Functionalization and post-functionalization: a step towards polyoxometalate-based materials

Abstract

Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach: immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir-Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated. Meanwhile, the field of organic-inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic-inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

Base Catalysis by Mono- and Polyoxometalates

“…This study provides the first example of catalytic synthesis from aromatic diamines and CO 2 . The TBA 2 [WO 4 ] catalyst shows a concerted action on both CO 2 and the substrates, and the hydrogen bonding interaction between [WO 4 ] 2− and diamine and formation of Lewis base-CO 2 adducts have been directly observed using 1 H, 13 C, and 183 W NMR spectroscopy. The proposed reaction mechanism for CO 2 fixation with TBA 2 [WO 4 ] is shown in Figure 10.…”

“…Isopolyoxometalates are often utilized as photocatalysts and building units for the synthesis of POM-based functional assemblies [12][13][14]17,35]. In addition, their basic properties have been extensively studied due to their simple compositions and structures.…”

Simulating the Favorable Aggregation of Monolacunary Keggin Anions

“…12,13 In addition, the rectangular lacuna in MKAs represents an ideal binding site wherein to anchor a variety of functional moieties and/or linkers: [14][15][16][17] in practice, this somewhat broadens MKAs' versatility with respect to that of PKAs. Notable examples are organic tethers to chromophores; 12,18,19 to (photo)catalytic centres; 13,[20][21][22] to other solid supports such as electrodes, silica, and metal oxides; 9,19,[23][24][25][26] and to distal metal chelating centres, for subsequent incorporation in co-ordination polymers.…”

Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo12-nWnO403– (n = 0–12)

“…Mixed addenda POMs have been examined previously by many research groups in an effort to access a range of electronic properties of interest to catalysis, energy storage, and chemical sensing [1,2,5,11]. By changing the ratio of the transition metals, one may tailor the reactivity and stability of mixed addenda POMs for a particular application.…”

“…Introduction P olyoxometalates (POMs) are a class of inorganic materials that are of interest for a variety of applications because of their remarkable redox, photochemical, and magnetic properties [1][2][3][4][5][6][7][8][9]. The Keggin POM [10], a class of stable, redox-active, triply-charged anions comprised of a metal-oxide cage structure (M 12 O 36 ; M = early transition metal) with an internal XO 4 n-group (typically X = Si, P; n = 4, 3, respectively), is one of the most widely studied POM systems.…”