**2.2 Structure of classical arsenomolybdates**

Up to now, various structures of arsenomolybdates were reported and discussed in detail. The following types are classical arsenomolybdates clusters: (i) {As2Mo6} type, Pope's group reported the first {As2Mo6} cluster [28], in which the Mo6O6 ring is constructed from six MoO6 octahedra connected via an edge-sharing mode, the opposing faces have two capped AsO4 tetrahedra. Then Zubieta's group and Ma's group reported [MoxOyRAsO3] <sup>n</sup>� (RAsO3 = organoarsenic acid) and [Mo6O18(O3AsPh)2] <sup>4</sup>�(Ph = PhAsO3H2) clusters [29, 30]. (ii) {As6Mo6} type, which is derived from the A-type Anderson anion [(MO6)Mo6O18] <sup>10</sup>�, the central {MO6} octahedron is coordinated with six {MoO6} octahedra hexagonally arranged by sharing their edges in a plane. The cyclic As3O6 trimers are capped on opposite faces of Anderson-type anion plane. Each As3O6 group consists of three AsO3 pyramids linked in a triangular arrangement by sharing corners and bonded to the central MO6 octahedron and two MoO6 octahedra via μ3-oxo groups. Wang and co-workers reported the compound (C5H5NH)2(H3O)2[(CuO6)Mo6O18(As3O3)2] [31], Zhao groups synthesized the compound [Cu(arg)2]2[(CuO6)Mo6O18(As3O3)2]�4H2O [32]. (iii) {AsMo12} type, has a AsO4 tetrahedron at the center and 12 surrounding MoO6 octahedra, such as [NBu4]6[Fe(C5H5)2][HAsMo12O40]2 [33]. {As2Mo9}) type, is derived from the trivacant Keggin moiety, which is capped by a triangular pyramidal {AsO3} group, e.g., [Cu(en)2H2O]2{[Cu(en)2][Cu(en)2AsIIIAsVMo9O34]} 2�4H2O and [Cu(en)2 (H2O)]4[Cu(en)2(H2O)2]{[Cu(phen)(en)] [AsIIIAsVMoVI 9O34]2} [34, 35]. (iv) {As2Mo18} type, as a classical Wells–Dawson cluster, can be described as two [AsMo9O34] <sup>9</sup>� units derived from an Keggin anion by the removal of a set of three corner-sharing MoO6 octahedra, e.g., [Himi]6[As2Mo18O62]�11H2O [36].

In comparison with the classical arsenomolybdates, many nonclassical arsenomolybdates have also been prepared in the past of years, such as Ag12.4Na1.6Mo18As4O71 [37], (NH4)11[AgAs2Mo15O54]3�6H2O�2CH3CN [38], [AsIII 2FeIII 5MMo22O85 (H2O)]<sup>n</sup>� (M = Fe3+, n = 14; M = Ni2+ and Mn2+, n = 15) [39], {Cu(2,2<sup>0</sup> -bpy)}2{H2As2Mo2O14} [40], [{Cu(imi)2}3As3Mo3O15]�H2O [41], and so on. The novel arsenomolybdate structure is gaining more and more attention.

high-efficient proton delivery, fast multi-electron transfer, strong solid acidity and

photocatalytic activities. In particular, the integration of metal-organic frameworks (MOFs) into arsenomolybdates for photocatalysis has attracted widespread attention over the past decade, since MOFs combine porous structural and ultrahigh

Arsenomolybdates crystals reported were almost synthesized via self-assembly processes using hydrothermal method (**Figure 2**). Many factors in the synthetic process should be considered, such as reaction time and temperature, concentration of staring materials, compactness, pH values, and so on. The some experiments indicate that the temperatures are in the range of 110–180°C for srsenomolybdates synthesized, when the pH value of the mixture is adjusted to approximately 3–6.8,

(6 x) (abbreviated {As2Mo6}), [(MO6)(As3O3)2Mo6O18]

were easy to formed, when the pH value is within the range of 2.5–5.5 and 2–4,

{As2Mo18}) types were successfully synthesized. At the same time, the choice of transition metal, organic ligand, and molybdenic source have also affect for

<sup>3</sup> (abbreviated {AsMo12}) and [As2Mo18O62]

4

<sup>6</sup> (abbreviated {As2Mo9}) types

<sup>6</sup> (abbreviated

excellent reversible redox activity [27], which may result to prominent

*Photophysics, Photochemical and Substitution Reactions - Recent Advances*

Based on these results, we provide a summary of recent works in the synthesis, structure, the photocatalytic activity, reaction kinetics and mechanism mechanisms of arsenomolybdates, which aim at finding the direction followed with the opportunities and challenges for the arsenomolybdates photocatalysis to accelerate the step to realize its practical application in degradation of

**2. Syntheses and structure of arsenomolybdates**

**2.1 Syntheses of arsenomolybdates**

*The potential application field of arsenomolybdates.*

(abbreviated {As6Mo6}) and [AsIIIAsVMo9O34]

internal surface areas.

organic dyes.

**Figure 1.**

[HxAs2Mo6O26]

[AsMo12O40]

**118**
