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The crystal structures of quinolinium 3‐carboxy‐4‐hydroxy­benzene­sulfonate trihydrate, C9H8N+·C7H5O6S−·3H2O, (I), 8‐hydroxy­quinolinium 3‐carboxy‐4‐hydroxy­benzene­sulfonate monohydrate, C9H8NO+·C7H5O6S−·H2O, (II), 8‐amino­quinolinium 3‐carboxy‐4‐hydroxy­benzene­sulfonate dihydrate, C9H9N2+·C7H5O6S−·2H2O, (III), and 2‐carboxy­quinolinium 3‐carboxy‐4‐hydroxy­benzene­sulfonate quinolinium‐2‐carboxylate, C10H8NO2+·C7H5O6S−·C10H7NO2, (IV), four proton‐transfer compounds of 5‐sulfosalicylic acid with bicyclic heteroaromatic Lewis bases, reveal in each the presence of variously hydrogen‐bonded polymers. In only one of these compounds, viz. (II), is the protonated quinolinium group involved in a direct primary N+—H⋯O(sulfonate) hydrogen‐bonding interaction, while in the other hydrates, viz. (I) and (III), the water mol­ecules participate in the primary intermediate interaction. The quinaldic acid (quinoline‐2‐carboxylic acid) adduct, (IV), exhibits cation–cation and anion–adduct hydrogen bonding but no direct formal heteromolecular interaction other than a number of weak cation–anion and cation–adduct π–π stacking associations. In all other compounds, secondary interactions give rise to network polymer structures.

Key indicatorsSingle-crystal X-ray study T = 293 K Mean '(C±C) = 0.002 A Ê R factor = 0.044 wR factor = 0.098 Data-to-parameter ratio = 11.2 For details of how these key indicators were automatically derived from the article, see

The crystal structures of the proton-transfer compounds of 3,5-dinitrosalicylic acid (dnsa) with a series of common monocyclic hetero-aromatic amines (pyridine, 4-cyanopyridine, pyridine-4-carboxylic acid, 2,6-diaminopyridine and 2-aminopyrimidine) have been determined and the hydrogen-bonding associations in each analyzed. The compounds are the adduct (C 5 H 6 N) + (dnsa) -

The structures of two pseudopolymorphic hydrates of brucine, C23H26N2O4·4H2O, (I), and C23H26N2O4·5.25H2O, (II), have been determined at 130 K. In both (I) and (II) (which has two independent brucine mol­ecules together with 10.5 water mol­ecules of solvation in the asymmetric unit), the brucine mol­ecules form head‐to‐tail sheet substructures, which associate with the water mol­ecules in the inter­stitial cavities through hydrogen‐bonding associations and, together with water–water associations, give three‐dimensional framework structures.