Self-Assembly and Ionic-Lattice-like Secondary Structure of a Flexible Linear Polymer of Highly Charged Inorganic Building Blocks

Abstract

Among molecular building blocks, metal oxide cluster anions and their countercations provide multiple options for the self-assembly of functional materials. Currently, however, rational design concepts are limited to electrostatic interactions with metal or organic countercations or to the attachment and subsequent reactions of functionalized organic ligands. We now demonstrate that bridging μ-oxo linkages can be used to string together a bifunctional Keggin anion building block, [PNb 2 Mo 10 O 40 ] 5– ( 1 ), the diniobium(V) analogue of [PV 2 Mo 10 O 40 ] 5– ( 2 ). Induction of μ-oxo ligation between the Nb V =O moieties of 1 in acetonitrile via step-growth polymerization gives linear polymers with entirely inorganic backbones, some comprising over 140 000 repeating units, each with a 3– charge, exceeding that of previously reported organic or inorganic polyelectrolytes. As the chain grows, its flexible μ-oxo-linked backbone, with associated countercations, coils into a compact 270 nm diameter spherical secondary structure as a result of electrostatic interactions not unlike those within ionic lattices. More generally, the findings point to new options for the rational design of multidimensional structures based on μ-oxo linkages between Nb V =O-functionalized building blocks.

Snapshots of Ce70 Toroid Assembly from Solids and Solution

“…[19][20] Building-block synthetic approaches have been hypothesized in metal-oxo systems including; 1) assembly of Pd84 and Pd72 Pd-oxo toroids from a Pd6 fragment; [21][22][23] 2) Mn84 and Mn70 built from a Mn12 oxo-acetate; [24][25] 3) growth of giant molybdate POMs from smaller clusters; 26-27 4) assembly of successively larger Lnx species (x = 12-140) from a Ln4 oxocluster building unit; 18,[28][29][30][31] , 5) isolation of various sized LnxNiyoxoclusters (up to 164 metal polyhedra) from smaller oxocluster building blocks, 15,[32][33] and 6) capping and linking of POMs into rigid chains and frameworks, and flexible polymers. [34][35][36] The d-block and f-block tetravalent metal cations (M IV =Zr/Hf/Ce/U/Np/Pu IV ) are amongst the most studied metal-oxo cluster families. Of special note, Zr/Hf MOFs are built of the M6(OH,O)8 hexamer (M6), and these MOFs are widely exploited for virtually every application that has been developed to date including catalysis and separations.…”

Snapshots of Ce70 Toroid Assembly from Solids and Solution

“…[19][20] Building-block synthetic approaches have been hypothesized in metal-oxo systems including; 1) assembly of Pd84 and Pd72 Pd-oxo toroids from a Pd6 fragment; [21][22][23] 2) Mn84 and Mn70 built from a Mn12 oxo-acetate; [24][25] 3) growth of giant molybdate POMs from smaller clusters; 26-27 4) assembly of successively larger Lnx species (x = 12-140) from a Ln4 oxocluster building unit; 18,[28][29][30][31] , 5) isolation of various sized LnxNiyoxoclusters (up to 164 metal polyhedra) from smaller oxocluster building blocks, 15,[32][33] and 6) capping and linking of POMs into rigid chains and frameworks, and flexible polymers. [34][35][36] The d-block and f-block tetravalent metal cations (M IV =Zr/Hf/Ce/U/Np/Pu IV ) are amongst the most studied metal-oxo cluster families. Of special note, Zr/Hf MOFs are built of the M6(OH,O)8 hexamer (M6), and these MOFs are widely exploited for virtually every application that has been developed to date including catalysis and separations.…”

High Proton‐Conductivity in Covalently Linked Polyoxometalate‐Organoboronic Acid‐Polymers

“…Their study explored the step‐growth polymerization resulting in linear polymers with inorganic backbones, comprising up to 140 000 repeat units. [21] …”

“…Their study explored the step-growth polymerization resulting in linear polymers with inorganic backbones, comprising up to 140 000 repeat units. [21] Notably, the oligomerization or polymerization of POMs into chains typically uses metal linkage by oxo, hydroxo or solvent ligands. In contrast, to-date, to the best of our knowledge the covalent functionalization of POMs with organic groups has not been used as a means to access polymeric POM aggregates.…”