NaLn9N4Se8 (Ln = Gd – Dy): The first sodium-containing nitride selenides of the lanthanoids

Three new compounds with the composition Na Ln 9 N 4 Se 8 ( Ln = Gd – Dy) could be synthesized and structurally characterized. Initially intended to achieve the ternary Ln 4 N 2 Se 3 representatives, the involvement of sodium-containing reactants led to the formation of these quaternary phases. They crystallize in the monoclinic system with the space group C 2/ m (lattice parameters: a = 1358 – 1341 pm, b = 399 – 394 pm, c = 1016 – 1026 pm and β = 109.1 – 109.3°) and one formula unit per unit cell. A group-subgroup relationship of both mentioned compound types can be shown, describing the structure of the title compounds as stuffed Sm 4 N 2 S 3 -type arrangement with infinite double-strands ( t = terminal, e = edge-connecting) of cis -edge connected [N Ln 4 ] 9+ tetrahedra as common structural element. All cations reside in quasi -octahedral coordination spheres (Na + / Ln 3+ : 6 Se 2– , ( Ln 1) 3+ : 1 N 3– + 5 Se 2– , ( Ln 2) 3+ : 3 N 3– + 3 Se 2– ). Raman-spectroscopic measurements reveal distinct bands at 374 and 622 cm –1 , which can be assigned to vibrations in the mentioned double-strands of fused [N Ln 4 ] 9+ tetrahedra.