Prepn: Rihl, Fricke, Z. Anorg. Allg. Chem. 251, 406 (1943); Leussing, Kolthoff, J. Am. Chem. Soc. 75, 2476 (1953). Oxidation products: Feitknecht, Keller, Z. Anorg. Chem. 262, 61 (1950); Mayne, J. Chem. Soc. 1953, 129; Shipko, Douglas, J. Phys. Chem. 60, 1519 (1956).