Sadiq H. Wasfi

Preparation and characterization of a new heteropolyoxofluorotungstate anion [InW17O56F6NaH4]8−

Abstract The ammonium salt of [InW 17 O 56 F 6 NaH 4 ] 8− has been isolated in crystalline form. X-ray powder patterns reveal that the anion has the Dawson structure. Other evidence from analytical results, fast atom bombardment mass spectrometry (FAB-MS), IR spectroscopy, and cyclic voltammetry has confirmed that the structure is a modification of the well-known Dawson structure. The indium atom in the anion is thought to occupy the octahedral site vacated by the missing tungsten atom. FAB-MS shows that the formula weight of the anhydrous salt is 4421 Da.

The Preparation and Characterization of Three New Fluorotungstate Anions Having the Dawson Structure [Cu+W17O54F8NaH4]8-, [MgW17O57F5NaH6]8-, and [Fe+3W+5W16 +6O55F7NaH4]8-

Abstract The ammonium salts of the above anions have been isolated in the crystalline form as (NH4)8[Cu+W17O54F8NaH4]˙13H2O, (NH4)8[MgW17O57F5NaH6]˙10H2O, and(NH4)8[Fe+3W+5W16 +6O55F7NaH4]˙12H2O. Evidence from chemical analysis, Fast Atom Bombardment Mass Spectrometry, spectroscopy (vis, IR), and X-ray powder patterns, indicated that the three anions have the Dawson-Wells structure. The metal ion is Cu+ in the first, Mg+2 in the second and Fe+3 in the third which replaces one W+6 of the eighteen tungsten atoms in the original Dawson structure.

The Preparation and Characterization of Two New Isomorphous Binuclear Heteropolytungstate Anions

Abstract The ammonium salts of [NiCoW11O36FH2]7- and [CuMnW11O40H2]8-have been isolated in the crystalline form. The cubic blue crystals of (NH4)6NaNiCoW11O3gFH210H2O crystalize in the cubic space group Pm3m with a = 11.170 A. Other evidence from analytical results, FABMS, spectroscopy (Vis., I.R.), polarography, and X-ray powder patterns have shown that the above two anions are isomorphous. The structure of the anion is a modification of the well known “Keggin” structure. The first transition metal ion in the above formulas is thought to occupy the octahedral site; the second is thought to occupy the inner tetrahedral cavity. The two are bridged by an oxide or fluoride ion.

The Preparation and Characterization of Two New Heteropolyoxofluorotungstate Anions [CuW11O38F2H6]4- and [MnW11O38F2H6]4-

Abstract The tetramethylammonium salts of [CuW11O38F2H6]4- and [MnW11O38F2H6]4- have been isolated in the crystalline form. Evidence from analytical results, FABMS, spectroscopy (Vis., IR), and cyclic voltammetry has shown that the structures are a modification of the well known “Keggin” structure. The transition metal ion in each compound is thought to occupy the octahedral site vacated by the missing tungsten atom; two protons might occupy the inner tetrahedral cavity. The magnetic susceptibility per gram of [N(CH3)4]4CuW11O38F2H6·10H2O is 0.28 × 10−6, and that of [N(CH3)4]4MnW11O38F2H6·10H2O is 3.95 × 10−6, indicating around five unpaired electrons present in the latter. The FABMS shows that the formula weights of the anhydrous salts are 2908 and 2907 for the Cu and Mn compounds, respectively.

The Preparation and Characterization of the Fluorinated Dinuclear Mixed-Valence Heteropolyoxotungstate Anion [Fe3+ZnW6+ 10W5+O36F4]6−

Abstract The ammonium salt of the mixed-valence fluorinated heteropoly anion, [Fe3+ZnW6+ 10W5+O36F4]6−, has been prepared in the crystalline form. Evidence from X-ray powder pattens, FABMS, cyclic voltammetry, and spectroscopy (VIS, IR) has shown that the anion has the Keggin structure. It is likely that the Zn(II) ion occupies the central tetrahedral cavity of the Keggin structure and the Fe3+ ion occupies the octahedral site vacated by the missing W(VI) ion. The molecular weight of the anhydrous, deaminated compound as found by FABMS is 2779.9 da. Referee I: T. J. R. Weakley Referee II: C. L. Hill and Xuan Zhang

The Preparation and Characterization of a New Heteropolytungstate Anion [CuW17O57F5H5Na]9-

Abstract The ammonium salt of the above anion has been isolated in the crystalline form as [(NH4)9CuW17O57F5H5].8H2O. Evidence from chemical analysis, x-ray powder pattern, spectroscopy (vis., I. R.), and fast atom bombardment mass spectroscopy, indicates that the anion has the Dawson-Wells structure. A Cu(II) ion replaces one W+6 of the eighteen tungsten in the original Dawson structure. The anion has been shown to have good in vitro anti-viral activity.

