Influence of the halogen substituent on the formation of halogen and hydrogen bonding in co-crystals formed from acridine and benzoic acids

In order to determine the influence of the ortho- and meta- halogen substituents in the phenyl ring of benzoic acid on the formation of C-H center dot center dot center dot X hydrogen bonds and X center dot center dot center dot O halogen bonds in crystal packing where the halogen (X) is a fluorine, chlorine, bromine or iodine atom, we synthesized and structurally characterized a series of nine co-crystals formed from acridine and benzoic acids: acridine center dot benzoic acid (1), acridine center dot 2-fluorobenzoic acid (2), acridine center dot 2-chlorobenzoic acid (3), acridine center dot 2-bromobenzoic acid (4), acridine center dot 2-iodobenzoic acid (5), acridine center dot 3-fluorobenzoic acid (6), acridine center dot 3-chlorobenzoic acid (7), acridine center dot 3-bromobenzoic acid (8) and acridine center dot 3-iodobenzoic acid (9). The number, type and strength of the hydrogen and halogen bonds, and the melting points of co-crystals 1-9 were compared. Systematic analysis of the intermolecular interactions taking place in the co-crystals of the title compounds indicates that competition between halogen and hydrogen bonding depends on the position and type of halo-substituent.