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Mixed Tristannides of the Series CaSn 3 – SrSn 3 – BaSn 3 : Synthesis, Crystal Structure, Chemical Bonding
Author(s) -
Wendorff Marco,
Röhr Caroline
Publication year - 2011
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201100012
Subject(s) - crystallography , stacking , octahedron , materials science , crystal structure , strontium , barium , type (biology) , tin , ternary operation , space group , x ray crystallography , diffraction , chemistry , physics , metallurgy , geology , computer science , programming language , paleontology , organic chemistry , optics
Ternary mixed Ca/Sr/Ba tristannides of overall composition A Sn 3 ( A = Ca, Sr, Ba) were synthesized from mixtures of the elements. The structures of the compounds were determined by means of single‐crystal X‐ray data or Rietveld powder refinements. All structures exhibit close packed ordered A Sn 3 layers containing Sn Kagomé nets, which are stacked in different orientations. Depending on the stacking sequences, the resulting tin polyanion resembles the oxygen nets of the cubic (corner sharing octahedra, c stacking, Cu 3 Au‐type structure, i.e. CaSn 3 ) or of the hexagonal perovskites (face sharing octahedra, h stacking, Ni 3 Sn‐type structure, i.e. BaSn 3 ). In the binary compound CaSn 3 (Cu 3 Au‐type) up to 46(5) % of calcium can be substituted against strontium (cubic, space group Pm $\bar{3}$ m , a = 479.75(3), Z = 1, R P = 0.0587, R Bragg = 0.0343). The known binary phase SrSn 3 forms the Mg 3 In structure type with a ( hhcc ) 3 stacking sequence and exhibits no noticeable phase width. A small partial substitution of strontium, against barium (Sr 0.91(2) Ba 0.09(2) Sn 3 to Sr 0.81(2) Ba 0.19(2) Sn 3 : trigonal, space group R $\bar{3}$ m , a = 698.9(2)/701.21(14), c = 2472.4(10)/2465.0(7) pm, Z = 9, R 1 = 0.0637/0.0738) causes the packing to switch to the ( hhc ) 3 stacking of the TaCo 3 ‐type structure. At a Ba proportion of 26(2) % (Sr 0.74(2) Ba 0.26(2) Sn 3 : hexagonal, space group P 6 3 / mmc , a = 704.21(12), c = 2197.6(5) pm, Z = 8, R 1 = 0.0705) a further structure change to the BaSn 2.57 Bi 0.43 structure type (( hhhc ) 2 ‐stacking) occurs. The series is terminated with the pure h stacking of BaSn 3 , the stability range of which starts at the composition Sr 0.22(2) Ba 0.78(2) Sn 3 (hexagonal, space group P 6 3 / mmc ; a = 717.92(12), c = 548.15(10) pm, Z = 2, R 1 = 0.0297). As easily noted from this series, the stacking sequence depends on the ratio of the atomic radii of the contributing atoms/ions. The observed trend can be rationalized by the decreasing coordination number of tin when going from c to h stacking. Covalent as well as metallic aspects of the chemical bonding in the tristannides are discussed on the basis of the results of FP‐LAPW calculations (density of states, band structure and valence electron densities).