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Compounds with Polar Metallic Bonding Volume II

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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (20 February 2023) | Viewed by 10127

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Special Issue Editor

Dr. Constantin Hoch

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Guest Editor

LMU Munich, Department for Chemistry, Butenandtstraße 5-13(D), D-81377 München, Germany
Interests: preparative inorganic chemistry; intermetallics; polar metals; subvalent compounds; crystallography; solid state chemistry; nitrido- and oxometalates; amalgams
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Special Issue Information

Dear Colleagues,

The second volume of this Special Issue of Crystals is meant to collect contributions on polar intermetallics from solid-state chemistry, solid-state physics, crystallography, material sciences, and all related disciplines. The different manifestations of polarity within metallic systems lead to special behavior and unusual combinations of properties. Polarity can indicate the interplay of conduction electrons with magnetic dipoles in the lattice. It can also describe the presence of long-range, ordered electric dipole moments within a ferroelectric metal. Additionally, the term is used when referring to an intermetallic phase crystallizing in a polar space group or when electronegativity differences between the constituent elements of an intermetallic phase induce Coulombic interactions within an overall metallic matrix. To understand the mechanisms in this field, it is necessary to understand the interplay between localized moments of electric or magnetic dipoles, as well as Coulombic monopoles, with the delocalized conduction electrons. For the establishment of structure–property relations for compounds with polar metallic bonding, it is indispensable to present reliable models of their electronic structures.

We would like to publish reports on synthetic approaches toward new polar intermetallics with crystallographic or metallurgic phase characterization and studies on reactivity, physical behavior, and property optimization in applied systems, as well as theoretical studies and method development, with the aim of shedding light on the nature of chemical bonding in polar intermetallic phases. The named topics may be considered only as examples; any advanced topic in the field of polar metallic bonding is welcome.

Dr. Constantin Hoch
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Synthesis of compounds with polar metallic bonding;
Reactivity of polar intermetallics;
Crystal structure reports of polar intermetallics;
Theoretical calculations and descriptions of chemical bonding in intermetallic systems;
Physical properties and structure–property relations;
Bulk phases, thin films, and cocrystals of polar intermetallics;
Polar metallic systems in application;
Development of modern methods for describing electronic structures and chemical bonding in polar intermetallic phases.

Published Papers (5 papers)

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Editorial

Jump to: Research

3 pages, 173 KiB

Open AccessEditorial

Compounds with Polar Metallic Bonding—Reloaded

by Constantin Hoch

Crystals 2023, 13(7), 1080; https://doi.org/10.3390/cryst13071080 - 10 Jul 2023

Viewed by 622

Abstract

In June 2019 the first volume of a Special Edition of Crystals with the subject Compounds with Polar Metallic Bonding was presented [...] Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding Volume II)

Research

Jump to: Editorial

15 pages, 8089 KiB

Open AccessArticle

Structure and Bonding in CsNa₂Hg₁₈, a New Ternary Amalgam with Strong Coulombic Bonding Contributions

by Timotheus Hohl, Frank Tambornino and Constantin Hoch

Crystals 2022, 12(11), 1679; https://doi.org/10.3390/cryst12111679 - 21 Nov 2022

Cited by 3 | Viewed by 1720

Abstract

The new ternary amalgam CsNa

_{2}

_{18}

The new ternary amalgam CsNa

_{2}

_{18}

was synthesised from the elements in an unconventional low-temperature procedure. It crystallises in a tetragonal structure type (space group I4/mmm, a = 7.3054(7) and c = 20.046 Å) and combines ionic and metallic bonding contributions. In the crystal structure, Cs and Na atoms are embedded in a Hg scaffold with highly covalent Hg–Hg bonding. The alkali metal atoms are coordinated exclusively by Hg atoms in unusual environments with coordination numbers CN = 24 for Cs and CN = 16 for Na. Polar amalgams are suitable model systems for studying the parameters influencing the ’bad metal behaviour’ in polar intermetallic phases. We present structural studies on the basis of powder and single crystal diffraction data together with measurements of the specific resistivity and DFT calculations of the electronic structure. For CsNa

_{2}

_{18}

, a high specific resistivity can be observed, but the Ioffe–Regel saturation of the resistivity is expressed much less than in other polar amalgams. Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding Volume II)

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25 pages, 3956 KiB

Open AccessArticle

A Coloring Study of the Ga Richest Alkali Gallides: New In- and Hg-Containing Gallides with the RbGa₇- and the K₃Ga₁₃-Type Structure

by Martha Falk, Marco Wendorff and Caroline Röhr

Crystals 2020, 10(11), 1052; https://doi.org/10.3390/cryst10111052 - 19 Nov 2020

Cited by 4 | Viewed by 1719

Abstract

The Ga-rich gallides of the alkali metals present an interesting, yet still scarcely investigated case of polyanionic cluster compounds with subtle variations in the character of their chemical bonding. In the present work, the Ga richest phases K

_{3}

_{13}

, RbGa [...] Read more.

