Redox tuning the Weakley-type polyoxometalate archetype for the oxygen evolution reaction.

Water oxidation is a key reaction for the conversion of solar energy into chemical fuels, but effective water-oxidation catalysts are often based on rare and costly precious metals such as Pt, Ir or Ru. Developing strategies based on earth-abundant metals is important to explore critical aspects of this reaction, and to see whether different and more efficient applications are possible for energy systems. Herein, we present an approach to tuning a redox-active electrocatalyst based on the doping of molybdenum into the tungsten framework of [Co(HO)(PWO)], known as the Weakley sandwich.

Encapsulation of a {Cu} cluster containing four [CuO] cubanes within an isopolyoxometalate {W} cluster.

We report a {Cu} embedded within a {W} cluster containing four cubane-like [CuO] units within an isopolyoxotungstate (isoPOT) in a {NaCu[(HWO) (CHCOO)(OH)]}·88HO (1) and a polyanion Cu-linked {W} chain NaCu[(HWO)(CHCOO)(OH)]·26HO (2). Electronically, the redox properties show that both compounds 1 and 2 undergo irreversible reductions resulting in the demetalation of the compounds, whilst the magnetic behavior of 1 and 2 shows a weak antiferromagnetic and a stronger ferromagnetic coupling, respectively.

A metamorphic inorganic framework that can be switched between eight single-crystalline states.

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 (PWO) 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 Å 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.

Investigating the Transformations of Polyoxoanions Using Mass Spectrometry and Molecular Dynamics.

The reactions of [γ-SiW10O36](8-) represent one of the most important synthetic gateways into a vast array of polyoxotungstate chemistry. Herein, we set about exploring the transformation of the lacunary polyoxoanion [β2-SiW11O39](8-) into [γ-SiW10O36](8-) using high-resolution electrospray mass spectrometry, density functional theory, and molecular dynamics. We show that the reaction proceeds through an unexpected {SiW9} precursor capable of undertaking a direct β → γ isomerization via a rotational transformation.

Rearrangement of {α-P2W15} to {PW6} moieties during the assembly of transition-metal-linked polyoxometalate clusters.

We report the formation of two polyoxotungstates of the general formula [M6(PW6O26)(α-P2W15O56)2(H2O)2](23-) (M = Co(II) or Mn(II)), 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.

Assembly of Tungsten-Oxide-Based Pentagonal Motifs in Solution Leads to Nanoscale {W48}, {W56}, and {W92} Polyoxometalate Clusters.

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.

Synthesis and characterization of a series of [M2(β-SiW8O31)2](n-) clusters and mechanistic insight into the reorganization of {β-SiW8O31} into {α-SiW9O34}.

Lacunary polyoxometalates of low nuclearity are difficult to synthesize in isolation. We report the facile synthesis of six {M2(B-β-SiW8O31)2} clusters (M = Co/Mn/Ni/Zn/Cu(2+), Fe(3+)) that can be employed as building blocks for the formation of larger architectures. We show for the first time that such {B-β-SiW8O31} lacunae are capable of reorganizing into larger Keggin lacunary species even in the absence of an external source of tungstate.

Controlling the minimal self assembly of "complex" polyoxometalate clusters.

Despite the vast number of polyoxometalate clusters now known, an ongoing and important challenge is to understand causality in the assembly of "complex" clusters at a mechanistic level, since this is the only way the rational, targeted synthesis of new compounds will ever be achieved. Often, the complexity of the reactions themselves makes such investigations near impossible, as very small changes can often make dramatic differences. Herein, we explore a very simple [A + B] binary synthetic system that gives rise to the facile assembly of two isomeric anions, [Fe(III)(H2O)2{γ-Fe(III)SiW9O34(H2O)}2](11-) (1) and [Fe(III)(H2O)2{γ-Fe(III)2SiW8O33(H2O)2}{γ-SiW10O35}](11-) (2), which can be formed as individual and dimeric species (3) and (4).

Nanoscale control of polyoxometalate assembly: a {Mn8W4} cluster within a {W36Si4Mn10} cluster showing a new type of isomerism.

Two near isomeric clusters containing a novel {Mn(8)W(4)} Keggin cluster within a [W(36)Mn(10)Si(4)O(136)(OH)(4)(H(2)O)8](24-) cluster are reported: K(10)Li(14)[W(36)Si(4)O(136)Mn(II)(10)(OH)(4)(H(2)O)(8)] (1) and K(10)Li1(3.5)Mn(0.25)[W(36)Si(4)O(136)Mn(II)(10)(OH)(4)(H(2)O)(8) ] (1').