From Tetrahedral to Octahedral Iron Coordination: Layer Compression in Topochemically Prepared FeLa 2 Ti 3 O 10 .

Synthesis, characterization, and thermal modification of the new layered perovskite FeLa ₂ Ti ₃ O ₁₀ have been studied. FeLa ₂ Ti ₃ O ₁₀ was prepared by ion exchange of the triple-layered Ruddlesden-Popper phase Li ₂ La ₂ Ti ₃ O ₁₀ with FeCl ₂ at 350 °C under static vacuum. Rietveld refinement on synchrotron X-ray diffraction data indicates that the new phase is isostructural with CoLa ₂ Ti ₃ O ₁₀ , where Fe ^II cations occupy slightly compressed/flattened interlayer tetrahedral sites. Magnetic measurements on FeLa ₂ Ti ₃ O ₁₀ display Curie-Weiss behavior at high temperatures and a spin-glass transition at lower temperatures (<30 K). Thermal treatment in oxygen shows that FeLa ₂ Ti ₃ O ₁₀ undergoes a significant cell contraction (Δc ≈ -2.7 Å) with a change in the oxidation state of iron (Fe ²⁺ to Fe ³⁺ ); structural analysis and Mössbauer studies indicate that upon oxidation the local iron environment goes from tetrahedral to octahedral coordination with some deintercalation of iron as Fe ₂ O ₃ to produce Fe _0.67 La ₂ Ti ₃ O ₁₀ .