The Preparation of a New Multinuclear Heteropolytungstate Anion [Fe3Co4W17O70H11]−10

Abstract The preparation of a salt of a new multinuclear heteropoly tungstate complex is reported. FABMS, analytical and spectroscopic (UV-VIS-IR) evidence is presented which strongly indicates that the new complex is isostructural with [Cu2Fe4W18O70H6]−10, for which the preparation and X-ray structure were reported earlier1. The new salt is tentatively formulated Na10H5[Fe3Co4W17O70H6]·37H2O, wherein one Fe+3 or Co+2 replaces one W+6 in the conventional [X2Z4W18O70] formulation of the earlier structure. Possibilities are thus foreseen for additional complexes, isostructural with the above and involving various combinations of transition metals. Such complexes have potential importance for magnetic interaction and bonding studies as well as for catalysis.

Investigation of Wells-Dawson Heteropoly Oxofluorotungstates by Scanning Tunneling Microscopy and Tunneling Spectroscopy

Ammonium salts of Wells-Dawson heteropoly oxofluorotungstates with different framework compositions. (NH 4 ) 9 Mn(II)W 17 O 56 F 6 NaH 4 .9H 2 O, (NH 4 ) 9 Cu(II)W 17 O 56 F 6 NaH 4 .9H 2 O, (NH 4 ) 8 Mn(III)W 17 O 56 F 6 NaH 4 .8H 2 O, and (NH 4 ) 8 Fe(III)W 17 O 56 F 6 NaH 4 .8H 2 O, were deposited on highly oriented pyrolytic graphite surfaces and imaged by scanning tunneling microscopy. All samples formed monolayers of two-dimensional, well-ordered, close-packed arrays. The lattice constants of these arrays in each case were roughly ca. 13 × 16 A; these values were consistent with the molecular dimensions of typical Wells-Dawson heteropolyanions (10.98 × 14.48 A), plus charge-compensating NH + 4 cations (ionic radius of 1.43 A) between the heteropolyanions. The presence and positions of these cations in the surface arrays were subsequently confirmed by tunneling spectroscopy (TS), and the positions were consistent with those found in the bulk crystal structures of these salts. TS measurements also showed that the oxofluorotungstates exhibited negative differential resistance (NDR) behavior in the negative sample bias regime of their current-voltage spectra. Their NDR peak voltages varied depending on the identity of the monosubstituted polyatom, Mn 2+ , Cu 2+ , Mn 3+ , and Fe 3+ . The reduction potentials of heteropoly oxofluorotungstates increased and NDR peak voltages appeared at less negative applied values with the decreasing electronegativity of the monosubstituted polyatom. The correlation between reduction potentials and NDR peak voltages established for these heteropolyacids (HPAs) was consistent with trends observed in the cation-exchanged and heteroatom-substituted HPAs; the more reducible HPAs showed NDR behavior at less negative applied voltages. However, the trends in NDR peak voltage and reduction potential with respect to the electronegativity of the monosubstituted polyatom were opposite of those observed for the cation-exchanged and heteroatom-substituted HPAs.

Preparation and characterization of two novel heteropolyfluorooxotungstate anions [NaCoW11O43FH12]6− and [NaNiW11O43FH12]6−

Abstract The ammonium salt of two isomorphous [NaMW 11 O 43 FH 12 ] 6− anions, whre M = Co(II) and Ni(II), were isolated in crystalline form. The structure of the anion was determined by X-ray crystallography. Evidence from visible spectra indicates that the heteroatom occupies an octahedral geometry. Other evidence from X-ray powder patterns confirms that the two anions are isomorphous. The molecular weights of the compounds were determined by fast atom bombardment mass spectrometry. The magnetic susceptibility per gram x g at room temperature is 4.42 × 10 −6 and 2.173 × 10 −6 for M = Co(II) and Ni(II), respectively. The density of each compound is 3.69 g cm −3 .

The Preparation and Characterization of the Fluorinated Dinuclear Heteropolyoxotungstate Anion with Loosely Coordinated Water Molecule: [(H2O)CuO5ZnO4W11O28F2]8−

Abstract The ammonium salt of the fluorinated heteropolyanion, [(H2O)CuO5ZnO4W11O28F2]8−, has been isolated in the crystalline form The X-ray powder pattern of this compound is similar to that of (NH4)8[Co2W11O40H2]·xH2O for which a single crystal structure has been solved10 The anion has the distorted Keggin structure Evidence from the visible spectrum indicates that the Cu2+ ion occupies the octahedral position vacated by the missing W6+ ion. Accordingly, we assigned the Zn2+ ion to occupy the inner tetrahedral cavity in the Keggin structure Other evidence from elemental analyses, thermal studies, infrared spectroscopy, ultraviolet-visible spectroscopy, and cyclic voltammetry support that the structure is a modification of the well known Keggin structure It appears that the water molecule coordinated to the Cu2+ ion in the heteropolyanion could be removed easily either by slight heating or exposure to a drying agent It could also be replaced by suitable ligands such as NH3, pyridine, pyrazine, SCN−, and...