Synthesis of the Double Infinite-Layer Ni(I) Phase La 3 Ni 2 O 5 F via Sequential Topochemical Reactions

High Resolution Image Download MS PowerPoint Slide Fluorination of the n = 2 Ruddlesden–Popper oxide, La 3 Ni 2 O 7, with polyvinylidene fluoride yields La 3 Ni 2 O 5 F 4, a phase in which fluoride ions have been inserted into interstitial sites in the Ruddlesden–Popper framework and also exchanged with the oxide ions residing on apical anion sites. Reaction with LiH at 190 °C reduces La 3 Ni 2 O 5 F 4 by extracting interstitial fluoride ions. The resulting phase, La 3 Ni 2 O 5 F 3, adopts a structure described in space group Pbcm in which the fluoride ions in the half-filled interstitial layer are arranged in chains parallel to the y -axis, and the NiO 5 F octahedra adopt an a – a – c + /–(a – a – )c + tilting pattern. Further reduction with LiH at 250 °C converts La 3 Ni 2 O 5 F 3 into La 3 Ni 2 O 5 F, a Ni 1+ phase which adopts a T′-structure consisting of double infinite-sheets of apex linked NiO 4 squares, stacked with LaOF fluorite-type layers. Magnetization and neutron diffraction data indicate La 3 Ni 2 O 5 F 3 adopts an antiferromagnetically ordered state below T N = 225 K, while magnetization data from La 3 Ni 2 O 5 F exhibit a broad maximum centered at 75 K, suggestive of antiferromagnetic order.