Hydrogen in Polar Intermetallics. Binary Pnictides of Divalent Metals with Mn₅Si₃-type Structures and Their Isotypic Ternary Hydride Solutions

Studies of the hydrogen-free binary A 5 Pn 3 systems for A = Ca, Sr, Ba, Sm, Eu, Yb and Pn (pnictogen) = As, Sb, Bi, reveal four new examples, (Ca,Yb) 5 Bi 3 and Eu 5 (Sb,Bi) 3, among the 16 that form with a hexagonal ( P 6 3 / mcm ) Mn 5 Si 3 -type structure. Most of the previous literature on unit cell dimensions for these correspond to those of smaller ternary hydrides (or other materials). Previously reported Ba 5 As 3 and cubic SmAs could not be reproduced. New cubic anti-Th 3 P 4 phases are also found in the Sm−As and Ba−Sb−F systems. Crystal structures have been refined from single-crystal X-ray data for hexagonal Sr 5 As 3 H ∼ 1, Ca 5 Sb 3, Ba 5 Sb 3 H ∼ 0.7, Sm 5 Sb 3 H ∼ 1, Eu 5 Sb 3, Yb 5 Sb 3, and Eu 5 Bi 3 . The widths of H solubility regions in the hexagonal parent structures in terms of cell constant changes have been determined for 12 examples, eight of which with more hydrogen further convert into known orthorhombic Ca 5 Sb 3 F-type phases. The Sm 5 Sb 3 and Sm 5 Bi 3 members contain trivalent cations according to several criteria. Magnetic susceptibility data are reported for Eu 5 Sb 3 and Eu 5 Bi 3, which contain normal Eu II states.