LANTHANUM ORTHOSILICATE SELENIDE, LA2SESIO4

The structure of La2SeSiO4 has been determined from single-crystal X-ray data, M(r) = 448.9, orthorhombic, space group D2h11-Pbcm, a = 6.279 (4), b = 7.306 (5), c = 11.177 (7) angstrom, V = 512.7 angstrom 3, Z = 4, D(x) = 5.813 g cm-3, lambda(Mo K-alpha-1) = 0.7093 angstrom, mu = 236.8 cm-1, F(000) = 771, (including anomalous dispersion), T = 111 K, R(F2) = 0.100 and wR(F2) = 0.121 for 3599 unique data, and R = 0.047 and wR = 0.054 for 2340 unique data with F(o)2 > 3-sigma(F(o)2). The structure, which is similar to that of calcium chloride phosphate Ca2ClPO4 [Greenblatt, Banks & Post (1967). Acta Cryst. 23, 166-171] contains discrete SiO4(4-) tetrahedra. The La atoms are eight-coordinate with six La-O bond lengths in the range 2.501 (3)-2.602 (4) angstrom and two La-Se bond lengths 3.048 (2), 3.233 (2) angstrom.