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+center dot C7H4NO4- (I), trihexyphenidylium 4-hydroxybenzoate, C20H32NO+center dot C7H5O- (II), trihexyphenidylium 4-bromobenzoate, C20H32NO+center dot C7H4BrO2- (III), and trihexyphenidylium thiophene-2-carboxylate hemihydrate, 2C(20)H(32)NO(+)center dot 2C(5)H(3)O(2)S(-)center dot 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 center dot center dot center dot O, O-H center dot center dot center dot O, and C-H center dot center dot center dot O interactions are observed, plus C-H center dot center dot center dot Br close contacts for III.