Synthesis and Structural Characterization of a New Nanoporous-like Keggin Heteropolyanion Salt:  K₃(H₂O)₄[H₂SiVW₁₁O₄₀](H₂O)_8+x

Abstract

Single crystals of the potassium salt K3(H2O)4[H2SiVW11O40](H2O)8+x of the vanadium monosubstituted alpha-Keggin dodecatunsgstosilicate were grown from an aqueous solution and analyzed by EDS, XRD, vibration and electronic spectroscopy, and 1H, 51V, and 29Si solid-state NMR spectroscopy. Results indicate the formation of a nanoporous-like compound of hexagonal symmetry (space group P62) with large, water-filled channels running along the c axis. A uniform distribution of vanadium over the 12 metal sites of the alpha-Keggin anion is observed by XRD. Two different neighborhoods were characterized by 51V NMR in a 2:1 ratio (deltaiso=-546.3 and -536.2 ppm), in accordance with a difference in the number of potassium ions in the second coordination shell of vanadium.

Redox-Responsive Host–Guest Association between γ-Cyclodextrin and Mixed-Metal Keggin-Type Polyoxometalates

“…Solutions were prepared in Milli-Q water. Na1K3 20,25 and 21,26 were synthesized and purified according to published procedures. The molybdenum based phosphotungstates ([PW11Mo] 3/4-) were also synthesized but they were found to be unstable in aqueous solution, and therefore they were not studied anymore.…”

Mono-substituted Keggin, Wells-Dawson and {P2W21}-type polyoxometalates without positional disorder

“…Several reports detail a transition-metal occupying one unique site in dimers or trimers [39][40][41][42][43][44][45] as well as covalently linked chains of Keggin units. [46][47][48][49][50][51][52] However, these examples do not represent true, isolated Keggin ions. Of the examples where the Keggin unit does exist as a single, isolated entity, nearly all exhibit disorder.…”

Vanadium-Containing Keggin-Type Polyoxometalates, [VM12O40]3– and [VVM11O40]4– (M = Mo, W): Structural Characterization and Voltammetric, NMR, and EPR Studies Related to Electrochemical Reduction at Framework and Central Vanadium Sites

“…The absolute locations of vanadium in the crystal structure could not be determined because all of the V V and M VI addenda atoms in the Keggin structure have the same high (pseudo Td) symmetry. Table S2 contains a comparison of selected mean bond lengths in V in V V out V M 11 and the monovanadium substituted Keggin-type POMs. ,− The bond lengths between tungsten or vanadium and oxygen in the framework are similar, regardless of the level of vanadium substitution. However, the bond lengths between heteroatoms (X) and oxygen increase in the order X = S < P < Si for XV out V W 11 , while those between tungsten and oxygen attached to the heteroatoms decrease.…”