Sodium 4-(2-pyridinyldiazenyl)-resorcinolate monohydrate and ammonium 2,4-dinitro-1-naphthalenolate from powder diffraction data

The crystal structures of two dyestuffs, Na+.C11H8N3O2-.H2O, (I), and NH4+. C10H5N2O5-, (II), were determined from X-ray powder diffraction data. In bo th structures, translationally related anions form stacks, and cations fill interstack channels. A comparison of the diffuse reflectance spectra of cr ystalline (I) and (II) with the absorption spectra of their aqueous solutio ns demonstrates that the geometry of their anions does not change significa ntly upon transfer from the crystalline to the solution state.