An Inclusion Complex of Hexamolybdate inside a Supramolecular Cage and Its Structural Conversion

A self-assembled cage compound consisting of four concave
ligands
and two square-planar-coordinated PdII ions was found to
quantitatively encapsulate a hexamolybdate dianion [Mo6O19]2– in solution. The addition of
1 equiv more of [Mo6O19]2– to the inclusion complex resulted in the formation of a precipitate
from which single crystals were grown. X-ray analysis showed that
a structural conversion had taken place upon crystallization: one
hexamolybdate anion was found to be wrapped in a chiral, cyclic arrangement
of three ligands in the absence of any PdII ions to give
a compound of the formula {[Mo6O19]2–@(ligand)3+2H+}. We postulate the stabilization
of this arrangement by attractive C–H···O and
CF3–pyridine interactions.