assumed a fast intermolecular proton exchange between the two phosphoryl oxygen atoms of the phosphazene forni of tetraalkyl imidodiphosphates on the basis of chemi-8. KULPE et al.

M r = 353.9, monoclinic, P 2Jc, a = 11.248(2), b = 11.323(2), c = 14.845(4) A, / 3 = = 95.87 (2)

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AbstraetThe crystal structure of C72H60NaOtaP6Yb has been determined by single-crystal X-ray diffraction techniques. The crystals are monoclinic, space group P2~/c, with cell constants a = 18.627 (6), b --15.761 (8), c = 26.553 (10)/i,, fl = 113.76 (2) °, V= 7135 (5)/1,3, Z = 4, D e = 1.50 Mg m -3. The structure was solved by Fourier and direct methods and refined by full-matrix least squares to an R factor of 0.051 for 7443 reflections including those below background. The structure consists of discrete Yb{N[PO(OC6Hs)2]2} 3 molecules. The Yb atom is six coordinated. The low coordination number is due to the bulky ligands. The six O atoms of the three bidentate chelate rings form the coordination environment of the Yb 3+ ion. The coordination polyhedron has virtual D a symmetry, more in the direction of a distorted octahedron than in the direction of a trigonal prism. The intrachelate O-O separation is 2.883/k and the interchelate separation is 3.07-3.39/k. The Yb atoms lie almost on a superposition lattice which has a quarter of the volume of the unit cell.