2 research outputs found
Evidence of New Fluorinated Coordination Compounds in the Composition Space Diagram of FeF<sub>3</sub>/ZnF<sub>2</sub>āH<i>amtetraz</i>-HF<sub>aq</sub> System
The
exploration of the composition space diagram of the FeF<sub>3</sub>/ZnF<sub>2</sub>āH<i>amtetraz</i>-HF<sub>aq</sub> system (H<i>amtetraz</i> = 5-aminotetrazole) by solvothermal
synthesis at 160 Ā°C for 72 h in dimethylformamide (DMF) has evidenced
five new hybrid fluorides (<b>1</b>ā<b>5</b>);
the structures are characterized from single crystal X-ray diffraction
data. [H<i>dma</i>]ĀĀ·(ZnFe<sup>III</sup>(H<sub>2</sub>O)<sub>4</sub>F<sub>6</sub>) (<b>1</b>) and [H<i>dma</i>]ĀĀ·[H<i>gua</i>]<sub>2</sub>ĀĀ·(Fe<sup>III</sup>F<sub>6</sub>) (<b>2</b>) contain anionic inorganic
chains (<b>1</b>) or isolated octahedra (<b>2</b>) weakly
hydrogen bonded (Class I hybrids) to dimethylammonium (H<i>dma</i>) and/or guanidinium (H<i>gua</i>) cations which are produced
from the tetrazole ligand and solvent decomposition. [H<i>dma</i>]<sub>2</sub>ĀĀ·[H<i>gua</i>]ĀĀ·[NH<sub>4</sub>]ĀĀ·[ZnFe<sup>III</sup>F<sub>5</sub>(<i>amtetraz</i>)<sub>2</sub>]<sub>2</sub> (<b>3</b>), [H<i>dma</i>]<sub>2</sub>ĀĀ·[Zn<sub>1.6</sub>Fe<sup>II</sup><sub>0.4</sub>Fe<sup>III</sup>F<sub>6</sub>Ā(<i>amtetraz</i>)<sub>3</sub>] (<b>4</b>), and [H<i>dma</i>]ĀĀ·[Zn<sub>4</sub>F<sub>5</sub>(<i>amtetraz</i>)<sub>4</sub>] (<b>5</b>) are considered as Class II hybrids in which the (<i>amtetraz</i>)<sup>ā</sup> anions are strongly linked
to divalent metal cations via NāM bonds. In <b>3</b>, <sub>ā</sub>{[NH<sub>4</sub>]ĀĀ·[ZnFe<sup>III</sup>F<sub>5</sub>Ā(<i>amtetraz</i>)<sub>2</sub>]<sub>2</sub>} layers are separated by [H<i>dma</i>]<sup>+</sup> and
[H<i>gua</i>]<sup>+</sup> cations. <b>4</b> and <b>5</b> exhibit three-dimensional (3D) hybrid networks that contain
small cavities where [H<i>dma</i>]<sup>+</sup> cations are
inserted. A porous 3D metalāorganic framework intermediate
is evidenced from the thermogravimetric analysis and X-ray thermodiffraction
of <b>5</b>
Exploring the Sm<sub>1ā<i>x</i></sub>Ca<sub><i>x</i></sub>F<sub>3ā<i>x</i></sub> Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F<sup>ā</sup> Ionic Conductivity
Pure tysonite Sm<sub>1ā<i>x</i></sub>Ca<sub><i>x</i></sub>F<sub>3ā<i>x</i></sub> solid solutions
for 0.05 ā¤ <i>x</i> ā¤ 0.17 have been prepared
by the solid-state route. For the first time, the partial Sm<sub>1ā<i>x</i></sub>Ca<sub><i>x</i></sub>F<sub>3ā<i>x</i></sub> solid solution is investigated on the basis of structural
features and ionic conductivity measurements. Powder X-ray diffraction
Rietveld refinements show an unexpected decrease of the hexagonal
unit cell volume related to the creation of fluorine vacancies. The
local environment of F1, which is mainly responsible for the ionic
conductivity, changes with the Ca content: the distortion of the F1Ā(Sm,Ca)<sub>4</sub> tetrahedral site decreases with the Ca content. Fluoride
ion exchanges have been qualitatively probed on two Sm<sub>1ā<i>x</i></sub>Ca<sub><i>x</i></sub>F<sub>3ā<i>x</i></sub> (<i>x</i> = 0.05 and <i>x</i> = 0.15) samples thanks to <sup>19</sup>F magic angle spinning NMR
experiments at various spinning frequencies and temperatures. At room
temperature, the ionic conductivity decreases exponentially with the
Ca content and the activation energy increases monotonously with the
Ca content. The highest conductivity is found for the lowest Ca content
or the smallest fluorine vacancy content stabilized in the Sm<sub>1ā<i>x</i></sub>Ca<sub><i>x</i></sub>F<sub>3ā<i>x</i></sub> tysonite network corresponding
to Sm<sub>0.95</sub>Ca<sub>0.05</sub>F<sub>2.95</sub> (10<sup>ā4</sup> SĀ·cm<sup>ā1</sup>, <i>E</i><sub>a</sub> =
0.36 eV at room temperature). For this composition, the largest dispersions
of F2ā(Sm,Ca) and F3ā(Sm,Ca) distances as well as (Sm,Ca)āF1ā(Sm,Ca)
angles are observed. The buckling of F2/F3 sheets around the <i>z</i> = 1/4 coordinate for low Ca content affects the large
F1 tetrahedral site with the strongest distortion. The higher the
buckling effect into the F2/F3 sheets, the higher the F1 local site
distortion and the higher the ionic mobility and conductivity