Cyanogels are an inorganic sol-gel system that results from the polymerization reaction that occurs when a chlorometalate ([MCl4]2-) and cyanometalate ([M(CN)n]2-/3-) are combined in aqueous solution. When combined, two of the chloride ligands on the chlorometalate are replaced by the nitrogen end of a cyanide ligand on the cyanometalate creating a cyanide bridge. This reaction results in a cyanide linked, transition metal polymer that is negatively charged in nature and alkali chloride salt. The Bocarsly lab has extensively studied these cyanogel systems utilizing a variety of metals (Pd, Pt, Fe, Co, Au, Ru) and it has been shown that these cyanogels can be used to produce various materials. One such material is a metal alloy that can be produced at much lower temperatures than traditional metal alloy synthesis. Heating the cyanogel under an inert atmosphere causes auto-reduction of the metal centers, releasing hydrogen cyanide and cyanogen, leaving behind metal alloys.
The polymer initially forms as small sol particles (cyanosol) that then undergo a sol-gel transition that ultimately forms the bulk hydrogel (cyanogel). The cyanogel consists of two separate phases, the inorganic, polymer phase and the solvent (water) phase. The solvent phase can be removed via evaporation leaving behind a porous zerogel. It has been shown that by introducing a large, positively charged counter-ion, the agglomeration that results in the sol-gel transition can be prevented and stable, soluble cyanosol nanoparticles of various metal compositions can be isolated with a narrow size distribution. Thermal processing of these cyanosol nanoparticles results in metal alloy nanoparticle isolation with very little variance in size compared to the parent cyanosol.
Publications on cyanogels:
- Stabilizing cyanosols: amorphous cyanide bridged transition metal polymer nanoparticles. J. Mater. Chem. 2009, 19 (46), 8846-8855.
- Cyanogel Coordination Polymers as Precursors to Transition Metal Alloys and Intermetallies – from Traditional Heating to Microwave Processing. Chem. Mater. 2007, 19 (9), 2203-2212.
- The Autoreduction of Pd-Co and Pt-Co Cyanogels: Exploration of Cyanometalate Coordination Chemistry at Elevated Temperatures. J. Am. Chem. Soc. 2008, 130 (16), 5563-5572.
- Supported Superparamagnetic Pd/Co Alloy Nanoparticles Prepared from a Silica/Cyanogel Co-gel. Chem. Mater. 2005,17, 6216-6218.
- Solid-State Chemistry in a Microwave Oven: Preparation of Pd/Co Alloy from Cyanogel Coordination Polymers. Chem. Mater. 2005, 17 (19), 4755-4757.
