Structure determinations for the dimethylsulphoxide (DMSO) solvates of uranyl triflate, nitrate, picrate and a tetranuclear basic acetate show DMSO to be bound in all cases as an O-donor ligand but with the sulphur atoms involved in a variety of close approaches which may be significant in determining details of the complex ion structures. These close approaches, which generally mean that S may be considered to have '3 + 2'coordination, usually involve 0 of an adjacent DMSO or oxyanion ligand, but can also involve uranyl-O and can be both intra- and inter-molecular. To cite this article: J.M. Harrowfield et al., C. R. Chimie 8 (2005). (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.