*2.2. Structures of Compounds* **1** *and* **2**

Single crystal X-ray diffraction analysis reveals that compounds **1** and **2** possess very similar architectures except the difference of the terminal groups of triol ligand, methyl for compound **1** and ethyl for compound **2**, as shown in Figure 2. Here, compound **1** is used as a representative for illustrating their structural characteristics.

#### 2.2.1. Inorganic Architecture

The inorganic architecture of the polyanion of compound **1** is composed of five {VO6} and two {MoO6} polyhedra in the edge-sharing style. A Lindqvist-type cluster including five {VO6} and one {MoO6} polyhedra can be distinguished with a μ6-O as the center, as shown in Figure S1a. The other {MoO6} polyhedron attaches to this cluster through three μ2-O atoms in a face-sharing style, in which one O atom is from the V–O–V unit and the other two O atoms are sourced from V–O–Mo units. This connection makes the two {MoO6} polyhedra neighbors, and therefore the polyanion of compound **1** can also be seen as the combination of a mono-lacunary Lindqvist {V5} cluster with a metal dimer {Mo2} in the presence of five shared O atoms, as shown in Figure S1b. In addition, all bond

lengths and angles in the cluster are in the normal ranges, which are listed as Tables S1–S4 in the Supporting Information.

**Figure 2.** Polyanionic structures of compounds (**a**) **1** and (**b**) **2** in ball-and-stick representation (left) and combined ball-and-stick and polyhedron representation (right). All H atoms are omitted for clarity. Dark cyan ball: V, olive ball: Mo, light grey ball: C, red ball: O, dark cyan polyhedron: {VO6}, olive polyhedron: {MoO6}.

The unique combination of compound **1** results in an unreported atomic V/Mo ratio of 5:2. As an important sub-class of POMs, many VMos have been synthesized and reported, which possess various atomic V/Mo ratios. The change of atomic V/Mo ratio has an obvious influence on the architectures of the clusters, as well as their properties, which generally originates from the following aspects: (1) The V ion is used as a heteroatom in VMos, such as 1:6 for an Anderson-type POM, 1:12 for a Keggin-type POM, and 2:18 for a Dawson-type POM. It can also be applied in the lacunary cluster, such as 1:9 for a trivacant Keggin-type POM. (2) The V ion is used to replace one or more addenda atoms of clusters. For isopolyoxometalates, the Lindqvist-type [Mo6O19] <sup>2</sup><sup>−</sup> can be substituted by one or two V ions to form a cluster with 1:5 or 2:4 atomic V/Mo ratios, while for octamolybdates, the substitution of one or two V ions results in products having 1:7 or 2:6 atomic V/Mo ratios, which derivatives have been widely investigated. For the heteropolyoxometalates, there are more possibilities due to the increase of the number of addenda atoms, which generate a series of VMos derivatives. (3) A V ion is used to build VMo clusters with nonclassical architectures. With this strategy, {VO4}/{VO6} can combine with {MoO6} in various manners, and with the aid of other organic or inorganic species, more clusters with novel structures are obtained. Through the above-mentioned strategies, VMos with different atomic V/Mo ratios have been achieved, which are briefly summarized in Table 1. It should be noted that partial VV ions can be reduced to VIV ions, which enriches the diversity of the structures. In the present case, by utilizing the strong coordination ability of the triol ligand, an extra {MoO6} octahedron is introduced into the [V5MoO19] <sup>7</sup><sup>−</sup> polyanion, resulting in the formation of architecture with an unreported atomic V/Mo ratio of 5:2. This result also proves that the atomic V/Mo ratio has an important influence on the structure of the cluster, which can be tuned and applied for finding new VMo species.


**Table 1.** Summary of atomic V/Mo ratios in some classical VMos.

*<sup>a</sup>* The atomic V/Mo ratios used here are the same with as those in formulas without an approximate process. *<sup>b</sup>* The apparent sequence of V and Mo in the formulas of polyanions are unified.

#### 2.2.2. The Decoration of Triol Ligand on the Cluster

As mentioned above, compounds **1** and **2** possess a unique inorganic architecture, as well as an unreported atomic V/Mo ratio. Another feature of these two compounds is that a triol ligand attaches to the inorganic cluster, which plays a key role in the formation of polyanions. As is well known, bare Lindqvist-type polyoxovanadates (POVs) are not stable, and they can only be achieved in the presence of alcohols replacing one or more μ2-O atoms to reduce the charge density of the surface. The used alcohols can be methanol and ethanol, as well as a triol ligand, which can provide a strong coordination environment and anchors on the cluster up to four times. As the derivatives of Lindqvist-type POVs, triol ligand is also the essential factor for the successful preparation of compounds **1** and **2**. It is the

same with those in the Lindqvist-type POVs; the triol ligands in compounds **1** and **2** also replace three μ2-O atoms of V–O–V units and cover on a {V3} cluster. The decoration of triol ligand has an obvious influence on the V–(μ2-O) bond lengths concerned, which possess an average value of 2.038 Å (in compound **1**). As a comparison, other V–(μ2-O) bonds, which are not involved in the coordination with triol ligands, have a relatively shorter average bond length of 1.862 Å. A similar phenomenon is also found in triol-liganddecorated trivacant Kegging-type cluster, showing the strong coordination ability of triol ligand [24].

A more interesting feature of the polyanions of compounds **1** and **2** is that the present cluster can be seen as the triol ligand and the {MoO6} polyhedron co-supported [V5MoO19] <sup>7</sup><sup>−</sup> polyanion. As shown in Figure S2a, both the triol ligand and {MoO6} polyhedron share three O atoms with the [V5MoO19] <sup>7</sup><sup>−</sup> cluster. This structure is different from the two-triol-ligand covalently decorated POVs [47]. As shown in Figure S2b,c, the triol ligands can anchor on the Lindqvist-type POVs in cis or trans configurations by replacing six different μ2-O atoms, while in the present case, the triol ligand shares an O atom with the additional {MoO6} polyhedron, resulting in their combination with the [V5MoO19] 7− cluster through a total of five shared O atoms. In addition, it should be noted that all three terminal O atoms of {MoO6} polyhedron are involved in the formation of Mo=O double bonds, with the bond lengths of 1.730, 1.730, and 1.744 Å, which are different from those in the triol-ligand-decorated heptavanadate cluster, with one water molecule serving as a terminal group with a much longer V–O bond length of 1.995 Å [48]. The triol ligand modification on the cluster also influences the packing model of the polyanions. As shown in Figure S3, a double layer comprised of polyanions forms, in which triol ligands face opposite directions towards the inside of the layer. This packing model can reduce the exposure possibility of methyl groups in an aqueous solution, which benefits the minimalization of interface energy and the crystallization of the compounds.
