Lu3O2F5: a new highly densified member (n = 3) of the MnX2n+1 series of fluorite-related vernier phases

Halide Replacement with Complete Preservation of Crystal Lattice in Mixed-Anion Lanthanide Oxyhalides

A challenge in anion control in periodic solids is to preserve the crystal lattice while substituting for different anions of widely varying size and hardness. Post-synthetic modification routes that place cations or anions in non-equilibrium configurations are promising; however, such methods remain relatively unexplored for anion placement. Here, we report the synthesis of LaOI nanocrystals by a non-hydrolytic sol-gel condensation reaction and their transformation into LaOBr, LaOCl, and LaOF nanocrystals along hard-soft acid-base principles using post-synthetic metathesis reactions with ammonium halides. Anion displacement proceeds along halide planes, preserving the tetragonal matlockite structure. Energy-variant X-ray excited optical luminesce signatures of alloyed Tb³⁺ -ions is a sensitive quantum reporter of the preservation of the cation sublattice and hardening of the crystal structure upon anion replacement.

Structural refinement of the RT LaOF phases by coupling powder X-Ray diffraction, (19)F and (139)La solid state NMR and DFT calculations of the NMR parameters

The structures of the β- and t-LaOF phases have been refined from XRPD patterns. For both phases, (19)F and (139)La solid-state NMR spectra recorded at high magnetic fields show the presence of a single F and a single La local environment, indicating a full anionic ordering in these oxyfluoride compounds. DFT calculations of the (19)F and (139)La chemical shielding tensors and of the (139)La EFG tensor have been performed for the proposed structural models. The observed good agreement between experimental and calculated NMR parameters for both phases highlights the accuracy of the structural data.

LuF[SeO3]: the structural chameleon of lanthanoid fluoride oxoselenates(IV)

LuF[SeO3] is a compound that can easily be obtained by a solid-state reaction of Lu2O3, LuF3, and SeO2 with CsBr as the fluxing agent. The outstanding property of LuF[SeO3] is the appearance of two phase transitions within a range of less than 200 K. With an increase in the coordination number for Lu(3+) from 7 to 8, the triclinic room-temperature modification changes at temperatures below -40 °C to the monoclinic low-temperature or high-pressure phase of LuF[SeO3]. At the same time, room-temperature modification retains the structure but gains higher symmetry at the second phase transition of around +110 °C. This second transition can even be observed under a microscope using polarized light to see twinning lamellae disappear and reappear during this reversible process.