Structure of Y3TaNi6+xAl26: a filled-up substitution variant of the BaHg11 type

The crystal structure of Y₃TaNi_6+xAl₂₆ (refined composition Y₄TaNi_6+[7]Al_20+[6]) was determined by single-crystal X-ray diffraction (λ(Mo K) −0.71073 A. μ −17.827 mm¹, F(000) = 700, T = 293 K, wR = 0.015 for [8] unique reflections). This new quaternary aluminide crystallizes with a cubic structure. Pearson code cP49-12.85, (221) Pm-3m-ji'gdba, a = 8.3600(1) Å. V = 584.28(2) Å, Z = 1, M₁ = 1510.25, D_x = 4.292 mg mm¹. The structure of Y_xTaNi_6+xAl₂₆ is filled-up substitution variant of the BaHg₁₁ structure type with one additional atom site, partly occupied (around 15%) by Ni atoms, located at the centre of a cube formed by Al atoms. Distinct atom coordinates were refined for Ni and Al atoms on a site for which mixed occupation (approximately 50% Ni/50% Al) was found. The Ta atoms centre regular Al atom cuboctahedra, and the Y atoms 20-vertex polyhedra, formed by Al and Ni atoms, similar to those observed in CeMn₄Al₈ and YbFe₂Al₁₀.