Zinc, cadmium, and mercury complexes of a pyridyloxy-substituted cyclotriphosphazene: syntheses, structures, and fluxional behavior.

The synthesis and characterization of the fluxional, d10 cyclotriphosphazene complexes, [MLCl2] (M = Zn, Cd, and Hg; L = spiro-[(1,1′-biphenyl)-2,2′-dioxy]tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene), are described. Single-crystal X-ray structures show that the zinc complex has crystallized into two crystal forms: one as a tetrahedral species, with a N2Cl2 donor set in which a geminal pair of the pendant pyridyloxy nitrogen atoms binds to the zinc, and the other as a trigonal-bipyramidal (tbp) one, with an N3Cl2 donor set. The third nitrogen atom comes from the phosphazene ring and the two pyridyl ligands are non-geminal. The asymmetric unit of the cadmium complex contains three structurally distinct molecules. One molecule has a tbp structure similar to that of the zinc complex. The second molecule has a six-coordinate, distorted octahedral geometry around the cadmium center with a N4Cl2 donor set, with three of the nitrogen donor atoms coming from the pendant pyridyloxy arms. The third site conta...