Subtle Ligand Modification Inverts Guest Binding Hierarchy in MII8L6 Supramolecular Cubes

Zinc­(II), a dimolybdenum­(II) paddlewheel tetramine A, and 2-formylpyridine self-assembled to generate a cubic ZnII8(LA)6 assembly. The paddlewheel faces of this assembly exhibited two distinct conformations, whereas the analogous FeII8(LA)6 framework displayed no such perturbation to its structure. This variation in behavior is attributed to the subtle difference in ligand rotational freedom between the ZnII- and FeII-cornered cubes. The incorporation of a fluorinated MoII2 paddlewheel, B, into analogous ZnII8(LB)6 and FeII8(LB)6 structures resulted in changes to the rotational dynamics of the ligands. These differing dynamics perturbed the energies of the frontier orbitals of these structures, as determined through spectroscopic and electrochemical methods. The result of these perturbations was an inversion of the halide binding preference of the ZnII8(LB)6 host as compared to its ZnII8(LA)6 congener, whereas the FeII8(LB)6 host maintained a similar binding hierarchy to FeII8(LA)6.