H-bond pattern in arylpiperazine structures. Structures of cis and trans 2-{4-[4-(2-methoxyphenyl)piperazin-1-yl]but-2-enyl}isoindoline-1,3-diones and their hydrochloride salts

The crystal structures of cis and trans-isomers of 2-{4-[4-(2-methoxyphenyl)piperazin-1-yl]but-2-enyl}isoindoline-1,3-diones have been solved in two different forms – as free bases and as hydrochlorides. It was concluded that the conformations of arylpiperazine derivatives with an aliphatic spacer in their neutral and protonated forms are similar and usually extended. The molecule bending found for the free cis-isomer is reflected in variation of the supramolecular synthons formation. The hydrogen bonds pattern in studied structure was analyzed. In the crystals of both free bases head-to-head dimers are predominant, while in hydrochlorides inter-ionic salt bridges form the main structure motifs. The most important difference in hydrogen bonds patterns of both forms lies in the fact that piperazine carbon atoms contribute to weak C O···H–C interactions as proton donors only in the structures of hydrochlorides. This article will also review selected arylpiperazine structures deposited in CSD from the point of view of their hydrogen bonds pattern.