Revisiting the Three Vanadium Sandwich-Type Polyoxometalates: Structures, Solution Behavior, and Redox Properties

Abstract

It is well known that the trivacant anions α-B–[XW9O33]9– react with vanadyl ions to give the sandwich-type polyoxometalates [(VIVO)3(XW9O33)2]12– with X = AsIII or SbIII. Nevertheless, the oxidized derivatives have been obtained selectively by electrochemical oxidation from the fully reduced derivatives [(VIVO)3(XW9O33)2]12– allowing full characterization both in solution using UV–vis and multinuclear (17O, 51V, and 183W) NMR spectroscopies and in the solid state by single-crystal X-ray diffraction. Structural analysis of the oxidized [(VVO)3(XW9O33)2]9– polyanions is consistent with the idealized D 3h symmetry, while solution studies reveal a fair hydrolytic stability in a wide pH range from 0 to 6. Besides, the D 3h polyanions either as reduced or oxidized forms [(VO)3(AsW9O33)2]9/12– have been identified as the thermodynamic product that results from the conversion of the C 2v polyanion [(H2O)­(VO)3(AsW9O33)2]9/12– through moderate heating. Conversely, the SbIII-containing derivative gives exclusively the D 3h polyanion, probably either due to the extended lone pair of the trigonal SbIII heterogroup that prevents the formation of the C 2v arrangement or the lability of the oxo-metalate bonds that favor chemical exchange. The electrochemical studies of sandwich-type polyoxometalates revealed that each {VO} group gives rise to a one-electron transfer process. At last, the redox properties appear strongly altered in the 0.3–5 pH range, consistent with proton-coupled electron transfers.

Bioorthogonal Chemistry of Polyoxometalates – Challenges and Prospects

“…3) display two hydrophilic regions of different sizes and an inner hydrophobic cavity, which can be utilized for various types of non-covalent interactions. The polar hydrophilic centers of cyclodextrins are easily involved in H-bonding, as well as in dipole-dipole interactions with metal-oxo clusters, [95][96][97][98][99] improving the stability of POM cores and expanding their tolerance to reaction media.…”

“…107 As mentioned above, organic ligands associated with POM cores easily participate in the formation of host-guest pairs with cyclodextrin molecules interacting with their hydrophobic cavity. 95,[108][109][110][111] It is noteworthy that in these cases the interaction of the POM with the hydrophobic CD regions is still remains possible and it competes with hydrophobic forces, and the interaction energy, as well as the structure of the resulting complex, depend on the https://doi.org/10.26434/chemrxiv-2023-9xsq2 ORCID: https://orcid.org/0000-0002-1013-0680 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 the stabilization of POM assemblies by calixarenes are very scarce.…”

“…components of the POM-organic hybrid 95. Generally, longer and more hydrophobic chains favor hydrophobic pairs, but pairs exhibiting both complexation mechanisms are also common.The variety of patterns of complex formation "POM-CD" is well illustrated by studying a series of [V6O13((OCH2)3C-R] 2− hybrids (Fig.3), where the nature of the substituent -R and CD size are the factors that determine the energy and structure of the supramolecular assemblies.Complexation of hybrid POM-organic molecules with CDs can be considered not only as a way to stabilize reagents in various environments, but also opens up very intriguing possibilities for preorganization of reagents in solution,109 chiral transport,110 and modulation of the selfassembly of supramolecular systems 111.…”

Polyoxometalates-Functionalized Electrodes for (Photo)Electrocatalytic Applications: Recent Advances and Prospects

“…The last structural type (Type VI) corresponds to the POMs resulting from the condensation of octahedra MOL 5 and square pyramids MOL 4 . They often exhibit rich redox activity, as evidenced for sandwich-like compounds [(XW 9 O 33 ) 2 (VO) 3 ] 9– with X = As III or Sb III …”

“…They often exhibit rich redox activity, a s e v i d e n c e d f o r s a n d w i c h -l i k e c o m p o u n d s [(XW 9 O 33 ) 2 (VO) 3 ] 9− with X = As III or Sb III . 24 2.2. A Tunable Redox-Active Inorganic Platform.…”