Special Issue "Compounds with Polar Metallic Bonding"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Interactions in Crystal Structures".

Deadline for manuscript submissions: 31 October 2018

Special Issue Editor

Guest Editor
Dr. Constantin Hoch

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

Special Issue Information

Dear Colleagues,

This Special Issue on “Compounds with Polar Metallic Bonding” is intended to open an exchange between chemical, physical and material-oriented disciplines committed to intermetallic systems with strongly correlated electrons. The term “polar metal” is ubiquitous here, and can describe numerous different effects. Polarity can indicate the interplay of conduction electrons with magnetic dipoles in the lattice. It can also describe the presence of electric dipole moments within a ferroelectric metal. Additionally, the term is used when referring to an intermetallic phase crystallising 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.

In all these cases, polarity induces new, interesting property combinations in metallic systems. To understand the mechanisms in this field, it is necessary to understand interplay between localised moments, as 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. In order to understand the electronic consequences of polarity on the basis of quantum-mechanical calculations, it is necessary to have detailed crystal structure models at hand. Additionally, prior to crystal structure elucidation there is, of course, chemical synthesis.

We would like to combine reports on all related topics in this special issue. Some specifically interesting topics that may be included are listed below as keywords. These should only be considered 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 papers will be 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 1200 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
  • Crystal structure reports in polar intermetallics
  • Band structure calculations and electronic structure modelling
  • Physical properties and structure-property relations
  • Bulk phases, thin films and cocrystals of polar intermetallic systems
  • Polar metallic systems in applications

Published Papers (8 papers)

