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Title: Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization

Abstract

Intermetallic compounds represent an extensive pool of candidates for energy related applications stemming from magnetic, electric, optic, caloric, and catalytic properties. The discovery of novel intermetallic compounds can enhance understanding of the chemical principles that govern structural stability and chemical bonding as well as finding new applications. Valence electron-poor polar intermetallics with valence electron concentrations (VECs) between 2.0 and 3.0 e /atom show a plethora of unprecedented and fascinating structural motifs and bonding features. Furthermore, establishing simple structure-bonding-property relationships is especially challenging for this compound class because commonly accepted valence electron counting rules are inappropriate.

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1417363
Report Number(s):
IS-J-9512
Journal ID: ISSN 0001-4842
Grant/Contract Number:
AC02-07CH11358
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Accounts of Chemical Research
Additional Journal Information:
Journal Volume: 51; Journal Issue: 1; Journal ID: ISSN 0001-4842
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Lin, Qisheng, and Miller, Gordon J. Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization. United States: N. p., 2017. Web. doi:10.1021/acs.accounts.7b00488.
Lin, Qisheng, & Miller, Gordon J. Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization. United States. doi:10.1021/acs.accounts.7b00488.
Lin, Qisheng, and Miller, Gordon J. 2017. "Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization". United States. doi:10.1021/acs.accounts.7b00488.
@article{osti_1417363,
title = {Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization},
author = {Lin, Qisheng and Miller, Gordon J.},
abstractNote = {Intermetallic compounds represent an extensive pool of candidates for energy related applications stemming from magnetic, electric, optic, caloric, and catalytic properties. The discovery of novel intermetallic compounds can enhance understanding of the chemical principles that govern structural stability and chemical bonding as well as finding new applications. Valence electron-poor polar intermetallics with valence electron concentrations (VECs) between 2.0 and 3.0 e–/atom show a plethora of unprecedented and fascinating structural motifs and bonding features. Furthermore, establishing simple structure-bonding-property relationships is especially challenging for this compound class because commonly accepted valence electron counting rules are inappropriate.},
doi = {10.1021/acs.accounts.7b00488},
journal = {Accounts of Chemical Research},
number = 1,
volume = 51,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on December 18, 2018
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  • Gold intermetallics are known for their unusual structures and bonding patterns. Two new compounds have been discovered in the cation-poor part of the Cs–Au–Ga system. We obtained both compounds directly by heating the elements at elevated temperatures. Structure determinations based on single-crystal X-ray diffraction analyses revealed two structurally and compositionally related formations: CsAu 1.4Ga 2.8 (I) and CsAu 2Ga 2.6 (II) crystallize in their own structure types (I: Rmore » $$\bar{3}$$, a = 11.160(2) Å, c = 21.706(4) Å, Z = 18; II: R$$\bar{3}$$, a = 11.106(1) Å, Å, c = 77.243(9) Å, Z = 54) and contain hexagonal cationic layers of cesium. Furthermore, this is a unique structural motif, which has never been observed for the other (lighter) alkali metals in combination with Au and post transition elements. The polyanionic part is characterized in contrast by Au/Ga tetrahedral stars, a structural feature that is characteristic for light alkali metal representatives, and disordered sites with mixed Au/Ga occupancies that occur in both structures with a more significant disorder in the polyanionic component of CsAu 2Ga 2.6. Examinations of the electronic band structure for a model approximating the composition of CsAu 1.4Ga 2.8 have been completed using density-functional-theory-based methods and reveal a deep pseudogap at E F. Bonding analysis by evaluating the crystal orbital Hamilton populations show dominant heteroatomic Au–Ga bonds and only a negligible contribution from Cs pairs.« less
