Na4SnSe4 und K4SnSe4, zwei neue Selenostannate mit isolierten Anionen / Na4SnSe4 and K4SnSe4, Two New Selenostannates with Discrete Anions

Transparent yellow single crystals of Na4SnSe4 and K4SnSe4 were prepared by reacting stoichiometric powdered mixtures of the binary compounds Na2Se or K2Se, Sn and Se at 850 K. Na4SnSe4 is tetragonal, s.g. P4̄21c, with a = 8.165(2) Å, c = 7.268(2) Å, Z = 2. K4SnSe4 is orthorhombic, s.g. Pnma, with a = 14.714(7) Å, b = 10.323(3) Å, c = 8.248(6) Å, Z = 4. The crystal structures were refined to conventional residuals of 0.058 and 0.031, respectively. Both com pounds are characterized as salts with discrete tetrahedral selenostannate anions. Na4SnSe4 is isostructural with Na4SnS4, K4SnSe4 is of a new type. The observed Sn -Se bond lengths range from 2.494 Å to 2.536 Å.