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Research

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Open AccessArticle Ammoniates of Zintl Phases: Similarities and Differences of Binary Phases A4E4 and Their Corresponding Solvates
Crystals 2018, 8(7), 276; https://doi.org/10.3390/cryst8070276
Received: 20 April 2018 / Revised: 22 June 2018 / Accepted: 23 June 2018 / Published: 29 June 2018
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Abstract
The combination of electropositive alkali metals A (A = Na-Cs) and group 14 elements E (E = Si-Pb) in a stoichiometric ratio of 1:1 in solid state reactions results in the formation of polyanionic salts, which belong to a class of intermetallics for
[...] Read more.
The combination of electropositive alkali metals A (A = Na-Cs) and group 14 elements E (E = Si-Pb) in a stoichiometric ratio of 1:1 in solid state reactions results in the formation of polyanionic salts, which belong to a class of intermetallics for which the term Zintl compounds is used. Crystal structure analysis of these intermetallic phases proved the presence of tetrahedral tetrelide tetraanions [E4]4− precast in solid state, and coulombic interactions account for the formation of a dense, three-dimensional cation-anion network. In addition, it has been shown that [E4]4− polyanions are also present in solutions of liquid ammonia prepared via different synthetic routes. From these solutions crystallize ammoniates of the alkali metal tetrahedranides, which contain ammonia molecules of crystallization, and which can be characterized by X-ray crystallography despite their low thermal stability. The question to be answered is about the structural relations between the analogous compounds in solid state vs. solvate structures, which all include the tetrahedral [E4]4− anions. We here investigate the similarities and differences regarding the coordination spheres of these anions and the resulting cation-anion network. The reported solvates Na4Sn4·13NH3, Rb4Sn4·2NH3, Cs4Sn4·2NH3, Rb4Pb4·2NH3 as well as the up to now unpublished crystal structures of the new compounds Cs4Si4·7NH3, Cs4Ge4·9NH3, [Li(NH3)4]4Sn4·4NH3, Na4Sn4·11.5NH3 and Cs4Pb4·5NH3 are considered for comparisons. Additionally, the influence of the presence of another anion on the overall crystal structure is discussed by using the example of a hydroxide co-crystal which was observed in the new compound K4.5Sn4(OH)0.5∙1.75 NH3. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessCommunication Ba4[Mn3N6], a Quasi-One-Dimensional Mixed-Valent Nitridomanganate (II, IV)
Crystals 2018, 8(6), 235; https://doi.org/10.3390/cryst8060235
Received: 25 April 2018 / Revised: 17 May 2018 / Accepted: 18 May 2018 / Published: 25 May 2018
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Abstract
The mixed-valent nitridomanganate Ba4[Mn3N6] was prepared using a gas–solid high temperature route. The crystal structure was determined employing high resolution synchrotron powder diffraction data: space group Pbcn, a = 9.9930(1) Å, b = 6.17126(8) Å, c
[...] Read more.
The mixed-valent nitridomanganate Ba4[Mn3N6] was prepared using a gas–solid high temperature route. The crystal structure was determined employing high resolution synchrotron powder diffraction data: space group Pbcn, a = 9.9930(1) Å, b = 6.17126(8) Å, c = 14.4692(2) Å, V = 892.31(2) Å3, Z = 4. The manganese atoms in the structure of Ba4[Mn3N6] are four-fold coordinated by nitrogen forming infinite corrugated chains of edge-sharing [MnN4] tetrahedra. The chains demonstrate a complete charge order of Mn species. Magnetization measurements and first principle calculations indicate quasi-one dimensional magnetic behavior. In addition, chemical bonding analysis revealed pronounced Mn–Mn interactions along the chains. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Optimization of Ca14MgSb11 through Chemical Substitutions on Sb Sites: Optimizing Seebeck Coefficient and Resistivity Simultaneously
Crystals 2018, 8(5), 211; https://doi.org/10.3390/cryst8050211
Received: 17 April 2018 / Revised: 6 May 2018 / Accepted: 8 May 2018 / Published: 13 May 2018
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Abstract
In thermoelectric materials, chemical substitutions are widely used to optimize thermoelectric properties. The Zintl phase compound, Yb14MgSb11, has been demonstrated as a promising thermoelectric material at high temperatures. It is iso-structural with Ca14AlSb11 with space
[...] Read more.
