Hamera Abbas

University of Glasgow, Glasgow, Scotland, United Kingdom

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Publications (10)68.05 Total impact

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    ABSTRACT: Cryospray mass spectrometry (CSI-MS) has been used to probe the mechanism of self-assembly of polyoxometalate clusters in solution. By using CSI-MS and electronic absorbance spectroscopy it was possible to monitor in real-time the self-assembly of polymeric chains based on [Ag 2Mo 8O 26] (2-) n building blocks. The role of the Ag (I) ion in the solution state rearrangement of molybdenum Lindqvist ({Mo 6}) into the silver-linked beta-octamolybdate ({Mo 8}) structure (( n-C 4H 9) 4N) 2 n [Ag 2Mo 8O 26] n ( 1) is revealed in unprecedented detail. A monoanionic series, in particular [AgMo m O 3 m+1 ] (-) where m = 2 to 4, and series involving mixed oxidation state polyoxomolybdate species, which illustrate the in-solution formation of the (Ag{Mo 8}Ag) building blocks, have been observed. CSI-MS detection of species with increasing metal nuclearity concomitant with increasing organic cation contribution supports the hypothesis that the organic cations used in the synthesis play an important structure-directing role in polyoxometalate (POM) growth in solution. A real-time decrease in [{Mo 6}] and associated increase in [{Mo 8}] have been observed using CSI-MS and electronic absorbance spectroscopy, and the rate of {Mo 6} interconversion to {Mo 8} was found to decrease on increasing the size of the countercation. This result can be attributed to the steric bulk of larger organic groups hindering {Mo 6} to {Mo 8} rearrangement and hindering the contact between silver cations and molybdenum anions.
    Journal of the American Chemical Society 10/2008; 130(42):13876-84. DOI:10.1021/ja802514q · 11.44 Impact Factor
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    ABSTRACT: The interaction of silver(I) cations with octamolybdate (Mo8O26) 4- has been investigated by applying the principles of the building-block concept to the well established silver-octamolybdate reaction system. The self-assembly of dimeric {Ag2} linkers allows the formation and isolation of chains and networks where (Mo8O26) 4- clusters are cross-linked by silver(I) cations. The influence of the solvent on the overall topology has been studied, and the role of the counterion on the resulting structure has been highlighted in each assembly. Fine-tuning of the metal-metal distances of the dimeric {Ag2} linking units has been achieved by using different coordinating solvents which act as bridges. Five compounds based on silver octamolybdate building blocks have been isolated, including an uncommon intermediate ((Ph4P)2(Ag2(CH3CN)2(Mo8O26))), three one-dimensional polymeric chains ((Ag(C7H12O2N)(CH3CN))2n(Ag2(CH3CN)2(Mo8O26))n ·2CH3CN, (Ph4P)2n(Ag2(DMF)2(Mo8O26))n ·2DMF, and (H2NMe2)2n- (Ag2(DMF)2(Mo8O26))n ·2DMF), and a two-dimensional cross-linked network (((Ag(DMF))2(Ag(DMF)2)2Mo8O26)n). Each compound has been characterized by single-crystal X-ray diffraction, elemental analysis, and FT-IR.
    Crystal Growth & Design 02/2008; 8(2):635-642. DOI:10.1021/cg700736v · 4.56 Impact Factor
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    ABSTRACT: Molecular growth processes utilizing polyoxometalate-based building blocks with silver connecting units have been used to produce four new materials: 1 , [Ag<sub>3</sub>(bhepH)<sub>8</sub>(W<sub>11.5</sub>Na<sub>0.5</sub>O<sub>40</sub>P)<sub>2</sub>]·8H<sub>2</sub>O (bhep = N,N -bis(2-hydroxyethyl)piperazine); 2 , [Ag<sub>4</sub>(DMSO)<sub>8</sub>(Mo<sub>8</sub>O<sub>26</sub>)]n; 3 , {Ag<sub>3</sub>[MnMo<sub>6</sub>O<sub>18</sub>{(OCH<sub>2</sub>)<sub>3</sub>CNH<sub>2</sub>}<sub>2</sub>(DMSO)5]·3(DMSO)}<sub>n</sub>; 4 , {Ag<sub>3</sub>[MnMo<sub>6</sub>O<sub>18</sub>{(OCH<sub>2</sub>)<sub>3</sub>CNH2}<sub>2</sub>(DMSO)<sub>6</sub>(CH<sub>3</sub>CN)<sub>2</sub>]·DMSO}<sub>n</sub>. The compounds were characterised using single crystal X-ray crystallography, elemental analysis, IR, TGA, DSC, and compounds 2–4 were imaged on silicon substrates using scanning electron microscopy. Compound 1 represents a 0D dimer connected by silver ions but was also found to form channels facilitated by the hydrogen bonding between the protonated [bhepH]<sup>+</sup> ligand and the cluster, and complex 2 forms 2D layered networks, whereas both compounds 3 and 4 form 1D networks; these networks are all connected by Ag(I) ions. Thermal studies show that the stabilities of compounds 2–4 are affected by the linking Ag(I) ions and the DMSO ligands and EM studies on compounds 3 and 4 showed the formation of fibres on silicon substrates.
