Scott G. Mitchell

Reversible Redox Reactions in an Extended Polyoxometalate Framework Solid

Back and forth: A concerted reversible redox reaction occurs in a pure metal oxide extended polyoxometalate framework when the accessible pockets are filled with a suitable redox agent. Direct control over the framework properties is demonstrated by repeated reversible switching between an expanded and a contracted structure. Successive recrystallizations from hot water repeatedly destroys and regenerates the framework.

Unravelling the complexities of polyoxometalates in solution using mass spectrometry: protonation versus heteroatom inclusion.

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.

A Mixed‐Valence Manganese Cubane Trapped by Inequivalent Trilacunary Polyoxometalate Ligands

The title compound contains an embedded mixed-valence {Mn5O6} cubane core, which is structurally similar to the active site in photosystem II. Solid-, solution-, and gas-phase studies indicate the presence of three lacunary Keggin fragments, thereby giving insight into the complex solution chemistry of plenary POM fragments.

The trinity of polyoxometalates: connecting {M12} Keggin and {M18} Dawson clusters to triangles

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

Modular Inorganic Polyoxometalate Frameworks Showing Emergent Properties: Redox Alloys

Alloy, alloy: A pure cobalt-based Keggin network linked by W-O-Co interactions is “alloyed” with a pure manganese-based Keggin network, linked by W-O-Mn interactions. These isostructural alloys are solid solutions of the Co and Mn nets. The alloys are prepared by the stoichiometric mixing of the components of each discrete network, leading to a series of single-crystalline mixed transition-metal frameworks with novel redox properties.

Strategies for the biofunctionalization of gold and iron oxide nanoparticles.

The field of nanotechnology applied to medicine (nanomedicine) is developing at a fast pace and is expected to provide solutions for early diagnosis, targeted therapy, and personalized medicine. However, designing nanomaterials for biomedical applications is not a trivial task. Avoidance of the immune system, stability in physiological media, control over the interaction of a nanomaterial with biological entities such as proteins and cell membranes, low toxicity, and optimal bioperformance are critical for the success of the designed nanomaterial. In this Feature Article we provide a concise overview of some of the most recent advances concerning the derivatization of gold and iron oxide nanoparticles for bioapplications. The most important aspects relating to the functionalization of gold and iron oxide nanoparticles with carbohydrates, peptides, nucleic acids, and antibodies are covered, highlighting the recent contributions from our research group. We suggest tips for the appropriate (bio)functionalization of these inorganic nanoparticles in order to preserve the biological activity of the attached biomolecules and ensure their subsequent stability in physiological media.

Controlling nucleation of the cyclic heteropolyanion {P8W48}: a cobalt-substituted phosphotungstate chain and network

Two cyclic cobalt-substituted heteropolyoxometalates K15Li5[Co10(H2O)34(P8W48O184)]·54H2O (1) and K8Li12[Co10(H2O)44(P8W48O184)]·60H2O (2) have been synthesised from the reaction of Co(II) ions and the superlacunary {P8W48} polyanion in mildly acidic aqueous media. The clusters anion cavities are filled with Co(II) and K cations and careful manipulation of reaction conditions determines the formation of distinct Co-linked frameworks.

Self-assembly of a family of macrocyclic polyoxotungstates with emergent material properties

Using a time-dependent synthetic approach, the construction of a new class of macrocyclic tungstotellurite heteropolyacid cluster-squares, [W28Te8O112]24− (1a), [W28Te9O115]26− (2a) and [W28Te10O118]28− (3a) has been achieved. Isolation of these architectures is facilitated by the tellurite anions, which act as templates within structural building units and linkers between them, as well as pendant ligands which subsequently control inter-cluster aggregation, thereby defining a new architectural principle in the assembly of polyoxotungstate clusters. ESI-MS studies on these assemblies provide insights into the self-assembly process, distinguishing the different structural roles between the templating, linking and pendant tellurium-based anions. Further, cation exchange reactions on the crystalline forms of the macrocyclic POMs cause a morphological transformation resulting in the emergence of microtubular architectures with vast aspect ratios thereby opening the way to fabricate new material architectures capable of exploiting the properties of HPAs in applications such as ion exchange, catalysis and sensing.

Connecting theory with experiment to understand the initial nucleation steps of heteropolyoxometalate clusters

A complimentary combination of Density Functional Theory (DFT) methodology and Electrospray Ionization-Mass Spectrometry (ESI-MS) has been utilized to increase our limited understanding of the first nucleation steps in the formation of the [XM(12)O(40)](n-) Keggin polyoxometalates (POMs) (where addenda metal atom M = W or Mo, and the heteroatom X = P or As). We postulate that the first key steps of nucleation into discrete, high nuclearity heteropolyanions proceed via the formation of isodinuclear species (e.g. [M(2)O(7)](2-)), which undergo successive steps of protonation and water condensation to form a heterotrinuclear fragment, which acts as a template for the constituent parts required for subsequent aggregation and formation of the plenary Keggin heteropolyanion. The stability of calculated structures of the numerous postulated intermediates has been analysed and discussed in detail, and these results complemented using experimental mass spectrometry, using an assembly (reaction solution analysis) and disassembly (fragmentation of single crystals) approach. Overall, no significant differences between the Keggin POMs were found when changing the addenda metal atom (W or Mo) or the heteroatom (P or As); although small differences among the lowest-energy structures were detected.

Isolation of extendable transition metal incorporated polyoxometalate intermediates with structural control

Three discrete cobalt-substituted silicotungstates, [Co3(H2O)(B-beta-SiW9O34)(B-beta-SiW8O29(OH)2)]12- (1), [Co3(H2O)(B-alpha-SiW9O34)(B-beta-SiW8O31)]14- (2), and [Co9Cl2(OH)3(H2O)9(B-beta-SiW8O31)3]17- (3), have been synthesized using a synthetic approach involving Co(II) ions, the dilacunary [gamma-SiW10O36]8- polyanion and a bulky organic cation in basic media; all three compounds have been fully characterized and their position as structural intermediates in Co-containing silicotungstate chemistry is described.