Au-rich polar intermetallics exhibit a wide variety of structural motifs, and this hexagonal-diamond-like gold host is unprecedented. The series Ba 2 Au 6 (Au,T) 3 (T = Zn, Cd, Ga, In, or Sn), synthesized through fusion of the elements at 700−800°C followed by annealing at 400−500°C, occur in space group R3̅ c (a ≈ 8.6−8.9 Å, c ≈ 21.9−22.6 Å, and Z = 6). Their remarkable structure, generated by just three independent atoms, features a hexagonal-diamond-like gold superstructure in which tunnels along the 3-fold axes are systematically filled by interstitial Ba atoms (blue) and triangles of disordered (Au,T) 3 atoms (green) in 2:1 proportions. The Au/Zn mixing in the latter spans ∼34 to 87% Zn, whereas the Au/Sn result is virtually invariant compositionally. Complementary bonding between the gold lattice and the disordered (Au,T) 3 units is substantial and very regular. Bonding and charge density analyses indicate delocalized bonding within the gold host and the (Au,T) 3 triangular units, and moderately polarized bonding between Ba and the electronegative framework. The new structure can also be viewed empirically as the result of an atom-by-triad [i.e., Ba by (Au,T) 3 triangle] topological substitution in a BaAu 2 (AlB 2 -type) superstructure.

Europium / Ytterbium / Antimonides / Magnetic properties / Mössbauer spectroscopy / Single crystal structure analysis / X-ray diffraction Abstract. The equiatomic antimonides EuTSb (T ¼ Cu, Pd, Ag, Pt, Au) and YbIrSb were synthesized from the elements in sealed tantalum tubes in an induction furnace. The samples were investigated by powder X-ray diffraction and the structures were refined on the basis of single crystal X-ray diffractometer data:166 F 2 values, 8 variables for EuAgSb, a ¼ 467.1(2), c ¼ 848.8(3) pm, wR2 ¼ 0.042, 162 F 2 values, 8 variables for EuAuSb, and TiNiSi type, space group Pnma, a ¼ 762.5(3), b ¼ 469.1(1), c ¼ 792.1(1) pm, wR2 ¼ 0.046, 670 F 2 values, 20 variables for EuPdSb, and a ¼ 700.7(1), b ¼ 444.68(8), c ¼ 781.3(1) pm, wR2 ¼ 0.075, 592 F 2 values, 20 variables for YbIrSb. The structures are ordered superstructure variants of the aristotype AlB 2 with planar T 3 Sb 3 hexagons in EuTSb (T ¼ Cu, Ag, Au) and puckered T 3 Sb 3 hexagons in EuTSb (T ¼ Pd, Pt) and YbIrSb. TiNiSi type EuPtSb was characterized via powder data: a ¼ 759.8(3), b ¼ 465.4(3), c ¼ 791.4(3) pm. Temperature dependent magnetic susceptibility measurements indicate antiferromagnetic ordering for all compounds. The samples were additionally characterized by 121 Sb and 151 Eu Möss-bauer spectra.

Quantitative syntheses, structure determinations and interpretations, and band calculations are reported for the nonstoichiometric rhombohedral (R3̅ c) and monoclinic (C2/c) Sr 2 Au 6 (Au 3−x T x ) (T = Zn, Ga) compounds. Several different compositions of the two Sr phases were similarly refined from single crystal X-ray diffraction data as R3̅ c: a ≈ 8.43 Å, c ≈ 21.85 Å, Z = 6 and C2/c: a ≈ 14.70 Å, b ≈ 8.47 Å, c ≈ 8.70 Å, β ≈ 123.2°, Z = 4. The R3̅ c Zn phase is stable in the composition region x ∼ 2.5−2.9 whereas its C2/c neighbor is the major product at x ∼ 2.2−2.3. Gallium versions of both were also identified. Both R3̅ c and C2/c structural types contain hexagonal-diamond-like gold superlattices stuffed with strings of interstitial Sr and disordered triangular (Au,T) 3 units. The latter space group is a maximal, nonisomorphic subgroup of the former, and the decrease in interstitial radius from Ba to Sr (∼0.08 Å experimentally) evidently drives the symmetry reduction, relaxation, and small distortions, principally around the Sr sites. Au−Au bonding among the Au hexagons in the host lattices and with gold components in the triangular interstitials is dominant and reflected in their tight packing and short interatomic separations.

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