Centric and Non-centric Ca3Au similar to 7.5Ge similar to 3.5: Electron-Poor Derivatives of La3Al11. Syntheses, Structures, and Bonding Analyses

TitleCentric and Non-centric Ca3Au similar to 7.5Ge similar to 3.5: Electron-Poor Derivatives of La3Al11. Syntheses, Structures, and Bonding Analyses
Publication TypeJournal Article
Year of Publication2009
AuthorsLin QS, Corbett JD
Journal TitleInorganic Chemistry
Volume48
Pages5403-5411
Date Published06/15
ISBN Number0020-1669
Accession NumberISI:000266809200042
Keywordsag-ga system, al system, approximant, gd, hypoelectronic srin4, icosahedral quasi-crystal, intermetallic compounds, mg2cu6ga5, phases, size
Abstract

Two La3Al11 type derivatives have been discovered in the Ca-Au-Ge system and structurally characterized by single-crystal X-ray diffraction. Compositions Ca3Au7.16(6)Ge3.84(6) (1) and Ca3Au7.43(9)Ge3.57(9) (2) lie within a non-centric Imm2 phase region with a approximate to 4.40 angstrom, approximate to 13.06 angstrom, c approximate to 9.60 angstrom. The Au-richer and electron-poorer Ca3Au7.50(1)Ge3.50(1) (3). and Ca3Au8.01(1)Ge2.99(1) (4) occur within a centric Pnnm phase region with a approximate to 9.50 angstrom, b approximate to 13.20 angstrom, c approximate to 4.43 angstrom. Both phases contain complex [Au,Ge],(6-)(11) polyanionic networks made up of hexagonal and pentagonal prisms that are filled with the electropositive Ca atoms. Both 3:11 phases represent opposed 1 x 3 x 1 superstructure distortions of CaAu2Ge2 (ThCr2Si2 type, 14/mmm), the structure of which has also been re-determined in this work. Linear muff in-tin-orbital (LMTO) calculations reveal that the symmetry variations induced by changes of the Au contents in the present 3:11 phases are consequences of bonding and structural optimizations. The hypothetical "CaAu2.33-2.67Ge1.33-1.00 square(0.33)" compositions, which are close to those of 1-4, follow through creation and elimination of vacancies within the electronegative networks of CaAu2Ge2.

URL<Go to ISI>://000266809200042
DOI10.1021/Ic900383d