Polymorphic and hydrate supramolecular solid state structures of a uracil derived nitronyl nitroxide

A nitronyl nitroxide bearing a uracil moiety has been shown to exist in at least three different forms in crystals. The first polymorph (space group P 1 ¯ ) contains a hydrogen bonded tape with two molecules stacked in the plane of the tape, while in the second (space group P21/c) unlike the α-phase shows cyclic non-covalent tetramers which come together to form a layer. The hydrate has quite a different structure, in which the amide groups interact with each other and the nitroxide group enters into weaker hydrogen bonds than in the pure material. All the materials are dominated by paramagnetic behaviour, but the structures suggest ways in which hydrogen bonds might be used to influence the packing of this kind of radical in the solid state.