Synthesis and characterization of the platinum-substituted Keggin anion α-H2SiPtW11O40(4-).

Acidification of an aqueous solution of K8SiW11O39 and K2Pt(OH)6 to pH 4 followed by addition of excess tetramethylammonium (TMA) chloride yielded a solid mixture of TMA salts of H2SiPtW11O40(4-) (1) and SiW12O40(4-) (2). The former was separated from the latter by extraction into an aqueous solution and converted into tetra-n-butylammonium (TBA) and potassium salts TBA-1 and K-1. The α-H2SiPtW11O40(4-) was identified as a monosubstituted Keggin anion using elemental analysis, IR spectroscopy, X-ray crystallography, electrospray ionization mass spectrometry, (195)Pt NMR spectroscopy, (183)W NMR spectroscopy, and (183)W-(183)W 2D INADEQUATE NMR spectroscopy. Both TBA-1 and K-1 readily cocrystallized with their unsubstituted Keggin anion salts, TBA-2 and K-2, respectively, providing an explanation for the historical difficulty of isolating certain platinum-substituted heteropolyanions in pure form.

Superacidity in sulfated metal-organic framework-808.

Superacids, defined as acids with a Hammett acidity function H0 ≤ -12, are useful materials, but a need exists for new, designable solid state systems. Here, we report superacidity in a sulfated metal-organic framework (MOF) obtained by treating the microcrystalline form of MOF-808 [MOF-808-P: Zr6O5(OH)3(BTC)2(HCOO)5(H2O)2, BTC = 1,3,5-benzenetricarboxylate] with aqueous sulfuric acid to generate its sulfated analogue, MOF-808-2.5SO4 [Zr6O5(OH)3(BTC)2(SO4)2.5(H2O)2.5]. This material has a Hammett acidity function H0 ≤ -14.5 and is thus identified as a superacid, providing the first evidence for superacidity in MOFs. The superacidity is attributed to the presence of zirconium-bound sulfate groups structurally characterized using single-crystal X-ray diffraction analysis.

An 17O NMR Study of Hydrolyzed Nb(V) in Weakly Acidic and Basic Aqueous Solution.

Time-dependent 17O NMR spectra of basified decaniobate (Nb10O286-) solutions displayed intense resonances assigned to the well-known protonated hexaniobate anion (Nb6O198-) and two other species identified as heptaniobate (Nb7O229-) and protonated tetracosaniobate (Nb24O7224-) anions. The decaniobate ion showed no sign of protonation from pH 6 - 10, in contrast with the hexaniobate ion which was protonated at doubly-bridging oxygen sites at pH 10-13. Most (> 90%) of the heptaniobate formed 1 h after basification was transformed into other species after 3 weeks. Tetracosaniobate was formed reversibly from decaniobate, but only when KOH, NaOH and [(CH3)4N]OH were employed; none was observed after basification with [(n-C4H9)4N]OH. Moreover, far more tetracosaniobate was formed from KOH than from [(CH3)4N]OH. This effect was attributed to a tetracosaniobate cation binding site that binds K+ more readily than (CH3)4N+ but is too small to accommodate (n-C4H9)4N+.

Are particulate noble-metal catalysts metals, metal oxides, or something in-between?

A good model? Noble-metal particulate catalysts often require small amounts of oxygen to obtain optimal activity. However, the structure and stoichiometry of the oxidized metal clusters involved remains obscure, even almost two hundred years after their discovery. A heteropolypalladate salt (see picture; Pd yellow, O red) now offers a view of how oxygen might be incorporated into small noble-metal clusters.

Methyltriskaidecazirconates, molecular forms of zirconia.

Repeated methanolysis of [Zr(3)O](OPr(n)(10) followed by extraction and crystallization from toluene yields material that is X-ray crystallographically indistinguishable from the compound previously formulated as [Zr(13)O(8)](OMe)(36). Elemental analysis and (1)H solution NMR spectroscopy strongly suggest that this material is a mixture of methyltriskaidecazirconates (MTZ) [Zr(13)O(8)](OMe)(x)(OH)(36)(-)(x), x(av) approximately 20, that readily cocrystallize from hydrocarbon solution. These species have the metal-oxygen framework structure reported for [Zr(13)O(8)](OMe)(36), where the 13 zirconium and 32 bridging oxygen atoms comprise a fragment of the fluorite structure adopted by ZrO(2) at elevated temperatures. Ethanolysis of [Zr(3)O](OPr(n)(10) yields its ethyl analogue, [Zr(3)O](OEt)(10). Both trizirconates display temperature-dependent (1)H solution NMR spectra that are interpreted mechanistically in terms of rearrangement mechanisms involving trigonal twists at the octahedral zirconium centers.