On the structure of KAsSe2

Abstract

The structure of the title compound w a s described [Sheldrick & H/iusler (1988), Z. Anorg. Allg. Chem. 561, 139148] as triclinic, space group P1. It should be described as monoclinic, space group Cc. The structure of KAsSe2 has been reported (Sheldrick & H/iusler, 1988) as triclinic, space group P1 [a = 6.558 (1), b = 12.628 (2), c = 6.554 (2) A, a = 100.43 (2), 13 = 107.53 (2), y = 100.48 (2) °, Z = 4 ] and refined to RF = 0075 (wR = 0081) on the basis of 1951 reflections with Fo 2 > 2.0o-(Fo2). It should be described in space group Cc. The lattice vectors [101], [10T] and [010] define a C-centred monoclinic cell with a' = 7.750, b' = 10.576, c' = 12.628 A,, a = 9003,/3 = 107.88, y = 89.96 °, Z = 8.* The corresponding coordinate t ransformat ions are: x ' = ~(x+ z), y ' = ~(x z) + 0.2806, z' = y. If the x coordinate of a tom K(3) is decremented by 1.0 and the above t ransformat ions are then applied, pairs of a toms are closely related as x, y, z and x, y, ~+ z. When * The lattice vectors []01], [121] and [101] describe an F-centred orthorhombic cell (a ' = 10-576, b ' = 24-036, c ' = 7-750A,, a = 8999, /3= 8996, y = 8998 °, Z = 16). However, no symmetry appropriate to an orthorhombic space group is present. 0108-2701/89/122029-01 $03.00 Table 1. Coordinates ( × 104), space group Cc Numbers in square brackets are the shifts necessary to achieve the Cc symmetry. x' y' z' K(1,3) 02183 [9] 02736 [2] 02591 [8] K(2,4) 0.1527 [5] 0.0188 [3] 0.4976 [2] As(l,3) 0.7222 [5] 0.1528 [1] 0-1768 [2] As(2,4) 0.6668 [3] 0.0695 [2] 0.4425 [1] Se(! 1,31) 0-9578 [6] 0.0094 [0] 0.2076 [4] Se(12,32) 0.5390 [5] 0.1286 [5] -0.0184 [2] Se(21,41) 0.5002 [2] 0.2196 [2] 0.4999 [1] Se(22,42) 0-4997 [4] 0-0428 [1] 0.2448 [0] these t ransformed coordinates are symmetrized and aver- aged, the values in Table 1 result. Since the original structure factors could not be retrieved (Sheldrick, 1989), we were unable either to carry out refinement in space group Cc or to confirm the systematic absences due to the c-glide plane (hkh with k odd in the triclinic description). References SHELDR1CK, W. S. (1989). Personal communication. SHELDRICK, W. S. & H~,USLER, H.-J. (1988). Z. Anorg. Allg. Chem. 561, 139-148. © 1989 Internat ional Union of Crys ta l lography International Union of Crystallography Acta Cryst. (1989). C45, 2029-2030 Prices of Acta Crystallographica and Journal of Applied Crystallography The Executive Commit tee of the Internat ional Union of Crys ta l lography has determined the following subscription rates and prices of back numbers for Acta Crystallo- graphica and Journal of Applied Crystallography as from 1 January 1990. Acta Crystallographica The following rates will apply for Volumes A46, B46 and C46 (1990). All subscription rates are fixed in Danish kroner. The US dollar equivalents are no longer given because of rapid f luctuations in exchange rates. Complete volumes, regular price per volume Sections A, B & C (combined subscription) Dkr 5800