Press to Success: Gd5FW3O16—The First Gadolinium(III) Fluoride Oxidotungstate(VI)

Ingo Hartenbach,Katharina V Dorn

doi:10.3390/cryst9080424

Abstract

The gadolinium(III) fluoride oxidotungstate(VI), with the formula Gd5FW3O16, represents the first published fluoride-derivative of a rare-earth metal oxidotungstate. It is synthesized by a mixture of GdF3, Gd2O3, and WO3 at 800 °C and a pressure of 2 GPa with the help of a belt press. The title compound crystallizes in the monoclinic space group P21/c (no. 14) with four formula units per unit cell and the following lattice parameters: a = 539.29 (4), b = 1556.41 (12), c = 1522.66 (11) pm, and β = 93.452 (4). The crystal structure comprises five crystallographically distinguishable Gd3+ cations, which are surrounded by either oxide and fluoride anions (Gd1–3) or by oxide anions only (Gd4, Gd5), with coordination numbers ranging between seven and nine. The fluoride anions are trigonal non-planar coordinated by three Gd3+ cations (Gd1–3). The distorted [WO6]6− octahedra in this structure form isolates edge- and vertex-connected entities of the compositions [W2O10]8− and [W2O11]10−, respectively. According to the presented units, a structured formula can be written as Gd4[FGd3]2[W2O10][W2O11]2. The single-crystal Raman spectrum reveals the typical symmetric stretching vibration mode of octahedral oxidotungstate(VI) units at about 871 cm−1.

Highlights

Fluoride oxidotungstates (VI), as well as mixed-ligand fluoridooxidotungstates, are known for several alkali, alkaline-earth, and transition metals but not yet for rare-earth elements
Cations, which are surrounded by either oxide and fluoride anions (Gd1–3) or by oxide anions only (Gd4, Gd5), with coordination numbers ranging between seven and nine
The fluoride anions are trigonal non-planar coordinated by three Gd3+ cations (Gd1–3)

Summary

Introduction

Fluoride oxidotungstates (VI), as well as mixed-ligand fluoridooxidotungstates, are known for several alkali, alkaline-earth, and transition metals but not yet for rare-earth elements. Fluoride-containing rare-earth metal oxidomolybdates with the compositions REF [MoO4 ]. = 1473 ◦ C) [18], a reaction in silica ampoules would only be possible with another compound as flux Appropriate candidates, such as alkali metal halides, boron oxide, or molybdenum oxide, all result in undesired side products, such as scheelite-type ARE[WO4 ]2 representatives (e.g., NaGd[WO4 ]2 [19]) or rare-earth metal borates and molybdates of various compositions, respectively. RE3Cl3[WO6] representatives of the smaller rare-earth metals [22,23], the high-pressure synthesis of the formula analogous, and presumably pseudo-isotypic (due to the replacement of OH− by F−) REF[WO4]. The high-pressure openssolution up a possibility to obtain rare-earth metal(III). 3 3 rare-earth metals [22,23], the high-pressure synthesis of the formula analogous, and presumably

Materials and Methods

O16 were

Single-Crystal Raman Spectroscopy

Crystal Structure

Single-Crystal Raman Spectrum

O10 synthesized via high-pressure methods in gold ampoules using a belt and