THE CRYSTAL-STRUCTURE OF SODIUM STRONTIUM SILICATE, NA4SRSI3O9

Na4SrSi3O9 is monoclinic, C2, a = 10.706(2), b = 10.866(2), c = 6.509(1) angstrom, beta = 144.14(2)-degrees, Z = 2. The structure was determined using 411 independent reflexions measured on a Nicolet P3 4-circle diffractometer; the coordinates (including anisotropic temperature factors for Sr only) refined to R = 10.4%. Extra very weak reflexions on film (with CuK-alpha) suggested a superstructure, but these could not be detected using the diffractometer (with MoK-alpha). The compound contains infinite SiO3 chains, of a conformation not described previously. Bond lengths and angles are normal, although the Si-O-Si angle is nearly 180-degrees; this rather large value is associated with large temperature factors for the bridging oxygen atoms. The structure is compared with those of other compounds of formula M'4M''(TO3)3 where M' = Na, K; M'' = Ca, Sr, Ba; T = Si, Ge.