Interconversion between a Pd3L2 trigonal prism and a Pd6L8 cube via anion exchange: binding affinity of monoatomic vs. polyatomic anions.

Systematic interconversion between trigonal prisms [Pd3X6L2] (X- = Cl-, Br-, and I-) and cubic cages [Pd6L8]12+(X-)12 (X- = BF4- and CF3SO3-) via anion exchange was established. Self-assembly of K2PdX4 (X- = Cl- and Br-) with a C3-symmetric tridentate 1,3,5-tris(2-isonicotinamidephenoxy)benzene (L) produces a trigonal prism, [Pd3X6L2]. Further photoreaction of the [Pd3X6L2] (X- = Cl- and Br-) with CH2I2 gives rise to a halide-exchanged species, [Pd3I6L2]. In contrast, anion exchange of [Pd3X6L2] (X- = Cl-, Br-, and I-) with BF4- yields cubic-shaped cages, [Pd6L8]12+(BF4-)12, with an inner cavity of 15.9 × 15.9 × 15.9 Å3. Successive anion exchange of [Pd6L8]12+(BF4-)12 with CF3SO3- gives rises to anion-exchanged [Pd6L8]12+(CF3SO3-)12 and vice versa without cage destruction. Thus, the cage system is specifically sensitive to anions, enabling cage formation to recognize the binding affinity and size of various anions.