Syntheses, crystal structures and Hirshfeld surface analyses of four mol-ecular salts of amitriptynol

The syntheses and crystal structures of four salts of amitriptynol (C₂₀H₂₅NO) with different carb-oxy-lic acids are described. The salts formed directly from solutions of amitriptyline (which first hydrolysed to amitriptynol) and the cor-responding acid in aceto-nitrile to form amitriptynolium [sys-tem-atic name: (3-{2-hy-droxy-tri-cy-clo[9.4.0.0^3,8]penta-deca-1(11),3,5,7,12,14-hexa-en-2-yl}pro-pyl)di-methyl-az-an-ium] 4-meth-oxy-benzoate monohydrate, C₂₀H₂₆NO⁺·C₈H₇O₃ ^-·H₂O, (I), ami-triptynolium 3,4-di-meth-oxy-benzoate trihydrate, C₂₀H₂₆NO⁺·C₉H₉O₄ ^-·3H₂O, (II), amitriptynolium 2-chloro-benzoate, C₂₀H₂₆NO⁺·C₇H₄ClO₂ ^-, (III), and amitriptynolium thio-phene-2-carboxyl-ate monohydrate, C₂₀H₂₆NO⁺·C₅H₃O₂S^-·H₂O, (IV). Compound (III) crystallizes with two cations, two anions and six water mol-ecules in the asymmetric unit. The different conformations of the amitriptynolium cations are determined by the torsion angles in the di-methyl-amino-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⋯O and O-H⋯O hydrogen bonds. Hirshfeld surface analyses show that the amitriptynolium cations make similar inter-species contacts, despite the distinctly different packing in each salt.