Structural consequences of anionic host-cationic guest interactions in a supramolecular assembly.

The molecular structure of the spontaneously assembled supramolecular cluster [M(4)L(6)](n-) has been explored with different metals (M = Ga(III), Fe(III), Ti(IV)) and different encapsulated guests (NEt(4)(+), BnNMe(3)(+), Cp(2)Co(+), Cp*(2)Co(+)) by X-ray crystallography. While the identity of the metal ions at the vertices of the M(4)L(6) structure is found to have little effect on the assembly structure, encapsulated guests significantly distort the size and shape of the interior cavity of the assembly. Cations on the exterior of the assembly are found to interact with the assembly through either pi-pi, cation-pi, or CH-pi interactions. In some cases, the exterior guests interact with only one assembly, but cations with the ability to form multiple pi-pi interactions are able to interact with adjacent assemblies in the crystal lattice. The solvent accessible cavity of the assembly is modeled using the rolling probe method and found to range from 253-434 A(3), depending on the encapsulated guest. On the basis of the volume of the guest and the volume of the cavity, the packing coefficient for each host-guest complex is found to range from 0.47-0.67.