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