In thermoelectric materials, chemical substitutions are widely used to optimize thermoelectric properties. The Zintl phase compound, Yb14MgSb11, has been demonstrated as a promising thermoelectric material at high temperatures. It is iso-structural with Ca14AlSb11 with space group I41/acd. Its iso-structural analog, Ca14MgSb11, was discovered to be a semiconductor and have vacancies on the Sb(3) sites, although in its nominal composition it can be described as consisting of fourteen Ca2+ cations with one [MgSb4]9− tetrahedron, one Sb37− linear anion and four isolated Sb3− anions (Sb(3) site) in one formula unit. When Sn substitutes Sb in Ca14MgSb11, optimized Seebeck coefficient and resistivity were achieved simultaneously although the Sn amount is small (<2%). This is difficult to achieve in thermoelectric materials as the Seebeck coefficient and resistivity are inversely related with respect to carrier concentration. Thermal conductivity of Ca14MgSb11-xSnx remains almost the same as Ca14MgSb11. The calculated zT value of Ca14MgSb10.80Sn0.20 reaches 0.49 at 1075 K, which is 53% higher than that of Ca14MgSb11 at the same temperature. The band structure of Ca14MgSb7Sn4 is calculated to simulate the effect of Sn substitutions. Compared to the band structure of Ca14MgSb11, the band gap of Ca14MgSb7Sn4 is smaller (0.2 eV) and the Fermi-level shifts into the valence band. The absolute values for density of states (DOS) of Ca14MgSb7Sn4 are smaller near the Fermi-level at the top of valence band and 5p-orbitals of Sn contribute most to the valence bands near the Fermi-level. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Lu5Pd4Ge8 and Lu3Pd4Ge4: Two More Germanides among Polar Intermetallics
Crystals 2018, 8(5), 205; https://doi.org/10.3390/cryst8050205
Received: 20 April 2018 / Revised: 3 May 2018 / Accepted: 3 May 2018 / Published: 5 May 2018
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Abstract
In this study, two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4
[...] Read more.
In this study, two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4Ge8 is monoclinic, P21/m, mP34, a = 5.7406(3), b = 13.7087(7), c = 8.3423(4) Å, β = 107.8(1), Z = 2; Lu3Pd4Ge4 is orthorhombic, Immm, oI22, a = 4.1368(3), b = 6.9192(5), c = 13.8229(9) Å, Z = 2. The Lu5Pd4Ge8 analysed crystal is one more example of non-merohedral twinning among the rare earth containing germanides. Chemical bonding DFT studies were conducted for these polar intermetallics and showing a metallic-like behavior. Gathered results for Lu5Pd4Ge8 and Lu3Pd4Ge4 permit to described both of them as composed by [Pd–Ge]δ– three dimensional networks bonded to positively charged lutetium species. From the structural chemical point of view, the studied compounds manifest some similarities to the Zintl phases, containing well-known covalent fragment i.e., Ge dumbbells as well as unique cis-Ge4 units. A comparative analysis of molecular orbital diagrams for Ge26– and cis-Ge10– anions with COHP results supports the idea of the existence of complex Pd–Ge polyanions hosting covalently bonded partially polarised Ge units. The palladium atoms have an anion like behaviour and being the most electronegative cause the noticeable variation of Ge species charges from site to site. Lutetium charges oscillate around +1.5 for all crystallographic positions. Obtained results explained why the classical Zintl-Klemm concept can’t be applied for the studied polar intermetallics. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Mixed Sr and Ba Tri-Stannides/Plumbides AII(Sn1−xPbx)3
Crystals 2018, 8(5), 204; https://doi.org/10.3390/cryst8050204
Received: 2 April 2018 / Revised: 25 April 2018 / Accepted: 26 April 2018 / Published: 4 May 2018
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Abstract
The continuous substitution of tin by lead (M IV ) allows for the exploration geometric criteria for the stability of the different stacking variants of alkaline-earth tri-tetrelides AIIM3IV . A series of ternary Sr and Ba mixed tri-stannides/plumbides
[...] Read more.
The continuous substitution of tin by lead (M IV ) allows for the exploration geometric criteria for the stability of the different stacking variants of alkaline-earth tri-tetrelides A II M 3 IV . A series of ternary Sr and Ba mixed tri-stannides/plumbides A II (Sn 1 x Pb x ) 3 (A II = Sr, Ba) was synthesized from stoichiometric mixtures of the elements. Their structures were determined by means of single crystal X-ray data. All structures exhibit close packed ordered A M 3 layers containing M kagomé nets. Depending on the stacking sequence, the resulting M polyanion resembles the oxygen substructure of the hexagonal (face-sharing octahedra, h stacking, Ni 3 Sn-type, border compound BaSn 3 ) or the cubic (corner-sharing octahedra, c stacking, Cu 3 Au-type, border compound SrPb 3 ) perovskite. In the binary compound BaSn 3 (Ni 3 Sn-type) up to 28% of Sn can be substituted against Pb (hP8, P 6 3 / mmc, x = 0.28(4): a = 726.12(6), c = 556.51(6) pm, R1 = 0.0264). A further increased lead content of 47 to 66% causes the formation of the BaSn 2.57 Bi 0.43 -type structure with a ( hhhc ) 2 stacking [hP32, P 6 3 / mmc, x = 0.47(3): a = 726.80(3), c = 2235.78(14) pm, R1 = 0.0437]. The stability range of the BaPb 3 -type sequence ( hhc ) 3 starts at a lead proportion of 78% (hR36, R 3 ¯ m, a = 728.77(3), c = 2540.59(15) pm, R1= 0.0660) and reaches up to the pure plumbide BaPb 3 . A second new polymorph of BaPb 3 forms the Mg 3 In-type structure with a further increased amount of cubic sequences [ ( hhcc ) 3 ; hR48, a = 