# Synthesis of the Double Infinite-Layer Ni(I) Phase La3Ni2O5F via Sequential Topochemical Reactions

## TL;DR

This paper describes a new method to synthesize a nickel-based material with unique structural and magnetic properties through a series of chemical reactions.

## Contribution

The synthesis of a new Ni(I) phase with a double infinite-layer structure via sequential topochemical reactions.

## Key findings

- Fluorination of La3Ni2O7 produces La3Ni2O5F4 with fluoride ions inserted and exchanged in the structure.
- La3Ni2O5F3 adopts a Pbcm structure with NiO5F octahedra tilting and fluoride chains.
- La3Ni2O5F exhibits a T′-structure with antiferromagnetic ordering at low temperatures.

## Abstract

Fluorination of the n = 2 Ruddlesden–Popper
oxide, La3Ni2O7, with polyvinylidene
fluoride yields La3Ni2O5F4, 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 La3Ni2O5F4 by extracting interstitial fluoride ions. The resulting
phase, La3Ni2O5F3, 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 NiO5F octahedra adopt an a
–
a
–
c
+
/–(a
–
a
–
)­c
+ tilting pattern.
Further reduction with LiH at 250 °C converts La3Ni2O5F3 into La3Ni2O5F, a Ni1+ phase which adopts a T′-structure
consisting of double infinite-sheets of apex linked NiO4 squares, stacked with LaOF fluorite-type layers. Magnetization and
neutron diffraction data indicate La3Ni2O5F3 adopts an antiferromagnetically ordered state
below T
N = 225 K, while magnetization
data from La3Ni2O5F exhibit a broad
maximum centered at 75 K, suggestive of antiferromagnetic order.