Liquid-assisted solid-state reaction: assembly of (6,3) and (10,3) hydrogen-bonded networks based on [M(Hbiim)3] by oxidation of [M(H2biim)3]2+ complexes in the presence of acetate anions

Abstract

Two complexes [Ru(Hbiim)₃] (1) and [Co(Hbiim)₃]·3H₂O (2) (H₂biim = 2,2′-biimidazole) were synthesized quantitatively and rapidly via a “liquid-assisted” solid-state reaction approach. The reaction occurs within minutes of grinding together [Ru(H₂biim)₃](PF₆)₂ or [Co(H₂biim)₃]Cl₂ and NH₄OAc with a few drops of H₂O₂ as an oxidant and solvent, concomitant with colour changes. The structures of the compounds obtained from the solid-state reaction were confirmed by comparison of their PXRD patterns with simulations based on their single crystal structures. Complex 1 is a 3-fold interpenetrating three-dimensional hydrogen bonded polycatenate network based on a (6,3) net, complex 2 is a double-layer network linked by the lattice water molecules and the Hbiim ligands viahydrogen bonds. For comparison with the solid-state reaction, control reactions were also carried out in solution. Complex 1 was also afforded from the solution reaction. However, a new phase [Co(Hbiim)₃]·0.5EtOH (3) was obtained from solution, rather than 2, although it also crystallized from an identical solution of EtOH–water. Complex 3 is a 4-fold interpenetrating three-dimensional hydrogen bonded polycatenate network based on a (10,3)-b net. Interesting, the [M(H₂biim)₃]²⁺ (M = Ru and Co) species can be oxidized to the corresponding [M(Hbiim)₃] species by oxygen in the presence of acetate anions, which play a determined role in the redox reaction. The deprotonation of the [M(H₂biim)₃]²⁺ species triggered by the acetate anions greatly increases the electron density at the M(II) center and shifts the oxidation potentials of M(II) complex to a less positive value. This may provide an effective approach for the generation of high status metal complexes via supramolecular interactions.