The authors present a series of amorphous zirconium metal-organic frameworks (aMOFs) synthesized by crosslinking ZrOAc clusters with flexible dicarboxylate linkers. Notably, the thiol functional groups in aMOFs can be post-synthetically oxidized to sulfonic acid groups while retaining the network structures. The study systematically examines how the linker length and functionalization affect properties such as porosity, proton conductivity, and hardness. Given the challenges in characterizing the structures of defective and amorphous MOFs, this work is commendable for its detailed characterization of the local coordination environments of Zr6-oxo moieties using PDF, EXAFS, and PXRD. This research could expand the scope of MOF studies and will attract interest from researchers in the MOF field and beyond. I am supportive of acceptance after minor revisions. The following are my suggestions:
1. The microscopic structures of aMOFs should be characterized using SEM or TEM. Understanding the morphology and particle sizes of the aMOFs is crucial for explaining their physical and mechanical properties.
2. The TGA results for the aMOFs indicate higher metal-to-ligand ratios than theoretically expected (ideally 6 linkers per Zr6 cluster), which was attributed to the presence of linker vacancies. The possibility of amorphous Zr oxide or hydroxide impurities in the aMOF samples should be considered. Elemental mapping using TEM-EDX could help identify any Zr-oxide/hydroxide phases present.
3. A decrease in the peak intensities for “Zr–Zradj” was observed for Zr-4L4 compared to Zr-4L3 (Fig. 3F). Since Zr-4L3 was treated under acidic conditions to form Zr-4L4, it is reasonable to suspect that Zr-oxide/hydroxide impurities in the aMOF samples may be removed during the post-synthetic modification. To verify phase purity, I recommend comparing the EXAFS of pure MOF-801 and Zr-oxide/hydroxide with the aMOFs.
4. The EXAFS data for aMOFs should be further analyzed by model fitting for structure validation.
5. The S 2p3/2 peaks at 168.5 eV (Fig. 3D) may correspond to sulfate anions, which could coordinate with the Zr6 cluster during H2SO4 treatment (Nat. Chem. 2019, 11, 170). To confirm the successful conversion of thiols to sulfonic acid groups, 1H-NMR of digested Zr-4L4 samples should be provided.
6. Related to the previous point, the impact of sulfuric acid, whether trapped in the pores or coordinated to the Zr sites, on the proton conductivity should be addressed.

The authors have conducted additional experiments and performed further data analysis to obtain more accurate structural models, particularly addressing the sulfate coordination to the Zr6 cluster in Zr-L4. The manuscript is now suitable for acceptance.