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We report the formation of two polyoxotungstates of the general formula [M6(PW6O26)(α-P2W15O56)2(H2O)2]23− (M = CoII or MnII), which contain {PW6} fragments generated from the [P2W15O56]12− precursor, which demonstrates for the first time the transformation of a Dawson lacunae into a Keggin lacunary building block. Solution analysis of the clusters has been conducted via electrospray ionisation mass spectrometry.

We report an approach to synthesize molecular tungsten-oxide-based pentagonal building blocks, in a new {W21 O72} unit, and show how this leads to a family of gigantic molecular architectures including [H12W48O164](28-) {W48}, [H20W56O190](24-) {W56}, and [H12W92O311](58-) {W92}. The {W48} and {W56} clusters are both dimeric species incorporating two {W21} units and the {W56} species is the first example of a molecular metal oxide cluster containing a chiral "double-stranded" motif which is stable in solution as confirmed by mass spectrometry. The {W92} anion having four {W21} units is one of the largest transition metal substituted isopolyoxotungstates known.

The Dawson-like “Trojan horse” cluster (Me2NH2)8 [W18O56(HPO3)2 (H2O)2]·20H2O is isolated from an aqueous solution of Na2WO4, H3PO3, and Me2NH (pH 2.8, stirring under heating).

A series of {B-β-SiW8O31}-based transition metal substituted polyoxometalates is synthesized using BHEP as an organic base to buffer the reactions.

The diastereoselective synthesis of fluorinated δ-lactams is achieved through an efficient five step process.

Compounds (III) and (IV) are synthesized by reduction of an acidified suspension of cerium polymolybdate in water and characterized by single crystal XRD, IR and Raman spectroscopy, and electrospray-ionization ion-mobility mass spectrometry.

Compounds (IV), (V), and (VI) are separated sequentially from the same mother liquor as a function of solvent evaporation time (slow evaporation at room temperature).

Compounds (IV), (V), and (VII) crystallize in the triclinic space group P with Z = 1, 2, and 2, respectively (single crystal XRD).

Five new selenotungstates are synthesized based on the formation and subsequent assembly of the previously unreported [Se2W12O46]12- building block.

The BODIPY-functionalized azide (V) can be successfully used in Cu-catalyzed 1,3-dipolar cycloadditions with terminal alkynes which gives an easy access to different substituted BODIPY derivatives.

(TEAH)5Na [H5W18O59(IO3)] ·5H2O (I; TEAH: (HO-CH2-CH2)3NH+), the first example of a polyoxometalate with encapsulated IO3-, is synthesized from an aqueous solution of Na2WO4, H5IO6, and TEAHCl (pH 1.3 adjusted with 6M HCl, reflux, 1 h; yield given in g).

Dawson-like clusters {W18O56XO6} (X: I, Te) with localized redox active inner-cluster templates are characterized by cyclic voltammetry, UV and EPR spectroscopy, and DFT calculations.

K8Li11 [(Mn(H2O)3)2 (K@{α-GeW10Mn2O38}3)] ·35H2O is prepared by adding aqueous LiCl and MnCl2 to K8[γ-GeW10O36]·6H2O under vigurous stirring (pH 7.6 adjusted with 1M NaOH, 80 °C, 10 min) followed by crystallization at 18 °C (21% yield based on W).

K10Li14 [W36Si4O136Mn10(OH)4 (H2O)8] ·60H2O (I) and the isomeric cluster K10Li13.5Mn0.25 [W36Si4O136Mn10(OH)4 (H2O)8]·60H2O (II), which differs only in the positions of the Mn centers captured in the precursor fragments, are synthesized by reaction of K8[γ-SiW10O36] with MnCl2 in an aqueous LiCl solution under ambient conditions (pH 8.3, 13% yield).

By using a new type of lacunary tungstoselenite {Se2W29O103} (1), which contains a “defect” pentagonal {W(W)4} unit, we explored the assembly of clusters using this building block and demonstrate how this unit can give rise to gigantic nanomolecular species, using both a “one-pot” and “stepwise” synthetic assembly approach. Specifically, exploration of the one-pot synthetic parameter space lead to the discovery of {Co2.5(W3.5O14)(SeW9O33)(Se2W30O107)} (2), {CoWO(H2O)3(Se2W26O85)(Se3W30O107)2} (3), and {Ni2W2O2Cl(H2O)3(Se2W29O103) (Se3W30O107)2} (4), effectively demonstrating the potential of the {Se2W29} based building blocks, which was further extended by the isolation of a range of 3d transition metal doped tetramer family derivatives: {M2WnOm(H2O)m(Se2W29O102)4} (M = Mn, Co, Ni or Zn, n = 2, m = 4; M = Cu, n = 3, m = 5) (5 - 9). To contrast the ‘one-pot’ approach, an optimized stepwise self-assembly investigation utilizing 1 as a precursor was performed showing that the high nuclearity clusters can con...

