The title compound, C5H9BrN4O, was obtained as a minor by-product in the synthesis of 4-di-methyl-amino-1-methyl-1,2,4-triazolin-5-one. Except for the methyl groups of the 4-dimethylamino moiety, all the non-H atoms lie on a crystallographic mirror plane." In the crystal, the mol-ecules are linked by C-Br⋯O=C inter-actions [Br⋯O = 2.877 (2) Å, C-Br⋯O = 174.6 (1)°] into infinite chains in the c-axis direction.
Keywords: 1,2,4-triazol-5(4H)-one; Br⋯O=C interactions; crystal structure; halogen interactions.