Accidental silicon-containing compounds: Crystal structures of La3Al0.44Si0.93S7, BaSm4(SiO4)(3)Se, and monoclinic and orthorhombic Ln(2)(SiO4)Te (Ln= Nd and Sm)

The compounds La3Al0.44Si0.93S7, BaSm4(SiO4)(3)Se, and mono-clinic and orth orhombic Ln(2)(SiO4)Te (Ln = Nd and Sm) were obtained accidentally by react ions in fused-silica tubes, La(3)Al(0.44)5Si(0.93)S(7) crystallizes in the hexagonal space group P6(3) with two formula units in a cell of dimensions a = 10.277(2), c = 5.793(1) Angstrom (T = 153 K), The structure consists of chains of face-sharing AIS(6) octahedra and isolated SiS4 tetrahedra. The LaS8 coordination polyhedron is a square antiprism, BaSm4(SiO4)(3)Se crysta llizes in the hexagonal space group P6(3)/m with two formula units in a cel l of dimensions a = 9.869(1), c = 6.851(1) Angstrom (T = 153 K), The struct ure is formed by orthosilicate ([SiO4](4-)) tetrahedra separated by Ba2+ an d Sm3+ cations, The Ba2+ and Sm(1)(3+) cations are disordered in an MS9 tri capped trigonal prism and the Sm(2)3+ cation is in a monocapped trigonal pr ism. Monoclinic (P2(1)/c) Ln(2)(SiO4)Te (Ln = Nd and Sm) is a layered struc ture with four formula units in a cell of dimensions a = 9.823(2), b = 6.42 1(1), c = 8.676(2) Angstrom, beta = 94.60(3)degrees (T = 153 K) for Ln = Nd , and a = 9.760(2), b = 6.357(1), c = 8.601(2) Angstrom, beta = 94,87(3)deg rees (T = 153 K) for L = Sm, The layer iis formed by [SiO4](4-) tetrahedra separated by Ln and Te atoms. The Ln(1)O7Te polyhedron is a square antipris m and the Ln(2)O4Te4 polyhedron is a bicapped trigonal prism. Orthorhombic Pbcm Ln(2)(SiO4)Te (Ln = Nd and Sm) is a layered structure with four formul a units in a cell of dimensions a = 6.279(1), b = 7.189(1), c = 11.168(2) A ngstrom (T = 153 K) for Ln = Nd, and a = 6.201(1), b = 7.091(1), c = 11.077 (2) Angstrom (T = 115K) for Ln = Sm, The layer is formed by [SiO4](4-) tetr ahedra separated by Ln and Te atoms. The Ln(1)O6Te3 polyhedron is a tricapp ed trigonal prism; the Ln(2)O6Te2 polyhedron is a dodecahedron. Orthorhombi c Ln(2)(SiO4,)Te, rho = 6.696 g/cm(3) for Ln = Nd and rho = 7.096 g/cm(3) f or Ln = Sm, are denser than the monoclinic forms, rho = 6.188 g/cm(3) for L n = Nd and rho = 6.500 g/cm(3) for Ln = Sm, (C) 2000 Academic Press.