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Structure and Bonding of an Intergrowth Phase Ca7Ag2+xGe7-x (x approximate to 2/3) Featuring a Zintl-Type Polyanionic Chain

Ponou, Simeon LU ; Doverbratt, Isa LU ; Lidin, Sven LU and Miller, Gordon J. (2016) In European Journal of Inorganic Chemistry p.169-176
Abstract
Single crystals of a new ternary phase, Ca7Ag2+xGe7-x [x = 0.48(3)], were obtained from as side-product of high-temperature solid-state reactions, and its crystal structure determined by X-ray diffraction methods. Following the Zintl concept, the anionic substructure consists of a novel pentameric Zintl anion [Ge-5](12-) with C-2v local symmetry, as well as [AgxGe2-x]((6-3x)-) units accounting for [Ge-2](6-) dimers and isolated Ge4- (and Ag+) species sharing the same atomic sites. DFT-level band structure calculations were carried out on a hypothetical, fully ordered model (x = 0). We found that the electronic structure associated with the planar W-shaped [Ge-5](12-) polyanions is more suited to optimize the structure's stability than the... (More)
Single crystals of a new ternary phase, Ca7Ag2+xGe7-x [x = 0.48(3)], were obtained from as side-product of high-temperature solid-state reactions, and its crystal structure determined by X-ray diffraction methods. Following the Zintl concept, the anionic substructure consists of a novel pentameric Zintl anion [Ge-5](12-) with C-2v local symmetry, as well as [AgxGe2-x]((6-3x)-) units accounting for [Ge-2](6-) dimers and isolated Ge4- (and Ag+) species sharing the same atomic sites. DFT-level band structure calculations were carried out on a hypothetical, fully ordered model (x = 0). We found that the electronic structure associated with the planar W-shaped [Ge-5](12-) polyanions is more suited to optimize the structure's stability than the helical configuration of the isoelectronic [Se-5](2-), in the context of incomplete charge transfer from the electropositive metal Ca. Thus, the antibonding states at the Fermi level that are centered on the two [Ge-n]((2n+2)-) oligomers can be depopulated by means of Ge-to-Ca electron back donation, strengthening at the same time the Ge-Ge bonds. These antibonding states also endow the system with substantial electronic flexibility, which may result in some phase width. Finally, plausible local ordering models of Ag/Ge mixing in [AgxGe2-x]((6-3x)-) units for x = 2/3, as expected from the Zintl concept, are briefly discussed within the coloring problem approach. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Zintl phases, Intermetallic compounds, Germanium, Electronic structure, Coloring problem
in
European Journal of Inorganic Chemistry
issue
1
pages
169 - 176
publisher
John Wiley & Sons
external identifiers
  • wos:000367727600021
  • scopus:84953835383
ISSN
1099-0682
DOI
10.1002/ejic.201501176
language
English
LU publication?
yes
id
bb61ad3d-923b-4fca-afa8-c694fbd3304f (old id 8747947)
date added to LUP
2016-02-23 09:58:02
date last changed
2017-01-01 03:14:50
@article{bb61ad3d-923b-4fca-afa8-c694fbd3304f,
  abstract     = {Single crystals of a new ternary phase, Ca7Ag2+xGe7-x [x = 0.48(3)], were obtained from as side-product of high-temperature solid-state reactions, and its crystal structure determined by X-ray diffraction methods. Following the Zintl concept, the anionic substructure consists of a novel pentameric Zintl anion [Ge-5](12-) with C-2v local symmetry, as well as [AgxGe2-x]((6-3x)-) units accounting for [Ge-2](6-) dimers and isolated Ge4- (and Ag+) species sharing the same atomic sites. DFT-level band structure calculations were carried out on a hypothetical, fully ordered model (x = 0). We found that the electronic structure associated with the planar W-shaped [Ge-5](12-) polyanions is more suited to optimize the structure's stability than the helical configuration of the isoelectronic [Se-5](2-), in the context of incomplete charge transfer from the electropositive metal Ca. Thus, the antibonding states at the Fermi level that are centered on the two [Ge-n]((2n+2)-) oligomers can be depopulated by means of Ge-to-Ca electron back donation, strengthening at the same time the Ge-Ge bonds. These antibonding states also endow the system with substantial electronic flexibility, which may result in some phase width. Finally, plausible local ordering models of Ag/Ge mixing in [AgxGe2-x]((6-3x)-) units for x = 2/3, as expected from the Zintl concept, are briefly discussed within the coloring problem approach.},
  author       = {Ponou, Simeon and Doverbratt, Isa and Lidin, Sven and Miller, Gordon J.},
  issn         = {1099-0682},
  keyword      = {Zintl phases,Intermetallic compounds,Germanium,Electronic structure,Coloring problem},
  language     = {eng},
  number       = {1},
  pages        = {169--176},
  publisher    = {John Wiley & Sons},
  series       = {European Journal of Inorganic Chemistry},
  title        = {Structure and Bonding of an Intergrowth Phase Ca7Ag2+xGe7-x (x approximate to 2/3) Featuring a Zintl-Type Polyanionic Chain},
  url          = {http://dx.doi.org/10.1002/ejic.201501176},
  year         = {2016},
}