Counterintuitive charge distribution in Ba8Si6Sn – A new tetralide Zintl phase containing -units

The mixed tetrel Zintl phase Ba8Si6Sn has been prepared and structurally characterized. The compound crystallizes in the orthorhombic space group Pbcn (No. 60). The lattice parameters are a = 8.7739(17) Å, b = 8.7599(17) Å and c = 27.162(5) Å. The compound consists of two different blocks of the composition Ba2Sn and a Ba 6 ( Si 3 6 - ) 2 , respectively. The Si 3 6 - -units are isolated three membered rings. By the Zintl–Klemm concept the triangles are best described as pseudo-sulfur units with two single bonds per atom. The tin atoms are isolated and have a formal charge of 4−. According to DFT calculations the phase is a semi conductor with a small band gap of 0.19 eV. Ba8Si6Sn is related to the double salt Ba4Si3Br2 = (Ba3Si3)(BaBr)2.