Honeycomb Constructs in the La-Ni Intermetallics: Controlling Dimensionality via p-Element Substitution

The new ternary compounds La₁₅Ni₁₃Bi₅ and La₉Ni₈Sn₅ were obtained by arc melting under argon from appropriate amounts of the elements and subsequent annealing at 800 °C for 2 weeks. Single-crystal X-ray diffraction reveals that they represent two new structure types: La₁₅Ni₁₃Bi₅ crystallizes in the hexagonal space group P62m [hP33, a = 14.995(3), c = 4.3421(10) Å, V = 845.5(4) ų, Z = 1] and La₉Ni₈Sn₅ in P6₃/m [hP88, a = 23.870(15), c = 4.433(3) Å, V = 2187(3) ų, Z = 4]. The crystal structures of both compounds are characterized by hexagonal honeycomb-based motifs formed by Ni and Sn that extend along the c axis. The building motif with its three-blade wind turbine shape is reminiscent of the organic molecule triptycene and is unprecedented in extended solids. First-principles calculations have been performed in order to analyze the electronic structure and provide insight into chemical bonding. They reveal significant electron transfer from La to Ni and the respective p-element, which supports the formation of the polyanionic Ni-p-element network. DFT calculations suggest paramagnetic-like behavior for both compounds, which was confirmed by magnetic measurements.