Synthesis and crystal structures of 1-benzoyl-4-(4-nitro-phen-yl)piperazine and 1-(4-bromo-benzo-yl)-4-phenyl-piperazine at 90 K.

Synthesis and crystal structures of 1-benzoyl-4-(4-nitro-phen-yl)piperazine, CHNO, () and 1-(4-bromo-benzo-yl)-4-phenyl-piperazine, CHBrNO, () are described. Compounds and crystallize in the ortho-rhom-bic and monoclinic crystal systems with space groups 2 (' = 2, ) and 2 (' = 1, ), respectively. The crystal of was a two-component aggregate, treated as a 'twin' for data-acquisition purposes. There are no conventional hydrogen bonds in either or , but there are weaker C-H⋯O contacts. Each mol-ecule consists of a central piperazine ring in a chair conformation, with either benzoyl and nitro-phenyl () or 4-bromo-benzoyl and phenyl () groups attached to different nitro-gen atoms of the piperazine. The various atom-atom contact coverages as qu-anti-fied by Hirshfeld surface analysis fingerprint plots are given.