  • The title compounds are obtained from reactions of KI, RI{sub 3}, R, and Os at 750--850 C in sealed Nb or Ta containers. The structure was established by single-crystal X-ray diffraction studies for three samples, La and Pr at 23 C and La at {minus} 100 C. This particular combination of large R, interstitial Z, and halogen results in the highest X:R ratio known among rare-earth-metal cluster halides and an unprecedented structure type. The cluster units are interconnected according to the pattern [(R{sub 6}Os)I{sub 8}{sup i}I{sub 4/2}{sup i-a}I{sub 4/2}{sup a-i}I{sub 2}{sup a}]{sup 4{minus}} in which four R in the waistmore » of each cluster, the Os, and four bridging I{sup i-a,a-i} pairs generate a planar 2D network of geometrically nearly ideal, 16-electron R{sub 6}Os octahedra. This contrasts with the tetragonal compression found for many other 16-e{sup {minus}} examples with the parallel disappearance of Curie-Weiss paramagnetism. Powdered {alpha}-K{sub 4}La{sub 6}I{sub 14}Os exhibits an exceptionally low resistivity for a cluster halide ({approximately} 120 {micro}{Omega}{center{underscore}dot}cm) over 110--280 K and a small paramagnetism over about 35 to {approximately} 250 K associated with a probable Mott-Hubbard state that changes to a temperature-independent (presumably Pauli) paramagnetism above about 300 K. EHTB band calculations show that a significant broadening of the HOMO ({approximately}t{sub 1u}) states takes place in the plane of the intercluster bridging. The unique structure, properties, and band picture for the compound indicate a transition to a delocalized (band) state.« less
  • Nanoclusters usually display exotic physical and chemical properties due to their intriguing geometric structures in contrast to their bulk counterparts. By means of first-principles calculations within density functional theory, we find that heavy noble metal Pt N nanoclusters around the size N = 55 begin to prefer an open configuration, rather than previously reported close-packed icosahedron or core-shell structures. Particularly, for Pt N, the widely supposed icosahedronal magic cluster is changed to a three-atomic-layered structure with D 6h symmetry, which can be well addressed by our recently established generalized Wulff construction principle (GWCP). But, the magic number of Pt Nmore » clusters around 55 is shifted to a new odd number of 57. The high symmetric three-layered Pt-57 motif is mainly stabilized by the enhanced covalent bonding contributed by both spin-orbital coupling effect and the open d orbital (5d 96s 1) of Pt, which result in a delicate balance between the enhanced Pt-Pt covalent bonding of the interlayers and negligible d dangling bonds on the cluster edges. Our findings about Pt N clusters are also applicable to Ir N clusters, but qualitatively different from their earlier neighboring element Os and their later neighboring element Au. The magic numbers for Os and Au are even, being 56 and 58, respectively. Finally, the findings of the new odd magic number 57 are the important supplementary of the recently established GWCP.« less
  • Nanoclusters usually display exotic physical and chemical properties due to their intriguing geometric structures in contrast to their bulk counterparts. By means of first-principles calculations within density functional theory, we find that heavy noble metal Pt{sub N} nanoclusters around the size N = 55 begin to prefer an open configuration, rather than previously reported close-packed icosahedron or core-shell structures. Particularly, for Pt{sub N}, the widely supposed icosahedronal magic cluster is changed to a three-atomic-layered structure with D{sub 6h} symmetry, which can be well addressed by our recently established generalized Wulff construction principle (GWCP). However, the magic number of Pt{sub N}more » clusters around 55 is shifted to a new odd number of 57. The high symmetric three-layered Pt{sub 57} motif is mainly stabilized by the enhanced covalent bonding contributed by both spin-orbital coupling effect and the open d orbital (5d{sup 9}6s{sup 1}) of Pt, which result in a delicate balance between the enhanced Pt–Pt covalent bonding of the interlayers and negligible d dangling bonds on the cluster edges. These findings about Pt{sub N} clusters are also applicable to Ir{sub N} clusters, but qualitatively different from their earlier neighboring element Os and their later neighboring element Au. The magic numbers for Os and Au are even, being 56 and 58, respectively. The findings of the new odd magic number 57 are the important supplementary of the recently established GWCP.« less