When crystallized with a quaternary ammonium cation, it can be obtained as a yellow solid.

Pentacyanocobaltate attracted attention as an early example of a metal complex that reacts with hydrogen.

Initially this reaction produces insoluble cobalt dicyanide, but this solid dissolves in the presence of the excess cyanide.

According to X-ray crystallography, the salt features square pyamidal [Co(CN)5]3−.

The complex attracted attention in the 1940s for its reactivity toward hydrogen, which is now understood to produce a cobalt hydride:[1] When allowed to stand as a dilute solution for several minutes, the complex reacts with water to give two Co(III) derivatives: In concentrated solution, the complex dimerizes: With benzyl chloride and related alkylating agents, Co(III) alkyls are formed:[3]