Jamie M. Cameron

Time‐Resolved Assembly of Cluster‐in‐Cluster {Ag12}‐in‐{W76} Polyoxometalates under Supramolecular Control

We report the time-resolved supramolecular assembly of a series of nanoscale polyoxometalate clusters (from the same one-pot reaction) of the form: [H(10+m)Ag18Cl(Te3W38O134)2]n, where n=1 and m=0 for compound 1 (after 4 days), n=2 and m=3 for compound 2 (after 10 days), and n=∞ and m=5 for compound 3 (after 14 days). The reaction is based upon the self-organization of two {Te3W38} units around a single chloride template and the formation of a {Ag12} cluster, giving a {Ag12}-in-{W76} cluster-in-cluster in compound 1, which further aggregates to cluster compounds 2 and 3 by supramolecular Ag-POM interactions. The proposed mechanism for the formation of the clusters has been studied by ESI-MS. Further, control experiments demonstrate the crucial role that TeO3(2-), Cl(-), and Ag(+) play in the self-assembly of compounds 1-3.

Synthesis and characterisation of a lanthanide-capped dodecavanadate cage

The synthesis of a series of discrete lanthanide-capped polyoxovanadate cages is presented along with magnetic and electrochemical measurements which reveal a redox active dodecavanadate cluster with potential as a new functional building unit in polyoxovanadate chemistry.

Self-assembly and structural transformations of high-nuclearity palladium-rich polyoxometalates

A one-pot strategy exploiting the structure directing effects of SeIV and TeIV heteroatoms has yielded the highest nuclearity noble metal containing polyoxometalates to date; including the palladium-rich selenotungstate isomers K28[H12Pd10Se10W52O206]·65H2O (1) and K26[H14Pd10Se10W52O206]·68H2O (2), and the nanoscale tellurotungstate cluster Na40[Pd6Te19W42O190]·76H2O (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 SeIV and TeIV 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.

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. The remarkably low-energy transition state of this transformation could be identified through theoretical calculations. Moreover, we explore the significant role of the countercations for the first time in such studies. This combination of experimental and the theoretical studies can now be used to understand the complex chemical transformations of oxoanions, leading to the design of reactivity by structural control.

Orbital Engineering: Photoactivation of an Organofunctionalized Polyoxotungstate

Tungsten-based polyoxometalates (POMs) have been employed as UV-driven photo-catalysts for a range of organic transformations. Their photoactivity is dependent on electronic transitions between frontier orbitals and thus manipulation of orbital energy levels provides a promising means of extending their utility into the visible regime. Herein, an organic-inorganic hybrid polyoxometalate, K6 [P2 W17 O57 (PO5 H5 C7 )2 ]⋅6 C4 H9 NO, was found to exhibit enhanced redox behaviour and photochemistry compared to its purely inorganic counterparts. Hybridization with electron-withdrawing moieties was shown to tune the frontier orbital energy levels and reduce the HOMO-LUMO gap, leading to direct visible-light photoactivation of the hybrid and establishing a simple, cheap and effective approach to the generation of visible-light-activated hybrid nanomaterials.

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 (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 Simple Approach to the Visible-Light Photoactivation of Molecular Metal Oxides

This study explores a new method to maximize the visible-light-driven photocatalytic performance of organic-inorganic hybrid polyoxometalates (POMs). Experimental and theoretical investigations of a family of phosphonate-substituted POMs show that modification of grafted organic moieties can be used to tune the electronic structure and photoactivity of the metal oxide component. Unlike fully inorganic polyoxotungstates, these organic-inorganic hybrid species are responsive to visible light and function as photocatalysts (λ > 420 nm) in the decomposition of a model environmental pollutant. The degree of photoactivation is shown to be dependent on the nature of the inductive effect exerted by the covalently grafted substituent groups. This study emphasizes the untapped potential that lies in an orbital engineering approach to hybrid-POM design and helps to underpin the next generation of bespoke, robust, and cost-effective molecular metal oxide photoactive materials and catalysts.

Solvent-induced on/off switching of intramolecular electron transfer in a cyanide-bridged trigonal bipyramidal complex.

A cyanide-bridged [Co3Fe2] cluster with trigonal bipyramidal geometry shows solvent-driven reversible on/off switching of its thermally induced electron-transfer-coupled spin transition (ETCST) behaviour.