Crystal Structures of [1,2,5]Selenadiazolo[3,4-d]Pyrimidin-7(6H-One and [1,2,5]Selenadiazolo[3,4-d]Pyrimidin-5,7(4H,6H)-Dione

Crystal structures of [1,2,5]selenadiazolo[3,4-d]pyrimidin-7(6H)-one (1), [1,2,5]selenadiazolo[3,4-d]pyrimidin-5,7(4H,6H)-dione (2) as solvates with pyridine, and individual 1 are determined by single crystal X-ray diffraction. In all cases, 1 and 2 molecules form planar π-stacked dimers with supramolecular synthon [Se⋯N]₂. The structures of compound 1 have shortened Se⋯N contacts involving the nitrogen atom of the pyrimidine ring. Oxygen atoms of C=O fragments and nitrogen atoms of pyridine solvate molecules form hydrogen bonds with N–H-fragments.