The crystal chemistry of some sulphato-compounds of thorium

The crystal structures of six sulphato-compounds of thorium(IV) have been determined from X-ray diffraction data collected by means of a Stoe 2-circle or a Syntex 4-circle diffractometer. Thorium is either 9- or 10-coordinated. Five of the six structures show the usual 3/3/3 or 1.4/4.1 geometry; the sixth structure is of a novel 10-coordinate type. The sulphate groups may be classified as (i) tridentate (chelating and bridging), (ii) bidentate chelating, (iii) bidentate bridging and (iv) monodentate and are distributed with coordinated water as shown in a table. The mean Th-O bond length is 2.478 A. The mean Th-O (sulphate) and Th-O (water) distances are 2.467 A and 2.558 A respectively, with no significant differences between 9- and 10-coordinate thorium. The sulphate groups show mean S-O bond length of 1.475 A and the mean S-O (coordinated) and S-O (terminal) are 1.497 A and 1.453 A respectively. The mean O-S-O chelate angle is 103.598 deg. In spite of the diversity of structures found there is a considerable degree of uniformity in steric crowding at the thorium atom. (author)