Exploring bimodal mesoporous aluminum MOFs: synthesis and defect analysis of rad net topology with imine-based ligand

Abstract

Metal–organic frameworks (MOFs) are a versatile class of porous crystalline materials whose properties can be finely tuned through reticular chemistry. Isoreticular expansion, a powerful strategy for increasing pore size without altering framework topology, has enabled the design of MOFs with hierarchical porosity and enhanced functionality. In this study, we report the scalable synthesis and structural characterization of a new aluminum-based MOF, designated AlDMDA-68, constructed using an imine-based dicarboxylate linker 4,4′-(hydrazine-1,2-iylidenebis(methanylylidene))dibenzoic (H₂DMDA). The framework exhibits a rad net analogous to MIL-68(Al), featuring dual-channel architectures with pore diameters up to 3.16 nm. Optimization of reaction parameters, including metal-to-ligand (M/L) ratio, yielded phase-pure materials with rod-like morphology. Powder X-ray diffraction and ²⁷Al MAS NMR confirmed framework formation and the presence of coordination defects, respectively. Nitrogen sorption measurements revealed a high Brunauer–Emmett–Teller (BET) surface area of 1866 m² g⁻¹ and substantial uptake, indicating a hierarchical microporous–mesoporous structure. The material also demonstrated high thermal stability (∼350 °C) and excellent scalability, achieving a fivefold increase in yield without compromising structural integrity. These findings highlight AlDMDA-68 as a promising candidate for various applications and establish elongated imine-based linkers as effective building blocks for designing mesoporous Al-MOFs with tunable functionality.