Darstellung und Kristallstruktur von Na4GeSe4: Ein neues ortho-Selenogermanat(IV)

Abstract

Abstract Na4GeSe4 was obtained from a stoichiometric melt of Na2Se, Ge and Se at 750 °C. It crystallizes with a new orthorhombic structure, space group Pnma, with a = 28.518(8), b - 9.447(5), c = 7.128(2) Å , Z = 8. The crystal structure was refined to a conventional R of 0.074 for 1236 reflections with I > 3 σ (I) (diffractometer data). It is characterized by discrete GeSe4 4--anions with almost regular tetrahedral geometry. Two independent anions appear in the structure, the mean Ge - Se-bond lengths are 2.345 and 2.353 Å, resp. The Na+-ions are coordinated to 4 -6 chalcogen atoms in the range 2.88-3.28 Å. The structure is composed of mixed cation-anion-slabs, 2 ∞ [Na2(GeSe4)2-], which run parallel to the bc-plane and are separated from each other by corrugated 36-layers of Na+-ions.