New Sr compounds with planar Al-Si/Ge anions and a correction of SrSi-II and SrGe0.76

作者：Eisenmann Brigitte; Rhode Michael; Wendorff Marco; Roehr Caroline

来源：Zeitschrift fur Anorganische und Allgemeine Chemie, 2008, 634(1): 153-165.

DOI：10.1002/zaac.200700347

• germanides
• silicides zintl phases
• crystal structure
• band structure calculation

Planar anions with considerable p(pi)-p(pi) 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: P (6) over bar m2, 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, A1B(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)(infinity)[Al2/2M2Al2/2] of condensed six-membered rings in the known intermetallics Sr3Al2M2IV (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 [OSr6] octahedra, chains of which (connected via common corners) exactly fit the distance between the planar anions. The structures of the two compounds Sr-10[Al4M6IV][O] (M-IV=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 Sr-13[Al6Si8][O] (C2/m, a=2245.1(4), b=482.76(5), c=1720.6(5) pm, beta=125.21(2)degrees, Z =2, R1=0.0579) and the germanide Sr-16[Al8Ge10][O] (C2/m, a=2287.23(14), b=484.94(3), c=2065.70(13) pm, beta=120.150(4)degrees, 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 - Sr-16[Al8M10][O] Sr-13[Al6M8][O] - Sr-10[Al4M6][O].

• 出版日期2008