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.

Functionalization via covalent grafting of organic functions allows to tune the redox and acid-base properties, and the solubility of polyoxometalates, to enhance their stability and biological activity and to reduce their toxicity, to facilitate their implementation in extended structures and functional devices. We discuss herein the electronic and binding connections, and the various synthesis methodologies. We emphasize on organonitrogen, organosilyl and organophosphonyl derivatives with special attention to synthesis, characterization and potential applications in catalysis and materials science. We also consider the giant molybdenum oxide-based clusters especially the porous capsule-type clusters (Keplerates) which have high relevance to this context.

ContentsI. Introduction 77 II. Scope and Organization of the Review 78 III. Polyoxometalates Incorporating Halides 79 IV. Polyoxometalates Incorporating Group 16 Element-Centered Ligands 81 A. Peroxopolyoxometalates 81 B. Polyoxoalkoxometalates 82 1. Polyoxoalkoxometalates Involving Unidentate Alcohols 82 2. Polyoxoalkoxometalates Involving Chelating Triols 83 C. Heavier Group 16 Element-Centered Ligands 85 1. Thiopolyoxometalates 85 2. Organosulfur and Organoselenium Ligands 85 V. Polyoxometalates Incorporating Group 15 Element-Centered Ligands 86 A. Singly Bonded Nitrogen-Donating Ligands 86 1. Amine and Related Ligands 86 2. Amide Oximes [RC(NH 2 )NOH] and Oximes 87 B. Multiply Bonded Nitrogen Ligands 89 1. Nitrido Derivatives 89 2. Organoimido Derivatives 89 3. Hydrazido and Diazenido Derivatives of Polyoxometalates 90 4. Nitrosyl Derivatives 92 C. Organophosphorus, Organoarsenic, and Organoantimony Ligands 94 1. Organophosphonate and Organoarsonate Ligands 94 2. Organophosphinate and Organoarsinate Ligands 97 VI. Polyoxometalates Incorporating Group 14 Element-Centered Ligands 97 A. Oxocarbon Ligands 97 1. Carbonate 97 2. Carboxylates 97 3. Oxalate and Squarate 97 4. Carbonyl Derivatives 98 B. Silicon Derivatives 98 C. Germanium Derivatives 99 D. Tin and Lead Derivatives 99 VII. Organometallic Derivatives of Polyoxometalates 100 A. Cyclopentadienyl Derivatives of Polyoxometalates 100 B. Cyclopentadienyl Oxide Clusters of Groups 5 and 6 100 C. Organometallic Polyoxometalates 100 1. Polyoxometalate-incorporated Organometalic Complexes 101 2. Polyoxometalate-Supported Organometallic Complexes 101 3. Integrated Cubane-Type Clusters 105 4. Organometallic Cation Salts of Keggin-Type Anions 105 VIII. Concluding Remarks 106 IX. Acknowledgments 106 X. Abbreviations 106 XI. References 106

Following Nature's lessons, today chemists can cross the boundary of the small molecule world to construct multifunctional and highly complex molecular nano-objects up to protein size and even cell-like nanosystems showing responsive sensing. Impressive examples emerge from studies of the solutions of some oxoanions of the early transition metals especially under reducing conditions which enable the controlled linking of metal-oxide building blocks. The latter are available from constitutional dynamic libraries, thus providing the option to generate multifunctional unique nanoscale molecular systems with exquisite architectures, which even opens the way towards adaptive and evolutive (Darwinian) chemistry. The present review presents the first comprehensive report of current knowledge (including synthesis aspects not discussed before) regarding the related giant metal-oxide clusters mainly of the type {Mo(57)M'(6)} (M' = Fe(III), V(IV)) (torus structure), {M(72)M'(30)} (M = Mo, M' = V(IV), Cr(III), Fe(III), Mo(V)), {M(72)Mo(60)} (M = Mo, W) (Keplerates), {Mo(154)}, {Mo(176)}, {Mo(248)} ("big wheels"), and {Mo(368)} ("blue lemon") - all having the important transferable pentagonal {(M)M(5)} groups in common. These discoveries expanded the frontiers of inorganic chemistry to the mesoscopic world, while there is probably no collection of discrete inorganic compounds which offers such a versatile chemistry and the option to study new phenomena of interdisciplinary interest. The variety of different properties of the sphere- and wheel-type metal-oxide-based clusters can directly be related to their unique architectures: The spherical Keplerate-type capsules having 20 crown-ether-type pores and tunable internal functionalities allow the investigation of confined matter as well as that of sphere-surface-supramolecular and encapsulation chemistry - including related new aspects of the biologically important hydrophobic effects - but also of nanoscale ion transport and separation. The wheel-type molybdenum-oxide clusters exhibiting complex landscapes do not only have well-defined reaction sites but also show unprecedented adaptability regarding the integration of various kinds of matter. Applications in different fields, e.g. in materials science and catalysis including those in small spaces, investigated by several groups, are discussed while possible directions for future work are outlined.

Anderson-type molybdopolyanions containing tris(alkoxo) ligands [MMo 6 O 18 {(OCH 2 ) 3 CR} 2 ] 3− (M = Mn III , Fe III ) and [H 2 MMo 6 O 18 {(OCH 2 ) 3 CR} 2 ] 2− (M = Ni II , Zn II ), (R = CH 3 , NO 2 , CH 2 OH), were prepared by treatment of [N(C 4 H 9 ) 4 ] 4 [α-Mo 8 O 26 ] with tris(hydroxymethyl)methane derivatives in the presence of manganese(III) acetylacetonate, iron(III) acetylacetonate, nickel(II) acetate, or zinc(II) acetate. The complexes were structurally characterized in solution, and also by single-crystal X-ray diffraction in the

No abstract

No abstract

Protein kinase CK2 is a multifunctional kinase of medical importance that is dysregulated in many cancers. In this study, polyoxometalates were identified as original CK2 inhibitors. [P2Mo18O62](6-) has the most potent activity. It inhibits the kinase in the nanomolar range by targeting key structural elements located outside the ATP- and peptide substrate-binding sites. Several polyoxometalate derivatives exhibit strong inhibitory efficiency, with IC50 values < or = 10 nM. Furthermore, these inorganic compounds show a striking specificity for CK2 when tested in a panel of 29 kinases. Therefore, polyoxometalates are effective CK2 inhibitors in terms of both efficiency and selectivity and represent nonclassical kinase inhibitors that interact with CK2 in a unique way. This binding mode may provide an exploitable mechanism for developing potent drugs with desirable properties, such as enhanced selectivity relative to ATP-mimetic inhibitors.