Recent Advances of Ti/Zr-Substituted Polyoxometalates: From Structural Diversity to Functional Applications

Abstract

Polyoxometalates (POMs), a large family of anionic polynuclear metal–oxo clusters, have received considerable research attention due to their structural versatility and diverse physicochemical properties. Lacunary POMs are key building blocks for the syntheses of functional POMs due to their highly active multidentate O-donor sites. In this review, we have addressed the structural diversities of Ti/Zr-substituted POMs based on the polymerization number of POM building blocks and the number of Ti and Zr centers. The synthetic strategies and relevant catalytic applications of some representative Ti/Zr-substituted POMs have been discussed in detail. Finally, the outlook on the future development of this area is also prospected.

Synthesis, structure, and characteristics of a hexa-Ti-oxo-cluster-added Keggin-type polyoxometalate

“…Compared with other TM ions, such as Fe 2+ , Co 2+ , and Ni 2+ , Ti 4+ ions exhibit relatively stronger Lewis acidity and are easily hydrolyzed in aqueous solutions, rendering the synthesis of Ti-oxo clusters in aqueous solutions difficult [11][12][13][14]. In this regard, lacunary POMs are ideal inorganic ligands for anchoring Ti-oxo clusters to construct Ti-added POMs (TiAPs) owing to the close ⊂ ⊂ ionic radii of W 6+ and Ti 4+ .…”

Tuning Reactivity of Zr-Substituted Keggin Phosphotungstate in Alkene Epoxidation through Balancing H2O2 Activation Pathways: Unusual Effect of Base

“…53,54 Although a large number of Zr-containing POMs have been reported in the literature (for reviews, see refs. 55,56 ) and many of them were extensively studied as acid−base catalysts, 57−61 only a few were assessed in oxidation catalysis. 22,57,62−69 Kortz and co-workers have synthesized a number of peroxo-Zrcontaining POMs and demonstrated their activity in the stoichiometric sulfoxidation of L-methionine 64 and catalytic oxidation of organic sulfides and alcohols with H 2 O 2 .…”

“…Although a large number of Zr-containing POMs have been reported in the literature (for reviews, see refs. , ) and many of them were extensively studied as acid–base catalysts, − only a few were assessed in oxidation catalysis. ,,− Kortz and co-workers have synthesized a number of peroxo-Zr-containing POMs and demonstrated their activity in the stoichiometric sulfoxidation of l -methionine and catalytic oxidation of organic sulfides and alcohols with H 2 O 2 . , A hexazirconium-containing tungstoarsenate (III), [Zr 6 O 4 (OH) 4 (H 2 O) 2 (CH 3 COO) 5 (AsW 9 O 33 ) 2 ] 11– revealed catalytic activity in the oxidation of CyH, methyl phenyl sulfide, and cyclohexanol . In the CyH oxidation, the products typical of heterolytic H 2 O 2 activation pathway, i.e., epoxide, diol, and ketol, prevailed, and the positive role of protons in heterolytic activation of H 2 O 2 was hypothesized.…”

Organic-Cation Modulated Assembly Behaviors of a Ureidopyrimidone-Grafting Cluster

“…By Polyoxometalates (POMs) are a class of clusters formed by early transition metal ions (V, Mo, W, Nb, Ta, et al) in high-valence through the corner-, edging-or facingshared O atoms [17,18]. They have the characteristics of rich compositions and diverse structures and have been widely used in the fields of energy, magnetism, catalysis, and materials science [19][20][21][22][23]. The bridging O atoms of some kinds of POMs can be replaced by organic molecules to obtain covalently modified organic-inorganic hybrids [24].…”