728.7(2), c = 3420.3(10) pm, R1 = 0.0669] and is thus isotypic with the border phase SrSn 3 of the respective strontium series. For the latter, a Pb content of 32% causes a small existence region of the PuAl 3 -type structure [hP24, P 6 3 / mmc, a = 696.97(6), c = 1675.5(2) pm, R1 = 0.1182] with a ( hcc ) 2 stacking. The series is terminated by the pure c stacking of SrPb 3 , the stability range of this structure type starts at 75% Pb (cP4, Pm 3 ¯ m; a = 495.46(9) pm, R1 = 0.0498). The stacking of the close packed layers is evidently determined by the ratio of the atomic radii of the contributing elements. The Sn/Pb distribution inside the polyanion (’coloring’) is likewise determined by size criteria. The electronic stability ranges, which are discussed on the basis of the results of FP-LAPW band structure calculations are compared with the Zintl concept and Wade’s/mno electron counting rules. Still, due to the presence of only partially occupied steep M-p bands the compounds are metals exhibiting pseudo band gaps close to the Fermi level. Thus, this structure family represents an instructive case for the transition from polar ionic/covalent towards (inter)metallic chemistry. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Rhombohedral Distortion of the Cubic MgCu2-Type Structure in Ca2Pt3Ga and Ca2Pd3Ga
Crystals 2018, 8(5), 186; https://doi.org/10.3390/cryst8050186
Received: 27 March 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
Two new fully ordered ternary Laves phase compounds, Ca2Pt3Ga and Ca2Pd3Ga, have been synthesized and characterized by powder and single-crystal X-ray diffraction along with electronic structure calculations. Ca2Pd3Ga was synthesized as
[...] Read more.
Two new fully ordered ternary Laves phase compounds, Ca2Pt3Ga and Ca2Pd3Ga, have been synthesized and characterized by powder and single-crystal X-ray diffraction along with electronic structure calculations. Ca2Pd3Ga was synthesized as a pure phase whereas Ca2Pt3Ga was found as a diphasic product with Ca2Pt2Ga. Electronic structure calculations were performed to try and understand why CaPt2 and CaPd2, which crystalize in the cubic MgCu2-type Laves phase structure, distort to the ordered rhombohedral variant, first observed in the magneto-restricted TbFe2 compound, with the substitution of twenty-five percent of the Pt/Pd with Ga. Electronic stability was investigated by changing the valence electron count from 22e/f.u. in CaPd2 and CaPt2 (2x) to 37e/f.u. in Ca2Pd3Ga and Ca2Pt3Ga, which causes the Fermi level to shift to a more energetically favorable location in the DOS. The coloring problem was studied by placing a single Ga atom in each of four tetrahedra of the cubic unit cell of the MgCu2-type structure, with nine symmetrically inequivalent models being investigated. Non-optimized and optimized total energy analyses of structural characteristics, along with electronic properties, will be discussed. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Crystal Structure, Spectroscopic Investigations, and Physical Properties of the Ternary Intermetallic REPt2Al3 (RE = Y, Dy–Tm) and RE2Pt3Al4 Representatives (RE = Tm, Lu)
Crystals 2018, 8(4), 169; https://doi.org/10.3390/cryst8040169
Received: 1 March 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 16 April 2018
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Abstract
The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c
[...] Read more.
The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c = 413.04(2) pm, wR2 = 0.0780, 942 F2 values, 46 variables) with space group Cmmm (oC48; q2pji2hedb). A comparison with the Pearson database indicated that YPt2Al3 forms a new structure type, in which the Pt and Al atoms form a [Pt2Al3]δ polyanion and the Y atoms reside in the cavities within the framework. Via a group-subgroup scheme, the relationship between the PrNi2Al3-type structure and the new YPt2Al3-type structure was illustrated. The compounds with RE = Dy–Tm were characterized by powder X-ray diffraction experiments. While YPt2Al3 is a Pauli-paramagnet, the other REPt2Al3 (RE = Dy–Tm) compounds exhibit paramagnetic behavior, which is in line with the rare-earth atoms being in the trivalent oxidation state. DyPt2Al3 and TmPt2Al3 exhibit ferromagnetic ordering at TC = 10.8(1) and 4.7(1) K and HoPt2Al3 antiferromagnetic ordering at TN = 5.5(1) K, respectively. Attempts to synthesize the isostructural lutetium compound resulted in the formation of Lu2Pt3Al4 (Ce2Ir3Sb4-type, Pnma, a = 1343.4(2), b = 416.41(8), c = 1141.1(2) pm), which could also be realized with thulium. The structure was refined from single-crystal data (wR2 = 0.0940, 1605 F2 values, 56 variables). Again, a polyanion with bonding Pt–Al interactions was found, and the two distinct Lu atoms were residing in the cavities of the [Pt3Al4]δ framework. X-ray photoelectron spectroscopy (XPS) measurements were conducted to examine the electron transfer from the rare-earth atoms onto the polyanionic framework. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Review

