Synthesis, crystal structure and band structure of EU3Sn5 with arachno-type zintl anions

A new polar intermetallic compound, Eu3Sn5, has been synthesized by solid-state reaction of the corresponding pure elements in a stoichiometric ratio in a welded tantalum tube at high temperature. Its crystal structure was established by single-crystal X-ray diffraction. EU3Sn5 crystallizes in orthorhombic, space group Cmcm with a = 10.466(11), b = 8.445(8), c = 10.662(12) angstrom, V = 942.4(17) angstrom(3), Z = 4, M-r = 1049.33, D-c = 7.396 g/cm(3), mu = 32.578 mm(-1), F(000) = 1756, the final R = 0.0236 and wR = 0.0472 for 535 observed reflections with I > 2 sigma(I). Its structure belongs to the modified PU3Pd5 type. It is isostructural with Sr3Sn5 and Ba3Sn5, featuring [Sn-5] square pyramidal clusters described as "arachno" according to the Wade-Mingos electron counting rules. The europium. cations are located at the voids between the square pyramidal clusters. Results of the extended Huckel band structure calculations indicate that EU3Sn5 is metallic.