The binary tin-rich lanthanum stannides La{sub 2}Sn{sub 5} and La{sub 3}Sn{sub 7}-A structural and bond theoretical study

Journal Article · Mon Aug 15 00:00:00 EDT 2011 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2011.06.035· OSTI ID:21580180

Duerr, Ines; Schwarz, Michael ^[1]; Roehr, Caroline ^[1]

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1. Institut fuer Anorganische und Analytische Chemie, University of Freiburg, Albertstr. 21, D-79104 Freiburg (Germany)

The three tin-rich lanthanum stannides LaSn{sub 3}, La{sub 2}Sn{sub 5} and La{sub 3}Sn{sub 7}, which were known only from indexed powder diagrams, have been synthesized from melts of the elements by slow cooling of sealed sample tubes or arc melting and quenching. Their crystal structures were refined from X-ray powder diffractometer data using the Rietveld method. LaSn{sub 3} (cubic, space group Pm3-bar m, a=477.77(1) pm, Z=1, R{sub F}{sup 2}=0.044) crystallizes with the common Cu{sub 3}Au structure type, which can be described either as an ordered close packing or as a network of [Sn{sub 6}] octahedra (closo clusters) connected via common vertices. The structures of La{sub 2}Sn{sub 5} (Ce{sub 2}Sn{sub 5} structure type, orthorhombic, space group Cmmm, a=463.85(3), b=3581.3(3), c=469.83(4) pm, Z=4, R{sub F}{sup 2}=0.075) and La{sub 3}Sn{sub 7} (Gd{sub 3}Sn{sub 7} structure type, orthorhombic, space group Cmmm, a=457.83(4), b=2628.40(2), c=467.99(4) pm, Z=2, R{sub F}{sup 2}=0.068), which retain some similarities to ordered close packings as well, show 2D blocks of corner-sharing [Sn{sub 6}] octahedra terminated by [Sn{sub 5}] square pyramids (nido clusters). In between these layers, isolated Sn zigzag chains similar to those observed in LaSn (CrB structure type) are interspersed. A simple v.e. count after Zintl and Wade/Jemmis for the polyanionic Sn building blocks resulting from these structure descriptions fits the observed v.e. numbers of the three compounds almost exactly. It is also possible to explain the minima of the tDOS close to E{sub F}, which have been calculated within the framework of the FP-LAPW DFT approach. However, the simple assumption of an exclusively Sn-p bonded polyanion would neglect the large Sn-La bonding contributions and the reduced amount of electron transfer from La to Sn when compared to related alkaline earth stannides. - Graphical Abstract: La{sub 2}Sn{sub 5} and La{sub 3}Sn{sub 7}, stacking variants of LaSn{sub 3} (Cu{sub 3}Au type, closo clusters) and LaSn (CrB type, zig-zag chains) Highlights: > Preparation of binary La stannides LaSn{sub 3}, La{sub 2}Sn{sub 5} and La{sub 3}Sn{sub 7}. > La{sub 2}Sn{sub 5} and La{sub 3}Sn{sub 7} do not appear in published phase diagrams. > Full pattern Rietveld refinements of the crystal structures of all compounds. > Revised description of the structure types emphasizes polyanionic Sn framework. > Structural motifs rationalized through DFT calculations and Zintl and Wade rules.

• OSTI ID: 21580180
• Journal Information: Journal of Solid State Chemistry, Vol. 184, Issue 8; Other Information: DOI: 10.1016/j.jssc.2011.06.035; PII: S0022-4596(11)00363-X; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHROMIUM BORIDES
ELECTRON TRANSFER
LANTHANUM
ORTHORHOMBIC LATTICES
PHASE DIAGRAMS
POWDERS
SPACE GROUPS
TIN
TIN COMPOUNDS
X RADIATION
BORIDES
BORON COMPOUNDS
CHROMIUM COMPOUNDS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIAGRAMS
ELECTROMAGNETIC RADIATION
ELEMENTS
INFORMATION
IONIZING RADIATIONS
METALS
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RARE EARTHS
SYMMETRY GROUPS
TRANSITION ELEMENT COMPOUNDS