Zwei strukturverwandte Oxidnitridchalkogenide der Lanthanoide: Tb3ONSe2 und La5O2NS4

Abstract

AbstractThe structurally related oxide nitride chalcogenides Tb3ONSe2 and La5O2NS4 can be prepared by the oxidation of the respective lanthanoid metal (M = Tb and La) with selenium or sulfur and sodium azide (NaN3) in the presence of oxygen‐containing impurities, when iodine (I2) or the corresponding lanthanoid trichloride (MCl3) is used as sodium trap for the formation of NaI or NaCl, respectively. The thermal treatment of these mixtures along with additional NaI or NaCl as flux at 900 °C in evacuated silica tubes yielded transparent, yellow polyhedra in the case of Tb3ONSe2 or orange, lath‐shaped crystals of La5O2NS4. Both monoclinic structures (C2/m, Z = 4) were determined from X‐ray single‐crystal diffraction data (Tb3ONSe2: a = 1548.85(9), b = 392.02(2), c = 968.61(6) pm, β = 97.194(3)°; La5O2NS4: a = 1571.13(8), b = 409.67(2), c = 1681.03(9) pm, β = 101.204(3)°). The crystal structure of Tb3ONSe2 comprises three crystallographically different Tb3+ cations residing in six‐ and sevenfold coordination of the respective anions, whereas the crystal structure of La5O2NS4 shows five different La3+ cations with coordination numbers from six to eight. For the first time in the chemistry of oxide nitride chalcogenides of the lanthanides, an ordering of the light anions (O2– and N3–) is observed, and proper structure descriptions based on vertex‐ and edge‐connected [OM4]10+ and [NM4]9+ tetrahedra (M = Tb and La) becomes possible. As main structural feature, a bulky chain {}^1_\infty{[ONTb3]4+} running along [010] can be detected in the crystal structure of Tb3ONSe2. The same morphology, but a different chemistry is realized in the related crystal structure of La5O2NS4, where these topologically equivalent strands {}^1_\infty{[O2La3]5+} and an additional second chain {}^1_\infty{[NLa2]3+}, built up by vertex‐ and edge connected [NLa4]9+ tetrahedra, compose the compound. As supporting tool for the distinction of the O2– and N3– anions in both crystal structures, the valence‐bond concept is also applied.