Structure of thorium sulphate octahydrate, Th(SO4)2.8H2O

Abstract

M r = 568.3, monoclinic, P21/n, a = 8.51 (2), b = 1 1 . 8 6 ( 2 ) , c = 1 3 . 4 6 ( 2 ) A , f l=92 .65 (1 ) °, U = 1357 (7) ./k 3, Z = 4, D x = 2.778, D m = 2.78 g cm -3 (by flotation in iodobenzene/diiodomethane), Mo Kt~,2 = 0.7107 A, ~t= 137.95 cm -1. Non-hydrogen atoms refined anisotropically to a final R of 0.1022. The thorium is ten-coordinate, both the sulphate groups being chelate, and six of the water oxygens being coordinated to thorium. The resulting complexes are linked together via hydrogen bonds. The thorium coordination polyhedron approximates closely to the bicapped square antiprism (1 .4/4 .1)of D4d symmetry and with 0 = 63 o Introduction. Thorium sulphate was first prepared by Berzelius (1829), who observed that the degree of hydration varied with the temperature of crystallization. Anhydrous thorium sulphate and hydrates containing 2, 4, 7.5, 8, and 9 water molecules are known (Molodkin & Arutyunyan, 1965). The octahydrate is obtained by crystallization from neutral aqueous solution at 293--298 K (Cleve, 1874). Lower hydrates may be obtained by drying at 373-383 K, and the anhydrous salt is formed at 673 K (Bagnall, 1972). The compound exists in solution as the neutral complex [Th(SO4)2] ° (Zebroski, Alter & Heumann, 1951). Gaussian interpolation (Busing & Levy, 1957), 6 x 8 x 10 Gaussian points; ~ = 137.95 cm -1, absorption coefficient of Th from Roof (1959), others from International Tables for X-ray Crystallography (1962); scattering factors for neutral atoms from International Tables for X-ray Crystallography (1974); anomalous dispersion corrections for Th from Roof (1961) (f ' = 12.0, f = 14.4 electron s); heavy-atom method, block-diagonal isotropic, full matrix anisotropic, H not located; final difference synthesis showed no peak interpretable as an atom. High final R (0.1022) attributed to incomplete absorption correction because of irregular crystal shape. The residual absorption errors are also reflected in the negative values of six of the bii's, t w o of which are more negative than 2 . 5 a (and the low values of Beq). * Present address: Department of Physics, University of Keele, Keele, Staffs., England. Discussion. Positional parameters are listed in Table 1 and interatomic distances and angles in Table 2fir The Th coordination polyhedron is a bicapped square ] Lists of structure factors and anisotropic thermal parameters have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 38105 (17 pp.). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England. Experimental. Plate-shaped crystals from slow evaporation of thorium sulphate at room temperature; chemical analysis: found: Th 40.79; S 11.21; H 2.78; calc. for Th(SO4)2.8H20: Th 40.85; S 11.27; H 2.82%; Th determined gravemetrically by precipitation as oxalate and ignition to the dioxide, S and H by Wh S(l) standard microanalytical techniques; 0.04 x 0.19 x s(2) 0.27 mm, Stoe 2-circle diffractometer, to-scan, Mo Ka o(1) (graphite monochromator), unit-cell parameters by least 0(2) 0(3) squares from 60 reflexions, hkl and hkl up to 20 = 60 °, 0(4) counting time for (h + k) odd twice that for (h + k) o(5) 0(6) even, because of systematic weakness of odd layers; 0(7) crystal mounted along [110], absences hOl with h + l 0(8) odd, 0k0 with k odd, non-standard setting of P2Jc. 0(9) o(10) 2639 independent with I > 3a(/), standard reflexion o(11) every 50, no signs of decay; absorption correction by o(12) 0(13) O(14) o(15) O(16) Table 1. Atomic positional parameters (× 104) for the non-hydrogen atoms with e.s.d.'s in parentheses, and equivalent isotropic thermal parameters (]~ 2)