Novel Arachno-type X56– Zintl Anions in Sr3Sn5, Ba3Sn5, and Ba3Pb5 and Charge Influence on Zintl Clusters

Abstract

Two new binary Zintl phases, Sr 3 Sn 5 and Ba 3 Sn 5 were synthesized and structurally characterized. The revised structure of Ba 3 Pb 5 is also reported. All three compounds are isotypic and crystallize with a modified Pu 3 Pd 5 structure type. The anionic substructure is composed of X 5 6± square pyramidal clusters (X = Sn, Pb), which are described as arachno clusters according to the Wade-Mingos electron counting rules. The electronic structure of the pyramidal Zintl anions and the influence of the number of skeletal electrons of these clusters are investigated using the electron localization function (ELF). The structural relationship between Ba 3 Sn 5 and the Zintl phases Ba 3 Si 4 and Ba 3 Ge 4 are analyzed. Additionally, two new Zintl phases Ba 3 Ge 2.82 Sn 2.18 and Ba 3 Ge 3.94 Sn 0.06 , have been synthezised and their structures are reported, which directly show that the exchange of tin against germanium leads to a change from the M 3 X 5 to the M 3 X 4 structure type. This effect is traced back to the maximal charge acquisition property of the Zintl anions of heavier and lighter tetralides.Neue Zintl-Anionen vom arachno-Typ im Sr 3 Sn 5 , Ba 3 Sn 5 und Ba 3 Pb 5 sowie der Ladungseinfluû auf die Zintl-Cluster Inhaltsu È bersicht. Sr 3 Sn 5 , Ba 3 Sn 5 und Ba 3 Pb 5 wurden durch Feststoffsynthese erhalten und strukturell charakterisiert. Die bisher bekannte Struktur von Ba 3 Pb 5 wurde korrigiert. Alle drei Verbindungen sind demnach isotyp und geho È ren einem modifizierten Pu 3 Pd 5 an und enthalten die quadratisch-pyramidalen Zintl-Anionen X 5 6± (X = Sn, Pb). Diese erfu È llen die Elektronenabza È hlregeln von Wade und Mingos fu È r arachno-Cluster. Mit Hilfe der Elektronenlokalisierungsfunktion (ELF) wird die ra È umliche Elektronenstruktur verdeutlicht und ihre Abha È ngigkeit von der Valenzelektronen-zahl untersucht. Die engen strukurellen Beziehungen zwischen Ba 3 Sn 5 , Ba 3 Si 4 und Ba 3 Ge 4 werden aufgezeigt. Des weiteren wird u È ber zwei neue Zintl-Phasen, Ba 3 Ge 2.82 Sn 2.18 und Ba 3 Ge 3.94 Sn 0.06 , berichtet, bei denen der Ûbergang vom M 3 X 5 -in den M 3 X 4 -Typ durch Austausch von Zinn gegen Germanium gezeigt werden kann. Dieser Wechsel wird nicht auf Gro È ûeneffekte sondern auf die maximale Ladungsaufnahmefa È higkeit der Zintl-Anionen der schwereren und der leichteren Tetralide zuru È ckgefu È hrt. Fig. 5 Top: Bandstructure and DOS for Ba 3 Sn 5 calculated using EHMO (left) and LMTO (right) methods. Bottom: Bandstructure and DOS for Sr 3 Sn 5 calculated using EHMO (left) and LMTO (right) methods.

Crystal structure of a new UGa2 phase

“…The stabilization of an orthorhombic UGa 2 metastable phase, probably formed due to kinetic or nucleation reasons, also points to the existence of a range of solubility with the Pu 3 Pd 5 structure type in the uranium-gallium binary system. Several Zintl phases have been previously described as adopting the Pu 3 Pd 5 structure type [15,16]. In the case of UGa 2 it is improbable that it belongs to this family of compounds if it is confirmed that a broad range of homogeneity adopting this Pu 3 Pd 5 structure type exists in the U-Ga system.…”

The phase diagram of the Sr–Sn system

“…The structure solution procedures and the subsequent refinement cycles were performed by means of the SHELXS-97 [9] and the SHELXL-97 [10] programs, respectively. .0446 (1) .0119 (6) .0208 (6) .0179 (5) −.0024 (4) .0168 (3) Sn2 4c 0 .5901 (1) 1/4 .0171 (9) .0195 (8) .0153 (6) 0 .0173 (4) Sn3 4a 0 0 0 .0124 (9) .0232 (9) .0250 (7) .0045 (6) .0202 (4) Metallographic examination was almost impossible so only few tin-richest alloys could be observed.…”

“…Five intermediate phases, that is Sr 2 Sn, Sr 5 Sn 3 , SrSn, SrSn 3 , and SrSn 4 , are reported in the diagram, of which only the first three fully characterized. More recent works, mainly of crystallographic type, concerned the following compounds: SrSn 3 , reported as a new trigonal type [5], Sr 3 Sn 5 , crystallizing with a modified Pu 3 Pd 5 -type [6] and the very newly determined SrSn 4 phase [7]. However, some questions like the presumed polymorphism of SrSn and Sr 2 Sn and some aspects of the thermal behaviour of SrSn 3 and SrSn 4 needed to be clarified.…”

Indium Doping in BaSn3–x Inx (0 ≤ x ≤ 0.2) with Ni3Sn Structure

“…Given the large excess of In employed in the synthesis, we can speculate that the homogeneity range of this phase is rather small, and that the discussed composition represents the maximum solubility range under these conditions, i.e., BaSn 3-x [19].…”