    Journal of Materials Chemistry 05/2007; 17(19). DOI:10.1039/B617830H · 7.44 Impact Factor
  • Angewandte Chemie 05/2005; 117(22):3387 - 3387. DOI:10.1002/ange.200590072
  • Angewandte Chemie International Edition 05/2005; 44(22):3323-3323. DOI:10.1002/anie.200590072 · 11.34 Impact Factor
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    DL Long, Hamera Abbas, P Kogerler, Leroy Cronin
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    ABSTRACT: For Abstract see ChemInform Abstract in Full Text.
    Angewandte Chemie International Edition 05/2005; 44(22). DOI:10.1002/anie.200500541 · 11.34 Impact Factor
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    ABSTRACT: Molecular growth processes utilizing a beta-octamolybdate synthon and {Ag2} dimers are described and the directing influence of "encapsulating" cations and coordinating solvent is also demonstrated. The growth of two 1D chains, (nBu4N)2n[Ag2Mo8O26]n (1) and (nBu4N)2n[Ag2Mo8O26(CH3CN)2]n (2), is achieved when nBu4N+ ions are used, and the diameter of the chains can be expanded by the coordination of CH3CN solvent (2). The formation of a type of gridlike structure in which 1D chains are crossed-over each other in alternatively packed layers is achieved in DMSO as the solvent; DMSO acts as a linking group to give (nBu4N)2n[Ag2Mo8O26(dmso)2]n (3), which, similar to 1 and 2, still incorporates the Bu4N+ ions that exert an "encapsulating" influence. However, in (HDMF)n[Ag3(Mo8O26)(dmf)4]n (4) the relatively bulky Bu4N+ ions are exchanged for protonated DMF cations, thereby allowing the chains to condense to a 2D array. The building block concept is further enforced by the isolation of a "monomeric" unit (Ph4P)2[Ag2Mo8O26(dmso)4] (5), which is isolated when the Ph4P+ ions are so "encapsulating" as to prevent aggregation of the {Ag-Mo8-Ag} building blocks. The nature of the AgAg dimers in each of the compounds 1-4 is examined by DFT calculations and the interplay between these Ag-Ag interactions and the structure types is described.
    Chemistry 03/2005; 11(4):1071-8. DOI:10.1002/chem.200401088 · 5.70 Impact Factor
  • DL Long, Hamera Abbas, P Kogerler, Leroy Cronin
    ChemInform 02/2005; DOI:10.1002/chin.200508019
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    ABSTRACT: Complexation of the highly branched, pentadecadentate chelating ligand cis,cis-1,3,5-cyclohexanetriamine-N,N,N',N',N",N"-hexaacetic acid (H(6)L) with iron(III) and sodium cations in the presence of carbonate anions leads to the formation of an [Fe6L2] cluster comprising an [Fe6] cage linked by 12 exo-coordinated sodium cations to form an extended 3D array.
    Inorganic Chemistry 12/2004; 43(23):7266-8. DOI:10.1021/ic049068w · 4.79 Impact Factor
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    ABSTRACT: A high-nuclearity {W36} isopolyoxotungstate cluster, [H12W36O120]12-, with a triangular shape has been isolated by using an encapsulating organic cation, protonated triethanolamine. In analogy to an 18-crown-6 crown ether, the cluster captures a potassium ion, present in trace amounts in the reaction system, within its cavity. DFT calculations suggest that the distribution of partial atomic charges over the oxygen framework shows maxima at certain "hotspot" sites, which imply possible routes for further cluster growth based on the {W36} system.
    Journal of the American Chemical Society 12/2004; 126(43):13880-1. DOI:10.1021/ja046410v · 11.44 Impact Factor

Publication Stats

445 Citations
68.05 Total Impact Points

Institutions

  • 2004–2008
    • University of Glasgow
      • School of Chemistry
      Glasgow, Scotland, United Kingdom
    • Iowa State University
      • Department of Physics and Astronomy
      Ames, Iowa, United States