Two-dimensional Pd-C bonded organometallic framework with dynamic packing transformations

Traditional metal-organic frameworks (MOFs) are predominantly constructed through metal-oxygen (M-O) or metal-nitrogen (M-N) coordination bonds. However, the limited softness of M-O and M-N bonds restricts the incorporation of softer linkages involving low-valent or noble metals, as described by the hard-soft acid-base (HSAB) principle. Although metal-carbon (M-C) linkages have been proposed as a potential alternative, their limited reversibility and the scarcity of suitable multidentate ligands have hindered their broader implementation in MOF synthesis. In this study, we report the synthesis of a two-dimensional organometallic framework, PdOF-1, which bears direct palladium-carbon (Pd-C) bonds. PdOF-1 was synthesized via a one-pot, carboxylate-directed ortho C-H activation process, employing terephthalate (bdc^2-) as the organic ligand. The activated carbon atoms of the benzene ring in the bdc^2- ligand effectively stabilize the soft palladium centers, yielding an extended network while suppressing palladium agglomeration. Single-crystal X-ray diffraction revealed a zigzag two-dimensional (2D) lattice with ordered layer-by-layer stacking and square-planar Pd coordination. Comprehensive structural and spectroscopic analyses reveal two-step solid-state structural transformations involving layer shearing and compression induced by the removal of intercalated DMSO molecules. In addition, the pristine PdOF-1 undergoes further structural transformation upon solvent exchange with coordinating solvents. This work establishes a new synthetic route bridging organometallic chemistry and reticular design, expanding the chemical space of MOFs toward frameworks with persistent covalent metal-carbon linkages and tunable structural adaptability.