Prussian blue, Fe₄[Fe(CN)₆]₃· x H₂O, is an iconic chemical that has been used as a pigment in paints for centuries. To a chemist, what might be more interesting than Prussian blue’s colour is its molecular structure. As the archetypal coordination polymer, Prussian blue has an extended network structure composed of metal ions connected through bridging ligands. The resulting structure of Prussian blue resembles a framework you might make out of marshmallows and toothpicks, where the marshmallows are iron centres and the toothpicks are cyanide linkers. (Metal-organic frameworks, like the ones Angela made, are a subset of coordination polymers.)
Hard templating is a method we also described in our post about Susan’s composite materials. A template is used to host the formation of a material. Once the material is formed and the template is removed, the resulting material has holes where the template used to be. Using templates with structures on the nano- or mesoscale can allow us to make materials with interesting properties.
To see if the synthesis of coordination polymers could be combined with the method of hard templation, Pei-Xi, a PhD student in our group, tried to build Prussian blue or its analogs onto a template before removing the template to obtain mesoporous structured Prussian blue.
With chiral nematic mesoporous silica used as a template, Pei-Xi was able to obtain films of mesoporous Zn/Fe Prussian blue analogs. Although this method did not work for other Prussian blue analogs or Prussian blue itself, this work shows that hard templating coordination polymers is a viable method toward making new materials.
A special note: this is our 100th paper! Congratulations Pei-Xi and Vitor! See here for the full paper.