The reaction of the tripodal tris-amido U(iii) complex [U(SiMe 2NPh)3-tacn] (tacn = 1,4,7-triazacyclononane), 1, with 0.0625 and 0.25 equiv. of elemental sulfur affords the sulfide-bridged U(iv) complex [U((SiMe2NPh)3-tacn)2(μ-S)], 2, and the terminal persulfide U(v) complex [U(SiMe2NPh) 3-tacn(η2-S2)], 4, respectively, in good yield. Two different electronic structures, U(v) persulfide and U(iv) supersulfide, were computed for complex 4 at the DFT level. The results show that complex 4 is best described as a U(v) persulfide species with a significant sulfur contribution. X-ray, magnetism and electrochemistry data support this description. Complex 4 is the first example of a terminal U(v) persulfide and of a two-electron reduction of S8 by a U(iii) complex. Complex 4 behaves as a S-atom transfer agent when reacted with PPh3, affording the persulfide-bridged diuranium(iv) complex [U((SiMe2NPh) 3-tacn)2(μ-η2:η2-S 2)], 5, and SPPh3. © 2014 The Royal Society of Chemistry.