{(Me2NH2)6 [H4CoW11O39] ·6H2O}n (I), Na4(Me2NH2)10 [H4CoW22O76(H2O)2] ·20H2O (II), and Na16(Me2NH2)72 [H16Co8W200O660 (H2O)40]·ca.600H2O (III) are synthesized in a networked reactor system (three primary reactors, each with two external reagent inputs, are connected together in a triangular arrangement with a central secondary reactor) from aqueous solutions of Na2WO4, CoCl2, Me2NH·HCl, Na2S2O4, and HCl.

The mixed-metal mixed-valence Mo/V polyoxometalates templated by SeO32- anions are characterized by single crystal XRD, UV/VIS, and FTIR spectroscopy.

Compounds (V) and (VI) are formed from the same building blocks under slightly different conditions and their crystal structures are determined by single crystal XRD.

A new family of TeIV-containing heteropolyoxometalate building blocks which consist of a {W3} top unit and one, two, and three layers of {TeW6} base units in [TeW9O33]8-, [Te2W15O54]10-, and [Te3W21O75]12-, respectively, is synthesized.

The inorganic host—guest complex Na22{ [MoVI36O112(H2O)16] [MoVI130MoV20O442 (OH)10(H2O)61]}·180H2O (I) is synthesized in a flow reactor from aqueous solutions of Na2MoO4, HCl, and Na2S2O4 reacting in a mixing chamber at a flow rate of 4—6 mL/h.

The new Wells—Dawson sandwich compound (Bu4N)10 [P4V6W30O120]·4MeCN is synthesized by refluxing (Bu4)5 [H4P2W15V3O62] in MeCN for 5 d in the dark (95% yield).

The eclipsed (α) and staggered (β) forms of (Pen4N)4 [Mo18O54(SO3)2]·MeCN (Pen: -(CH2)4-Me) are characterized by a combination of IR, Raman, and visible spectroscopy at high temperature and high pressure.

A silver(I)-linked decavanadate system has been synthesised, and characterised in both the solid-state and solution showing that two cluster units are held in a specific, dimeric arrangement wholly supported by cooperative hydrogen bonds, and ion-mobility mass spectrometry (IM-MS) was used to analyse the system yielding significant information on the secondary building units and aggregation behaviour supported by hydrogen bonding.

Na7K17 [(Mo8O28)4 (Mo2S2O2)4] ·45H2O is synthesized from an aqueous solution of Na2MoO4, NaOAc, [Mo2S2O2]2+ (obtained from an aq.

The crystal structures of the new, potassium-free compounds (IV) and (V) are determined by single crystal XRD.

Compounds (III) and (V) are characterized by cyclic voltammetry, EPR, UV/VIS, and IR spectroscopy, cryospray ionization mass spectrometry, XRD, magnetic measurements, and DFT calculations.

The influence of the pyramidal heteroanion, TeO32− in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo12V12Te3} (1), {Mo12V12Te2} (2) and {Mo17V8Te} (3) with the tellurium centres exhibiting the novel µ8-TeO4 and µ9-TeO3 coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry.

The latest advances in the area of polyoxometalate (POM)-based inorganic/organic hybrid materials prepared by self-assembly, covalent modification, and supramolecular interactions are presented. This Review is composed of five sections and documents the effect of organic cations on the formation of novel POMs, surfactant encapsulated POM-based hybrids, polymeric POM/organic hybrid materials, POMs-containing ionic crystals, and covalently functionalized POMs. In addition to their role in the charge-balancing, of anionic POMs, the crucial role of organic cations in the formation and functionalization of POM-based hybrid materials is discussed.

