New members of the A(2)M ' M ''(2) structure family (A= Ca, Sr, Yb, La; M ' In, Sn,Pb; M '' = Si, Ge)

作者：Jehle Michael^*; Duerr Ines; Fink Saskia; Lang Britta; Langenmaier Michael; Steckhan Julia; Roehr Caroline

来源：Journal of Solid State Chemistry, 2015, 221: 351-363.

DOI：10.1016/j.jssc.2014.10.009

• Tetrelides
• Alkaline-earth
• Rare earth
• Crystal structure
• Band structure calculation

The new mixed tetrelides Sr2PbGe2 and Yb2SnGe2, several mixed Ca/Sr (A(II)) germanides AI(Sn,Pb)Ge-2 and two polymorphs of La2InSi2 represent new members of the general structure family of ternary alkaline-earth/lanthanoid main group silicides/germanides A(2)M'A/1 (M' = In, Sn, Pb; M" = Si, Ge). All compounds were synthesized from melts of the elements and their crystal structures have been determined by means of single crystal X-ray diffraction. Sr2PbGe2 (Cmmm, a=402.36(11), b =1542.3(4), c=463.27(10) pm) crystallizes with the Mn(2)AIB(2) type structure. In exhibiting infinite planar Ge zig-zag chains, it represents one border of the compound series. The other borderline case, where only [Ge-2 dumbbells are left as Ge building units, is represented by the Ca/Yb tin germanides Ca2SnGe2 and Yb2SnGe2 (MO2FeB2 type: P4Imbm, a=748.58(13)/740.27(7), c=445.59(8)/435.26(5) pm). In between these two border structures compounds with variable Si/Ge chain lengths could be obtained by varying the averaged size of the All cations: Ca0-45Sr1.55PbGe2 (new structure type; Pbam, a=791.64(5), b =2311.2 (2), c=458.53(3) pm) contains planar six-membered chain segments [Ge-6]. Tetrameric pieces [Ge-4 are the conspicuous structure elements in Ca1-16Sr0.84SnGe2 and La2InSi2 (La2InNi2 type; Pbam, a=781.011 (2)/762.01(13), b=1477.95(3)/1494.38(6), c=457.004(9)/442.1(3) pm). The tetragonal form of La2InSi'2 (exact composition: La2In1.07Si1o3, P-4/mbm, a=1309.11(12), c=443.32(4) pm) also crystallizes in a new structure type, containing only [Sid trimers as cutouts of the planar chains. In all structures the Si/Ge zigzag chains/chain segments are connected by In/Sn/Pb atoms to form planar M layers, which are separated by pure A layers. Band structure calculations within the FP-LAPW OFT approach together with the Zintl formalism, extended by the presence of hypervalent bonding of the heavier M' elements, give insight into the chemical bonding of this series of p-block metallides. An analysis of the band structure for the border phases Sr2PbGe2 and Ca2SnGe2 shows the considerable sr bonding contributions within the Ge building units, which also become apparent from the short Ge Ge bond lengths. C 2014 Elsevier Inc.

• 出版日期2015-1