Darstellung und Kristallstruktur von NaCu3Te2/ Preparation and Crystal Structure of NaCu3Te2

Abstract

Abstract The title compound was prepared by reacting a corresponding mixture of Na2Te2 , copper and tellurium at 700 °C. NaCu3Te2 forms crystals of metallic lustre which are rapidly decomposed in humid atmosphere. It crystallizes with a rhombohedral structure, space group R3m, with a = 4.276(3) Å, c = 23.78(1) Å, Z = 3. The crystal structure was determined from diffractometer data and refined to a conventional R of 0.050 for 135 independent reflections. The atomic arrangement of NaCu3Te2 is based on a c.c.p. array of tellurium atoms with stacking sequence c6 . Na and Cu occupy alternatingly the interstitial layers. Na is in an octahedral coordination (d̄Na-Te : 3.22 Å), the Cu atoms occupy the tetrahedral and the octahedral voids. They are, however, shifted from the centers of these sites, resulting in an 1 + 3 coordination (d̄Cu-Te : 2.70 Å) for Cu on the tetrahedral. and an essentially trigonal coordination (dCu-Te : 2.575 Å) for Cu on the octahedral sites. NaCu3Te2 shows no closer structural relationships to the other alkali-copper-chalcogenides known so far. However, its crystal structure may be interpreted as an ordered defect derivative structure of the CaCu4P2 -type [1].