Three closely related 1-[(1,3-benzodioxol-5-yl)methyl]-4-(halobenzoyl)piperazines: Similar molecular structures but different intermolecular interactions

In each of the compounds 1-[(1,3-benzodioxol-5-yl)methyl]-4-(3-fluorobenzoyl)piperazine, C 19 H 19 FN 2 O 3 (I), 1-[(1,3-benzodioxol-5-yl)methyl]-4-(2,6-difluorobenzoyl)piperazine, C 19 H 18 F 2 N 2 O 3 (II), and 1-[(1,3-benzodioxol-5-yl)methyl]-4-(2,4-dichlorobenzoyl)piperazine, C 19 H 19 Cl 2 N 2 O 3 (III), the piperazine rings adopt a chair conformation with the (1,3-benzodioxol-5-yl)methyl substituent occupying an equatorial site: the five-membered rings are all slightly folded across the O⋯O line leading to envelope conformations. The dihedral angle between the planar amidic fragment and the haloaryl ring is 62.97 (5)° in (I) but 77.72 (12)° and 75.50 (5)° in (II) and (III), respectively. Despite their similarity in constitution and conformation, the supramolecular interactions in (I)-(III) differ: in (I), a combination of C - H⋯O and C - H⋯π(arene) hydrogen bonds links the molecules into a three-dimensional framework structure, but there are no hydrogen bonds of any sort in either (II) or (III), although the structure of (III) contains a short Cl⋯Cl contact between inversion-related pairs of molecules.