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 Pna2(1) (Z' = 2, I) and P2(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.