Structure of the polytypic β-form of P₃N₃(OCH₂CF₂CF₂CH₂O)F₄

Crystals of the β-form of the title compound, 1,1,3,3-tetrafluoro-5,5-(2,2,3,3-tetrafluorotetramethylenedioxy)cyclotri(phosphazene), are triclinic, P, with lattice constants a = 12.392 (2), b = 16.569 (3), c = 19.257 (4) Å, α = 110.22 (3), β = 90.02 (3), γ = 97.10 (3)° and V = 3677.9 (12) ų with Z = 12, to yield P_calc = 2.010 Mg m⁻³ for M_r = 371.0 and F(000) = 2184. The structural data was refined to R = 0.0548 and wR = 0.0567 for 5536 observed reflections [|F| ≥ 3σ(F)] with a goodness-of-fit of 1.61 and a maximum residual of 0.47 e Å⁻³. The six crystallographically independent molecules are all structurally equivalent, with approximately the same orientation for each molecule. The molecules are roughly arranged in layers lying parallel to the ac plane. Two types of these layers exist within the structure. Each layer exhibits approximate noncrystallographic symmetry elements. For layers at y ~ and , the appropriate layer-group symmetry notation is pc2a, while the layer at y ~ has idealized p2₁/c11 symmetry. The difference in the symmetries of the two types of layers arises from different sequencing of molecules with right- and left-handed chirality. Both layer groups require β to be equal to 90°, explaining its observed value. The structure can be described as a polytype structure, in which stacking faults occur every third layer. An ABAABA stacking pattern exists, where A corresponds to the layer at y = and while B corresponds to the layer at y = . In addition, successive layers are related by the following set of idealized translation vectors

Superimposed upon these translation vectors is modulation of the chirality of the molecules.

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