Synthesis of Heavy Cyanide Analogues (CP- and CAs-) for the Design of Novel Prussian Blue Analogues

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Although cyanide is most well known for being a potent poison, it is a fundamental chemical building block and an important component of a large number of non-toxic materials. For example, cyanide-containing materials are commonly used in disposable gloves, blue paints, and even as anti-caking agents for table salt. Replacing the nitrogen atom in cyanide (CN-) with a phosphorus or arsenic atom would result in cyanide's "heavy analogues", cyaphide (CP-) and cyarside (CPs-). Like cyanide, these heavier analogues have the potential to be utilized in a wide range of applications. However, there is currently no known way to synthesize either cyaphide or cyarside ions, so these applications remain unaccessible. Previous attempts to synthesize the heavy cyanide analogues have only been successful in making them in non-ionic forms that are unsuitable for subsequent use in materials chemistry. The goal of this project is to develop a method for producing cyaphide and cyarside as ionic salts. These ionic salts would be much more versatile than existing cyaphide and cyarside containing compounds, and would allow the many potential applications of heavy cyanide analogues to be explored. A particularly exciting application for cyaphide and cyarside would be as components in a class of magnetic materials called Prussian Blue Analogues (PBAs). PBAs are materials consisting of metal atoms connected by cyanide linkers, and can exhibit useful magnetic properties such as the ability to respond to stimuli like heat or light. Significant effort is currently being directed toward optimizing the magnetic behaviour of PBAs for use in technologies such as chemical sensing. A major design constraint that limits current research efforts is that cyanide is the only available ion that is suitable for constructing PBAs. Ionic salts of cyaphide and cyarside would allow heavy cyanide analogues to also be used in PBAs, opening up many possibilities for their development. This project aims to explore novel methods for synthesizing ionic cyaphide and cyarside salts from the heavy cyanate analogues, an emerging family of compounds that show promise as chemical precursors to the heavy cyanide analogues. This research would enable heavy cyanide analogues to be utilized in designer materials for emerging technologies, and falls within the EPSRC's "Manufacturing the Future" research theme. Following the development of a synthesis for ionic salts of the heavy cyanide analogues, the next research objective is to use them to make novel PBAs or other similar magnetic materials, and to investigate how they can be utilized to design materials with advantageous magnetic properties.