Ein Erdalkalimetallpolyphosphid ungewöhnlicher Zusammensetzung: Die Kristallstruktur von Ba5P9

A Polyphosphide of Unusual Composition: The Crystal Structure of Ba₅P₉ The metallic grey compound Ba₅P₉ can be synthesised from the elements in stoichiometric amounts. It reacts easily with moist air. In the crystal structure (orthorhombic, Fdd2 , a = 1562.6(1) pm, b = 1896.8(2) pm, c = 1027.2(2) pm; Z = 8) anionic P₉ chain fragments are separated by Ba cations. With respect to the stoichiometry a charge of 10‐ results for the polyphosphide anion, but 11 electrons are needed following the (8‐N) rule. According to magnetic measurements the anionic unit is no radical, so a stabilisation by double bonds is discussed.