Pentacalciumhexaphosphahypodiphosphat,Ca5P8: Eine Verbindung mit isolierten Anionen P810− mit der gestaffelten Konformation von Ethan

Pentacalcium Hexaphosphahypodiphosphate, Ca₅P₈, a Compound with Isolated Anions P₈^10? in the Staggered Ethane Conformation Ca₅P₈ is prepared from calcium and red phosphorus in a molar ratio 5:8 in argon atmosphere in corundum crucibles inserted in quartz ampullae (3.5 d 1 000°C). It is a red-brown powder which is hydrolyzed by moisture. Single crystals are formed from powder at 1 100°C within 60 d. Ca₅P₈ crystallizes in a new structure type (mC26) with isolated anions P₈^10? in staggered conformation: C2/m (no. 12); a = 689.9(4) pm, b = 1 188,3(4) pm, c = 748.4(3) pm, β = 108.25(2)°, Z = 2; d = 2.56(1). Ca₅P₈ is the first compound containing polyphosphide anions with fourfold and single bonded phosphorus atoms (formally P⁺ and P^2?, resp.). The cations Ca²⁺ are arranged in a distorted cubic close-packing. The centers of the polyphosphide anions replace in an ordered way one third of Ca²⁺ in every second layer. The terminal P atoms occupy all octahedral interstices, so that P₈^10? is coordinated by 18 Ca²⁺ in form of a cuboctahedron with capped squaric faces.