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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>R</mml:mi> <mml:mover><mml:mn>3</mml:mn> <mml:mo>‾</mml:mo></mml:mover> <mml:mi>m</mml:mi></mml:mrow> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>P</mml:mi> <mml:mover><mml:mn>3</mml:mn> <mml:mo>‾</mml:mo></mml:mover> <mml:mi>m</mml:mi></mml:mrow> </mml:math> 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.