Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 35 [1]

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 35. Eu₃P₄, Sr₃P₄, and Ba₃P₄. Polyphosphides with P₄^6? Chains in a α-ThSi₂ Type Defect Structure Eu₃P₄, Sr₃P₄, and Ba₃P₄ are formed by direct synthesis from the respective elements and by thermal decomposition of the diphosphides. The black, brittle compounds are very sensitive to hydrolysis. According to single crystal studies, the compounds have the Sr₃As₄ structure (space group Fdd2) with P₄^6?-chains. It is shown, that this structure type is a defect α-ThSi₂ structure. The central P—P-bonds are essentially longer than the peripheral bonds (232 pm vs. 223 pm, respectively). The bond angles and torsion angles are influenced by the trigonal-prismatic arrangement of the metal atoms. Eu₃P₄ is paramagnetic with μ = 7.78 B. M. per Eu and orders ferromagnetically at 19 K. Sr₃P₄ and Ba₃P₄ substitute the former incorrect identified phosphides M₄P₅. — The lattice constants of the isotypic arsenides Eu₃As₄, Sr₃As₄, and Ba₃As₄ were redetermined.