Zeolite-entrapped organized molecular assemblies. New evidence for highly efficient adjacent cage dyad formation and...

The primary objectives of the present work are to investigate the extent to which an entrapped, tris-ligated polypyridine complex of divalent ruthenium is restricted from rotating within the supercage of Y-zeolite and to provide additional evidence for the high efficiency of synthetic procedures developed for the preparation of adjacent cage dyads entrapped within the Y-zeolite framework. Specifically, the Y-zeolite entrapped complex, Z-[Ru(bpy)(2)(pypz)(2+) ] (where the prefix, Z, indicated a zeolite entrapped complex, bpy = 2,2'-bipyridine and pypz = 2-2-pyridylpyrazine), which contains only one reactive peripheral nitrogen atom, is shown to react with the reagent, (H(2)O)Ru(NH(3))(5)(2+), to yield the entrapped Z-[Ru(bpy)(2)(pypz)-Ru(NH(3))(5)](4+) complex. Treatment with a large excess of bpy, according to previously documented procedures, leads to the formation of the entrapped adjacent cage dyad, Z-[Ru(bpy)(2)(pypz)(2+)/Ru(bpy)(3)(2+)], wherein the two-component complexes are entrapped in adjacent supercages. Spectroscopic measurements confirm the integrity of the component complexes and document a strong interaction between them. Most importantly, it is shown that a second treatment of this material with a large excess of the[(H(2)O)Ru(NH(3))(5)](2+) reagent does not lead to formation of significant amounts of Z-[Ru(bpy)(2)(pypz)-Ru(NH(3))(5)](4+); i.e., the presence of the Ru(bpy)(3)(2+) in the cage adjacent to the primary complex shields the latter from further reaction with the ruthenium pentammine reagent. This result demonstrates that, during the formation of the Ru(bpy)(3)(2+) secondary complex, the detached Ru(NH(3))(5)(2+) fragment does not drift into remote supercages, thereby providing unequivocal evidence for the high efficiency of the synthetic procedure for adjacent cage dyad formation. Furthermore, this result also makes it clear that rotation of the tris-ligated primary complex is restricted by the confinement of the Y-zeolite supercage to the extent that the single reactive peripheral nitrogen cannot be repositioned to a different window of the surrounding supercage.