Tb 3 O 2 Cl[SeO 3 ] 2 and Tb 5 O 4 Cl 3 [SeO 3 ] 2 : Oxide Chloride Oxoselenates(IV) of Trivalent Terbium with “Lone‐Pair” Channel or Layer Structures

Orthorhombic Tb 3 O 2 Cl[SeO 3 ] 2 (Pnma; a = 535.16(4), b = 1530.51(9), c = 1081.72(7) pm; Z = 4) is formed by reacting a stoichiometric mixture of Tb 4 O 7 , Tb, TbCl 3 , and SeO 2 in a suitable molar ratio (12 : 8 : 7 : 42) within seven days in an evacuated sealed silica tube at 850 °C. The needle‐shaped, colourless single crystals (light, water and air stable) exhibit one‐dimensional strands   ∞ 1 {[(Tb1) 3/3 (Tb2) 2/1 O 4/2 ] 5 +} (≡   ∞ 1 {[O 2 Tb 3 ] 5+ }) along [100] formed by two parallel chains   ∞ 1 {[OTb 4/2 ] 4+ } of trans ‐edge connected [OTb 4 ] 10+ tetrahedra (d(O‐Tb) = 220 ‐ 231 pm) which share an extra edge per chain link. The crystal structure contains two crystallographically different Tb 3+ cations: Tb1 is coordinated as bicapped trigonal prism, while Tb2 resides in square antiprismatic coordination. The Se 4+ coordination is best described as Ψ 1 tetrahedral ([SeO 3 E] 2‐ ; E: non ‐binding electron pair). The non‐binding “lone‐pair” electrons of four [SeO 3 ] 2‐ groups and two Cl ‐ anions form pseudo ‐hexagonal empty channels along [100] between four cationic double chains. Tb 5 O 4 Cl 3 [SeO 3 ] 2 was prepared likewise as plate‐like, colourless single crystals by solid‐state reaction of an admixture of Tb 4 O 7 , Tb, TbOCl, TbCl 3 , and SeO 2 (molar ratio: 9 : 6 : 21 : 7 : 28) in an evacuated sealed silica tube during seven days at 850 °C. This compound crystallizes in the monoclinic system (C2/m; a = 1229.13(9), b = 546.17(4), c = 978.79(7) pm, β = 90.485(6)°; Z = 2) and contains three crystallographically different Tb 3+ cations in seven‐ and eightfold coordination of O 2‐ and Cl ‐ anions, respectively. The crystal structure of Tb 5 O 4 Cl 3 [SeO 3 ] 2 is layered and built up of corrugated terbium‐oxygen sheets   ∞ 2 {[O 4 Tb 5 ] 7+ } formed by edge‐ and vertex‐ shared [OTb 4 ] 10+ tetrahedra (d(O‐Tb) = 226‐232 pm) spreading parallel (001). The structure is strongly related to the “lone‐pair” channel structures of Tb 2 O[SeO 3 ] 2 and Tb 3 O 2 Cl[SeO 3 ] 2 , where single (   ∞ 1 {[OTb 2 ] 4+ }) and double chains (   ∞ 1 {[O 2 Tb 3 ] 5+ }) of trans‐ edge connected [OTb 4 ] 10+ tetrahedra are present. As an extension of this kind of connectivity, the double chains (   ∞ 1 {[O 2 Tb 3 ] 5+ }) of the Tb 3 O 2 Cl[SeO 3 ] 2 structure are further condensed via common vertices to form the above‐mentioned   ∞ 2 {[O 4 Tb 5 ] 7+ } layers in Tb 5 O 4 Cl 3 [SeO 3 ] 2 .