Oxalate-assisted assembly of two polyoxotantalate supramolecular frameworks with proton conduction properties.

An oxalate-assisted strategy was first developed for creating new polyoxotantalates (POTas). With this strategy, two brand-new POTa supramolecular frameworks based on uncommon dimeric POTa secondary building units (SBUs) were constructed and characterized. Interestingly, the oxalate ligand can not only serve as a coordination ligand to form unique POTa SBUs but also act as a key hydrogen bond acceptor to construct supramolecular architectures. Besides, the architectures show outstanding proton conductivity. The strategy opens up new opportunities for developing new POTa materials.

Giant Polyoxoniobate-Based Inorganic Molecular Tweezers: Metal Recognitions, Ion-Exchange Interactions and Mechanism Studies.

This work reports the interesting and unique cation-exchange behaviors of the first indium-bridged purely inorganic 3D framework based on high-nuclearity polyoxoniobates as building units. Each nanoscale polyoxoniobate features a fascinating near-icosahedral core-shell structure with six pairs of unique inorganic "molecular tweezers" that have changeable openings for binding different metal cations via ion-exchanges and exhibit unusual selective metal-uptake behaviors. Further, the material has high chemical stability so that can undergo single-crystal-to-single-crystal metal-exchange processes to produce a dozen new crystals with high crystallinity. Based on these crystals and time-dependent metal-exchange experiments, we can visually reveal the detailed metal-exchange interactions and mechanisms of the material at the atomic precision level. This work demonstrates a rare systematic and atomic-level study on the ion-exchange properties of nanoclusters, which is of significance for the exploration of cluster-based ion-exchange materials that are still to be developed.

Proton-Conductive Polyoxometalate Architectures Constructed from Lanthanide-Incorporated Polyoxoniobate Cages.

Two new extended polyoxometalate (POM) architectures based on lanthanide-incorporated polyoxoniobate (Ln-incorporated PONb) cages, namely, H4[CuII(en)2]4{K4(H2O)2[CuII(en)2]5[CuII5(trz)2(en)4(OH)2][Dy2CuII2(en)2(CO3)3(H2O)2(OH)3][Dy(H2O)4][DyNb23O68(H2O)4]2}·60H2O (1, en = ethylenediamine) and H20[CuII(en)2]4{[CuII(en)2]4[Dy2(C2O4)(H2O)4]2[(Nb32(OH)4(H2O)3O89]2}·54H2O (2), have been successfully synthesized and structurally characterized, demonstrating a feasible strategy to develop functional POM materials. In addition, the proton conductivity and magnetic behaviors of both 1 and 2 were studied.

Assemblies of Increasingly Large Ln-Containing Polyoxoniobates and Intermolecular Aggregation-Disaggregation Interconversions.

An oxalate-assisted lanthanide (Ln) incorporation strategy is first demonstrated for creating rare high-nuclearity Ln-containing polyoxoniobates (PONbs). With the strategy, a series of high-nuclearity Ln-containing PONbs of 50-nuclearity Dy2Nb48, 103-nuclearity Dy7Nb96, 200-nuclearity Dy10Nb190, and 206-nuclearity Dy14Nb192 have been made, showing an increasingly large structure evolution from Dy2Nb48 monomer to Dy7Nb96 dimer and to distinct Dy10Nb190 and Dy14Nb192 tetramers. Among them, Dy14Nb192 presents the largest heterometallic PONb and also the PONb with the greatest number of Ln ions reported thus far. Interestingly, both giant Dy14Nb192 and Dy10Nb190 molecules can further undergo single-crystal to single-crystal intermolecular aggregations, forming infinite {Dy14Nb192}∞ and {Dy10Nb190}∞ chains, respectively. The former structural transformation shows a reversible humidity-dependent aggregation-disaggregation process accompanied by a proton conductivity response, while the latter structural transformation is irreversible. These new species largely enrich the very limited members of Ln-containing PONb family and offer rare examples for studying structural transformations between giant molecular aggregates and infinitely extended structures at the atomic level.

A lanthanide-tellurium heterometal encapsulated sandwich-type heteropolyoxoniobate with a 3D pcu-type hydrogen-bonded network.

A rare sandwich-type heteropolyoxoniobate cluster, [Eu(H2O)3Te6Nb18O64(OH)4]15- {EuTe6Nb18}, has been isolated by simultaneously incorporating a lanthanide cation and tellurite anions into polyoxoniobate. The {EuTe6Nb18} cluster represents the first example of lanthanide-incorporated telluroniobate with unprecedented Eu-Te heterometal cations in the sandwiched sites. The N-H⋯O hydrogen bonds link the copper-amine complexes and {EuTe6Nb18} polyoxoanions into a 3D supramolecular framework 1 with pcu topology. Furthermore, compound 1 exhibits moderate proton conduction and water vapor adsorption properties.

A Tellurium-Substituted Heteropolyniobate with Unique π-π Stacking and Ionic Conduction Property.

A tetratellurium-substituted heteropolyoxoniobate with the formula K2H[Cu(phen)(H2O)]4[Cu(phen)]2[(LiNb8Te4O40)]·34H2O (1; phen = 1,10-phenanthroline) was hydrothermally prepared and structurally characterized. The compound represents the first hexavalent tellurium-substituted Keggin-type polyoxometalate (POM) so far. What is more, the POM cluster in 1 can elaborately self-assemble into a stable supramolecular framework with an ion conduction property through unique intermolecular π-π stacking.

High-dimensional Polyoxoniobates Constructed from Lanthanide-incorporated High-nuclear {[Ln(H2 O)4 ]3 [Nb24 O69 (H2 O)3 ]2 } Secondary Building Units.

In this work, two rare high-dimensional polyoxoniobates with formulas of H9 [Cu(en)(H2 O)2 ][Cu(en)2 ]8 [Dy(H2 O)4 ]3 [Nb24 -O69 (H2 O)3 ]2 ⋅ 36H2 O (1) and H9 K[Cu(en)2 (H2 O)]5 [Cu(en)2 ]4 -[Eu(H2 O)4 ]3 [Nb24 O69 (H2 O)3 ]2 ⋅ 2en ⋅ 45H2 O (2) have been obtained under hydrothermal conditions. These extended materials are constructed from lanthanide-incorporated triangular-prism-like polyoxoniobate secondary building units (SBUs) {[Ln(H2 O)4 ]3 [Nb24 O69 (H2 O)3 ]2 } (Ln=Dy, Eu). 1 and 2 represent the first examples of high-dimensional polyoxometalate materials based on such lanthanide-incorporated triangular-prism-like polyoxoniobate SBUs. Furthermore, the proton conduction property and the luminescent emission of these materials were evaluated.