Liquid-Assisted Solid-State Reaction: Formation of a Three-Dimensional Hydrogen-Bonded Network and Evidence for Proton Induced Electron Transfer

We describe the first observation of the quantitative and rapid synthesis of a (10,3)-b three-dimensional hydrogen bonded network {[Ru(H2biim)3](TMA)}·5H2O (1·H2O) (H2biim = 2,2′-biimidazole; H3TMA = trimesic acid) via a “liquid-assisted” solid-state reaction approach. The reaction occurs within minutes of grinding together [Ru(H2biim)3](PF6)2 and Na2HTMA with a few drops of H2O2 as an oxidant and solvent, concomitant with a color change from yellow (Ru(II) ion) to blue-green (Ru(III) ion). The characterization of the solid-state product was achieved by a combination of a single crystal obtained via seeding and powder diffraction experiments. To compare with the solid-state reaction, similar reactions were also carried out in an EtOH solution. Two complexes {[Ru(H2biim)3](TMA)}·10H2O (2·H2O) and [Ru(H2biim)3](HTMA) (3) were isolated in the presence of a polypyridine base, such as 2,2-dipyridylamine or 2,2′:6′,2′′-terpyridine or 1,10-phenanthroline. Complex 2 is a (6,3) honeycomb two-dimensional hydrogen-bonded network. Complexes 1 and 2 are topological isomers. The formation of multiple robust hydrogen bonds between [Ru(H2biim)3]3+ and TMA may trigger the proton transfer from H2biim to TMA, then electron transfer, resulting in Ru(III) status. This may provide an effective approach for the generation of high status metal complexes via supramolecular interactions. Importantly, our experiments suggest that solution crystallization may at times offer more product diversity than grinding.