Novel S = 1/2 kagome lattice materials: Cs₂TiCu₃F₁₂ and Rb₂TiCu₃F₁₂

Two new members of the A₂B′Cu₃F₁₂ family of kagome-related materials have been prepared, in order to further understand the crystal-chemical relationships, phase transitions and magnetic behaviour within this family of potentially frustrated S = ½ two-dimensional quantum magnets. Cs₂TiCu₃F₁₂ adopts a crystal structure with the ideal kagome lattice topology (space group R m) at ambient temperature. Diffraction studies reveal different symmetry-lowering structural phase transitions in single crystal and polycrystalline forms at sub-ambient temperatures, with the single crystal form retaining rhombohedral symmetry and the powder form being monoclinic. In both cases, long-range antiferromagnetic order occurs in the region 16–20 K. Rb₂TiCu₃F₁₂ adopts a distorted triclinic structure even at ambient temperatures.