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Neue Sr‐Verbindungen mit planaren Al‐Si/Ge‐Anionen und eine Korrektur zu SrSi‐II und SrGe 0.76
Author(s) -
Eisenmann Brigitte,
Rhode Michael,
Wendorff Marco,
Röhr Caroline
Publication year - 2008
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.200700347
Subject(s) - crystallography , octahedron , crystal structure , chemistry , metal , intermetallic , materials science , stereochemistry , organic chemistry , alloy
New Sr Compounds with Planar Al‐Si/Ge Anions and a Correction of SrSi‐II and SrGe 0.76 Planar anions with considerable p π ‐ p π interactions between heavier group 13 and 14 elements are observed in several alkaline earth trielides and tetrelides. In the intermetallics of the series SrAl x Ge 2−x (border phases: x = 1: $P{\bar 6}m\rm 2$ , a = 429.4(3), c = 474.4(3) pm, Z = 1, R 1 = 0.0305, SrPtSb type and x = 1.6: P 6/ mmm , a = 440.4(2), c = 478.2(2) pm, Z = 1, R 1 = 0.0125, AlB 2 type) graphite analogue planar Al/Ge nets with short Al‐Ge bonds are stacked in identical orientation, showing inter‐layer distances of approx. 475 pm. Starting from the related planar ribbons $^{1}_{\infty}{\rm [Al_{2/2}}M{\rm _{2}Al_{2/2}}]$ of condensed six‐membered rings in the known intermetallics ${\rm Sr_{3}Al_{2}}M{^{IV}_{2}}$ ( M IV = Si, Ge) a series of new metal‐rich oxides with chain pieces consisting of three, two and finally only one six‐membered ring have been prepared and characterized on the basis of single crystal X‐ray data. The formal fragmentation of the ribbons is achieved by the incorporation of [OSr 6 ] octahedra, chains of which (connected via common corners) exactly fit the distance between the planar anions. The structures of the two compounds ${\rm Sr_{10}[Al_{4}}M{^{IV}_{6}}][O]$ ( M IV = Si, Ge; formerly erroneously reported as SrSi and SrGe 0.76 , space group Immm , a = 482.48(5)/484.55(8), b = 1306.5(2)/1342.2(2), c = 1814.0(2)/1857.4(3) pm, Z = 2, R 1 = 0.0369/0.0316) contain isolated planar anions [ M 2 Al 2 M 2 Al 2 M 2 ] 18− with only one six‐membered ring. In the monoclinic structures of the silicide Sr 13 [Al 6 Si 8 ][O] ( C 2/ m , a = 2245.1(4), b = 482.76(5), c = 1720.6(5) pm, β=125.21(2)°, Z = 2, R 1 = 0.0579) and the germanide Sr 16 [Al 8 Ge 10 ][O] ( C 2/ m , a = 2287.23(14), b = 484.94(3), c = 2065.70(13) pm, β =120.150(4)°, Z = 2, R 1 = 0.0730) anions [Si 2 Al 2 Si 2 Al 2 Si 2 Al 2 Si 2 ] and [Ge 2 M 2 Ge 2 M 2 Ge 2 M 2 Ge 2 M 2 Ge 2 ] with two and three six‐membered rings are left as fragments of the ribbons in Sr 3 Al 2 M 2 . The puzzling bonding situation in these type of polar intermetallics at the Zintl border is calculated (using the DFT FP‐LAPW approach) for the structures with manageably small unit cells and discussed for the series SrAl M – Sr 3 Al 2 M 2 – Sr 16 [Al 8 M 10 ][O] – Sr 13 [Al 6 M 8 ][O] – Sr 10 [Al 4 M 6 ][O].