La3NSe3 and La3PSe3: Two Isostoichiometric, but not Isostructural Lanthanum‐Selenide Derivatives

Abstract

AbstractThe two non‐isostructural lanthanum pnictogenide selenides La3NSe3 and La3PSe3 are formed by oxidizing lanthanum metal with sodium azide (NaN3) in the presence of selenium and an excess of iodine for eight days at 850 °C and by reacting the two binary compounds lanthanum sesquiselenide (La2Se3) and lanthanum monophosphide (LaP) for four days at 900 °C in torch‐sealed glassy silica ampoules. La3NSe3 crystallizes with the well‐known Sm3NS3‐type structure in the orthorhombic space group Pnma with the lattice parameters a=1278.56(8) pm, b=424.18(3) pm, c=1358.73(9) pm, while La3PSe3 adopts the cubic Th3P4‐type structure in the space group with the lattice parameter a=901.42(6) pm, both for Z=4. It features one crystallographically distinct cationic La3+ site and a mixed anionic site with both P3− and Se2− anions sharing the same crystallographic position in its crystal structure. In contrast, the crystal structure of La3NSe3 is comprised of three different La3+ cations with one N3− and three distinct Se2− anions. The key structural elements are N3− centered (La3+)4 tetrahedra connected via vertices to form one‐dimensionally infinite chains (t=terminal, v=vertex‐sharing). The comparatively large La3+ cation adopts coordination numbers of six (1×) and seven (2×) in La3NSe3, whereas in La3PSe3, the coordination number of the single cation site is eight.