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The well-known BaAl4-type structure consists of three ordered ternary derivatives, i.e., BaNiSn3-(I4mm), ThCr2Si2-(I4/mmm), and CaBe2Ge2-type (P4/nmm). Few systems, such as Ba-Au-Sn, have been confirmed to manifest all three types as a function of valence electron count. In this work, the SrAuxSn4-xsolid solution at the 600 ° C section was studied thoroughly using both single crystal and powder X-ray diffraction. The crystal structures and phase width for the CaBe2Ge2-type SrAuxSn4-xsolid solution were established to be α = 4.6528(2)-4.6233(3) Å and c = 11.3753(4)-11.2945(10) Å for x ≈ 1.65(1)-2.19(1). In the structure of SrAu2Sn2, no Au/Sn mixing was found, but for x < 2 compositions, Au/Sn mixings were only located at the Wyckoff 2α (3/4 1/4 0) site and for x > 2 compositions, at the 2b (3/4 1/4 1/2) site. Differential scanning calorimetry (DSC) analyses indicated that no phase transition occurred for the CaBe2Ge2-type SrAuxSn4-xphase up to 950 ° C. Attempts to synthesize the ThCr2Si2-and BaNiSn3-type SrAuxSn4-xphases under the same reaction conditions were unsuccessful, and the BaNiSn3-type phase could not be attained even at a pressure of 3 GPa. The instability of a BaNiSn3-type "SrAuSn3" was investigated by both DSC measurements and first principles electronic structure calculations.

Eu2Ni8Si3 and its anti‐type representative Sr2Pt3Al8 were synthesized from the elements. They crystallize in the tetragonal crystal system with space group P42/nmc and with lattice parameters of a=997.9(1) and c=747.6(1) pm (Eu2Ni8Si3) as well as a=1082.9(2) and c=823.3(2) pm (Sr2Pt3Al8). Both compounds were investigated via single crystal X‐ray diffraction, indicating slight Si/Ni mixing for the silicide. Sr2Pt3Al8 exhibits a temperature independent magnetic susceptibility, suggesting superimposed dia‐ and Pauli‐paramagnetic contributions. The independent Al and Pt sites of the platinide were further characterized by 27Al and 195Pt solid‐state NMR spectroscopy, which were assigned with the help of electronic structure calculations. ICOHP calculations and Bader charges were used to analyze the bonding situation. Eu2Ni8Si3 in contrast is paramagnetic with a ferromagnetic transition at TC=46.9(2) K and exhibits an effective magnetic moment of μeff=6.61(1) μB per Eu atom. The latter is in line with an intermediate valence that was further proven by 151Eu Mößbauer spectroscopic investigations. At 300 K, the refined Eu2+/Eu3+ ratios are 60 %/40 %, at 78 K 62 % and 38 % (Eu2+/Eu3+) are observed, being in line with the ratio deduced from the magnetic susceptibility. Finally, at 6 K a ratio of 68 % Eu2+ and 32 % Eu3+ was observed. Below the Curie temperature, the Eu2+ signal shows a full magnetic hyperfine splitting, with an internal magnetic field value of B0=28.4 T. [ABSTRACT FROM AUTHOR]

The new Y2Co3Ga9 and Gd3Ru4Al12 type representatives M2T3Al9 (M = Ca, Sr, Eu; T = Ir, Pt) and M3Rh4Al12 (M = Ca, Eu) have been synthesized from the elements by heating the respective elemental compositions in sealed tantalum tubes. The samples were analysed by powder X-ray diffraction to check their purity. By applying different temperature treatments, their phase purity and crystallinity were enhanced. The crystal structures of Ca3Rh4Al12 and Eu3Rh4Al12 (hexagonal Gd3Ru4Al12 type, P63/mmc) as well as Ca2Ir3Al9 and Ca2Pt3Al9 (orthorhombic Y2Co3Ga3 type, Cmcm) were refined from single-crystal X-ray diffraction data. All structures can be described based on distorted cube-like T@Al8 units that are connected to form strands. Additionally, an Al11 supertetrahedral building block can be identified within the structures. While the trigonal bipyramidal core of the cluster contains substantial bonding interactions in the case of the M3Rh4Al12 members, the connection via common edges in the case of the M2Ir3Al9 compounds seems to weaken these interactions. The differences in the bonding situation and the question why these different structure types are formed for the different transition metals has been targeted by quantum-chemical calculations. The calculated formation energy using three different reaction paths suggests that the stability of these phases is highly dependent on the side phases involved, even though Ca3T4Al12 phases are in general thermodynamically more favourable. According to the Bader analysis of the two polyanions, an improved covalent bonding can be observed in the [T4Al12]δ− over the [T3Al9]δ− framework. [ABSTRACT FROM AUTHOR]

The new ternary compound Nb1–xOs1+xB (x = 0.17) was synthesized by arc‐melting of the elements in a water‐cooled crucible under an argon atmosphere and was characterized by powder and single‐crystal X‐ray diffraction as well as energy‐dispersive X‐ray spectroscopy (EDX). The compound crystallizes with a new orthorhombic structure type in the space group Pnma (no. 62) with the lattice parameters a = 11.283(2) Å, b = 3.0101(4) Å, and c = 12.883(2) Å. The structure contains isolated boron atoms in osmium trigonal prisms, and boron chains in face‐sharing niobium trigonal prisms. Electronic structure relaxation has confirmed the crystallographic parameters, and crystal orbital Hamilton population (COHP) bonding analysis was used to understand the chemical bonding. It is shown that a local stabilizing effect from replacing Nb with Os is favored despite a global destabilization. [ABSTRACT FROM AUTHOR]

