Crystal structures of four organic salts of trihexyphenidyl at 90 K

The syntheses and crystal structure studies of four organic salts of trihexyphenidyl, viz., trihexyphenidylium [1-(3-cyclo­hexyl-3-hy­droxy-3-phenyl­prop­yl)piperidin-1-ium] 4-nitro­benzoate, C20H32NO+·C7H4NO4 - (I), trihexyphenidylium 4-hy­droxy­benzoate, C20H32NO+·C7H5O- (II), trihexyphenidylium 4-bromo­benzoate, C20H32NO+·C7H4BrO2 - (III), and trihexyphenidylium thio­phene-2-carboxyl­ate hemihydrate, 2C20H32NO+·2C5H3O2S-·H2O (IV), con­ducted at 90 K are described. Structures I, II, and III are solvent free with one cation-anion pair per asymmetric unit, while IV crystallizes as a hemihydrate, having two cation-anion pairs and one water of crystallization in its asymmetric unit. Structures I and III exhibit configurational disorder of the cation. Structure IV also exhibits disorder, but only of the thio­phene-2-carboxyl­ate anions. Structure II is a non-merohedric twin by a twofold rotation about [403]. The main supra­molecular motifs in I, II, and III are similar R 2 2(10) rings between cation-anion pairs, although their packing within the crystals is distinct. As a consequence of having two cation-anion pairs and a water mol­ecule in its asymmetric unit, the packing in IV is by far the most complex of the four structures, its hydrogen-bonding patterns being quite different from I, II, or III. In all the crystals studied, N - H⋯O, O - H⋯O, and C - H⋯O inter­actions are observed, plus C - H⋯Br close contacts for III.