Phosphonitrilic Compounds. IX.¹ the Crystal and Molecular Structure of Tris(2,2'-dioxybiphenyl)cyclotriphosphazene

The crystal structure of tris(2,2'-dioxybiphenyl)cyclotriphosphazene (II) has been determined by three-dimensional Patterson, Fourier, and difference syntheses, and refinement to an R index of 0.068 was accomplished by difference-Fourier and least-squares techniques. o The crystals are monoclinic with the space group C2/c, and with a = 15.377 (2), b = 10.810 (1), c = 20.152 (7) Å, β = 108.88 (0.02)°, Z = 4. The cyclotriphosphazene ring has a slight boat conformation. Two of the biphenyldioxyphosphole units are twisted propellor-like at 43° in one direction while the third is twisted at 52° in the opposite direction. The P-N bond distances are 1.568 (7), 1.582 (6), and 1.566 (4) Å the N-P-N angles are 118.6 (0.3) and 118.3 (0.2)°; the P-N-P angles are 120.8 (0.3) and 121.2 (0.2)°; and the O-P-O angles are 103.0 (0.2) and 102.4 (0.3)°. The asymmetry of twist of the side group units is discussed and reasons are suggested for the failure of this compound to polymerize or form molecular inclusion adducts.