Die Oxidnitridselenide M 3 ONSe 2 dreiwertiger Lanthanoide (M = Ce – Nd)

The Oxide Nitride Selenides M 3 ONSe 2 of Trivalent Lanthanoids (M = Ce – Nd) Oxide nitride selenides of the trivalent lanthanoids (M = Ce – Nd) with the composition M 3 ONSe 2 can be prepared by the oxidation of the respective lanthanoid metal with selenium and sodium azide (NaN 3 ) in presence of impurities containing oxygen when the corresponding lanthanoid trichloride (MCl 3 ) is used as sodium trap for the coformation of NaCl. The thermal treatment of these mixtures along with additional NaCl as flux at 900 °C in evacuated silica tubes secures the formation of fawn, transparent, lath‐shaped crystals. The monoclinic structure ( C 2/ m , Z = 6) was determined from X‐ray single‐crystal diffraction data (Ce 3 ONSe 2 : a = 2480.51(14), b = 406.85(3), c = 952.83(6) pm, β = 95.506(4)°; Pr 3 ONSe 2 : a = 2462.72(14), b = 403.74(3), c = 947.26(6) pm, β = 95.731(4)°; Nd 3 ONSe 2 : a = 2440.35(14), b = 401.48(3), c = 944.02(6) pm, β = 95.763(4)°). Five crystallographically different M 3+ cations reside in six‐ to eightfold coordination of the respective anions (three independent O 2− /N 3− and Se 2− each), for which a statistic distribution of the light elements (O 2− : N 3− = 1 : 1) has to be assumed. However, the main features of the crystal structure are (O 2− /N 3− )‐centred (M 3+ ) 4 tetrahedra. For the first time ever within the same structure of this kind, condensation of these anion‐centred cation polyhedra forming strands and layers simultaneously could be detected. Cis ‐edge connected [(O/N)M 4 ] 9.5+ tetrahedra build up the chain components $^{1}_{\infty}\rm \{[(O/N)(M4)_{3/3}(M5)_{1/1}]^{3,5+}\}$ running along [010], which are already known as dominating core in some crystal structures of pure nitride chalcogenides ( e.g. Sm 4 N 2 S 3 and Tb 4 N 2 Se 3 ). A new motif of condensed tetrahedral units comprises the second feature. By fusing [(O/N)M 4 ] 9.5+ tetrahedra via vertices and edges, one‐dimensional strand sections from the cationic sheets $^{2}_{\infty}\rm \{([OC_{4/4}]^{+})_{2}\}$ of the Ce 2 O 2 S‐type structure, which are further connected only via common vertices to form a lower‐condensed steplike two‐dimensional layer $^{2}_{\infty}\rm \{[(O/N)_{4}M_{5}]^{5+}\}$ , spreading parallel to the (100) plane, emerge for the very first time.