Structural Diversity and Magnetic Properties of Hybrid Ruthenium Halide Perovskites and Related Compounds.

Abstract

There has been a great deal of recent interest in extended compounds containing Ru3+ and Ru4+ in light of their range of unusual physical properties. Many of these properties are displayed in compounds with the perovskite and related structures. Here we report an array of structurally diverse hybrid ruthenium halide perovskites and related compounds: MA2 RuX6 (X=Cl or Br), MA2 MRuX6 (M=Na, K or Ag; X=Cl or Br) and MA3 Ru2 X9 (X=Br) based upon the use of methylammonium (MA=CH3 NH3 + ) on the perovskite A site. The compounds MA2 RuX6 with Ru4+ crystallize in the trigonal space group and can be described as vacancy-ordered double-perovskites. The ordered compounds MA2 MRuX6 with M+ and Ru3+ crystallize in a structure related to BaNiO3 with alternating MX6 and RuX6 face-shared octahedra forming linear chains in the trigonal space group. The compound MA3 Ru2 Br9 crystallizes in the orthorhombic Cmcm space group and displays pairs of face-sharing octahedra forming isolated Ru2 Br9 moieties with very short Ru-Ru contacts of 2.789 Å. The structural details, including the role of hydrogen bonding and dimensionality, as well as the optical and magnetic properties of these compounds are described. The magnetic behavior of all three classes of compounds is influenced by spin-orbit coupling and their temperature-dependent behavior has been compared with the predictions of the appropriate Kotani models.