Synthese und Kristallstrukturen von α‐ und β ‐Ba 3 (PS 4 ) 2 sowie von Ba 3 (PSe 4 ) 2

Synthesis and Crystal Structures of α‐, β ‐Ba 3 (PS 4 ) 2 and Ba 3 (PSe 4 ) 2 Ba 3 (PS 4 ) 2 and Ba 3 (PSe 4 ) 2 were prepared by heating mixtures of the elements at 800 °C for 25 h. Both compounds were investigated by single crystal X‐ray methods. The thiophosphate is dimorphic and undergoes a displacive phase transition at about 75 °C. Both modifications crystallize in new structure types. In the room temperature phase (α‐Ba 3 (PS 4 ) 2 : P2 1 / a ; a = 11.649(3), b = 6.610(1), c = 17.299(2) Å, β = 90.26(3)°; Z = 4) three crystallographically independent Ba atoms are surrounded by ten sulfur atoms forming distorted polyhedra. The arrangement of the PS 4 tetrahedra, isolated from each other, is comparable with the formation of the SO 4 2− ions of β ‐K 2 SO 4 . In β ‐Ba 3 (PS 4 ) 2 ( C 2/ m ; a = 11.597(2), b = 6.727(1), c = 8.704(2) Å; β = 90.00(3)°; Z = 2) the PS 4 tetrahedra are no more tilted along [001], but oriented parallel to each other inducing less distorted tetrahedra and polyhedra around the Ba atoms, respectively. Ba 3 (PSe 4 ) 2 ( P 2 1 / a ; a = 12.282(2), b = 6.906(1), c = 18.061(4) Å; β = 90.23(3)°; Z = 4) is isotypic to α‐Ba 3 (PS 4 ) 2 and no phase transition could be detected up to about 550 °C.