Organometallic crystal engineering with multidentate building blocks and template guest size effect. Supra-anionic organic frameworks obtained from cyclobutane-1,2,3,4-tetracarboxylic and trans-acotinic acids†

Abstract

The organic acids cyclobutane-1,2,3,4-tetracarboxylic C₄H₄(CO₂H)₄, and trans-acotinic acid C₃H₃(CO₂H)₃, have been treated in thf with the organometallic hydroxides [Co(η⁵-C₅H₅)₂]⁺[OH]^–, [Co(η⁵-C₅Me₅)₂]⁺[OH]^–, and [Cr(η⁶-C₆H₆)₂]⁺[OH]^– prepared in situ from the oxidation of the corresponding neutral complexes, to yield the novel organic–organometallic crystalline materials [Co(η⁵-C₅H₅)₂]⁺[C₄H₄(CO₂H)₃COO]^– 1, [Cr(η⁶-C₆H₆)₂]⁺[C₄H₄(CO₂H)₃CO₂]^–·H₂O 2, and [Co(η⁵-C₅Me₅)₂]⁺[C₃H₃(CO₂H)₂CO₂(H)·C₃H₃(CO₂H)₂CO₂]^–·H₂O 3. Self-assembly of the monodeprotonated organic acid C₄H₄(CO₂H)₄ generates supra-anionic framework structures held together by O–H· · ·O and O–H· · ·O^– hydrogen bonds which accommodate the diamagnetic [Co(η⁵-C₅H₅)₂]⁺ and paramagnetic [Cr(η⁶-C₆H₆)₂]⁺ cations, respectively. Crystalline 1 does not form single crystals with defined shapes but rather an “enamel” like material which grows parallel to the crystallographic bc plane. The same reaction between trans-acotinic acid and [Co(η⁵-C₅Me₅)₂]⁺[OH]^–generates a large honeycomb-type structure in [Co(η⁵-C₅Me₅)₂]⁺[C₃H₃(CO₂H)₂CO₂(H)·C₃H₃(CO₂H)₂CO₂]^–·H₂O 3. The effect of the size of the templating units [Co(η⁵-C₅H₅)₂]⁺ and [Co(η⁵-C₅Me₅)₂]⁺ is discussed. The previously unknown structure of the starting material [Co(η⁵-C₅Me₅)₂]⁺[PF₆]^– 4, used for the preparation of [Co(η⁵-C₅Me₅)₂]⁺[OH]^–, has also been determined.