Alkaline-Earth Metal Mercury Intermetallics A11−xHg54+x (A = Ca, Sr)

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• 作者：Andriy V. Tkachuk ; Arthur Mar
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：February 18, 2008
• 年：2008
• 卷：47
• 期：4
• 页码：1313 - 1318
• 全文大小：1923K
• 年卷期：v.47,no.4(February 18, 2008)
• ISSN：1520-510X

文摘

Re-examination of the mercury-rich regions of the Ca−Hg and Sr−Hg phase diagrams has shown that the phases previously identified as “AHg_3.6” should be reformulated as A_11−xHg_54+x (A = Ca, Sr). The crystal structures for representative members of these A_11−xHg_54+x phases were determined from single-crystal X-ray diffraction data (Pearson symbol hP65, space group P6̅; a = 13.389(1) Å, c = 9.615(1) Å for Ca_10.92(2)Hg_54.08 (x = 0.08(2)); a = 13.602(2) Å, c = 9.818(1) Å for Sr_10.48(4)Hg_54.52 (x = 0.52(4))) and confirmed by powder Rietveld refinements (R_B = 0.020 for Ca_10.7(2)Hg_54.3 and 0.014 for Sr_10.7(3)Hg_54.3). Diverse coordination polyhedra surround the A (CN14–16, multiply capped pentagonal or hexagonal prisms as well as Friauf polyhedra) and Hg atoms (CN11–13, pentacapped trigonal prisms and icosahedra). Partial disorder of Hg into one of the A sites accounts for the nonstoichiometry in the A_11−xHg_54+x phases. If this disordered A site is completely occupied by Hg atoms, the composition is constrained to a maximum of x = 2 in A_11−xHg_54+x, corresponding to a small homogeneity range of “A_{0.14–0.17}Hg_{0.86–0.83}”; the true homogeneity range is likely narrower. The structure can be regarded as being built up from a stacking of triangular nets with hexagonal voids that are filled with single atoms or various clusters. In particular, the presence of triangular Hg₃ clusters in ordered orientations distinguishes this structure from that of the related Gd₁₄Ag₅₁-type structure, in which triangular Ag₃ clusters are in disordered orientations. Band structure calculations reveal a small degree of electron transfer from the A to Hg atoms, supporting the presence of a partially anionic mercuride substructure.