EU7Ga6Sb8:: A Zintl phase with Ga-Ga bonds and polymeric gallium antimonide chains

The Zintl phase Eu7Ga6Sb8 was obtained from a direct element combination reaction at 900degreesC. It crystallizes in the orthorhombic space group Pbca (No. 61) with a = 15.6470(17) Angstrom, b = 17.2876(19) Angstrom, c = 17.9200(19) Angstrom, and Z = 8. In Eu7Ga6Sb8, the anionic framework forms infinite chains of [Ga6Sb8](14-) which are arranged side by side to make a sheet-like arrangement but without linking. The sheets of chains are separated by Eu2+ atoms and also within the sheet, Eu2+ atoms fill the spaces between two chains. The chain is made up of homoatomic tetramers (Ga-4)(6+) and dimers (Ga-2)(4+) connected by Sb atoms. The compound is a narrow band-gap semiconductor with E-g similar to 0.6 eV and satisfies the classical Zintl concept. Extended Huckel band structure calculations confirm that the material is a semiconductor and suggest that the structure is stabilized by strong Ga-Ga covalent bonding interactions. Magnetic susceptibility measurements for Eu7Ga6Sb8 show that the Eu atoms are divalent and the compound has an antiferromagnetic transition at 9 K. (C) 2004 Elsevier Inc. All rights reserved.