Synthesis, characterization and bonding of Ba3Li4Sn8

The ternary compound Ba3Li4Sn8 was obtained by slow cooling of a stoichiometric mixture of the elements that was heated at 800 degreesC for 2 days. Its structure (monoclinic, C2/m, Z=2, a=18.549(1), b=6.685(1), c=6.792(1) Angstrom, V=833.2(2) Angstrom(3), R-1/wR(2)=4.03/11.33%) contains one-dimensional chains of (1)(infinity)[Sn-8](10-) made of edge-sharing cyclodecane-like units in their `all-chair' conformations. The cations screen the chains from each other and provide the extra electrons needed for bonding in the chains. The structure and the electron count can be rationalized in terms of the Zintl concept as (Ba2+)(3)(Li+)(4)[(2b-Sn2-)(2)(3b-Sn1-)(6)], i.e. the compound is an electronically balanced, Zintl phase. Nevertheless, Ba3Li4Sn8 exhibits temperature-independent paramagnetism that is, most likely, of van Vleck type as a result of the very small band gap of about 0.3 eV. (C) 2002 Elsevier Science B.V. All rights reserved.