Mixed Valency in Extended Materials

Since the characterization of the extended coordination network Prussian blue as a mixed-valence material last century, the phenomenon has continued to be a source of inspiration for understanding fundamental aspects of electron transfer in three-dimensional coordination space. Over the past 20 years, burgeoning interest in the field of coordination polymers and metal–organic frameworks has delivered a new suite of exquisite materials that have shed further light on structure–function relationships underpinning mixed valency in extended solids. This chapter provides an overview of the historical context for mixed-valence materials and discusses the very latest developments in the field, along with new avenues for the application of the phenomenon.