Preparation and crystal structure of Na4TiSe4. A selenotitanate with discrete tetrahedral anions

Red crystals of Na4TiSe4 were obtained by reacting an intimate mixture of N a2Se, Ti and Se at 750 degrees C. Na4TiSe4 is monoclinic, space group I2/a with a = 24.027(6), b = 7.346(4), c = 21.572(6) Angstrom, beta = 104.52(2)d egrees, Z = 16. Its crystal structure was determined from diffractometer da ta (AgK alpha-radiation) and refined to a conventional R of 0.036 for 2673 F-0's and 158 variables. The crystal structure is of a new type, characteri zed by the presence of discrete tetrahedral complex anions, [TiSe4](4-), wh ich are arranged in slabs parallel to (100). The average Ti-Se bond length is 2.385(1) Angstrom. The Na+ cations are in different chalcogen environmen ts with distorted octahedral, square pyramidal or planar configurations, re spectively.