Syntheses, crystal structures and Hirshfeld surface analyses of four molecular salts of amitriptynol

The syntheses and crystal structures of four salts of amitriptynol (C20H25NO) with different carboxylic acids are described. The salts formed directly from solutions of amitriptyline (which first hydrolysed to amitriptynol) and the corresponding acid in acetonitrile to form amitriptynolium [systematic name: (3-{2-hydroxytricyclo[9.4.0.0(3,8)]pentadeca-1(11),3,5,7,12,14-hexaen-2-yl}propyl)dimethyl-azanium] 4-methoxybenzoate monohydrate, C20H26NO+center dot C8H7O3-center dot H2O, (I), amitriptynolium 3,4-dimethoxybenzoate trihydrate, C20H26NO+center dot C9H9O4-center dot 3H(2)O, (II), amitriptynolium 2-chlorobenzoate, C20H26NO+center dot C7H4ClO2-, (III), and amitriptynolium thiophene-2-carboxylate monohydrate, C20H26NO+center dot C5H3O2S-center dot H2O, (IV). Compound (III) crystallizes with two cations, two anions and six water molecules in the asymmetric unit. The different conformations of the amitriptynolium cations are determined by the torsion angles in the dimethylamino-propyl chains and the -CH2-CH2- bridge between the benzene rings in the tricyclic ring system, and are complicated by disorder of the bridging unit in II and III. The packing in all four salts is dominated by N-H center dot center dot center dot O and OH center dot center dot center dot O hydrogen bonds. Hirshfeld surface analyses show that the amitriptynolium cations make similar inter-species contacts, despite the distinctly different packing in each salt.