The well-known BaAl4-type structure consists of three ordered ternary derivatives, i.e., BaNiSn3- ( I4 mm), ThCr2Si2- ( I4/ mmm), and CaBe2Ge2-type ( P4/ nmm). Few systems, such as Ba-Au-Sn, have been confirmed to manifest all three types as a function of valence electron count. In this work, the SrAu xSn4- x solid solution at the 600 °C section was studied thoroughly using both single crystal and powder X-ray diffraction. The crystal structures and phase width for the CaBe2Ge2-type SrAu xSn4- x solid solution were established to be a = 4.6528(2)-4.6233(3) Å and c = 11.3753(4)-11.2945(10) Å for x ≈ 1.65(1)-2.19(1). In the structure of SrAu2Sn2, no Au/Sn mixing was found, but for x < 2 compositions, Au/Sn mixings were only located at the Wyckoff 2 a (¾ ¼ 0) site and for x > 2 compositions, at the 2 b (¾ ¼ ½) site. Differential scanning calorimetry (DSC) analyses indicated that no phase transition occurred for the CaBe2Ge2-type SrAu xSn4- x phase up to 950 °C. Attempts to synthesize the ThCr2Si2- and BaNiSn3-type SrAu xSn4- x phases under the same reaction conditions were unsuccessful, and the BaNiSn3-type phase could not be attained even at a pressure of 3 GPa. The instability of a BaNiSn3-type 'SrAuSn3' was investigated by both DSC measurements and first principles electronic structure calculations. [ABSTRACT FROM AUTHOR]

A seriesof four new analogue phases Ca2M2X (M = Pd,Pt and X = Al, Ge) were prepared by direct combinationof the respective elements in stoichiometric mixtures at high temperaturein order to analyze the impact of valence electron count (vec) andelectronegativity differences (Δχ) on the structure selectionand stability. Their crystal structures, as determined from single-crystalX-ray diffraction data, correspond to two different but closely relatedstructure types. The first compound, Ca2Pd2Ge(I), is an unprecedented ternary ordered variant of theZr2Al3-type (orthorhombic, Fdd2). The three other phases, Ca2Pt2Ge (II), Ca2Pd2Al (III) andCa2Pt2Al (IV), adopt the Gd2Ge2Al-type structure (monoclinic, C2/c). All title structures feature linear chainsof the noble metals (Pd or Pt). The Pd linear chains in Iare undistorted with equidistant Pd···Pd atoms, whereasthe metal chains in II–IVare pairwisedistorted, resulting in short connected {Pd2} or {Pt2} dumbbells that are separated by longer M···Mcontacts. The occurrence and magnitude of the pairing distortion inthese chains are controlled by the vecand the Δχbetween the constituent elements, a result which is supported by analysisof the calculated Badereffective charges. The metalchains act as charge modulation units, critical for the stabilityand the electronic flexibility of the structures by an adequate adjustmentof the metal–metal bond order to both the vecand the degree of charge transfer. Thus, Ca2Pd2Ge (28 ve/f.u) is a Zintl-like, charge optimized phase with formallyzerovalent Pd atoms forming the undistorted metal chains; semimetallicproperties are predicted by TB-LMTO calculations. In contrast, theisoelectronic Ca2Pt2Ge is predicted to be agood metal with the Fermi level located at a local maximum of theDOS, a fingerprint of potential electronic instability. This is dueto greater charge transfer to the more electronegative Pt atoms formingthe metal chains and probably to packing frustration in the well packedstructure that may prevent a larger distortion of the Pt chains. However,the instability is suppressed in the aliovalent but isostructuralphases Ca2M2Al (27 ve/f.u) with an enhancementof the pairing distortion within the metal chains but lower M–Mbond order. Further reduction of the vecas in Ca2M2Cd (26 ve/f.u) may induce a transition towardthe more geometrically flexible W2CoB2-typewith a low dimensional structure, to create more room for a largerdistortion of the metal chain as dictated by the shortage of valenceelectrons. [ABSTRACT FROM AUTHOR]

Eu2Ni8Si3 and its anti‐type representative Sr2Pt3Al8 were synthesized from the elements. They crystallize in the tetragonal crystal system with space group P42/nmc and with lattice parameters of a=997.9(1) and c=747.6(1) pm (Eu2Ni8Si3) as well as a=1082.9(2) and c=823.3(2) pm (Sr2Pt3Al8). Both compounds were investigated via single crystal X‐ray diffraction, indicating slight Si/Ni mixing for the silicide. Sr2Pt3Al8 exhibits a temperature independent magnetic susceptibility, suggesting superimposed dia‐ and Pauli‐paramagnetic contributions. The independent Al and Pt sites of the platinide were further characterized by 27Al and 195Pt solid‐state NMR spectroscopy, which were assigned with the help of electronic structure calculations. ICOHP calculations and Bader charges were used to analyze the bonding situation. Eu2Ni8Si3 in contrast is paramagnetic with a ferromagnetic transition at TC=46.9(2) K and exhibits an effective magnetic moment of μeff=6.61(1) μB per Eu atom. The latter is in line with an intermediate valence that was further proven by 151Eu Mößbauer spectroscopic investigations. At 300 K, the refined Eu2+/Eu3+ ratios are 60 %/40 %, at 78 K 62 % and 38 % (Eu2+/Eu3+) are observed, being in line with the ratio deduced from the magnetic susceptibility. Finally, at 6 K a ratio of 68 % Eu2+ and 32 % Eu3+ was observed. Below the Curie temperature, the Eu2+ signal shows a full magnetic hyperfine splitting, with an internal magnetic field value of B0=28.4 T. [ABSTRACT FROM AUTHOR]