Persistent CH•••π Interactions in Mefenamic Acid Complexes with Cyclic and Acyclic Amines

Interaction of mefenamic acid [2-(2,3-dimethylphenyl)aminobenzoic acid, maH] with piperazine (ppz), 1,4,7, 10-tetraazacyclododecane (cyclen), meso-5,7,7,12,12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (teta), and tris(hydroxymethyl)aminomethane (iris) resulted in crystalline proton-transfer complexes of the compositions (ppzH(2))(ma)(2)center dot 4H(2)O 1, (cyclenH(2))(ma)(2)center dot 2H(2)O 2, (tetaH(2))(ma)(2)center dot 2H(2)O 3, and (trisH)(ma)center dot H2O 4. Immediate cation-anion hydrogen bonds and those mediated by water molecules are the prime driving forces for the maH and amine assembly. Persistent CH center dot center dot center dot pi interactions involving the aromatic rings were found to play an important role in the formation of final structures. All complexes reveal the pronounced segregation of hydrophilic and hydrophobic regions.