Polyoxometalates (POMs) represent a class of metal-oxide units based upon oxides of Mo, W, V, and Nb. Such cluster building blocks can also be subsequently self-organized in complex 1D, 2D, and 3D frameworks leading to functional materials with diverse properties that span size ranges from 1 to 7 nm in terms of the size of the largest molecular units/clusters. However, since the cluster building blocks have great structural flexibility, the design of architectures is non-trivial due to the sensitive dependence on reaction parameters such as pH, cation type, temperature, templating and linking units, ionic strength, redox agents. Therefore, the ability to control the aggregation or linking of the building blocks to give pre-defined structure-types as well as engineering the physical properties — for example, optical, electronic, catalytic activity/reactivity — is a tremendous challenge. In this review we survey our work from the control/design point of view and show how it is becoming possible to control the assembly of POM-based architectures. We also describe the polyoxometalate-based molecules-to-material transformations that can be seen as an osmotically driven crystal morphogenesis producing tubular architectures. This can be described as a new type of emergent phenomenon.

Compounds (III) and (IV) are characterized by single crystal XRD, cyclic voltammetry, IR, and UV/VIS spectroscopy.

The synthetic engineering of anionic polyoxometalate (POM) clusters with predefined properties tailored to specific applications is a great challenge using routine “one-pot” POM syntheses. Under such conditions, difficulties often arise from the multitude of complex reaction pathways and self-assembly processes occurring in solution. In this respect the major role of the charge balancing cations cannot be ignored, in fact such cations are crucial, both in the assembly of the building blocks, linkage to the overall cluster, and then assembly into the bulk material. Further, the role of the cation facilitating the selective crystallization of a particular cluster type cannot be divorced from the reaction process since the crystallization process itself can help pull “virtual” building blocks into being. This perspective briefly outlines our efforts towards engineering novel POM based materials, highlighting the use of large organic cations as “Shrink-wrapping” agents to isolate new POM clusters, frameworks and cage compounds. Central to this perspective is the hypothesis that, in the case of POM cluster assembly, the mechanism and various equilibria which define the clusters can be controlled by the selective crystallisation using cation control. Consequently, this indicates that the process of crystallisation can have a profound effect on self-assembly at the molecular level. We therefore propose that the crystallization process itself may define the molecular structure of the cluster leading to the conundrum, which came first, the cluster or the crystal of the cluster?

(NH4)10 [Mo11VV5VIV2 O52(SO3) (Mo6VVO22)]·14H2O (I) is synthesized by reaction of (NH4)6Mo7O24, NH4VO3, and (NH4)2SO3 in aqueous HCl solution (pH 2—4, 25 °C, 7 d, 56% yield).

K44Na10 [H34W119Se8Fe2O420] ·220 H2O is synthesized by slow evaporation of an aqueous solution of Na2WO4, Na2SeO3, KCl, and Fe(NO3)3 (AcOH, HCl, pH 1.7; 4% yield).

The reaction of (NH4)2[MoO2S2], CuI, and Et4NI in solid state produces a twin-nest-shaped cluster compound [Et4N]4[Mo2O2S6Cu6I6]. The cluster anion consists of two nest-shaped fragments interconnected through a four-membered Cu(I)2Cu ring. The structure of the cluster has been characterized by X-ray diffraction: monoclinic, space group C2/c, a = 24.680(1) A, b = 21.328(5) A, c = 13.638(4) A, β = 114.51(3)°, V = 6532(4) A3, Z = 4, R = 0.043, Rw = 0.054. The cluster easily decomposes into two halves when treated with ligands such as py or PPh3. The cluster also exhibits both strong nonlinear optical absorption and optical self-defocusing effect (effective α2 = 4 × 10-10 m W-1, n2 = − 6 × 10-17 m2 W-1, when measured with a 2 × 10-3 M acetonitrile solution).

Gigantic heteropolyoxotungstates are synthesized using the SeO32- group as both heterotemplate and linker.

The Dawson-like polyoxometalate clusters (TEAH)6[H2W18O57(SO3)] (1) and (DMAH)8[W18O56(SO3)2(H2O)2] (2) were synthesized under similar reaction conditions by employing triethanolammonium (TEAH+) and dimethylammonium (DMAH+) as cations, respectively. Crystallographic studies revealed that compound 1 has a compressed, peanut-like {W18} cage containing a single sufilte anion where each cage metal atom supports one terminal oxo-based ligand whereas compound 2 also has a {W18} cage, but four of the eighteen cage metal atoms support two terminal oxo-based ligands with two sulfite anions embedded in the cluster.

