(690f) Deciphering the Spatial Configuration, Reaction Pathways and Polymorphism in Porphyrin-Based Multivariate (MTV) MOFs ((Fe-Co-Ni-Cu-Zn)-Tcpp)

Recently, there has been notable progress in the development of multivariate metal-organic frameworks (MOFs) utilizing a limited array of linkers, demonstrating their efficacy in various catalytic and storage applications. These MOFs exhibit significantly enhanced performance compared to their single metal counterparts. Porphyrin-coordinated networks (PCNs) particularly stand out for their exceptional electrocatalytic and photocatalytic properties. Despite this, a synthetic approach to incorporate more than four elements into these networks has not yet been reported.

This study presents the synthesis of porphyrin-based multi-elemental MOF with TCPP as the porphyrin linker. Commonly referred to as PCN-600, this MOF has predominantly been investigated with single and bi-metallic nodes incorporating Fe, Co, and Ni. The key building unit for this system is represented by (M₃O)₂ (TCPP)₃. Additionally, a polymorph featuring the paddlewheel SBU structure (M-TCPP) exists which has been also investigated for multi-elemental incorporation. By adjusting synthesis conditions through appropriate modulators, the reaction pathway is altered, and phase-pure polymorphs have been obtained, further shedding light on the underlying mechanism of formation of these SBUs with multiple metallic nodes integrated into the lattice. Utilizing ex-situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), the spatial arrangement of the metallic nodes has been elucidated. Furthermore, STEM coupled with EDS confirms the uniform distribution of multiple elements at smaller length scales, thereby affirming the structural integrity of the lattice in comparison to their single metal counterparts. Finally, by integrating these experimental findings with molecular dynamics simulations and precursor metal-salt dissociation energies, a plausible reaction mechanism for the formation of this multivariate structure is proposed.