**4. Conclusions**

In conclusion, triol-ligand and {MoO6} polyhedron co-decorated [V5MoO19] <sup>7</sup><sup>−</sup> polyanion is constructed with different terminal groups. The prepared compounds present a new type of derivative of Lindqvist-type clusters, which have never been reported previously. The organic and inorganic parts both attach to the main polyanion by replacing three O atoms in a *cis* conformation, in which one O atom is shared by three components and further improves the stability of the cluster. This manner of combination is different from those two triol-ligand-decorated Lindqvist-type clusters, in which no O atoms are shared by organic species. Another feature of the prepared compounds is that they express a new type of VMos with an unreported atomic ratio of 5:2. In addition, the Na<sup>+</sup> cations in compounds assemble into 1D channels, whose walls are full of water molecules. The further proton conductivity experiments show that this structure facilitates the transport of protons, which bears a Grotthuss mechanism for both compounds.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules27217447/s1. Figure S1: Ball-and-stick representation of the cluster comprising of five {VO6} and one {MoO6} polyhedra, showing a Lindqvist-type structure, and polyhedron representation of inorganic architecture of compound **1** comprising of a mono-lacunary {V6} cluster and a {Mo2} dimer; Figure S2: Ball-and-stick representation of polyanion of compound **1**, and two triol ligands covalently modified Lindqvist {V6} cluster in *cis* and *trans* conformations; Figure S3: The packing model of polyanion of compound **1** along *a* axis, showing a double-layer structure; Figure S4: FT-IR spectra of compounds **1** and **2**; Figures S5 and S6: XPS spectra for Mo and V of compounds **1** and **2**; Figure S7: PXRD patterns of the as-synthesized and simulated for (a) compound **1**, and (b) compound **2**; Figure S8: TGA curves of compounds **1** and **2**; Figure S9: 1H NMR spectra of triol ligand TME and compound **1** after its dissolving in water for different amounts of time; Figure S10. 1H NMR spectra of triol ligand TMP and compound **2** after its dissolving in water for different amounts of time; Figure S11: Linear fitness of ln(σT) versus 1/T of compounds **1** and **2**; Table S1: Important bond lengths in the cluster of compound **1**; Table S2: Important bond angles in the cluster of compound **1**; Table S3: Important bond lengths in the cluster of compound **2**; Table S4: Important bond angles in the cluster of compound **2**; Table S5: The proton conductivity performance of different POMs.

**Author Contributions:** Conceptualization, B.L.; formal analysis, T.C.; investigation, T.C. and D.Q.; writing—original draft preparation, T.C.; writing—review and editing, B.L. and L.W.; supervision, B.L.; funding acquisition, B.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is funded by the Natural Science Foundation of China, grant number 22172060.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Crystallographic data is obtainable free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data\_request/cif (accessed on 9 September 2022).

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the compounds **1** and **2** are available from the authors.

#### **References**

