The New Neodymium(III) Oxide Chloride Oxoselenate(IV) Nd 7 O 5 Cl 3 [SeO 3 ] 4

Pale violet, needle‐shaped single crystals of the new neodymium(III) oxide chloride oxoselenate(IV) Nd 7 O 5 Cl 3 [SeO 3 ] 4 were obtained by the reaction of Nd 2 O 3 and NdCl 3 with SeO 2 (molar ratio: 3:1:4) in evacuated silica ampoules within seven days at 775 °C, if an excess of CsCl worked as fluxing agent. Nd 7 O 5 Cl 3 [SeO 3 ] 4 crystallizes in the triclinic space group P $\bar{1}$ with the lattice parameters a = 694.46(4), b = 944.53(5), c = 1567.92(9) pm, α = 87.821(3), β = 81.849(3), γ = 84.852(3)° and Z = 2. Its structure exhibits seven crystallographically different Nd 3+ cations, of which (Nd1) 3+ – (Nd4) 3+ are coordinated by O 2– anions forming distorted square prisms. The polyhedra of (Nd1) 3+ and (Nd2) 3+ receive additional caps by one Cl – anion each, and (Nd5) 3+ – (Nd7) 3+ show mixed square antiprismatic environments of O 2– and Cl – anions too. However, the polyhedra of (Nd5) 3+ and (Nd6) 3+ include two, the polyhedron about (Nd7) 3+ even three Cl – anions. Two‐dimensional ${}^2_\infty \{[\textrm{O}_5\textrm{Nd}_7]^{11+}\}$ layers of edge‐ and vertex‐linked [ONd 4 ] 10+ tetrahedra are built up by (O1) 2– – (O5) 2– together with all Nd 3+ cations. All the other oxygen atoms belong to four crystallographically different Se 4+ cations erecting ψ 1 ‐tetrahedral oxoselenate(IV) units [SeO 3 ] 2– with stereochemically active non ‐bonding electron pairs (“ lone pairs ”) pointing into the free space between the ${}^2_\infty \{[\textrm{O}_5\textrm{Nd}_7]^{11+}\}$ layers. Three independent Cl – anions in threefold coordination of Nd 3+ cations interconnect the ${}^2_\infty \{([\textrm{O}_5\textrm{Nd}_7][\textrm{SeO}_3]_4)^{3+}\}$ layers to form a three‐dimensional network, thereby achieving the charge balance.