Jump to: Research

Open AccessReview The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds
Crystals 2018, 8(5), 225; https://doi.org/10.3390/cryst8050225
Received: 25 April 2018 / Revised: 13 May 2018 / Accepted: 14 May 2018 / Published: 18 May 2018
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Abstract
Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the
[...] Read more.
Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the Crystal Orbital Hamilton Population (COHP) method has been established as an efficient and reliable tool to extract the chemical-bonding information based on electronic-structure calculations of various quantum-chemical types. In this review, we present a brief introduction into the theoretical background of the COHP method and illustrate the latter by diverse applications, in particular by looking at representatives of the class of (polar) intermetallic compounds, usually considered as “black sheep” in the light of valence-electron counting schemes. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Ammoniates of Zintl phases: Structural relations between intermetallic compounds A4E4 (A=Li-Cs, E=Si-Sn) and their corresponding ammoniate structures
Authors: Corinna Lorenz, Stefanie Gärtner, Nikolaus Korber
Abstract: The combination of electropositive alkali metals A (A=Na-Cs) and group 14 elements E (E= Si-Pb) in a stoichiometric ratio of 1 : 1 in solid state reactions results in the formation of polyanionic salts, which are commonly known as Zintl compounds. Crystal structure analysis of these intermetallic phases proved the presence of tetrahedral tetrelide tetraanions [E4]4− precast in solid state,[[1]] and coulombic interactions account for the formation of a dense, three-dimensional cation-anion network. In addition, it has been shown that [E4]4− polyanions are also present in solutions of liquid ammonia prepared via different synthetic routes. From these solutions crystallize ammoniates of the alkali metal tetrahedranides, which contain ammonia molecules of crystallization and which can be characterized by X-ray crystallography despite their low thermal stability. The question to be answered is about the structural relations between the analogous compounds in solid state vs solvate structures, which all include the tetrahedral [E4]4− anions. We will investigate the similarities and differences regarding the coordination spheres of these anions as and the resulting cation - anion network. Specifically, we will include the reported solvates Na4Sn4·13NH3,[[2]] Rb4Sn4·2NH3, Cs4Sn4·2NH3, Rb4Pb4·2NH3[[3]] as well as the up to now unpublished crystal structures of the new compounds Cs4Si4·7NH3, Cs4Ge4·9NH3, [Li(NH3)4]4Sn4·4NH3, Na4Sn4·11.5NH3 and Cs4Pb4·5NH3 . Additionally, the influence of the presence of another anion on the overall crystal structure is discussed by using the example of a hydroxide co-crystal which was observed in the new compound K4Sn4(OH)0.5 ∙ 1.75 NH3

[1] E. Busmann, Z. Anorg. Allg. Chem.1961, 313, 90; H. G. v. Schnering, M. Schwarz, J.-H. Chang, K. Peters, E.-M. Peters, R. Nesper, Z.Kristallogr. New Cryst. Struct. 2005, 220, 525; T. Goebel, Y. Prots, F. Haarmann, Z. Kristallogr. New Cryst. Struct 2008, 223, 187; H. G. v. Schnering, J. Llanos, J.-H. Chang, K. Peters, E.-M. Peters, R. Nesper, Z. Kristallogr. New Cryst. Struct. 2005, 220, 324; J. Witte, H. G. v. Schnering, Z. Anorg. Allg. Chem. 1964, 327, 260; M. Baitinger, Y. Grin, R. Kniep, H. G. v. Schnering, Z. Kristallogr. 1999, 214, 457; M. Baitinger, K. Peters, M. Somer, W. Carillo-Cabrera, Y. Grin, R. Kniep, H. G. v. Schnering, Z. Kristallogr. 1999, 214, 455; R. Schäffer, W. Klemm, Z. Anorg. Allg. Chem. 1961, 312, 214; E. Hohmann, Z. Anorg. Allg. Chem. 1948, 257, 113; T. Goebel, A. Ormeci, O. Pecher, F. Haarmann, Z. Anorg. Allg. Chem. 2012, 638, 1437 – 1445; Grin, Y., Baitinger, M., Kniep, R., & Von Schnering, H. G. (1999). Z. Kristallogr-NCS 1999, 214(4), 453-454; Marsh, R. E., and D. P. Shoemaker, Acta Crystallogr. 1953, 6, 197-205; Hewaidy, I. F., Busmann, E., Klemm, W., Z. anorg. allg. Chem. 1964 , 328, 283–293

[2] M. Waibel, T. F. Fässler Z. Naturforsch. 2013, 68b, 732–734.

