Hybrid Layered Double Perovskite Halides of Transition Metals

Hybrid layered double perovskite (HLDP) halides comprise hexacoordinated 1+ and 3+ metals in the octahedral sites within a perovskite layer and organic amine cations between the layers. Progress on such materials has hitherto been limited to compounds containing main group 3+ ions isoelectronic with Pb^II (such as Sb^III and Bi^III). Here, we report eight HLDP halides from the A₂M^IM^IIIX₈ family, where A = para-phenylenediammonium (PPDA), 1,4-butanediammonium (1,4-BDA), or 1,3-propanediammonium (1,3-PDA); M^I = Cu or Ag; M^III = Ru or Mo; X = Cl or Br. The optical band gaps, which lie in the range 1.55 to 2.05 eV, are tunable according to the layer composition, but are largely independent of the spacer. Magnetic measurements carried out for (PPDA)₂Ag^IRu^IIICl₈ and (PPDA)₂Ag^IMo^IIICl₈ show no obvious evidence of a magnetic ordering transition. While the t_2g³ Mo^III compound displays Curie-Weiss behavior for a spin-only d³ ion, the t_2g⁵ Ru^III compound displays marked deviations from the Kotani theory.