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

We report five new isostructural compounds in the Ln 3 MBi 5 (Ln=Pr, Nd, Sm; M=Zr, Hf) family, and compare them to the recently reported Sm 3 ZrBi 5 analogue. Ln 3 MBi 5 crystallizes in the P 6 3 / mcm space group, hosting the anti ‐Hf 5 Sn 3 Cu structure type. The one‐dimensional structure consists of hypervalent Bi 2− chains and face‐sharing MBi 6 octahedra that form chains along the c axis. A framework of Ln 3+ 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 La 3+ and U 3+ as the largest cations and Sm 3+ as the smallest cation. X‐ray photoelectron spectra suggest ambiguous valence states in the Ln 3 MBi 5 structure depending on the identity of the M atom. This work further expands the Ln 3 MBi 5 family and sheds new light on how their bonding behavior may vary based on chemical composition.