Mixed-valence fluoropolytungstates

Abstract

Electrochemical reduction of fluoropolytungstates leads to a new series of mixed-valence compounds. Valence trapping and electron delocalization have been studied by optical spectroscopy and e.s.r. in the temperature range 4-300 K. This shows that at l o w temperature the unpaired electrons are

Present General Status of Understanding of Heteropoly Electrolytes and a Tracing of Some Major Highlights in the History of Their Elucidation

“…The pre-1971 contributions of Francoise Chauveau were indicated in section B. Over the period 1974−1983 Chauveau, Doppelt, Lefebvre, et al. − published a series of papers on fluoroisopolytungstate complexes, chiefly derivatives of Keggin structure metatungstate, [H 2 W 12 O 40 ] 6- , wherein F - ions replaced O 2- ions. Complexes based on the following central tetrahedra were prepared: F 2 O 2 H 2 , FO 3 H 2 , F 3 OH, and F 2 O 2 H, and their structures were proved by combinations of elemental analysis, ultracentrifugation, Raman and IR spectroscopy, polarography, and especially 1 H, 19 F, and 183 W NMR.…”

“…In 1981 183 W NMR spectra of [FO 3 H 2 W 12 O 36 ] 5- , β-[SiW 12 O 40 ] 4- , and the previously designated “tungstate X” allowed classification of J W - F couplings and showed that “tungstate X” is β-metatungstate . In 1982 the blue reduction product of a fluoropolytungstate was studied . In 1986 Chauveau wrote a review (74 references) of the application of 1 H, 19 F, 183 W, 31 P, 17 O, 51 V, and 27 Al NMR to study of polyoxometalates .…”

Multielectron Reduction of α-[S2Mo18O62]4- in Aprotic and Protic Media: Voltammetric Studies

“…Polyoxometalate cluster anions such as α-[S 2 Mo 18 O 62 ] 4- (structure I ) are reducible to mixed-valence compounds, commonly known as “poly blues” due to the presence of intervalence charge transfer transitions in the visible spectrum. − Multielectron reduction is observed for those anions which contain structural octahedra bearing a single terminal oxo ligand. − Reduction is accompanied by minor structural changes only, as the extra electrons enter orbitals that are essentially nonbonding. Thus, the reduced forms are class II mixed-valence compounds in which thermally mobile electrons “hop” between octahedra. ,,− As reduction proceeds, the anions acquire an increasing negative charge which encourages protonation. This lowers the negative charge, encouraging further reduction.…”

Photoredox chemistry of Keggin dodecatungstoborate [BW12O40]5? and role of heterogeneous catalysis in hydrogen formation

“…1/T in the high-temperature region where the spin-spin relaxation time, t,, is much longer than the spin-lattice relaxation time, t . 22 Then, the transfer integral J = 0.43 eV between two tungsten sites can 1671 be calculated from expression (3).,, The high value of J i s due to the large extension of the tungsten 5d orbitals.…”