Heteroanionic Materials by Design: Progress Toward Targeted Properties

The burgeoning field of anion engineering in oxide‐based compounds aims to tune physical properties by incorporating additional anions of different size, electronegativity, and charge. For example, oxychalcogenides, oxynitrides, oxypnictides, and oxyhalides may display new or enhanced responses not readily predicted from or even absent in the simpler homoanionic (oxide) compounds because of their proximity to the ionocovalent‐bonding boundary provided by contrasting polarizabilities of the anions. In addition, multiple anions allow heteroanionic materials to span a more complex atomic structure design palette and interaction space than the homoanionic oxide‐only analogs. Here, established atomic and electronic principles for the rational design of properties in heteroanionic materials are contextualized. Also described are synergistic quantum mechanical methods and laboratory experiments guided by these principles to achieve superior properties. Lastly, open challenges in both the synthesis and the understanding and prediction of the electronic, optical, and magnetic properties afforded by anion‐engineering principles in heteroanionic materials are reviewed. Heteroanionic materials are solid‐state inorganic compounds with multiple unique elements forming distinct anionic sublattices. A scheme is described to disentangle the structural and chemical degrees‐of‐freedom stimulated by the addition of a secondary anion and to understand and design novel heteroanionic materials with targeted properties. Technologically interesting oxyfluorides are reviewed within this framework.