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, C 17 H 17 N 3 O 3 , ( I ) and 1-(4-bromo-benzo-yl)-4-phenyl-piperazine, C 17 H 17 BrN 2 O, ( II ) are described. Compounds I and II crystallize in the ortho-rhom-bic and monoclinic crystal systems with space groups Pna 2 1 ( Z ' = 2, I ) and P 2 1 ( Z ' = 1, II ), respectively. The crystal of II was a two-component aggregate, treated as a 'twin' for data-acquisition purposes. There are no conventional hydrogen bonds in either I or II , 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 ( I ) or 4-bromo-benzoyl and phenyl ( II ) 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.