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

Abstract

In each of the compounds 1-[(1,3-benzodioxol-5-yl)methyl]-4-(3-fluorobenzoyl)piperazine, C19H19FN2O3 (I), 1-[(1,3-benzodioxol-5-yl)methyl]-4-(2,6-difluorobenzoyl)piperazine, C19H18F2N2O3 (II), and 1-[(1,3-benzodioxol-5-yl)methyl]-4-(2,4-dichlorobenzoyl)piperazine, C19H19Cl2N2O3 (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.

Keywords

• piperazines
• crystal structure
• molecular conformation
• hydrogen bonding
• supramolecular assembly