Sm3Cl[SiO4]2:: A chlorine-poor chloride orthosilicate of samarium

Pale yellow, plate-like single crystals of Sm3Cl[SiO4](2) (orthorhombic, Pnma; a = 701.74(8), b = 1800.8(2), c = 626.63(7) pm; Z = 4) are obtained upon the reaction of SmCl3, Sm2O3 and SiO2 ("Kieselgel") in 1:4:6 molar ratios, most advantageously in the presence of substantial amounts of NaCl as fluxing agent, after seven days at 850 degrees C in evacuated silica ampoules. The B-type crystal structure (isotypic with e.g. Yb3Cl[SiO4](2)) contains discrete orthosilicate tetrahedra [SiO4](4-) which form anionic double layers ({(Sml)(2)[SiO4](2)}(2-)) with (Sml)(3+). These are alternatingly sheethed along [010] with cationic monolayers ({(Sm2)Cl}(2+)) consisting of (Sm2)(3+) and Cl-. Both crystallographically independent Sm3+ cations exhibit coordination numbers of eight (Sml: 1 Cl +/- 7 O; Sm2: 2 Cl + 6 O) with respect to the involved electronegative particles.