Prepd by the action of ammonia on an ether soln of magnesium diethyl or on magnesium activated with iodine (at 400°): Terentiew, Z. Anorg. Chem. 162, 351 (1927); Schlenk, Jr., Ber. 64, 738 (1931). Prepd from metal and liquid ammonia at high pressure: Juza, Jacobs, Angew. Chem. Int. Ed. 5, 247 (1966); eidem, Z. Anorg. Allg. Chem. 370, 245 (1969).