Copper Diphosphonate Frameworks Incorporating Dianthracene: Capture of a Metastable Intermediate, Framework...

The crystallization pathways of metal phosphonate frameworks (MPFs) remain poorly understood because the strong coordination ability of phosphonate ligands often leads to rapid precipitation, making the isolation of transient intermediates challenging. Herein, we report two 3D Cu-based MPFs, [Cu₂(amp₂H₂)]·2H₂O·DMF (Cu-3D) and [Cu₂(INA)₂(amp₂H₂)(H₂O)₂] (Cu-INA-3D), where amp₂H₄ is photodimerized 9-anthracenemethylphosphonic acid and INAH is isonicotinic acid. By shortening the reaction time, we isolated a metastable intermediate, [Cu₂(INA)₂(amp₂H₂)]·2H₂O (Cu-INA-2D), which can gradually transform into the thermodynamically more stable Cu-INA-3D phase via reconstruction of the Cu-PO₃ connectivity and reorganization of the {Cu(INA)} chains. The crystals of Cu-INA-2D can undergo solvent-assisted cleavage to yield an accordion-like morphology. Further, thermal de-dimerization of the dianthracene units in Cu-3D and Cu-INA-3D induces framework transformation, generating new phases containing anthracene moieties. We studied the photothermal properties of Cu-3D, Cu-INA-3D and their de-dimerized products. All exhibited near-infrared (NIR) photothermal responses under 808 nm laser irradiation. Benefiting from its photothermal conversion capability and the redox activity of Cu^II centers, Cu-INA-3D was employed to serve as a photothermally driven catalyst for pyrrole polymerization. These findings provide insight into the crystallization mechanism of copper diphosphonate frameworks and demonstrate the potential of dianthracene-based MPFs as multifunctional photothermal materials.