Assembly of hybrid organic - Organometallic materials through mechanochemical acid-base reactions

Manual grinding of the organometallic complex [Fe(eta(5)-C5HCOOH)(2)] with a number of solid bases, namely 1,4-diazabicyclo[2.2.2] octane, C6H12N2, 1,4-phenylenediamine, p-(NH2)(2)C6H4, Piperazine, HN(C2H4)(2)NH, trans-1,4-cyclohexanediamine, p-(NH2)(2)C6H10, and guanidinium carbonate [(NH2)(3)C](2)[CO3], generates quantitatively the corresponding adducts, [HC6H12N2][Fe(eta(5)-C5H4-COOH)(eta(5)-C5H4COO)] (1), [HC6H8N2][Fe(eta(5)-C5H4COOH)(eta(5)-C5H4COO)] (2), [H2C4H10N2][Fe(eta(5)-C5H4COO)(2)] (3), [H2C6H14N2][Fe(eta(5)-C5H4COO)(2)].2H(2)O, (4 . 2 H2O), and [C(NH2)(3)](2)[Fe(eta(5)-C5H4COO)(2)].2H(2)O, (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(eta(5)-C5H4COOH)(eta(5)-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.