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-cyclo-hexyl-3-hy-droxy-3-phenyl-prop-yl)piperidin-1-ium] 4-nitro-benzoate, C₂₀H₃₂NO⁺·C₇H₄NO₄ ^- (I), trihexyphenidylium 4-hy-droxy-benzoate, C₂₀H₃₂NO⁺·C₇H₅O^- (II), trihexyphenidylium 4-bromo-benzoate, C₂₀H₃₂NO⁺·C₇H₄BrO₂ ^- (III), and trihexyphenidylium thio-phene-2-carboxyl-ate hemihydrate, 2C₂₀H₃₂NO⁺·2C₅H₃O₂S^-·H₂O (IV), con-ducted 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 thio-phene-2-carboxyl-ate anions. Structure II is a non-merohedric twin by a twofold rotation about [403]. The main supra-molecular 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 mol-ecule 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 inter-actions are observed, plus C-H⋯Br close contacts for III.