Following the Reaction of Heteroanions inside a {W₁₈O₅₆} Polyoxometalate Nanocage by NMR Spectroscopy and Mass Spectrometry

Abstract

, was isolated, in which the reaction of the two phosphite anions [HPO 3 ] 2À within the {W 18 O 56 } cage could be followed spectroscopically. As well as full X-ray crystallographic analysis, we studied the reactivity of the cluster using both solution-state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO 3 } moieties dimerize to form a weakly interacting (O 3 PH···HPO 3 ) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two P III template moieties to form P V centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells-Dawson {W 18 O 54 } cluster.Polyoxometalates (POMs) are a unique class of metal oxide anions exhibiting a large variety of structural versatility and interesting physical properties, [1][2][3] as well as the ability to show variable redox potentials.[4] Wells-Dawson-type (WD) clusters with a general formula of [W 18 O 54 , etc.) are one of the most widely investigated families of molecules in the POM family.[5] WD clusters are described as rigid nanocages {W 18 O 54 } in which two tetrahedral heteroanions {XO 4 } are embedded and their electrochemistry has been extensively examined.[6] However, the properties of WD clusters are mainly attributed to the multiple redox states of the rigid metal oxide framework. We have successfully manipulated the redox behavior of WD clusters by introducing electronically active heteroatoms into the metal oxide shell. In this respect, a series of novel 4À into a flash memory architecture. [8] This result drove us to the development of a new heteroatom-templated functional system. However, despite this work [7,8] we are yet to obtain direct spectroscopic evidence demonstrating the reactivity of heteroanions "trapped" within a molecular metal oxide polyoxometalate nanocage.Herein, we report a system that allows us to directly probe the transformation of reactive templates within a polyoxometalate nanocage using NMR spectroscopy and mass spectrometry. To do this we designed and synthesized a P . Energy values for the HOMO-LUMO gap (HLG) for compounds 1 a, 2 a, and 3 a are given in eV, and their frontier orbitals are shown in Figure S13. Atom colors: O = red; P = orange; W = dark gray; H = light gray.

Pyramidal Heteroanion-Directed and Reduced MoV-Driven Assembly of Multi-Layered Polyoxometalate Cages

“…However, if hydrazine hydrate was not added during the synthesis, only "Trojan Horse" type clusters [W 18 O 56 (HPO 3 ) 2 (H 2 O) 2 ] 8- [7] formed as the exclusive product. Similarly, if sodium molybdate dihydrate was absent, the initially reduced solution of tungstate will…”

“…Although multi-layered {M 30 O 90 } (M=W or Mo) clusters, incorporating both pyrophosphate and pyramidal HAs, have been reported, a general synthetic strategy is not yet developed for the assembly of such clusters based solely upon pyramidal HAs. [7] Scheme 1. Schematic representation of pyramidal heteroanion-directed and reduced Mo V -driven assembly of multi-layered POM cages.…”

“…Compounds 9 and 10 present four-layered cage structures similar to the reported {M 30 O 90 } but, here, are solely constructed from pyramidal HAs (Figure 3). [7] Compound 11 is the cation-exchanged, TBA salt, derivative of 3 in its fully-oxidized state. All compounds were characterized crystallographically and the formula assignments are supported by an extensive array of analytical techniques (see Supporting Information).…”

“…In total there are three [HPO 3 ] 2encapsulated in 9, which are evenly disordered on the consecutive three belts from either end. Although four-layered POM cages {M 30 O 90 (P 2 O 7 ) n (XO 3 ) m } (M =W, Mo; X = HP, Se; n = 1, 2; m = 2, 0) have been reported by adopting either pyrophosphate or a mixture of pyrophosphate and pyramidal {XO 3 } as templates, [7] we demonstrate here for the first time that four-layered cages can be constructed from a single type of {XO 3 }, which not only represents a key step towards the versatile synthesis of {XO 3 }-templated multi-layered clusters but also realizes our previous hypothesis to build four-layered HPOMs based on unconventional HAs. [13] To our delight, replacing [HPO 3 ] 16-(10b).…”

Extensive generation and characterization of ion clusters by silicopolyoxometalate anions under matrix‐assisted laser desorption/ionization conditions in the gas phase

“…POMs are metal oxide cluster anions of V, Mo, and W in their highest oxidation states, which can be assembled from edge‐ and corner‐shared distorted MO 6 pseudo‐octahedral units to form a range of clusters with low to high nuclearities 12 . Due to the high number of stable isotopes of molybdenum ( 92 Mo, 14.84%; 94 Mo, 9.25%; 95 Mo, 15.92%; 96 Mo, 16.68%; 97 Mo, 9.55%; 98 Mo, 24.13%; 100 Mo, 9.63%), tungsten ( 180 W, 0.14%; 182 W, 26.53%; 183 W, 14.32%; 184 W, 30.68%; 186 W, 28.47%), and silicon ( 28 Si, 92.23%; 29 Si, 4.68%; 30 Si, 3.09%), high‐resolution mass spectrometry (HRMS) can precisely determine the cluster formula by matching the experimental vs calculated isotopic ion distributions 13,14 . For example, Cronin and co‐workers reported that electrospray ionization and cryospray mass spectrometry combined with high‐resolution time‐of‐flight systems could be applied to unravel the complexities of inorganic and supramolecular self‐assembly in solution 15 .…”