Crystal Coulomb Energies. I. The Electrostatic Binding Energy of Wurster's Blue Perchlorate by Ewald's Method

Wurster's blue perchlorate, an ion-radical salt which is a Curie-Weiss paramagnet above 188°K and exhibits spin pairing below 188°K, was found by Ewald's method to have an electrostatic binding energy of −4.15 ± 0.06 eV/molecule. In the isomorphous Wurster's blue iodide the crystal binding energy is very slightly greater. Nearest-neighbor linear-chain cation-cation repulsions play a minor role in the overall stability of both lattices. From room-temperature crystallographic data, no conclusions could be drawn about the changes in perchlorate geometry at the first-order phase transition in Wurster's blue perchlorate.