Prepd by passing dry ammonia over selenium tetrachloride: W"ohler, Bull. Soc. Chim. [1] 1, 25 (1859); by treating a dil soln of selenium oxychloride in benzene with dry ammonia and washing the precipitate with water and potassium cyanide: Lenher, Wolesensky, J. Am. Chem. Soc. 29, 215 (1907); by the action of dry ammonia on a dilute soln of selenium monochloride in carbon disulfide: van Valkenburg, Bailar, ibid. 47, 2134 (1925); by the action of dry ammonia on diethyl selenite or dimethyl selenite dissolved in benzene and washing with potassium cyanide: Strecker, Schwarzkopf, Z. Anorg. Chem. 221, 193 (1934); by reacting anhydr, liquid ammonia with selenium dioxide: Jander, Doetsch, Ber. 93, 561 (1960). Crystal structure: Baernighausen et al., Acta Crystallogr. 15, 615 (1962); 21, 571 (1966).