Organic–inorganic hybrid polyoxometalates are versatile building blocks for the self-assembly of functional supramolecular materials.

In this Tutorial Review, we describe the critical role redox active molecular species are playing in the development of the next generation of “beyond-lithium ion” battery technologies.

Tungsten-based polyoxometalates( POMs) have been employeda sU V-driven photo-catalysts for ar ange of organic transformations. Their photoactivityi sd ependent on electronic transitionsb etween frontier orbitals and thus manipulation of orbital energy levels provides ap romising meanso fe xtending their utility into the visible regime. Herein, an organic-inorganic hybrid polyoxometalate, K 6 [P 2 W 17 O 57 (PO 5 H 5 C 7 ) 2 ]·6C 4 H 9 NO, was foundt o exhibite nhanced redox behaviour andp hotochemistry compared to its purely inorganicc ounterparts. Hybridization with electron-withdrawingm oieties was shownt o tune the frontier orbitale nergy levels and reduce the HOMO-LUMO gap, leading to direct visible-lightp hotoactivationof the hybrid and establishing as imple, cheap and effective approacht ot he generation of visible-lightactivated hybrid nanomaterials.Systemst hat harness energy from visible light are among the most prized targets in modern materials design.[1] Ap romising group of photoactive materials, polyoxometalates (POMs), are discrete early transition-metal-oxide clusters that exhibite xcellent stability,s olubility in both aqueous and organic mediaa nd aw ide range of potentialc ompositions and structures.[2] These nanoscopic clusters are characterized in large part by their rich redox chemistry,l eadingt op otentiala pplicationsi nm ulti-electron transfer and charge-storaget echnologies.[3] Most importantly,t heir capacity to form highly active photo-excited states (oxo-centred radicals) upon excitation of the O!Ml igand-tometal charge transfer (LMCT) band [4] has led to sustainedi nterest in their use as both heterogeneous and homogeneous photocatalysts for ar ange of transformations.[5] In particular, tungstate-based POMs have been successfully employed in ar ange of UV-light-driven photooxidationr eactions. [4a, 6] In their native state, POMs typically exhibit negligible visible light absorption, with the broad LMCT band located almostentirely within in the UV region of the spectrum.P OMs have thus had limited application in visible-light-driven catalysis and while the absorption profiles of molybdate-and vanadatebased POMs often tail into the near-visible/blue range, [4, 7] they do not generally exhibit the stability or easeo ff unctionalization seen in tungstate-baseda nalogues.Mizuno and co-workersr ecently reported two examples of polyoxotungstate photoactivation in systemsb ased on the lacunary POM [g-SiW 10 O 36 ] 8À ,i nw hich charget ransferf rom secondary components (Ce III or bound substrates) facilitated photo-reduction of the POMcorea nd allowedo xidative catalysis on the appended moieties.[8] Another approach to the visible-lighta ctivation of POMs is through functionalization with (typically, preciousm etal-based) visible-light-activec hromophores or 'photosensitizers' (PS), throughe ither supramolecular or covalenta pproaches.[9] Subsequentp hoto-excitation can lead to PS!POMc harge transfer.[10] Indeed, to the best of our knowledge,a ll previous reports of polyoxot...

The design of highly flexible framework materials requires organic linkers, whereas inorganic materials are more robust but inflexible. Here, by using linkable inorganic rings made up of tungsten oxide (P8W48O184) building blocks, we synthesized an inorganic single crystal material that can undergo at least eight different crystal-to-crystal transformations, with gigantic crystal volume contraction and expansion changes ranging from −2,170 to +1,720 Å3 with no reduction in crystallinity. Not only does this material undergo the largest single crystal-to-single crystal volume transformation thus far reported (to the best of our knowledge), the system also shows conformational flexibility while maintaining robustness over several cycles in the reversible uptake and release of guest molecules switching the crystal between different metamorphic states. This material combines the robustness of inorganic materials with the flexibility of organic frameworks, thereby challenging the notion that flexible materials with robustness are mutually exclusive.

A one-pot strategy exploiting the structure directing effects of Se IV and Te IV heteroatoms has yielded the highest nuclearity noble metal containing polyoxometalates to date; including the palladium-rich selenotungstate isomers K 28 [H 12 Pd 10 Se 10 W 52 O 206 ]·65H 2 O (1) and K 26 [H 14 Pd 10 Se 10 W 52 O 206 ]·68H 2 O (2), and the nanoscale tellurotungstate cluster Na 40 [Pd 6 Te 19 W 42 O 190 ]·76H 2 O (3). These reaction systems exhibit remarkable structural flexibility and point to a new route towards the synthesis of complex heterometallic species, in which multiple lacunary polyoxometalate 'building blocks' have been assembled to trap a transient oxopalladate species suspected to play a role in the assembly of several common polyoxopalladates.Mass spectrometry has been applied to explore and compare the solution stability of compounds 1-3, demonstrating the markedly different properties of the Se IV and Te IV templated systems. Electrochemical analysis of 1 has been provided and is dominated by Pd redox processes, with reduction of the cluster resulting in electrodeposition of Pd metal and observation of the subsequent formation of PdO species, concurrent with previously reported oxopalladate containing species.