The crystal structure of sopcheite, Ag4Pd3Te4, from the Lukkulaisvaara intrusion, Karelia, Russia

Abstract

The crystal structure of sopcheite, Ag₄Pd₃Te₄, has been solved using single-crystal diffraction data for a crystal from the Lukkulaisvaara intrusion, Karelia. The crystal structure is orthorhombic, space group Cmca, a = 12.212(2)Å, b = 6.138(2)Å, c = 12.234(3)Å, V = 917.1(4)ų and Z = 4. The refinement of the fully anisotropic model led to an R index of 6.47% for 413 unique reflections. Sopcheite crystallizes in a layered structure. The Pd(1) and Pd(2) atoms assume a nearly planar coordination by four Te atoms. Each of the [PdTe₄] rectangles shares two opposite Te–Te edges with adjacent rectangles forming six-membered rings with the shape of elongated hexagons. These hexagons are oriented parallel to (1 0 0) and form layers of a herringbone pattern. Silver atoms form four-membered rings [Ag₄] of almost square shape. The [Ag₄] rings are located approximately in the centre of elongated hexagons composed of [PdTe₄] rectangles. The crystal structure is stabilised by a number of metal–metal interactions. The crystal structure of the synthetic phase Ag₄Pd₃Te₄ was also determined by single-crystal X-ray diffraction (XRD). It corresponds to the structure of sopcheite from the Lukkulaisvaara intrusion. Electron backscatter diffraction data obtained on material from other reported sopcheite occurrences are entirely consistent with this structure model, which is however incompatible with the sole powder XRD pattern reported so far for sopcheite. Combined with the absence of phase transition in Ag₄Pd₃Te₄ up to its breakdown temperature, these results imply revision of the previously published crystallographic data of sopcheite.