Polyoxometalate (POM)-based organic-inorganic hybrid materials have attracted extensive attention in the last ten years due to their potential applications in catalysis, nonlinear optics, photovoltaic, and self-assembly research. [1] Currently, trisalkoxo tripodal ligand (Tris)-functionalized Lindqvist-, Anderson-, and Dawson-type POMs show high stability and varied functionalities. [1a] Zubieta et al. used Tris ligands to stabilize macro-POM clusters and to functionalize hexavanadate. [2] The functionalized hexavanadate was further developed by Hill and co-workers for the construction of metal-organic frameworks, which can function as highly efficient heterogeneous catalytic materials. [3] Due to the high reactivity of vanadate, vanadium-containing Dawsontype POMs were observed to be capped by only one Tris ligand. [4] In particular, after Hasenknopf et al. had established the synthesis of Tris derivatives of Anderson-type POMs in 2002, [5] the groups of Cronin and Hasenknopf introduced different kinds of functional groups to the system through further organic reactions. The resulting materials show interesting functions including high biological activity against cells, photocatalytic properties, and interesting selfassembly behavior. [6] Due to their high symmetry (D 3d ), both sides of Anderson-type POMs are easily functionalized simultaneously by Tris ligands during their synthesis, which seems to be an unquestionable fact (Figure 1), and there has never been any report on a single-sided functionalized Anderson-type POM with Tris. Herein, we report the synthesis and characterization of Anderson-type POMs with only one side functionalized by a Tris ligand, which not only afforded asymmetric POM-based hybrid materials for further research, but also uncovered more structural and reactive properties of Anderson-type POMs, and the reaction mechanism for the functionalization of POMs with Tris.
In the previous protocol, to synthesize the double-sided functionalized Anderson-type POMs, octamolybdate, a salt of the central heteroatom, and organic ligands (Tris) were mixed in an organic solvent, such as acetonitrile, and the final products were obtained after heating to reflux for approximately 16 hours, which is a classical one-pot reaction. [5] However, our new protocol to synthesize the single-side organically functionalized Anderson-type POM, [(C 4 H 9