Modulating the guest binding ability within mixed-coordination geometry [Pd(μ-L)4RuCl2]2+ and [Pd(μ-L)4Pt]4+ cage architectures

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

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.

Pd(μ-L)4Pt vs. Pd(μ-L)4RuCl2: chlorido ancillary ligands as defining factors in the host-guest interactions of M(μ-L)4M' heterodimetallic supramolecular architectures

In supramolecular architectures, the interactions between host and guest molecules are governed by non-covalent forces such as hydrogen (H) bonding, hydrophobic and electrostatic interactions. We alter here the cavity microenvironment to control the interactions between guest and host molecules and study the effects of introducing axial chlorido ligands through the use of an octahedral building block in M(μ-L)4M' architectures. We prepared the heterodimetallic Pd(μ-L)4Pt C4 Pt and Pd(μ-L)4RuCl2C4 Ru architectures and demonstrated the role of 'classic' non-covalent forces in their host-guest chemistry with anionic and neutral molecules, while the cages also underwent disassembly and reassembly upon addition of external stimuli. This culminated in the isolation of a 1 : 1 host-guest complex between C4 Pt and the dianionic 1,5-naphthalenedisulfonate which was characterized by single crystal X-ray diffraction studies. These showed the guest occupied the central cavity and was held in place by H bonding. The endo-chlorido ligand in C4 Ru played an important role in the capture of neutral guest molecules. In particular, it allowed for finetuning of the cavity properties of the supramolecular architectures by limiting the formation of H bonds and restricting the cavity size while offering alternative interactions.