All three cages, 1-3, are made from the self-assembly of four molar equivalents of ligand molecule L with two molar equivalents of the corresponding metal salt ( ), followed by one molar equivalent of guest (2-3) (see the Supporting Information for full details). Complex formation was confirmed by electrospray ionization mass spectrometry (ESI-MS), the spectra showing 1-3 remain intact in solution (Figures ). The 1 H spectra of [Pd II 2L4](BF4)4 shows the expected seven signals, while the 1 H spectra of the hostguest complex 2 show only five signals (Figures S4-6). The missing signals correspond to the cavity protons (Ha and He) that strongly interact with the paramagnetic guest (H ) are ~10 Å, confirming that the guest has been encapsulated in the host cavity (Figure ).