In or out? Adaptive metal binding by a diphosphine-based Zr metal-organic cage.

A lantern-type Zr metal-organic cage (MOC), Zr-P2N2, has been synthesized using ditopic carboxylate linkers based on the 1,5-diaza-3,7-diphosphacyclooctane (P2N2) ligand platform. Single-crystal X-ray diffraction shows that the diphosphine groups of the P2N2 linkers point into the confined MOC cavity. Postsynthetic metalation of the diphosphine groups with Pd and Pt precursors generates the heterobimetallic cages Zr-P2N2-PdCl2 and Zr-P2N2-PtCl2. Structural characterization reveals that the linkers flip to accommodate metal chelation, resulting in outward facing metal diphosphine groups. Conversely, reaction of Zr-P2N2 with AgPF6 results in formation of Zr-P2N2-Ag, containing a hexasilver core supported by phosphine complexation within the cage interior. This work highlights the adaptive structural behavior of Zr-P2N2 which provides new opportunities for designing responsive MOCs.