Crystal data of tris(2-cyanoethyl)phosphine oxide, tris(2-cyanoethyl)phosphine sulphide and tris(2-cyanoethyl)phosphine selenide

Tris(2-cyanoethyl)phosphine oxide, OP(C₂H₄CN)₃, C₉H₁₂N₃OP, is hexagonal (rhombohedral), space group R3c, with a = 13.484 (1) and c = 10.162 (1) Å. The sulphide and selenide are triclinic, space group P. Cell dimensions for SP(C₂H₄CN)₃, C₉H₁₂N₃PS, are a = 8.363 (8), b = 9.026 (4), c = 9.777 (6) Å; α = 98.75 (4), β = 107.31 (5), γ = 115.85 (5), and for SeP(C₂H₄CN)₃, C₉H₁₂N₃PSe, a = 8.497 (5), b = 9.148 (2), c = 9.972 (8) Å; α = 98.85 (2), β = 107.20 (6), γ = 116.96 (3)°. X-ray powder diffraction data are quoted.