N,N-Diethyldithiocarbamate complexes, M dtc4(M = Th, U, Np, and Pu) have been prepared in non-aqueous media, but the proctactinium(IV) compound could not be isolated. The four compounds are isomorphous, and the uranium compound is monoclinic, space group C2/c(C2h6). I.r. spectral measurements between 200–4000 cm.–1 are consistent with bidentate dithiocarbamate groups. The uranium compound is monomeric in benzene, and the metal ion is probably eight-co-ordinate. Spectra in benzene solution, between 6000–30,000 cm.–1, have been recorded. Similar complexes with ethyl xanthate, cis-1,2-dicyano-1,2-ethylenedithiol, and toluene-3,4-dithiol could not be isolated.