Transition metal substituted polyoxometalate

The ample field of transition metal substituted polyoxometallates (POM), which are often other precursors for peroxo derivatives in catalytic processes, will be discussed in brief. 

A relatively recent field of study, which, will be expanded upon later, is that of transition metal substituted polyoxometallates.43 The fact that they are, in most cases, completely inorganic means that they are inherently robust to oxidative degradation, hence, offering good prospects for industrial application. 

Zhang, X. Hill, C. L. Alkene Epoxidation by p-Cyano-lV-lV-dimethylaniline IV-oxide Catalyzed by d-Electron-transition-metal-substituted Polyoxometalates. In Catalysis of Organic Reactions. Malz, R. E. J., Ed. Marcel Dekker New York, 1996 pp 445-450. 

C. L. Hill, R. B. Brown Jr., Sustained epoxidation of olefins by oxygen donors catalyzed by transition metal-substituted polyoxometalates, oxidatively resistant inorganic analogs of metalloporphyrins, J. Am. Chem. Soc. 108 (1986) 536. 

In recent years, a breakthrough in this field concerned the adoptirm of totally inorganic transition metal substituted polyoxometalates (POMs) as molecular catalysts for water oxidation. 

This book has been divided into three areas chemical detection, biological detection, and decontamination. The subject matter in the chapters include cross-linked divinyl benzene-substituted methacrylate polymers (Chapter 2), porous silicon (Chapter 3), reactive glass surfaces (Chapter 4), polycarbosilanes (Chapter 5), non-aqueous, chemically cross-linked polybutadiene gels (Chapter 6), conducting polyaniline nanofibers (Chapter 7), organically doped polystyrene and polyvinyltoluene (Chapter 8), electroplated polymer cast resins (Chapter 9), self assembled monolayers (Chapter 10), amphiphilic functionalized norbomene polymers (Chapter 11), transition metal substituted polyoxometalates (POMs) (Chapter 12), cross-linked divinyl-benzamide phospholipids (Chapter 13), and silica and organo silyl polymers (Chapter 14). 

The first reported transition metal substituted polyoxometalate, able to oxidize water was the Nai4[Ru2Zn2(H20)2(ZnW9034)2] reported by... 

Maksimchuk NV, Timofeeva MN, Melgunov MS, Shmakov AN, Chesalov YA, Dybtsev DN, et al. Heterr eneous selective oxidation catalysts based on coordination polymer MIL-101 and transition metal-substituted polyoxometalates. J Catal 2008 257 315-23. 

Figure 9.3 Various transition metal-substituting polyoxometalates.

Figure 5.1 General structure of the Keggin-type (a) and sandwich-type (b) transition metal substituted polyoxometalates (TMSPs) used in catalysis W (green) O (red) heteroatom X (yellow) transition metal M (pink). See insert for color representation of the figure.)...

III. TRANSITION METAL-SUBSTITUTED POLYOXOMETALLATES AS ELECTROCHEMICAL OXIDATION CATALYSTS... 

Polyoxometalates are able to act as ligands for different redox-active transition metals (M ) such as iron, manganese, cobalt and ruthenium or d metals (such as zirconium, hafnium, titanium). The coordination of a heterometal by a polyoxometalate framework takes place either through the superficial coordination of a metal cation by electrostatic interaction, or by incorporation of the transition metal within the POM structure resulting in the formation of transition metals substituted polyoxometalates (TMSPs), which generally exhibit a higher stability. 

Transition metals substituted polyoxometalates are obtained starting from vacant or lacunary POMs. The latter are derived from the saturated parent POM, through formal loss of one or more MOe octahedral units. Such complexes present several coordinatively unsaturated oxygen atoms, which surround the defect and form a polydentate site, able to coordinate a multitude of transition metals, M . Fundamental modes of coordination of the transition metals are in pocket and out of pocket , the latter including sandwich-like structures and metal oxide cluster stabilization, depending both on the dimensions of M and on the stoichiometic ratio between M and the vacant units. " ... 

Maksimchuk, N., Timofeeva, M., Melgunov, M., et al. (2008). Heterogeneous Selective Oxidation Catalysts Based on Coordination Polymer MIL-101 and Transition Metal-Substituted Polyoxometalates, J. Catal, 257, pp. 315-323 Maksimchuk, N., Kovalenko, K., Arzumanov, S., et al. (2010). Hybrid Polyoxotungstate/MlL-101 Materials synthesis. Characterization, and Catalysis of H202-Based AUcene Epoxidation, Inorg. Chem., 49, pp. 2920-2930. 

---