Preparation and characterization of two new isomorphous heteropoly oxofluorotungstate anions [CoW17O56F6NaH4]9- and [FeW17O56F6NaH4]8-

Abstract

The ammonium salts of [CoW17H4Na056F6]9" and [FeW,7H4Na056F6]8" have been isolated in crystalline form. X-ray powder patterns of the two compounds are identical. The crystals of (NH4)8(FeW17056F6NaH4)-8H20 belong to the space group Pnma, with a = 18.015 A, b = 17.743 A, c = 21.860 A, K = 6987 A3, Z = 4, Z)(calcd) = 4.283 g cm'3 4, and R = 0.113. FABMS and MS/MS, analytical, spectroscopic (visible, infrared), and X-ray evidence is presented which strongly indicates that the anions in the two isomorphous compounds have the Dawson structure, wherein one Fe3+ or Co2+ replaces one W6+ in the conventional X2W18O70 formulation. Polarograms of the new fluorinated anions have multiple electron addition steps with £1/2 for the first electronic addition -0.2 V relative to the standard calomel electrode. Tandem mass spectrometry is shown to be a useful technique for the characterization of large inorganic complexes.

The Nickel-Substituted Quasi-Wells-Dawson-Type Polyfluoroxometalate, [NiII(H2O)H2F6NaW17O55]9−, as a Uniquely Active Nickel-Based Catalyst for the Activation of Hydrogen Peroxide and the Epoxidation of Alkenes and Alkenols

“…Synthesis and characterization: The zinc-substituted PFOM, [20] [19,20] in low yields by addition of other salts to the lacunary [H 2 F 6 NaW 17 O 55 ] 11À , our attempts to convincingly repeat these reported syntheses were unsuccessful, especially for M Fe 2 , Mn 2 and Ni 2 . Therefore, we chose to change the synthetic strategy and to prepare the further transition metal substituted PFOMs, [M(L)H 2 F 6 -NaW 17 O 55 ] qÀ , where M Co 2 , Mn 2 , Fe 2 , Ru 2 , Ni 2 and V 5 and L H 2 O, O 2À , by metathetical exchange of the zinc atom by the other transition metals.…”

“…Further characterization of the [M(L)H 2 F 6 NaW 17 O 55 ] qÀ compounds was by 19 F NMR and 183 W NMR spectroscopy. It is important to note that for the series of PFOMs, the spectra were essentially the same, regardless of the substituted transition metal.…”

“…There is a doublet due to coupling with fluorine associated to the belt tungsten atoms and a singlet from the tungsten atom in the capped position. The inclusion of a transition metal very significantly changes the 183 W{ 19 F} NMR spectrum (measured as the lithium salt for maximum solubility) ( Figure 5), because of the reduction in symmetry. As was observed for 19 F NMR, the substituted transition metal did not affect the 183 W NMR spectra.…”

“…[17] In a second group of PFOMs, compounds of an elliptical egg shape akin to Wells ± Dawsontype polyoxometalates (herein termed quasi-Wells ± Dawson structures; Figure 1) were prepared. Both nonsubstituted (all tungsten) [18] and cobalt-and iron [19] -substituted compounds have been reported. A zinc-substituted compound has also been well-characterized in a doctoral thesis.…”

Intriguing Role of a Quaternary Ammonium Cation in the Dissociation Chemistry of Keggin Polyoxometalate Anions

“…The study of POM system by MS can be dated back to the 1980s [3]. Fast atom bombardment (FAB) was then used to examine a range of species [4][5][6][7]. The use of comparatively hard ionization techniques and resolution problems given by the unresolved isotope patterns of Mo-and W-containing clusters hampered MS from wide applications for complex problems in POM chemistry.…”