The title compounds, 2, 4, 6, 8-tetraazabicyclo [3.3. 1] nonane-3, 7-dione,(I)(C5H8N4O2), and 2, 4, 6, 8-tetraacetyl-2, 4, 6, 8-tetraazabicyclo [3.3. 1] nonane-3, 7-dione,(II)( C13H16N4O6), display similar conformations with the cyclic urea moieties and bridgehead atoms forming two mean planes having a dihedral angle of approximately 110°. The CO of each acetyl group is anti to the CO of the cyclic urea to which it is attached.