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Title: Gold Polar Intermetallics: Structural Versatility through Exclusive Bonding Motifs

Journal Article · · Accounts of Chemical Research
ORCiD logo [1];  [2];  [2]; ORCiD logo [3]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States); Stockholm Univ. (Sweden). Dept. of Materials and Environmental Chemistry
  2. Ames Lab. and Iowa State Univ., Ames, IA (United States). Dept. of Chemistry
  3. Ames Lab. and Iowa State Univ., Ames, IA (United States). Dept. of Materials Science and Engineering; Stockholm Univ. (Sweden). Dept. of Materials and Environmental Chemistry
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The design of new materials with desired chemical and physical characteristics requires thorough understanding of the underlying composition–structure–property relationships and the experimental possibility of their modification through the controlled involvement of new components. From this point of view, intermetallic phases, a class of compounds formed by two or more metals, present an endless field of combinations that produce several chemical compound classes ranging from simple alloys to true ionic compounds. Polar intermetallics (PICs) belong to the class that is electronically situated in the middle, between Hume–Rothery phases and Zintl compounds and possessing e/a (valence electron per atom) values around 2. In contrast to the latter, where logical rules of formation and classification systems were developed decades ago, polar intermetallics remain a dark horse with a huge diversity of crystal structures but unclear mechanisms of their formation. Partial incorporation of structural and bonding features from both nonpolar and Zintl compounds is commonly observed here. A decent number of PICs can be described in terms of complex metallic alloys (CMAs) following the Hume–Rothery electron-counting schemes but exhibit electronic structure changes that cannot be explained by the latter. Our research is aimed at the discovery and synthesis of new polar intermetallic compounds, their structural characterization, and investigation of their properties in line with the analysis of the principles connecting all of these components. Understanding of the basic structural tendencies is one of the most anticipated outcomes of this analysis, and systematization of the available knowledge is the initial and most important step. Here in this Account, we focus on a well-represented but rather small section of PICs: ternary intermetallic compounds of gold with electropositive and post-transition metals of groups 12 to 15. The strong influence of relativistic effects in its chemical bonding results in special, frequently unique structural motifs, while at the same time gold participates in common structure types as an ordinary transition element. Enhanced bonding strength leads to the formation and stabilization of complex homo- and heteroatomic clusters and networks that are compositionally restricted to just a few options throughout the periodic table. Because it has the highest absolute electronegativity among metals, comparable to those of some halogens, gold usually plays the role of an anion, even being able to form true salts with the most electropositive metals. We discuss the occurrence of the structure types and show the place of gold intermetallics in the general picture. Among the structures considered are ones as common as AlB2 or BaAl4 types, in line with the recently discovered diamond-like homoatomic metal networks, formation of local fivefold symmetry, different types of tunneled structures, and more complex intergrown multicomponent structures.

Research Organization:
Ames Lab., Ames, IA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC02-07CH11358
OSTI ID:
1487216
Report Number(s):
IS-J-9522
Journal Information:
Accounts of Chemical Research, Vol. 50, Issue 11; ISSN 0001-4842
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 20 works
Citation information provided by
Web of Science

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Cited By (2)

Tb 3 Pd 2 , Er 3 Pd 2 and Er 6 Co 5– x : structural variations and bonding in rare-earth-richer binary intermetallics journal August 2018
Controlling magnetism via transition metal exchange in the series of intermetallics Eu(T1,T2) 5 In (T = Cu, Ag, Au) journal January 2018

Figures / Tables (10)

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36 MATERIALS SCIENCE