For Copper: A Unique Behaviour within Prussian Blue Analogues

In Prussian blue (PB) analogues the 3D framework is formed by practically linear T-N-C-M-C-N-T- chains, and the solids crystallize with a cubic unit cell where the metal centers (M, T) are found with octahedral coordination. In that framework the T-N-C-M-C-N-T chain length coincides with the unit cell edge (a). Within PB analogues for copper deviation from the usual regularities in the materials properties are observed, among them: the smallest cell edge, an extremely low dehydration temperature, the largest metal-metal electron cloud overlapping, the highest affinity for the H2 adsorption, and a well ordered system of vacancies [1–4]. Within divalent transition metals octahedral compounds for the copper ion a non cubic structure due to the Jahn-Teller effect for the copper (2+) ion is usually observed. However, with the exception of M = Pt, which crystallizes with a tetragonal unit cell, the remaining copper PB analogues show cubic structure. All these features stimulated a detailed structural study in that series of copper compounds from magnetic measurements, and HR-XRD, Mössbauer, IR, TG and H2 adsorption data. The obtained results are herein summarized