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§

Abstract

The polycarboxylic acids C₆H₃(CO₂H)₃-1,3,5 (trimesic acid, H₃tma) and O ²,O ³-dibenzoyl-L-tartaric acid (L-H₂bta) reacted in water or thf with [Co(η⁵-C₅H₅)₂][OH] prepared in situ by oxidation of [Co(η⁵-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–H^δ+· · ·O^δ– hydrogen bonds between organometallic and organic components. Crystalline [Co(η⁵-C₅H₅)₂]⁺[(H₃tma)(H₂tma)]^–·2H₂O 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 [(H₃tma)(H₂tma)]^– and water molecules. The mixed salt [Co(η⁵-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(η⁵-C₅H₅)₂]⁺ cation. When dibenzoyl-L-tartaric acid was used the chiral crystal [Co(η⁵-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(η⁵-C₅H₅)₂]⁺[OH]^–·4H₂O 4, which is liquid at ambient temperature, is discussed.