On the effect of Ga and In substitutions in the Ca 11 11 Bi 10 10 and Yb 11 11 Bi 10 10 bismuthides crystallizing in the tetragonal Ho 11 11 Ge 10 10 structure type

摘要

The Ga‐ and In‐substituted bismuthides Ca 11 Ga x Bi 10– x , Ca 11 In x Bi 10– x , Yb 11 Ga x Bi 10– x , and Yb 11 In x Bi 10– x ( x 2) can be readily synthesized employing molten Ga or In metals as fluxes. They crystallize in the tetragonal space group I 4/ mmm and adopt the Ho 11 Ge 10 structure type (Pearson code tI 84; Wyckoff sequence n 2 m j h 2 e 2 d ). The structural response to the substitution of Bi with smaller and electron‐poorer In or Ga has been studied by single‐crystal X‐ray diffraction methods for the case of Ca 11 In x Bi 10– x [ x = 1.73?(2); octabismuth undecacalcium diindium]. The refinements show that the In atoms substitute Bi only at the 8 h site. The refined interatomic distances show an unconventional – for this structure type – bond‐length distribution within the anionic sublattice. The latter can be viewed as consisting of isolated Bi 3? anions and [In 4 Bi 8 20? ] clusters for the idealized Ca 11 In 2 Bi 8 model. Formal electron counting and first‐principle calculations show that the peculiar bonding in this compound drives the system toward an electron‐precise state, thereby stabilizing the observed bond‐length pattern.