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 ų. 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.