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Blue Electron Distributions in Diamagnetic Reduced Heteropoly Tungstates. Insights Concerning Conduction Pathways and Spin Coupling Patterns. 183W NMR Chemical Shift Calculations

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Polyoxometalates: From Platonic Solids to Anti-Retroviral Activity

Part of the book series: Topics in Molecular Organization and Engineering ((MOOE,volume 10))

Abstract

This is a paper in a continuing series about roles played by delocalized “blue” electrons and by unpaired electrons in determining properties and structures of heteropoly complexes and their blue reduction products. 183W NMR data for α-[SiW12O40]4-, α-[P2W18O62]6-, α-[P2Mo3W15O62]6-, α-[P2Mo6W12O62]6-, α1-[P2MoW17O62]6-, and α2-[P2MoW17O62]6- and the diamagnetic 2-electron reduction products of these, are combined with our earlier interpretations, yielding new insights about blue electron distributions, pathways for blue electron conduction and delocalization, and energy factors that determine these. MoVI is more easily reduced than WVI. Therefore, in each diamagnetic completely spin-coupled 2e-reduction product of the monomolybdenum derivatives, one of the added electrons is “anchored” on the Mo while the other is rapidly thermally hopping among several belt W’s.

A special extended spin echo pulse sequence was used to suppress acoustic ringing for those α1-and α2-183W spectra which have very large sweep widths.

The results show: (1) Those W’s that participate in delocalization of the blue electron(s) can be readily distinguished from those that do not. (2) The chemical shift for each W that receives blue electrons represents a coalesced signal from WVI, in which the W has no blue electron, and Wv in which it does. The chemical shifts for such W’s can therefore be used to calculate relative residency times of the blue electron on the various W’s. (3) This interpretation concludes that the delocalized blue electrons in the monomolybdenum blues inhabit in each case almost exclusively just the one 6W belt adjacent to the Mov atom, spending the greatest proportion of time on the W atom(s) immediately adjacent to (corner sharing with) the Mov, and progressively less time on the progressively more distant W’s of the 6W belt adjacent to the Mov. (4) The added paired electrons prefer, by a substantial but not overwhelming margin, to reside on addenda atoms that are relatively close to one another. The blue electron’s spins are always completely paired by multiroute superexchange even though they are often not on adjacent addenda atoms. The electron pairing puts the complex in a lower energy state. The closer the atoms having added electrons, the shorter the superexchange pathways and the greater the opportunity for randomization of spins. This provides an electronic entropy drive favoring keeping the added electrons on atoms that are close to one another. (5) Orbital geometries make the preferred electron hopping and superexchange routes via corner sharing of MO6, octahedra rather than via edge sharing. Thus, at a given instant the 2 added electrons prefer to be on adjacent corner-sharing addenda; and, in the 18-tungsto complex, this would most commonly involve one Wv in each belt in corner-sharing eclipsed positions.

Addressee for the correspondence and reprints at Goergetown University

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Notes and References

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Author notes

  1. Mariusz Kozik

    Present address: Department of Chemistry, Canisius College, Buffalo, NY, 14208, USA

Authors and Affiliations

  1. Chemistry Department, Georgetown University, Washington, DC, 20057, USA

    Mariusz Kozik & Louis C. W. Baker

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Michael T. Pope Achim Müller

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Kozik, M., Baker, L.C.W. (1994). Blue Electron Distributions in Diamagnetic Reduced Heteropoly Tungstates. Insights Concerning Conduction Pathways and Spin Coupling Patterns. 183W NMR Chemical Shift Calculations. In: Pope, M.T., Müller, A. (eds) Polyoxometalates: From Platonic Solids to Anti-Retroviral Activity. Topics in Molecular Organization and Engineering, vol 10. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-0920-8_14

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  • DOI: https://doi.org/10.1007/978-94-011-0920-8_14

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  • Print ISBN: 978-94-010-4397-7

  • Online ISBN: 978-94-011-0920-8

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