Pinalites: Optical Properties and Quantum Magnetism of Heteroanionic A 3 MO 5 X 2 Compounds.

Heteroanionic compounds, which contain two or more types of anions, have emerged as a promising class of materials with diverse properties and functionalities. In this paper, I review the experimental findings on Ca 3 ReO 5 Cl 2 and related compounds that exhibit remarkable pleochroism and novel quantum magnetism. I discuss how the heteroanionic coordination affects the optical and magnetic properties by modulating the d-orbital states of the transition metal ions. Subsequently, I compare these materials with other heteroanionic and monoanionic compounds and highlight the potential of A 3 MO 5 X 2 materials for future exploration of materials and phenomena.