[3] K. Wiesler, K. Brandl, A. Fleischmann, N. Korber, Z. Anorg. Allg. Chem. 2009, 635, 508.

 

Title: Lu5Pd4Ge8 and Lu3Pd4Ge4: two more germanides among polar intermetallics
Authors: Riccardo Freccero 1, Pavlo Solokha 1,  Davide M. Proserpio 2, 3, Adriana Saccone1, Serena De Negri 1
Affiliation:
1 Università degli Studi di Genova, Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, I-16146 Genova, Italy
2 Università degli Studi di Milano, Dipartimento di Chimica, Via Golgi 19, 20133 Milano, Italy
3 Samara Center for Theoretical Materials Science (SCTMS), Samara National Research University, Ac. Pavlov St 1, Samara 443011, Russia
Abstract:  The two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structure was determined by single crystal X-ray diffraction analysis: Lu5Pd4Ge8 is monoclinic, P21/m, mP34, a = 5.7406(3), b = 13.7087(7), c = 8.3423(4) Å, b = 107.8(1), Z = 2; Lu3Pd4Ge4 is orthorhombic, Immm, oI22, a = 4.1368(3), b = 6.9192(5), c = 13.8229(9) Å, Z = 2. The Lu5Pd4Ge8 analyzed crystal is one more example of non-merohedral twinning among the rare earth containing germanides.

The crystal structure analysis of all known Ge-rich Lu-Pd-Ge compounds reveals a regular change of the type of Ge covalent fragments and their connection by means of Pd atoms, as a function of composition. The complexity of covalent Ge motifs increases along with Ge and Lu content evolving from Ge-Ge dumbbells to chains and from cis-Ge4 units to infinite corrugated 3-bonded layers.

Electronic structure calculations on the title compounds confirm the role of Lu in stabilization of Ge covalent fragments. The type/energy of the different interactions were evaluated in the framework of the projected COHP method.

 

 

 

Title: Crystal Structure, Spectroscopic Investigations and Physical Properties of the Ternary Intermetallic REPt2Al3 (RE = Y, Dy–Tm) and RE2Pt3Al4 Representatives (RE = Tm, Lu)
Authors: Oliver Janka et al.
Abstract: The /RE/Pt_2 Al_3 compounds of the late rare-earth metals (/RE/ = Y, Dy–Tm) were found to crystallize isostructural. Single crystal X-ray investigations of YPt_2 Al_3 revealed an orthorhombic unit cell (/a/ = 1080.73(6), /b/ = 1871.96(9), /c/ = 413.04(2) pm, /wR/2 = 0.0780, 942 F^2 values, 46 variables) with space group /Cmmm/ (/oC/48; /q/^2 /pji/^2 /hedb/). Comparison with the Pearson database indicated that YPt_2 Al_3 forms a new structure type, in which the Pt and Al atoms from a [Pt_2 Al_3 ]/^δ /^–polyanion, the Y atoms reside in cavities within the framework. Via a group-subgroup scheme, the relationship between the PrNi_2 Al_3 type structure and the new YPt_2 Al_3 type was illustrated. The compounds with /RE/ = Dy–Tm were characterized by powder X-ray diffraction experiments. While YPt_2 Al_3 is a Pauli-paramagnet, the other /RE/Pt_2 Al_3 (/RE/ = Dy–Tm) compounds exhibit paramagnetic behavior, in line with the rare-earth atoms being in the trivalent oxidation state. Attempts to synthesize the isostructural lutetium compound resulted in the formation of Lu_2 Pt_3 Al_4 (Ce_2 Ir_3 Sb_4 type, /Pnma/, /a/ = 1343.4(2), /b/ = 416.41(8), /c/ = 1141.1(2) pm). The structure was refined from single crystal data (/wR/2 = 0.0940, 1605 F^2 values, 56 variables). Again a polyanion with bonding Pt–Al interactions is found, the two distinct Lu atoms reside in cavities of the [Pt_3 Al_4 ]/^δ /^– framework. XPS measurements were conducted to examine the electron transfer from the rare-earth atoms onto the polyanionic framework.

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