The structures of the title compounds, C(9)H(8)O(3)S, (I), and C(13)H(11)NO(5)S, (II), were determined by X-ray powder diffraction. Both were solved using the direct-space parallel tempering algorithm and refined using the Rietveld method. In (I), the C-S-C bond angle is slightly smaller than normal, indicating more p character in the bonding orbitals of the S atom. The carboxylic acid group joins across an inversion centre to form a dimer. The crystal packing includes a weak C-H···O hydrogen bond between an aromatic C-H group and a carboxylic acid O atom to form a two-dimensional network parallel to (10 ̅1). The C-S-C bond angle in (II) is larger than its counterpart in (I), indicating that the S atom of (II) has less p character in its bonding orbitals than that of (I), according to Bent's rule. The crystal structure of (II) includes weak C-H···O hydrogen bonds between the H atoms of the methylene groups and carbonyl O atoms, forming a three-dimensional network.