The first metal-rich binary chalcogenides of the lanthanides: Dy2Te and Gd2Te

Two new tellurides have been synthesized in Ta with particular attention to the use of finely divided Dy (Gd) and a sequence of reactive sintering rea ctions of pressed pellets up to similar to 1060 degreesC. Both phases dispr oportionate to Ln and LnTe at only slightly higher temperatures so that are -melting procedures are relatively unproductive. The two compounds crystall ize with a Sc2Te-type structure. Single-crystal X-ray diffraction results f or Dy2Te were detailed in the orthorhombic space group Pnma (No. 62), Z = 1 2, a = 21.922(4) Angstrom, b = 4.0650(6) Angstrom, and c = 11.428(2) Angstr om (Guinier data). There is good evidence for the existence of additional m etal-rich binary chalcogenides of the heavy lanthanides. Extended Huckel ca lculations were performed within the tight binding approximation to aid the understanding of the metal-metal bonding in this system. In terms of metal -metal overlap populations, the isotypic Sc2Te is more 1D in aggregation, w hile the larger atoms and orbitals and stronger bonding in Dy2Te make it so mewhat more 3D, Electrical resistivity and magnetic susceptibility measurem ents on polycrystalline Dy2Te indicate it is metallic and ferromagnetic (T- c= 161.3 K) with an effective moment at higher temperatures close to that o f ground-state Dy3+. The connections between heavy lanthanide-rich chalcoge nide chemistry and that of the early transition metals seem significant.