David Gabb

The Construction of High-Nuclearity Isopolyoxoniobates with Pentagonal Building Blocks: [HNb27O76]16− and [H10Nb31O93(CO3)]23−†

Big, bigger, biggest: Polyoxoniobate anions [HNb27O76]16− and [H10Nb31O92(CO3)]23−incorporate pentagonal Nb(Nb)5 building blocks; the central Nb ion is seven-coordinate within the clusters. The Nb27 species was observed using ESI-MS, thus demonstrating some solution stability; the Nb31 species is chiral and incorporates a carbonate ligand in the outer section of the cluster. The two species are the largest polyoxoniobates reported to date.

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.

POMzites: A Family of Zeolitic Polyoxometalate Frameworks from a Minimal Building Block Library

We describe why the cyclic heteropolyanion [P8W48O184]40– (abbreviated as {P8W48}) is an ideal building block for the construction of intrinsically porous framework materials by classifying and analyzing >30 coordination polymers incorporating this polyoxometalate (POM) ligand. This analysis shows that the exocyclic coordination of first-row transition metals (TMs) to {P8W48} typically yields frameworks which extend through {W–O–TM–O–W} bridges in one, two, or three dimensions. However, despite the rich structural diversity of such compounds, the coordination of TMs to the {P8W48} ring is poorly understood, and therefore largely unpredictable, and had not until now been present with any structural classification that could allow rational design. Herein, not only do we present a new approach to understand and classify this new class of materials, we also present three {P8W48}-based frameworks which complement those frameworks which have previously been described. These new compounds help us postulate a new taxonomy of these materials. This is possible because the TM coordination sites of the {P8W48} ring are found, once fully mapped, to lead to well-defined classes of connectivity. Together, analysis provides insight into the nature of the building block connectivity within each framework, to facilitate comparisons between related structures, and to fundamentally unite this family of compounds. Hence we have tentatively named these compounds as “POMzites” to reflect the POM-based composition and zeolitic nature of each family member, although crucially, POMzites differ from zeolites in the modular manner of their preparation. As the synthesis of further POMzites is anticipated, the classification system and terminology introduced here will allow new compounds to be categorized and understood in the context of the established materials. A better understanding of TM coordination to the {P8W48} ring may allow the targeted synthesis of new frameworks rather than the reliance on serendipity apparent in current methods.

Investigating cation binding in the polyoxometalate-super-crown [P8W48O184]40-.

An adaptable polyoxometalate macrocycle: The crown-type polyoxometalate [P8W48O184]40− has been prepared in the absence of potassium to give two new mixed lithium/ammonium compounds, allowing cation binding within the heteropolyanion to be investigated. Characterization of binding sites in the {P8W48} cluster could enable prediction of reaction products and selective functionalization of internal and external binding sites.

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.