2,3,4-Trihy-droxy-benzoic acid 0.25-hydrate.

The asymmetric unit of the title compound, C(7)H(6)O(5)·0.25H(2)O, contains two mol-ecules of 2,3,4-trihy-droxy-benzoic acid, with similar conformations, and one water mol-ecule which lies on a twofold rotation axis. Both acid mol-ecules are essentially planar [maximum r.m.s deviations = 0.0324 (2) and 0.0542 (3) Šfor the two acid molecules]. The mol-ecular conformations are stabilized by intra-molecular O(phenol)-H⋯O(carbox-yl/phenol) inter-actions. A cyclic inter-molecular association is formed between the two acid and one water mol-ecule [graph set R(3) (3)(12)] involving O-H⋯O hydrogen bonds. The two acid mol-ecules are further linked through a cyclic R(2) (2)(8) carb-oxy-lic acid hydrogen-bonding association, which together with inter-molecular O-H⋯O hydrogen-bonding inter-actions involving the phenol groups and the water mol-ecule, and weak π-π inter-actions [minimum ring centroid separation = 3.731 (3) Å], give a three-dimensional network.

Gallic acid pyridine monosolvate.

IN THE TITLE COMPOUND (SYSTENATIC NAME: 3,4,5-trihy-droxy-benzoic acid pyridine monosolvate), C(5)H(5)N·C(7)H(6)O(5), the gallic acid mol-ecule is essentially planar (r.m.s deviation = 0.0766 Šfor non-H atoms) and is linked to the pyridine mol-ecule by an O-H⋯N hydrogen bond. An intra-molecular O-H⋯O hydrogen bond occurs in the gallic acid mol-ecule. The gallic acid and pyridine mean planes make a dihedral angle 12.6 (3)°. Inter-molecular O-H⋯O and O-H⋯N hydrogen bonding involving the hy-droxy and carboxyl groups and the pyridine mol-ecule, and π-π inter-actions between inversion-related pyridines [centroid-centroid distance = 3.459 (6) Å] and between pyridine and benzene rings [centroid-centroid distance = 3.548 (6) Å], lead to a three-dimensional network in the crystal.