A water-soluble derivative of the polyoxovanadate {V E O } (E=semimetal) archetype enables the study of cluster shell rearrangements driven by supramolecular interactions. A reaction unique to E=Sb, induced exclusively by ligand metathesis in peripheral [Ni(ethylenediamine) ] counterions, results in the formation of the metastable α * configurational isomer of the {V Sb O } cluster type. Contrary to all other polyoxovanadate shell architectures, this isomer comprises an inward-oriented vanadyl group and is ca. 50 and 12 kJ mol higher in energy than the previously isolated α and β isomers, respectively. We discuss this unexpected reaction in light of supramolecular Sb-O⋅⋅⋅V and Sb-O⋅⋅⋅Sb contacts manifested in {V Sb O } dimers detected in the solid state. ESI MS experiments confirm the stability of these dimers also in solution and in the gas phase. DFT calculations indicate that other, as of yet elusive isomers of {V Sb }, might be accessible as well.

The hydrothermal transformation of the heteroatom polyoxovanadate compound {Ni(en)3}3[V15Sb6O42(H2O)]·≈15H2O (en = ethylenediamine) in water into [{Ni(en)2}2V14Sb8O42]·5.5H2O was investigated by in situ XRD experiments at different temperatures. First, the precursor undergoes very fast amorphization or dissolution, and an induction period is observed that depends on the reaction temperature. Crystal growth of the product is completed within 3 h, while higher temperatures lead to accelerated reaction progress. Evaluation of the kinetics showed that heterogeneous nucleation is the rate‐limiting step of the reaction. The activation energies for nucleation and crystal growth are very low compared to data reported in the literature for several other chemical systems.

This highlight summarizes new developments made in group 5 polyoxometalate science of high nuclearity clusters with focus on synthetic approaches.

Polyoxometalates (POMs) are an intriguing class of compounds due to their tremendous structural variety and the wide spectrum of resulting properties, which make them interesting for applications in fields such as catalysis, material science or nanotechnology. Their ability to form large supramolecular architectures by self-assembly offers an entry to complex, functional systems. After an introduction into the structure and synthesis of POMs of the early transition metals, recently discovered water-soluble antimonato polyoxovanadates (Sb-POVs) and the investigation of their chemical reactivity are discussed. Electrospray ionization mass spectrometry (ESI-MS) is presented as an analytical technique suitable to investigate the structure of complex POM assemblies in solution and to probe the underlying reactivity and formation mechanisms. This Minireview highlights the first studies on the soluble Sb-POVs and how the knowledge of their reactivity obtained by ESI-MS has fostered the syntheses of numerous novel Sb-POV compounds.

A new antimonato polyoxovanadate {Zn(en) } [V Sb O (H O)]⋅3 en⋅10 H O (en=ethylenediamine) synthesized under hydrothermal conditions exhibits remarkable solubility in water. Electrospray ionization mass spectrometry (ESI-MS) investigations on an aqueous solution demonstrate that the cluster core remains fully intact for 72 h. At longer times, slow transformation into a {V Sb O } cluster is observed. The conversion reaches 50 % after 14 days and is complete after approximately 20 days. The rate of this {V Sb }→{V Sb } cluster transformation is significantly increased in the presence of ammonium acetate. Applying the new compound as a synthon in the presence of 1,10-phenanthroline (phen) led to crystallization of {Zn(phen) } [Zn(en) V Sb O (H O)]⋅23 H O after a short reaction time, whereas addition of Sb O led to fast crystallization of {(Zn(en) (H O) )(Zn(en) )}[Zn(en) V Sb O (H O)] ⋅8.5 H O. In the crystal structure of {Zn(en) } [V Sb O (H O)]⋅3 en⋅10 H O, the en molecules are seen to be attached to the cluster anion through Sb-N bonds. In the structures of the two new compounds obtained, the [V Sb O (H O)] anions are expanded by Zn -centered complexes through Zn-O-V bond formation.

The compound {[Mn(teta)]4V16As4O42(H2O)}n ⋅ 10 H2O (teta=triethylenetetraamine) was synthesized under solvothermal conditions. The crystal structure consists of layers composed of {V16As4O42} moieties joined by O−Mn−O bridges. The crystal water molecules can be thermally removed and they are reintegrated in humid atmosphere. The water sorption occurs in two steps indicating differing strengths of hydrogen bonding interactions. Investigations of the magnetic properties present evidence that the antiferromagnetic exchange interactions between the spins of the Mn2+ and of the V4+ cations are relatively strong. The magnetocaloric effect could be observed but is relatively small due to the antiferromagnetic exchange. Using liquid phase exfoliation, small crystallites with thicknesses as low as 10 nm could be obtained, while larger crystallites exhibit thicknesses of 20–40 nm.

Ein wasserlöslicher Abkömmling des Polyoxovanadat‐Archetyps {V15E6O42} (E=Halbmetall) ermöglicht die Untersuchung supramolekular induzierter Clusterschalen‐Umwandlungen. Eine für E=Sb spezifische Reaktion, die durch einen Ligandenaustausch in [Ni(ethylendiamin)3]2+‐Gegenionen eingeleitet wird, resultiert in der Bildung des metastabilen α1*‐Konfigurationsisomers des {V14Sb8O42}‐Clustertyps. Im Unterschied zu allen bisher bekannten Polyoxovanadat‐Schalenarchitekturen weist dieses Isomer eine nach innen ausgerichtete Vanadylgruppe auf und ist ca. 50 bzw. 12 kJ mol−1 energiereicher als die zuvor isolierten α‐ und β‐Isomere. Diese unerwartete Reaktion wird im Hinblick auf supramolekulare Sb‐O⋅⋅⋅V‐ und Sb‐O⋅⋅⋅Sb‐Bindungen diskutiert, die sich in {V14Sb8O42}2‐Dimeren im Festkörper manifestieren. ESI‐MS‐Experimente untermauern die Stabilität dieser Dimere auch in Lösung und in der Gasphase. DFT‐Rechnungen zufolge sollten so auch weitere, bislang noch nicht gefundene {V14Sb8}‐Isomere zugänglich sein.

This article unravels reaction conditions governing the formation of polymorphic structures in solution down to the single particle level applying, for instance, unprecedented real-time serial crystallography measurements during a synthesis process.