(Z)-3-(1-Hy-droxy-3-oxobut-1-en-yl)-6-nitro-2H-chromen-2-one.

In the title compound, C(13)H(9)NO(6), the coumarin system has the benzene ring aligned at 0.61 (18)° with respect to the pyrone ring. An intra-molecular O-H⋯O hydrogen bond stabilizes the mol-ecular conformation and a C-H⋯O contact also occurs. In the crystal, weak C-H⋯O inter-actions link the mol-ecules, forming inversion dimers.