Tb3O2Cl[SeO3]2 and Tb5O4Cl3[SeO3]2: Oxide Chloride Oxoselenates(IV) of Trivalent Terbium with “Lone‐Pair” Channel or Layer Structures

Abstract

AbstractOrthorhombic Tb3O2Cl[SeO3]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 Tb4O7, Tb, TbCl3, and SeO2 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 {[(Tb1)3/3(Tb2)2/1O4/2]5+} (≡ {[O2Tb3]5+}) along [100] formed by two parallel chains {[OTb4/2]4+} of trans‐edge connected [OTb4]10+ tetrahedra (d(O‐Tb) = 220 ‐ 231 pm) which share an extra edge per chain link. The crystal structure contains two crystallographically different Tb3+ cations: Tb1 is coordinated as bicapped trigonal prism, while Tb2 resides in square antiprismatic coordination. The Se4+ coordination is best described as Ψ1 tetrahedral ([SeO3E]2‐; E: non‐binding electron pair). The non‐binding “lone‐pair” electrons of four [SeO3]2‐ groups and two Cl‐ anions form pseudo‐hexagonal empty channels along [100] between four cationic double chains. Tb5O4Cl3[SeO3]2 was prepared likewise as plate‐like, colourless single crystals by solid‐state reaction of an admixture of Tb4O7, Tb, TbOCl, TbCl3, and SeO2 (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 Tb3+ cations in seven‐ and eightfold coordination of O2‐ and Cl‐ anions, respectively. The crystal structure of Tb5O4Cl3[SeO3]2 is layered and built up of corrugated terbium‐oxygen sheets {[O4Tb5]7+} formed by edge‐ and vertex‐shared [OTb4]10+ tetrahedra (d(O‐Tb) = 226‐232 pm) spreading parallel (001). The structure is strongly related to the “lone‐pair” channel structures of Tb2O[SeO3]2 and Tb3O2Cl[SeO3]2, where single ({[OTb2]4+}) and double chains ({[O2Tb3]5+}) of trans‐edge connected [OTb4]10+ tetrahedra are present. As an extension of this kind of connectivity, the double chains ({[O2Tb3]5+}) of the Tb3O2Cl[SeO3]2 structure are further condensed via common vertices to form the above‐mentioned {[O4Tb5]7+} layers in Tb5O4Cl3[SeO3]2.