Facile solid-state molecular assembly: the crystal structure of the unique 2∶2 proton-transfer oxine-salicylic acid compound

The previously reported product from the solid-state reaction of quinolin-8-ol (oxine) with salicylic acid has been characterized using single crystal X-ray diffraction methods and confirmed as the discrete dimeric proton-transfer sandwich compound [(C9H8NO+)2(C7H5O3–)2] (1). As with similar compounds of carboxylic acids and oxine, protonation of the quinoline nitrogen occurs. However, in the case of 1, the two salicylate anions provide unusual duplex carboxylato-(O,O′) hydrogen-bonding bridges [(oxine)-N+H⋯O,O′(salicylate)⋯H′–O′-(oxine)′] which stitch together the pairs of π–π-associated oxine cations. This structure determination may provide a possible explanation of the mechanism involved in the facile solid-state reaction of oxine with salicylic acid.

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