Dipotassium Sodium Diantimonidoindate,K2Na[InSb2], a compound with the polyanion [In2Sb2Sb4/2]6−

The novel compound K₂NaInSb₂] was synthesized from the elements at 900 K in sealed niobium ampoules. The compound forms plate-like crystals with silver metallic luster, which are very unstable in air and moisture. The crystal structure of K₂NaInSb₂ has been determined using single-crystal X-ray diffraction methods (space group Cmca (No. 64); a = 14.032(2), b = 16.399(3), c = 7.009(1) Å; Z = 8; Pearson symbol oC48). The structure contains pairs of edge-sharing InSb₄ tetrahedra which are linked to four other pairs via common vertices and form a two-dimensional In₂Sb₂Sb_4/2]^6? anionic partial structure. The resulting pairs of tetrahedral holes are filled by Na⁺ cations. These In₂Sb₂Sb_4/2]^6? layers are stacked along the b-axis and are interconnected by K⁺ cations. The whole structure can be considered as an ordered derivative of the KMnP structure (PbFCl type).