Chemical Control of Spin‐Orbit Coupling and Charge Transfer in Vacancy‐Ordered Ruthenium(IV) Halide Perovskites

Vacancy-ordered double perovskites are attracting significant attention due to their chemical diversity and interesting optoelectronic properties. With a view understanding both the optical magnetic properties of these compounds, two series RuIV halides presented; A2RuCl6 A2RuBr6, where A is K, NH4, Rb or Cs. We show that spin-orbit coupling (SOC) behavior can be tuned through changing cation halide. Within series, energy ligand-to-metal charge transfer increases as unit cell expands with larger cation, band gaps higher for respective chlorides than bromides. The moments systems temperature dependent non-magnetic ground state Jeff=0 caused by SOC. Ru-X covalency, consequently, delocalization metal d-electrons, result in systematic trends SOC constants variations halide anion.