Single-Step Synthesis of a Heterometallic [Cu2PdL4]2+ Hybrid Metal–Organic Coordination Cage

Abstract

Traditional methods of assembling low-symmetry heterometallic cage architectures are limited to stepwise construction and combinations of inert and labile metal ions, affording complex, anisotropic cage structures by sacrificing synthetic ease. Herein, a heterometallic [Cu₂PdL₄]²⁺ lantern-type cage has been assembled in a single self-assembly step through the use of a heteroditopic ligand with two different metal-binding groups. The resultant cage complex is a fusion of two common lantern-type cage motifs—carboxylate-based metal-organic Cu₄L₄ cages and pyridyl-based Pd₂L₄ coordination cages. Evidence for heterometallic cage formation in solution was provided by ¹H and diffusion-ordered NMR spectroscopy and electrospray ionization mass spectrometry (ESIMS) data, whereas circular dichroism (CD) spectra confirmed the helical nature of the assembly. The heterometallic cage was then exploited in binding heterotopic guests. It is envisioned that the simple design strategy presented herein will ease the assembly of other structurally complex, low-symmetry cage architectures.