LiLa4N2I7 as the first lithium-containing nitride halide of the lanthanides: Synthesis, crystal structure and spectroscopic characterization

doi:10.1016/j.solidstatesciences.2019.106047

Solid State Sciences

Volume 99, January 2020, 106047

Dedicated to the German Founding Editor of Solid State Sciences, Prof. Dr. Dr. h.c. Martin Jansen, on the Occasion of his 75th Birthday.

https://doi.org/10.1016/j.solidstatesciences.2019.106047 Get rights and content

Highlights

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Single-phase material obtained by metathesis reaction.
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Li-MAS NMR spectroscopy for derivation of Li-ion conduction.
•
Temperature-depending crystal structure analysis.

Abstract

Initially, the quaternary nitride iodide LiLa₄N₂I₇ was synthesized at 600 °C by a partial metathesis reaction of lithium nitride (Li₃N) and lanthanum triiodide (LaI₃) within 7 days. Single-phase samples were obtained through annealing of the corresponding binary compounds (LiI, LaN and LaI₃) for 20 days overall (4 days at 600 °C prior to 16 days at 500 °C). The title compound crystallizes in the orthorhombic space group Pnma with four formula units per unit cell (a = 1374.17(9), b = 1213.45(8), c = 1079.91(7) pm at 100 K). The dominating structural features are trans-edge shared [NLa₄]⁹⁺ tetrahedra building up ${}_{\infty}^{1}{{[{NLa}_{4 / 2}^{e}]}^{3 +}}$ chains running along [010]. The linkage of these chains via iodide anions leads to a three-dimensional framework, which embeds isolated trigonal bipyramids [LiI₄₊₁]^4– with one long besides four short Li⁺–I^– contacts. Infrared spectra of crystalline samples show four main bands between 300 and 600 cm⁻¹, which can probably be assigned as vibrational modes of the condensed [NLa₄]⁹⁺ tetrahedra. ⁷Li-MAS NMR spectroscopy reveals a different coordination sphere of Li⁺ in rocksalt-type LiI than in LiLa₄N₂I₇, but no significant lithium-cation mobility.

Graphical abstract

Introduction

Lithium-containing materials have developed to a highly vivid scientific field as the Li⁺-cation battery is now state of the art in daily life. The group of Rabenau [[1], [2], [3], [4]] investigated lithium nitride iodides in more detail based on the pioneer work of Hahn [5] as possible active materials for a Li⁺-cation conductor. Unfortunately, this system did not show sufficiently good properties [6]. Further knowledge about this topic was generated in the late 1990s with the determination of the crystal structures of Li₇N₂I and Li₆NI₃ [7,8].

Cationic derivatization of ternary nitride halides of the lanthanides containing [NLn₄]⁹⁺ tetrahedra is rarely investigated up to now. Next to the cluster-containing compound CsPr₉NbN₆Br₁₅ [9], the quasi-quaternary phase Cs_0.64Na_0.36La₉N₄I₁₆ represented the first example for this class exhibiting unusual structural features: long Na⁺–I^– distances and ${}_{\infty}^{1}{{[NLa]}_{4 / 2}^{e}}^{3 +}$ chains, which are not aligned parallel to each other [10]. However, the second example, CsNaLa₆N₂Br₁₄ [11], was described just two years later, while the third one, the sodium-containing derivatives NaLn₄N₂I₇ (Ln = La – Nd), has just been published recently [12,13]. The dominating structural feature of both are ${}_{\infty}^{1}{{[{NLa}_{4 / 2}^{e}]}^{3 +}}$ chains running parallel to each other. Other cationic derivatization illustrated in literature goes along with an oxide implementation as demonstrated for the Na_2–xLn₄O_1+xN_1–xX₉ series (Ln = La – Nd, Gd; X = Cl and Br) [[14], [15], [16], [17]] and BaLn₄N_2–xO_xI₈ (Ln = La and Ce) [18]. To the best of our knowledge no lithium-containing representative was hitherto reported.

