Ln₃MBi₅ (Ln=Pr, Nd, Sm; M=Zr, Hf): Intermetallics with Hypervalent Bismuth Chains

Abstract

We report five new isostructural compounds in the Ln3MBi5 (Ln=Pr, Nd, Sm; M=Zr, Hf) family, and compare them to the recently reported Sm3ZrBi5 analogue. Ln3MBi5 crystallizes in the P63/mcm space group, hosting the anti‐Hf5Sn3Cu structure type. The one‐dimensional structure consists of hypervalent Bi2− chains and face‐sharing MBi6 octahedra that form chains along the c axis. A framework of Ln3+ cations charge balances and separates the two motifs. The Bi−Bi and M−Bi bond lengths decrease as the Ln cation becomes smaller across the period, but there is almost no difference in either bond length when the identity of M changes, as expected because Zr and Hf have the exact same radii due to lanthanide contraction. We present a structural stability map showing the limits of cation stability in the structure, with La3+ and U3+ as the largest cations and Sm3+ as the smallest cation. X‐ray photoelectron spectra suggest ambiguous valence states in the Ln3MBi5 structure depending on the identity of the M atom. This work further expands the Ln3MBi5 family and sheds new light on how their bonding behavior may vary based on chemical composition.