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 Pd-II 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 Pd-II ions to give a compound of the formula {[Mo6O19](2-)@(ligand)(3)+2H(+)}. We postulate the stabilization of this arrangement by attractive C-H center dot center dot center dot O and CF3-pyridine interactions.