Metatheses reactions of lithium nitride (Li₃N) with a huge selection of metal halides were mostly carried out aiming at the production of binary nitrides, especially those of the transition metals [[19], [20], [21]]. An induction heating (or hot wires for example) starts the rapid reaction (so-called SHS: self-propagating high-temperature synthesis), which is very useful for the preparation of nitrides with high-temperature stability like TiN or LaN [22,23]. More complicated synthesis systems with the help of pressure effects and added alkali-metal halides provided nitrides with low temperature stability, for example WN_2.22 and GaN [24,25]. For the synthesis of lanthanide nitrides (LnN) the corresponding lanthanide trichlorides (LnCl₃) act as starting materials in combination with Li₃N, NaN₃, Mg₃N₂ or Ca₃N₂ as nitrogen sources [23,26,27]. All these reactions take place within a few minutes or hours. Neither long-term treatments of such mixtures for several days nor reactions with lanthanide triiodides (LnI₃) as starting materials in order to produce lanthanide nitrides or their derivatives have been reported so far.

Here we present a study of long-term metathesis reactions of the binary starting materials (Li₃N and LaI₃) along with synthesis attempts for the single-phase LiLa₄N₂I₇. In addition to the crystal structure of this cationic derivative, infrared (IR) and ⁷Li-MAS NMR spectroscopy were carried out for the spectroscopic characterization of the title compound.

Section snippets

Syntheses

All reactions took place in graphitated fused silica ampoules. Single crystals of LiLa₄N₂I₇ were synthesized by partial metathesis reaction of 3.3 mg lithium nitride (Li₃N) with 100.0 mg lanthanum triiodide (LaI₃) according to equation (1):2 Li₃N + 4 LaI₃ → LiLa₄N₂I₇ + 5 LiI

After sealing and evacuating the ampoule, the mixture was heated up to 600 °C for seven days and cooled down to room temperature within 36 h.

Single-phase samples can be synthesized by the reaction of the binary compounds.

Syntheses

The endothermal partial metathesis reaction of Li₃N and LaI₃ in a molar ratio of 2:4 starts at around 430 °C (Fig. 1, left) with the production of LiI, since an endothermal peak at 465 °C indicates the melting of LiI (melting point: 450 °C).³² Furthermore, the cooling curve already gives evidence for the presence LiI formed in the chemical reaction, because an exothermal peak at 420 °C is most likely due to its solidification. The powder diffractogram of the resulting material confirms the

Conclusion

The first quaternary lithium-containing lanthanum nitride iodide LiLa₄N₂I₇ was synthesized via a partial metathesis reaction of Li₃N with LaI₃, as well as with an annealing procedure of LiI, LaN and LaI₃. Its centrosymmetric crystal structure is dominated by ${}_{\infty}^{1}{{[{NLa}_{4 / 2}^{e}]}^{3 +}}$ chains built up from trans-edge connected [NLa₄]⁹⁺ tetrahedra and contains lithium in a 4+1-fold coordination by exclusively iodide anions. In comparison with the non-centrosymmetric crystal structure of NaLa₄N₂I₇, a close

Declaration of competing interest

The authors declare no conflict of interest.

Acknowledgments

We thank Dr. Sabine Strobel and Dr. Falk Lissner for the crystal data collection as well as Wolfgang König (Spectroscopy Service), Dr. Dilahan Aydin-Cantürk and Dr. Fanny Schurz (both in the former group of Prof. Dr. Dr. h.c. Martin Jansen) at the Max-Planck-Institute for Solid-State Research for providing the IR-spectroscopic measurements. Additionally, Dr. Marc Widenmeyer is gratefully acknowledged for supporting thermal analyses and Dr. Thomas Bräuniger (former group of Prof. Dr. Dr. h.c.

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LiLa4N2I7 as the first lithium-containing nitride halide of the lanthanides: Synthesis, crystal structure and spectroscopic characterization

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Syntheses

Syntheses

Conclusion

Declaration of competing interest

Acknowledgments

Solid State Ionics

J. Less Common. Met.

J. Power Sources

Eur. J. Solid State Inorg. Chem.

Z. Naturforsch.

Inorg. Chem.

Z. Anorg. Allg. Chem.

J. Mater. Process. Technol.

Appl. Phys. Lett.

Chem. Mater.

New Cryst. Struct.

Angew. Chem.

Angew. Chem. Int. Ed. Engl.

Naturwissenschaften

Mater. Res. Bull.

Angew. Chem.

Angew. Chem. Int. Ed. Engl.

Eur. J. Solid State Inorg. Chem.

Inorg. Chem.

J. Solid State Chem.

Z. Anorg. Allg. Chem.

Z. Anorg. Allg. Chem.

J. Alloys Compd.

Allg. Chem.

Chem. Soc. Rev.

J. Chem. Soc., Dalton Trans.

LiLa₄N₂I₇ as the first lithium-containing nitride halide of the lanthanides: Synthesis, crystal structure and spectroscopic characterization