Aluminum Germanides of the Divalent Lanthanoides Eu and Yb: Synthesis, Structural Chemistry and Chemical Bonding

作者：Bauer Britta; Roehr Caroline

来源：Zeitschrift fur Naturforschung Section B-A Journal of Chemical Sciences, 2011, 66(8): 793-812.

• Aluminum
• Ytterbium
• Europium
• Germanides
• Crystal Structure
• Band Structure Calculation

In the course of attempts to substitute Ca by Yb and Sr by Eu in known alkaline earth Al-germanides, the four new ternary compounds Eu(3)Al(1.8)Ge(2.2), Eu(3)Al(2)Ge(4), Yb(2)AlGe(3), and Yb(17)Al(8)Ge(19) have been synthesized from mixtures of the elements and their crystal structures determined by means of single-crystal X-ray data. The two europium compounds Eu(3)Al(1.8)Ge(2.2) (Ta(3)B(4) structure type, orthorhombic, space group Immm, a = 417.68(3), b = 470.70(3), c = 1897.2(2) pm, Z = 2, R1 = 0.0439) and Eu(3)Al(2)Ge(4) (Sr(3)Al(2)Ge(4) structure type, monoclinic, space group C2/m, a = 1235.9(6), b = 416.8(2), c = 878.4(4) pm, beta = 110.615(13)degrees, Z = 2, R1 = 0.0978) are isotypic with the corresponding strontium phases. After ionic decomposition, the layers [Al(2)(-)Ge(4)(-)](6-) in Eu(3)Al(2)Ge(4) with four-bonded Al and three-bonded Ge atoms can be interpreted as electron-precise Zintl anions. In contrast, the planar ribbons (1)(infinity) [Al(2/2)Ge(2)Al(2/2)] of condensed six-membered rings in Eu(3)Al(1.8)Ge(2.2) exhibit considerably shorter Al-Ge bonds and an Al-AI bond length of only 251 pm. Yb(2)AlGe(3) (orthorhombic, space group Pnma, a = 682.20(10), b = 417.87(9), c = 1813.9(3) pm. Z = 4, R1 = 0.0415) crystallizes with the Y(2)AlGe(3) structure type. Folded [Al(2)Ge(2)] ladders, also found in Eu(3)Al(2)Ge(4) and the known compound Yb(7)Al(5)Ge(8), are connected by planar cis/trans chains of Ge atoms. The total density of states calculated within the FP-LAPW DFT band structure approach shows a distinct minimum at the Fermi level for the electron precise Zintl compound Eu(3)Al(2)Ge(4), whereas g-bonding contributions are evident from the band structures of Eu(3)Al(2)Ge(2) and Yb(2)AlGe(3). In full accordance, the tDOS of both compounds exhibits no minimum at E(F), small phase widths are possible for Eu(3)Al(2)Ge(2) and related alkaline earth compounds, and Yb(2)AlGe(3) is isotypic with several other more electron-rich Ln(III) compounds. The complicated structure of the new compound Yb(17)Al(8)Ge(19) (tetragonal, space group P4/nmm, a = 1542.50(2), c = 788.285(8) pm, Z = 2, R1 = 0.0282) contains three different building blocks: distorted [Al(4)Ge(4)] heterocubane units are interconnected by four-bonded Ge atoms to form columns running along the c axis. Secondly, eight-membered rings are formed by alternating Al and Ge atoms, each being in a trigonal-planar Al/Ge coordination. The rings are terminated by Ge atoms (bonded to Ge of the ring) and linked to the first structural unit by a further Ge atom (bonded to Al of the ring). Thirdly, inside the large channels, which are formed by the packing of the eight-membered rings, Ge(2) dumbbells are interspersed as a third structural element.

• 出版日期2011-8