Unusual Hybrid Materials Prepared by the Oxidation of a Ketone

Four new layered phases have been synthesized by the hydrothermal reactions of zinc and magnesium salts with fenbufen (γ-oxo-(1,1′-biphenyl)-4-butanoic acid) as a result of the oxidation of fenbufen at the ketone forming biphenylcarboxylate. Reactions with zinc nitrate give different degrees of oxidation, yielding Zn(C16H13O3)(C13H9O2)(H2O) (1) and Zn5(OH)6(C13H9O2)4 (2), depending on the reaction temperature. Compound 2 has an unusual zinc hydroxide layer structure which contains hydroxide-centered Zn4OH(OH)4 units where the central hydroxide has two long and two short bonds to the Zn atoms. The mechanism for the ketone oxidation has been investigated by a series of DFT calculations which indicate that a concerted, metal-mediated pathway is lower in energy than a two-step process. The importance of the metal cation in this oxidation reaction has been shown by demonstrating that oxidation of fenbufen also occurs during reactions with magnesium nitrate and zinc chloride. These reactions yielded fully oxidized Mg(C13H9O2)2(H2O)2 (3) and half-oxidized Zn(C16H13O3)(C13H9O2)(H2O) (4), a polymorph of 1. Reactions with ammonium salts gave only recrystallized fenbufen, providing further evidence for the role of the metal cation in these oxidation reactions.