Crystal engineering via negatively charged O-H•••O- and charge-assisted C-Hδ+•••Oδ- hydrogen bonds from the reaction of [Co(η5-C5H5)2][OH] with polycarboxylic acids

The polycarboxylic acids C6H3(CO2H)(3)-1,3,5 (trimesic acid, H(3)tma) and O-2, O-3-dibenzoyl-L-tartaric acid (L-H(2)bta) reacted in water or thf with [Co(eta(5)-C5H5)(2)][OH] prepared in situ by oxidation of [Co(eta(5)-C5H5)(2)] to generate organic superanions self-assembled via negatively charged O-H ... O- and neutral O-H ... O hydrogen bonds. The resulting organic host accommodates the cations via charge assisted C-Hdelta+... Odelta- hydrogen bonds between organometailic and organic components. Crystalline [Co(eta(5)-C5H5)(2)](+)[(H(3)tma)(H(2)tma)](-). 2H(2)O 1 was obtained as the major product from acid and base in a 1:2 stoichiometric ratio. Compound 1 contains a complex hydrogen bonded honeycomb-type structure formed by superanions [(H(3)tma)(H(2)tma)](-) and water molecules. The mixed salt [Co(eta(5)-C5H5)(2)]+[Co(H2O)(6)](2+)[tma](3-) 2 was obtained as a minor product from the same reaction. In crystalline 2 the water molecules of the aqua complex form hydrogen bonds with the three carboxylic groups of the organic anion resulting in a caged structure that encapsulates the [Co(eta(5)-C5H5)(2)](+) cation. When dibenzoyl-L-tartaric acid was used the chiral crystal [Co(eta(5)-C5H5)(2)](+)[L-Hbta](-) 3 is obtained. The crystal contains chains of O-H ... O- hydrogen bonded anions. These results are used to discuss a design strategy for the engineering of organometallic crystals with predesigned structures. Though on a limited data set, the structure of the elusive crystalline hydrate [Co(eta(5)-C5H5)(2)](+)[OH](-) . 4H(2)O 4, which is liquid at ambient temperature, is discussed.