The first metal-rich binary chalcogenides of the lanthanides: Dy(2)Te and Gd(2)Te

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 reactions of pressed pellets up to approximately 1060 degrees C. Both phases disproportionate to Ln and LnTe at only slightly higher temperatures so that arc-melting procedures are relatively unproductive. The two compounds crystallize with a Sc(2)Te-type structure. Single-crystal X-ray diffraction results for Dy(2)Te were detailed in the orthorhombic space group Pnma (No. 62), Z =12, a = 21.922(4) A, b = 4.0650(6) A, and c = 11.428(2) A (Guinier data). There is good evidence for the existence of additional metal-rich binary chalcogenides of the heavy lanthanides. Extended Hückel calculations 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 Sc(2)Te is more 1D in aggregation, while the larger atoms and orbitals and stronger bonding in Dy(2)Te make it somewhat more 3D. Electrical resistivity and magnetic susceptibility measurements on polycrystalline Dy(2)Te indicate it is metallic and ferromagnetic (T(c)= 161.3 K) with an effective moment at higher temperatures close to that of ground-state Dy(3+). The connections between heavy lanthanide-rich chalcogenide chemistry and that of the early transition metals seem significant.