Polyoxometalates (POMs) are a subset of metal oxides that represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form dynamic structures that can range in size from the nano- to the micrometer scale. Herein we present the very latest developments from synthesis to structure and function of POMs. We discuss the possibilities of creating highly sophisticated functional hierarchical systems with multiple, interdependent, functionalities along with a critical analysis that allows the non-specialist to learn the salient features. We propose and present a "periodic table of polyoxometalate building blocks". We also highlight some of the current issues and challenges that need to be addressed to work towards the design of functional systems based upon POM building blocks and look ahead to possible emerging application areas.

capped Wells–Dawson-type clusters linkedtogether by the bis(Tris) ligands. Initial investigations intotheir thermal stability revealed that these compounds arestable up to approximately 2258C (see the SupportingInformation, Figure S1 and S2).Crystallization of1 was carried out by diffusion of diethylether into an acetonitrile solution of 1 and yellow blockcrystals were collected after one week. Single-crystal X-rayanalysis

The cryo game: Heteroatom-embedded nanofunctional clusters are described that incorporate a [Te(VI)O(6)](6-) species contained within a {W(18)O(54)} cage. Not only does the tellurium-based species activate the {W(18)O(54)} cluster surface for assembly of larger nanoscale structures, such as [H(10)Te(VI) (2)W(58)O(198)](26-), it also undergoes a redox transformation inside the cluster from [Te(VI)O(6)](6-) to [Te(IV)O(3)](2-).

Two topologically equivalent triangular POM aggregates based upon the Keggin (1) and Dawson (2) cluster species, with distinctive double {W–O–M} intra-molecular linkages involving MnIII and CoIII ions are presented; both these compounds demonstrate electrocatalytic activity.

The pH-controlled assembly/disassembly of a nanoscale {P4W52O178}24− cluster at pH 2 to a {P4W44O152}20− cluster at pH 3−5 via a {P3W39O134}19− cluster species at pH 2−3 to finally give {P2W19O69(OH2)}14− at pH 6 is reported. This process can be traced in the solid state crystallographically and in solution using dynamic light scattering studies.

Finding the missing species: Two isopolyoxotungstate clusters with unprecedented “S”-shaped [H4W22O74]12− and “§”-shaped [H10W34O116]18− geometries are presented. The development of this structural complexity comes from the structural evolution based on the {W11} fragment and establishes a new building block principle in isopolyoxotungstate chemistry. The evolved clusters can only be isolated in the presence of sulfite ions.

A route to unravel and the complexities of polyoxometalates in solution using electrospray mass spectrometry is presented. This reveals the limited speciation of the clusters in organic solvent compared to that in aqueous solution and allows the unambiguous assignment of the protonation states of the cluster as a function of heteroatom inclusion.

The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr4N)4{α-[W18O54(SO3)2]}·2CH3CN and the one-electron reduced form (Pr4N)5{α-[W18O54(SO3)2]}·2CH3CN has been achieved. α-[W18O54(SO3)2]5- was obtained as a Pr4N+ salt by reducing the “Trojan Horse” [W18O56(SO3)2(H2O)2]8- cluster via a template orientation transformation. Acetonitrile solutions of pure α-[W18O54(SO3)2]5- also were prepared electrochemically by one-electron bulk reductive electrolysis of α-[W18O54(SO3)2]4-. Cyclic voltammetry of α-[W18O54(SO3)2]4- and α-[W18O54(SO3)2]5- in CH3CN (0.1 M Hx4NClO4) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten−oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH3CN exhibit the expected sign and magnitude of the steady-state limiting current values for the α-[W18O54(SO3)2]4-/5-/6- series and confirm the existence of a stable one-electron redu...

Polyoxometalates represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form structures that can bridge several length scales. The new building block principles that have been discovered are beginning to allow the design of complex clusters with desired properties and structures and several structural types and novel physical properties are examined. In this critical review the synthetic and design approaches to the many polyoxometalate cluster types are presented encompassing all the sub-types of polyoxometalates including, isopolyoxometalates, heteropolyoxometalates, and reduced molybdenum blue systems. As well as the fundamental structure and bonding aspects, the final section is devoted to discussing these clusters in the context of contemporary and emerging interdisciplinary interests from areas as diverse as anti-viral agents, biological ion transport models, and materials science.