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Assembly of Hybrid Organic–Organometallic Materials through Mechanochemical Acid–Base Reactions



Manual grinding of the organometallic complex [Fe(η5-C5H4COOH)2] with a number of solid bases, namely 1,4-diazabicyclo[2.2.2]octane, C6H12N2, 1,4-phenylenediamine, p-(NH2)2C6H4, piperazine, HN(C2H4)2NH, trans-1,4-cyclohexanediamine, p-(NH2)2C6H10, and guanidinium carbonate [(NH2)3C]2[CO3], generates quantitatively the corresponding adducts, [HC6H12N2][Fe(η5-C5H4COOH)(η5-C5H4COO)] (1), [HC6H8N2][Fe(η5-C5H4COOH)(η5-C5H4COO)] (2), [H2C4H10N2][Fe(η5-C5H4COO)2] (3), [H2C6H14N2][Fe(η5-C5H4COO)2]⋅2 H2O, (4⋅2 H2O), and [C(NH2)3]2[Fe(η5-C5H4COO)2]⋅2 H2O, (5⋅2 H2O), respectively. Crystallization from methanol in the presence of seeds of the ground sample allows the growth of single crystals of these adducts; therefore we were able to determine the structures of the adducts by single-crystal X-ray diffraction. This information was used in turn to identify and characterize the polycrystalline materials obtained by the grinding process. In the case of [HC6N2H12][Fe(η5-C5H4COOH)(η5-C5H4COO)] (1), the base can be removed by mild treatment regenerating the starting dicarboxylic acid, while in all other cases decomposition is observed. The solid–solid processes described herein imply molecular diffusion through the lattice, breaking and reassembling of hydrogen-bonded networks, and proton transfer from acid to base.

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