Fractal MOF Architectures: Reaction–Diffusion–Mediated Transmutation of Crystalline Scaffolds

Abstract

Reaction–diffusion precipitation of benzoic acid (BA) in gelatin yields diffusion-limited aggregation (DLA) fractals whose dimension (D ≈ 1.56–1.74) depends on the inner sodium benzoate (NaBZ) concentration. Here, we demonstrate that these stochastic structures can be conformally transmuted into the metal–organic framework HKUST-1 (MOF-199), while preserving fractal geometry and local crystallinity. Hybrid dendrites, formed by co-precipitating benzene-1,3,5-tricarboxylic acid (H₃BTC) with BA undergo ligand-exchange conversion upon copper diffusion to yield fractal HKUST-1 replicas. Ethanol content, gel matrix composition, and the NaBZ:H₃BTC ratio cooperatively govern phase selection, transmutation efficiency, and fidelity. A brief NaOH pretreatment further broadens the transmutation window by smoothing crystal facets. This strategy couples stochastic fractal growth with reticular chemistry, enabling hierarchical MOF architectures that are inaccessible via conventional routes.