Linkage Position-Controlled Synthesis of Diverse Zirconium Metal–Organic Frameworks with Prominent Intrinsic Proton Conductivities

Herein, by engineering the geometries of the organic linkers, two pyrrolo-pyrrole-based low-symmetry tetracarboxylate linkers (TAPPs) were successfully designed and subsequently used for the construction of two new zirconium-based metal–organic frameworks (Zr-MOFs) (IAM-10 and IAM-11). The reduction of the linker symmetry arises from both the asymmetric pyrrolo-pyrrole core and the integration of both the para- and meta-benzoate coordination groups on the linkers. Both MOFs are composed of 8-connected Zr₆ nodes and 4-connected highly deformed TAPP^4– linkers with the same scu topology, but distinct linker arrangements can be observed in two structures. The specific rhomb-shaped geometry together with the flexible m-benzoate groups through the rotation of the peripheral phenyl rings allows this type of TAPP linker to generate unique conformations and arrangements in MOF structures to optimize the coordination bonds with the inorganic building blocks and adapt to the final topologies. Furthermore, the presence of well-defined hydrophilic channels in the reported MOFs allowed us to evaluate the potential for proton conduction. Both IAM-10 and IAM-11 show the prominent intrinsic proton conductivities of 1.13 × 10^–2 and 2.69 × 10^–3 S cm^–1 at 90 °C and 95% RH, making them the top-performing proton-conductive Zr-MOFs.