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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

In English

Författare

Summary, in English

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.

Publiceringsår

2016

Språk

Engelska

Sidor

169-176

Publikation/Tidskrift/Serie

European Journal of Inorganic Chemistry

Issue

1

Dokumenttyp

Artikel i tidskrift

Förlag

John Wiley & Sons Inc.

Ämne

  • Inorganic Chemistry

Nyckelord

  • Zintl phases
  • Intermetallic compounds
  • Germanium
  • Electronic structure
  • Coloring problem

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 1099-0682