Neue Sr-Verbindungen mit planaren Al-Si/Ge-Anionen und eine Korrektur zu SrSi-II und SrGe0.76

Autor: Caroline Röhr, Michael Rhode, Marco Wendorff, Brigitte Eisenmann
Rok vydání: 2008
Předmět:
Zdroj: Zeitschrift für anorganische und allgemeine Chemie. 634:153-165
ISSN: 1521-3749
0044-2313
DOI: 10.1002/zaac.200700347
Popis: New Sr Compounds with Planar Al-Si/Ge Anions and a Correction of SrSi-II and SrGe0.76 Planar anions with considerable pπ-pπ interactions between heavier group 13 and 14 elements are observed in several alkaline earth trielides and tetrelides. In the intermetallics of the series SrAlxGe2−x (border phases: x = 1: , a = 429.4(3), c = 474.4(3) pm, Z = 1, R1 = 0.0305, SrPtSb type and x = 1.6: P6/mmm, a = 440.4(2), c = 478.2(2) pm, Z = 1, R1 = 0.0125, AlB2 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 of condensed six-membered rings in the known intermetallics (MIV = 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 [OSr6] octahedra, chains of which (connected via common corners) exactly fit the distance between the planar anions. The structures of the two compounds (MIV = Si, Ge; formerly erroneously reported as SrSi and SrGe0.76, 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, R1 = 0.0369/0.0316) contain isolated planar anions [M2Al2M2Al2M2]18− with only one six-membered ring. In the monoclinic structures of the silicide Sr13[Al6Si8][O] (C2/m, a = 2245.1(4), b = 482.76(5), c = 1720.6(5) pm, β=125.21(2)°, Z = 2, R1 = 0.0579) and the germanide Sr16[Al8Ge10][O] (C2/m, a = 2287.23(14), b = 484.94(3), c = 2065.70(13) pm, β=120.150(4)°, Z = 2, R1 = 0.0730) anions [Si2Al2Si2Al2Si2Al2Si2] and [Ge2M2Ge2M2Ge2M2Ge2M2Ge2] with two and three six-membered rings are left as fragments of the ribbons in Sr3Al2M2. 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 SrAlM – Sr3Al2M2 – Sr16[Al8M10][O] – Sr13[Al6M8][O] – Sr10[Al4M6][O].
Databáze: OpenAIRE
Externí odkaz: