The tetrachloride and tetrabromide of thorium and of uranium react at room temperature with anhydrous methyl cyanide to form the complexes MX4,4CH3CN (M = Th and U; X = Cl and Br). The tetrabromide complexes react with NN-dimethylacetamide (DMA) to form the compounds MBr4,4DMA. Methyl cyanide and DMA complexes of uranyl chloride and uranyl bromide, UO2Cl2,CH3CN and UO2X2,2DMA (X = Cl and Br) have also been prepared. Some chemical properties, infrared spectra, and magnetic susceptibilities are reported for these complexes.