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

• Published in: Angewandte Chemie (International ed.) Vol. 60; no. 10; pp. 5184 - 5188
• Main Authors: Vishnoi, Pratap, Zuo, Julia L., Cooley, Joya A., Kautzsch, Linus, Gómez‐Torres, Alejandra, Murillo, Jesse, Fortier, Skye, Wilson, Stephen D., Seshadri, Ram, Cheetham, Anthony K.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.03.2021; Wiley Blackwell (John Wiley & Sons)
• Edition: International ed. in English
• Subjects: Bromides; Cations; Charge transfer; Chemical control; Coupling; Halides; Kotani model; Magnetic moments; Magnetic properties; Optical properties; Optoelectronics; Perovskites; Ruthenium; ruthenium halides; spin-orbit coupling; Temperature dependence; Unit cell; Vacancies; vacancy-ordered double perovskite; ruthenium halides; vacancy-ordered double perovskite; Charge transfer; spin-orbit coupling; Kotani model
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202013383

Vacancy‐ordered double perovskites are attracting significant attention due to their chemical diversity and interesting optoelectronic properties. With a view to understanding both the optical and magnetic properties of these compounds, two series of RuIV halides are presented; A2RuCl6 and A2RuBr6, where A is K, NH4, Rb or Cs. We show that the optical properties and spin‐orbit coupling (SOC) behavior can be tuned through changing the A cation and the halide. Within a series, the energy of the ligand‐to‐metal charge transfer increases as the unit cell expands with the larger A cation, and the band gaps are higher for the respective chlorides than for the bromides. The magnetic moments of the systems are temperature dependent due to a non‐magnetic ground state with Jeff=0 caused by SOC. Ru‐X covalency, and consequently, the delocalization of metal d‐electrons, result in systematic trends of the SOC constants due to variations in the A cation and the halide anion. Vacancy‐ordered double perovskites, A2RuCl6 and A2RuBr6, were studied. The synthesis, crystal structures, and optical and magnetic properties of the materials were determined. Differences in the halide and the A cation size influence the charge‐transfer spectra. On the basis of temperature‐dependent magnetic moments, accurate values were estimated for the spin‐orbit coupling constants of the RuIV d4 ion.