimensional Zintl Phases AMSb2 (A = Rb, Cs; M = Ga, In) Composed of Pentagonal M-Sb Rings

Three new antimonide Zintl phases, RbGaSb₂, CsGaSb₂, and CsInSb₂, were discovered during exploration of corresponding A-M-Sb (A = Rb, Cs; M = Ga, In) ternary systems while searching for new clathrates. The AGaSb₂ phases crystallize in the tetragonal space group P4₂/nmc (No. 137) in the LiBS₂ structure type, while CsInSb₂ crystallizes in lower symmetry in the orthorhombic space group Cmce (No. 64) in the KGaSb₂ structure type with additional disorder of one of the Cs sites. The crystal structures of all three reported AMSb₂ compounds are composed of two-dimensional [MSb₂]^- tetrahedral layers separated by Rb⁺ or Cs⁺ cations. [MSb₂]^- layers are built from fused M-Sb pentagons and hexagons, which are also the main structural units for A₈M₂₇Sb₁₉ clathrate cages. The semiconductor nature of AMSb₂ was suggested by band structure calculations and confirmed by transport property characterization. CsGaSb₂ is a rare example of an n-type pnictide Zintl phase. All reported compounds exhibit low thermal conductivity typical for complex antimonides of heavy elements.

Metallic alloys at the edge of complexity: structural aspects, chemical bonding and physical properties

Complex metallic alloys belong to the vast family of intermetallic compounds and are hallmarked by extremely large unit cells and, in many cases, extensive crystallographic disorder. Early studies of complex intermetallics were focusing on the elucidation of their crystal structures and classification of the underlying building principles. More recently, ab initio computational analysis and detailed examination of the physical properties have become feasible and opened new perspectives for these materials. The present review paper provides a summary of the literature data on the reported compositions with exceptional structural complexity and their properties, and highlights the factors leading to the emergence of their crystal structures and the methods of characterization and systematization of these compounds.

New structure type in the mixed-valent compound YbCu4Ga8

The new compound YbCu(4)Ga(8) was obtained as large single crystals in high yield from reactions run in liquid gallium. Preliminary investigations suggest that YbCu(4)Ga(8) crystallizes in the CeMn(4)Al(8) structure type, tetragonal space group I4/mmm, and lattice constants are a = b = 8.6529(4) Å and c = 5.3976(11) Å. However, a detailed single-crystal XRD revealed a tripling of the c axis and crystallizing in a new structure type with lattice constants of a = b = 8.6529(4) Å and c = 15.465(1) Å. The structural model was further confirmed by neutron diffraction measurements on high-quality single crystal. The crystal structure of YbCu(4)Ga(8) is composed of pseudo-Frank-Kasper cages occupying one ytterbium atom in each ring which are shared through the corner along the ab plane, resulting in a three-dimensional network. The magnetic susceptibility of YbCu(4)Ga(8) investigated in the temperature range 2-300 K showed Curie-Weiss law behavior above 100 K, and the experimentally measured magnetic moment indicates mixed-valent ytterbium. Electrical resistivity measurements show the metallic nature of the compound. At low temperatures, variation of ρ as a function of T indicates a possible Fermi-liquid state at low temperatures.

Sr2MnSb2: A New Ternary Transition Metal Zintl Phase

A transition metal-containing Zintl phase, Sr2MnSb2, was prepared from a stoichiometric combination reaction of the elements in Sn flux, and its structure was determined by single-crystal X-ray diffraction methods. The compound crystallizes in the orthorhombic space group Pnma with a = 15.936(3) A, b = 14.498(3) A, c = 8.2646(17) A, and Z = 12. The structure of Sr2MnSb2 is composed of corrugated layers of corner- and edge-shared MnSb4 tetrahedra. The basic building unit of the layer is a [Mn3Sb6]12- cluster composed of three edge-shared MnSb4 tetrahedra. These trinuclear clusters share four Sb vertexes to form a layer with cavities. Sr2+ cations are located at the inter- and intralayer space. Magnetic susceptibility measurements indicate an effective magnetic moment of 4.85 mu(B), a value smaller than what would be expected from Mn2+ ions.