Strontium-Metallide im Bereich des Schnitts SrIn4 – SrHg4 / Strontium Metallides along the Section SrIn4 – SrHg4

Abstract

In a combined synthetic, X-ray single-crystal and bond-theoretical study the phase widths of SrIn4 and the related Sr3In11 upon a sucessive substitution of indium against the more electronpoor, more electronegative and only slightly smaller element mercury have been studied. Along the 1 : 4 section Sr(In1-xHgx)4 the monoclinic structure of SrIn4 ( EuIn4-type structure) is stable up to x =0.14(1) ( SrIn3.44Hg0.56: monoclinic, C2/m, a = 1208.3(6), b = 502:5(2), c = 997.7(6) pm, b = 115.16(3)°, Z = 4, R1 = 0.0324). Further increased mercury content results in a distinct stability region of the very common BaAl4 structure type (tetragonal, I4=mmm, Z = 2), which starts at x =0.241(7) ( SrIn3.04Hg0.96: a = 4694(2), c = 1246.4(7) pm, R1 = 0.0374) and reaches up to the fully ordered compound SrIn2Hg2 (x =0.5: a = 456.4(3), c = 1273.5(11) pm, R1 = 0.0572). Unexpectedly, in the small composition range from x=0.68(1) to 0.758(6) ( SrIn1.16Hg2.84: a=1178.5(4), b = 495.20(12), c = 1016.8(4) pm, b = 119.67(2)°, R1 = 0.0542; SrIn0.97Hg3.03: a = 1167.30(4), b = 495.32(2), c = 1018.50(3) pm, b = 119.657(2)°, R1 = 0.0426) the EuIn4 structure type exhibits a further small stability range. The structures of the two slightly different In- and Hg-rich variants of the EuIn4 type are described and compared, indicating the similarities to the KHg2 (layers of folded In=Hg ladders) and the BaAl4 structure type (flat square pyramids) as well as to the structure of elemental mercury (rhombohedra). From samples of an intermediate In=Hg ratio (e. g. x =0.55), the new 1 : 3 compound SrIn1.2Hg1.8 (monoclinic, C2=m, a = 1168.5(13), b = 497.0(4), c = 1471(2) pm, b = 92.07(10)°, Z = 8, R1 = 0.0818) is formed. It crystallizes in a new structure type, which - according to the compound’s composition - can be described as a stacking variant of the EuIn4 and the KHg2 structure type. In contrast to the wide stability ranges of the 1 : 4 compounds, only a very small substitution of In ranging up to only 6% of Hg is possible in the binary indide Sr3In11 ( Sr3In10.32(8)Hg0.68(8): La3Al11 structure type, orthorhombic, Immm, a = 487:6(2), b = 1140.2(5), c = 1421.1(7) pm, Z = 2, R1 = 0.0703). The formation, stability ranges and the In=Hg ‘coloring’ of the polyanions are discussed for all compounds taking into account geometric (radius ratios, molar volumes, Sr coordination polyhedra etc.) and electronic aspects, which have been evaluated using FP-LAPW band structure calculations.