Two-Dimensional Pd–C Bonded Organometallic Framework with Dynamic Packing Transformations

Abstract

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 (bdc2−) as the organic ligand. The activated carbon atoms of the benzene ring in the bdc2− 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.