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 FeLa2 Ti3 O10 have been studied. FeLa2 Ti3 O10 was prepared by ion exchange of the triple-layered Ruddlesden-Popper phase Li2 La2 Ti3 O10 with FeCl2 at 350 °C under static vacuum. Rietveld refinement on synchrotron X-ray diffraction data indicates that the new phase is isostructural with CoLa2 Ti3 O10 , where FeII cations occupy slightly compressed/flattened interlayer tetrahedral sites. Magnetic measurements on FeLa2 Ti3 O10 display Curie-Weiss behavior at high temperatures and a spin-glass transition at lower temperatures (<30 K). Thermal treatment in oxygen shows that FeLa2 Ti3 O10 undergoes a significant cell contraction (Δc ≈ -2.7 Å) with a change in the oxidation state of iron (Fe2+ to Fe3+ ); 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 Fe2 O3 to produce Fe0.67 La2 Ti3 O10 .