Syntheses and crystal structures of four 4-(4-meth-oxyphenyl)piperazin-1-ium salts: trifluoroacetate, 2,3,4,5,6-pentafluorobenzoate, 4-iodobenzoate, and a polymorph with 4-methylbenzoate

Syntheses and X-ray crystal structures of four 4-(4-methoxyphenyl)piperazin-1-ium (MeOPP) salts, with 2,2,2-trifluoroacetate, C₁₁H₁₇N₂O⁺·C₂F₃O₂^– (I), 2,3,4,5,6-pentafluorobenzoate, C₁₁H₁₇N₂O⁺·C₇F₅O₂^–·H₂O (II), 4-iodobenzoate C₁₁H₁₇N₂O⁺·C₇H₄IO₂^–·H₂O (III), and 4-methylbenzoate, C₁₁H₁₇N₂O⁺·C₈H₇O₂^–·H₂O (IV) anions are presented. The salts form directly from equimolar quantities of N-(4-methoxyphenyl)piperazine and the corresponding organic acid in methanol and crystallize from 1:1 methanol/ethyl acetate. Salt I is anhydrous whereas II, III, and IV are all monohydrates. In all cases, the MeOPP cation conformation is determined by the torsion about the N—C bond between the piperazinium and 4-methoxybenzene rings. Crystal packing in each structure is largely dictated by N—H· · ·O and (in II, III, and IV) O—H· · ·O hydrogen bonds, although each also features weak C—H· · ·O-type hydrogen bonds. Salt II also has π–π-stacking interactions between cation and anion arene rings, and III exhibits I· · ·I close contacts.