Synthesis and crystal structures of 1-benzoyl-4-(4-nitro­phen­yl)piperazine and 1-(4-bromo­benzo­yl)-4-phenyl­piperazine at 90 K

Synthesis and crystal structures of 1-benzoyl-4-(4-nitro­phen­yl)piperazine, C(17)H(17)N(3)O(3), (I) and 1-(4-bromo­benzo­yl)-4-phenyl­piperazine, C(17)H(17)BrN(2)O, (II) are described. Compounds I and II crystallize in the ortho­rhom­bic 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 mol­ecule consists of a central piperazine ring in a chair conformation, with either benzoyl and nitro­phenyl (I) or 4-bromo­benzoyl and phenyl (II) groups attached to different nitro­gen atoms of the piperazine. The various atom–atom contact coverages as qu­anti­fied by Hirshfeld surface analysis fingerprint plots are given.