_{3}

_{13}

, RbGa

_{7}

, and CsGa

_{7}

, which are formally electron-precise Zintl/Wade cluster compounds, are systematically studied with respect to a partial substitution of Ga by In and Hg. The pure hepta-gallides AGa

_{7}

(A = Rb/Cs;

R \bar{3} m

), which were formerly obtained from Ga-rich melts in powder form only, were crystallized from Hg-rich melts. Herein, up to 9.9/13.6% (Rb/Cs) of Ga could be substituted by In, which partly takes the four-bonded [M

_{2}

] dumbbells connecting layers of Ga-icosahedra. Even though the structures are electron precise, the pseudo band gap does not coincide with the Fermi level. In the most Ga-rich potassium compound K

_{3}

_{13}

(

C m c m

) only 1.2% of In and 2.7% of Hg could be incorporated. Although Rb

_{3}

_{13}

remains unknown, ternary variants containing 5.2 to 8.2% In could be obtained; this structure is also stabilized by a small Hg-proportion. The likewise closed-shell 3D polyanion consists of all-exo-bonded Ga-icosahedra and closo [Ga

_{11}

] clusters, which are connected by two tetrahedrally four-bonded Ga

^{-}

and a trigonal-planar three-bonded Ga

^{0}

. The aspects of the electronic structures and the site-specific Ga↦Hg/In substitution in the polyanion (“coloring”) are discussed for the title compounds and other mixed Ga/In trielides. Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding Volume II)

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13 pages, 1193 KiB

Open AccessArticle

On the New Oxyarsenides Eu₅Zn₂As₅O and Eu₅Cd₂As₅O

by Gregory M. Darone, Sviatoslav A. Baranets and Svilen Bobev

Crystals 2020, 10(6), 475; https://doi.org/10.3390/cryst10060475 - 03 Jun 2020

Cited by 3 | Viewed by 2437

Abstract

The new quaternary phases Eu₅Zn₂As₅O and Eu₅Cd₂As₅O have been synthesized by metal flux reactions and their structures have been established through single-crystal X-ray diffraction. Both compounds crystallize in the centrosymmetric space group Cmcm (No. 63, Z = 4; Pearson symbol oC52), with unit cell parameters a = 4.3457(11) Å, b = 20.897(5) Å, c = 13.571(3) Å; and a = 4.4597(9) Å, b = 21.112(4) Å, c = 13.848(3) Å, for Eu₅Zn₂As₅O and Eu₅Cd₂As₅O, respectively. The crystal structures include one-dimensional double-strands of corner-shared MAs₄ tetrahedra (M = Zn, Cd) and As–As bonds that connect the tetrahedra to form pentagonal channels. Four of the five Eu atoms fill the space between the pentagonal channels and one Eu atom is contained within the channels. An isolated oxide anion O^2– is located in a tetrahedral hole formed by four Eu cations. Applying the valence rules and the Zintl concept to rationalize the chemical bonding in Eu₅M₂As₅O (M = Zn, Cd) reveals that the valence electrons can be counted as follows: 5 × [Eu²⁺] + 2 × [M²⁺] + 3 × [As^3–] + 2 × [As^2–] + O^2–, which suggests an electron-deficient configuration. The presumed h⁺ hole is confirmed by electronic band structure calculations, where a fully optimized bonding will be attained if an additional valence electron is added to move the Fermi level up to a narrow band gap (Eu₅Zn₂As₅O) or pseudo-gap (Eu₅Cd₂As₅O). In order to achieve such a formal charge balance, and hence, narrow-gap semiconducting behavior in Eu₅M₂As₅O (M = Zn, Cd), europium is theorized to be in a mixed-valent Eu²⁺/ Eu³⁺ state. Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding Volume II)

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Graphical abstract

13 pages, 2217 KiB

Open AccessArticle

Revisiting the Zintl‒Klemm Concept for ALn₂Ag₃Te₅-Type Alkaline-Metal (A) Lanthanide (Ln) Silver Tellurides

by Katharina Eickmeier, Kai S. Fries, Fabian C. Gladisch, Richard Dronskowski and Simon Steinberg

Crystals 2020, 10(3), 184; https://doi.org/10.3390/cryst10030184 - 07 Mar 2020

Cited by 13 | Viewed by 2962

Abstract

Understanding the bonding nature of solids is decisive, as knowledge of the bonding situation for any given material provides valuable information about its structural preferences and physical properties. Although solid-state tellurides are at the forefront of several fields of research, the electronic structures, particularly their nature of bonding, are typically understood by applying the Zintl‒Klemm concept. However, certain tellurides comprise ionic as well as strong (polar) mixed-metal bonds, in obvious contrast to the full valence-electron transfers expected by Zintl‒Klemm’s reasoning. How are the valence-electrons really distributed in tellurides containing ionic as well as mixed-metal bonds? To answer this question, we carried out bonding and Mulliken as well as Löwdin population analyses for the series of ALn₂Ag₃Te₅-type tellurides (A = alkaline-metal; Ln = lanthanide). In addition to the bonding analyses, we provide a brief description of the crystal structure of this particular type of telluride, using the examples of RbLn₂Ag₃Te₅ (Ln = Ho, Er) and CsLn₂Ag₃Te₅ (Ln = La, Ce), which have been determined for the first time. Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding Volume II)

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