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.