PREPARATION AND CRYSTAL-STRUCTURE OF THE ALKALINE-EARTH PNICTIDE OXIDES SR4P2O, SR4AS2O, BA4P2O, AND BA4AS2O

Sr4P2O (light-brown), Sr4As2O (red-brown), Ba4As2O (grey-black), and Ba4P2O (grey-black) were prepared by the reaction of the metals, red phosphorus (arsenic), and metal oxide in molar ratios 3:2:1 in corundum crucibles sealed in quartz ampoules under argon (3 d 630-degrees-C, 2 d 1000-degrees-C, 2 d 1100-degrees-C). The compounds are microcrystalline, easily hydrolysable powders. Black single crystals of Ba4As2O and Ba4P2O were obtained by annealing specimens in molybdenum ampoules under argon (3 d 1200 and 1300-degrees-C resp.). Sr4P2O, Sr4As2O, and Ba4As2O crystallize in the K2NiF4-type structure; Ba4P2O is rhombically distorted and possess the La2CuO4-type structure (Crystallographic data: see "Inhaltsubersicht"). The influence of the size of the pnictide ion (Pn = P to Bi) on crystal chemical properties of the compounds M4Pn2O with the same cation is discussed.