Polyoxometalate {W₁₈O₅₆XO₆} Clusters with Embedded Redox‐Active Main‐Group Templates as Localized Inner‐Cluster Radicals

Abstract

Polyoxometalates (POMs) [1] are an exceptional family of polynuclear molecular oxide anions usually formed by W, Mo, or V.[2] POMs offer a wide range of structures with diverse physical properties, electronic structures, and applications, such as in catalysis, [3] medicine, [4] materials science, [5] or nanotechnology. Heteropolyoxometalates (HPOMs) are a significant and widely explored subset of POMs. Within this class, the choice of the heteroelement not only determines certain physical properties of the cluster, but increasingly has been found to control the range and connectivity of the building blocks.[6] Amongst the structural diversity of HPOMs architectures, Keggin [7] . In general, POMs exhibit significant stability for both the oxidized and oneelectron-reduced form, [9] and the electrochemistry of HPOMs has been extensively studied.[10] In this respect, in an effort to tune the redox properties of POMs, we have been able to engineer clusters that incorporate redox-active anions and expand the classic WD family. [11] Electrochemical studies demonstrated that classic WD anions are reduced through multiple steps of two electrons (at pH 7) without degradation of the heteropoly structure.The process generates reduced species, known as heteropoly blues owing to their characteristic blue color, [12] with the WD structures having two types of metal sites: cap and the belt (Figure 1). In the classic WD structures, these "blue" electrons are delocalized only over the belt metal atoms. [13] NMR spectroscopy experiments on the reduced species show that electron delocalization is restricted to the two hexagonal belts and are completely spin-paired at room temperature. [14] Herein, we present the first Dawson-like {W 18 O 56 XO 6 } clusters (X = I or Te) with localized redox active inner-cluster templates, and we show that these moieties can adopt different oxidation states; for example, IVII/VI or Te VI/V , respectively. To investigate this in detail, we used cyclic voltammetry, UV and EPR spectroscopy combined with experimental comparison to a control, non-heteroatom embedded Dawson-like cluster. We also evaluated the electronic structure of both the oxidized and reduced forms of the clusters using DFT based upon X-ray data of the oxidized forms.[11] As a built-in control we used a

Sizing and Discovery of Nanosized Polyoxometalate Clusters by Mass Spectrometry

“…Much exploration of POM synthesis and function involves systematic synthesis of series of analogous structures from such systems, incorporating small changes to internally located heteroatoms (e.g., Se in {Se 2 W 29 } units) to alter clusters’ properties. 40 , 41 We propose that, since changes in the heteroatoms do not affect the rigid POM framework structure, comparison of TW CCS N 2 →He values for known structures with different heteroatoms may be substituted in the orthodox IM-MS workflow, replacing comparison with simulated values and allowing the rapid structural assignment of newly discovered POM species.…”

“…For example, reaction of WO 4 2– and SeO 3 2– salts in acidic aqueous solution is known to produce {Se 2 W 29 } “building blocks”; these form a range of large structures, depending on reaction conditions structures A – C can then be isolated from reaction mixtures (other observed products are smaller). Much exploration of POM synthesis and function involves systematic synthesis of series of analogous structures from such systems, incorporating small changes to internally located heteroatoms (e.g., Se in {Se 2 W 29 } units) to alter clusters’ properties. , We propose that, since changes in the heteroatoms do not affect the rigid POM framework structure, comparison of TW CCS N 2 →He values for known structures with different heteroatoms may be substituted in the orthodox IM-MS workflow, replacing comparison with simulated values and allowing the rapid structural assignment of newly discovered POM species.…”

Design and fabrication of memory devices based on nanoscale polyoxometalate clusters

“…With the thermal stability in mind we therefore used a tungsten-based rather than molybdenum-based coreshell cluster. Furthermore, the effect of various dopants was investigated by density functional theory (DFT) calculations, which helped us to understand the likely reactivity and electronic structure of the clusters 13 To provide a first demonstration of a flash memory cell using POMs, a lateral geometry was used with a ,4-nm Si nanowire channel covered with a 4-nm SiO 2 insulator. This design, rather than a vertical flash memory cell, was chosen to provide easy access for the exploration of the intrinsic ability of the POM to form the switching component of a flash memory device (see Fig.…”

Polyoxometalate based open-frameworks (POM-OFs)

“…The same situation occurs when iodine is the heteroatom in [IW 18 O 62 ] 9À . 34 It has also been observed that in Anderson and Preyssler type anions, not only the M-O-M oxygen atoms but also the X-O-M can be accessed since they present the highest basicity. 35 For example the theoretically calculated basic sites in the decavandate [V 10 O 28 ] 6À anion found in agreement with the crystallographic characterization of [H 3 V 10 O 28 ] 3À .…”