Synthesis and crystal structures of Ln(2)Al(3)Si(2) and Ln(2)AlSi(2) (Ln :Y, Tb-Lu)

Eight new ternary aluminium silicides were prepared by heating mixtures of the elements and investigated by means of single-crystal X-ray methods. Tb2 Al3Si2 (a = 10.197(2), b = 4.045(1), c = 6.614(2) Angstrom, beta = 101.11(2 )degrees) and Dy2Al3Si2 (a = 10.144(6), b = 4.028(3), c = 6.580(6) Angstrom , beta = 101.04(6)degrees) crystallize in the Y2Al3Si2 type structure, whic h contains wavy layers of Al and Si atoms linked together by additional Al atoms and linear Si-Al-Si bonds. Through this there are channels along [010 ], which are filled by Tb and Dy atoms respectively. The silicides Ln(2)AlS i(2) with Ln = Y (a = 8.663(2), b = 5.748(1), c = 4.050(1) Angstrom), Ho (a = 8.578(2), b = 5.732(1), c = 4.022(1) Angstrom), Er (a = 8.529(2), b = 5. 719(2), c = 4.011(1) Angstrom), Tm (a = 8.454(5), b = 5.737(2), c = 3.984(2 ) Angstrom) and Lu (a = 8.416(2), b = 5.662(2), c = 4.001(1) Angstrom) crys tallize in the W2CoB2 type structure (Immm; Z = 2). whereas the structure o f Yb2AlSi2 (a = 6.765(2), c = 4.226(1) Angstrom; P4/mbm, Z = 2) corresponds to a ternary variant of the U3Si2 type structure. In all compounds the Si atoms are coordinated by trigonal prisms of metal atoms, which are connecte d by common faces so that Sit pairs (d(Si-Si): 2.37-2.42 Angstrom) are form ed.