Low-temperature electron spin resonance spectra of heteropoly blues derived from some 1:12 and 2:18 molybdates and tungstates

Abstract

agreement with the qualitative trend in electronegativities reported earlier.26*27 A final point of interest relates to the sensitivity of the various series of mercurials, RHgR', to alkyl substitution. In Figure 5, the ionization potentials of a series of dialkylmercury compounds R-Hg-R' have been plotted against the oxidation potentials of the corresponding Grignard reagent (representing a common scale). The slopes decrease in the order R'HgMe > R'HgEt > R'Hg-i-Pr > R'Hg-t-Ru. We attribute this result to the fact that partial delocalization of charge by the first R group in the molecular ion diminishes the effect of the second group R'; or, stated alternatively, there is less charge remaining to be delocalized. The apparent intercept at about 7.2 eV (disregarding the experimental scatter in the highly substituted compounds) represents a limiting example, in which one group, extremely effective at delocalizing charge, completely nullifies the effect of the second group. Acknowledgment.X-Band ESR spectra of nine reduced heteropoly anions (heteropoly blues) have been recorded at temperatures between 4.2 K and room temperature. The spectrum of PM0~Mo11040~-is isotropic (g = 1.945) at all temperatures and exhibits hyperfine structure (six lines) below 64 K, with ( u ) = 55 X cm-'. The intensity of the hyperfine spectrum relative to the central (nonmagnetic) line increases as the temperature is lowered. The spectra of five reduced 1:12 tungstates are rhombic at low temperatures, with gl = 1.848-1.852, g2 = 1.805-1.827, and g3 = 1.759-1.79. Above 50-80 K, depending on the anion, the spectra appear isotropic' due to line broadening. The spectra of reduced ~~P 2 W 1 8 0 6 2~ and a-As2W180& remain rhombic at higher temperatures, with gl = 1.905, g2 = 1.85, and g3 = 1.81, The spectrum of the reduced / 3 isomer of P2w180626-is isotropic (g = 1.852) at all temperatures down to 13 K. All of the ESR spectra are discussed in terms of weakly trapped Mo(V) or W(V) valences. The rate of intraionic electron delocalization in PMoVMo110404-at 6 K must be greater than ca. lo8 s-l implying a much lower activation energy than predicted by the Hush model for mixed valence compounds. The source of the rhombic crystal field for tungsten atoms in the 1:12 (Keggin) structure is discussed and the major differences between the spectra of 1:12 and 2:18 anions are rationalized. Two-electron heteropoly blues appear diamagnetic, probably through antiferromagnetic coupling of electrons localized on adjacent metal atoms.A Cobalt-59, Indium-1 15, Gallium-69, Gallium-71, Bromine-79, Bromine-81, and

Electron Transfer Behavior of Multi‐Iron Sandwich‐Type Polyoxometalates and Electrocatalytic Reduction Reactions

“…[24] The accumulation of adjacent edge-sharing Fe III centers in Fe4As4 gives more favorable electrocatalytic properties to the complex than those observed in the monosubstituted complex, α 2 -As 2 (FeOH 2 )W 17 O 61 7Ϫ . Analogous complexes containing phosphorus heteroatoms (instead of arsenic) are known, [25Ϫ30] but the presence of arsenic facilitates the reduction of both Fe III [25] However, a comprehensive investigation of the equivalence of the heterometallic centers in the sandwichtype derivatives, highlighting their eventual interactions and rationalizing their electrochemistry, is lacking.…”

Cyclic Voltammetry Study of the Mn‐Substituted Polyoxoanions [MnII4(H2O)2(H4AsW15O56)2]18− and [((MnIIOH2)MnII2PW9O34)2(PW6O26)]17−: Electrodeposition of Manganese Oxides Electrocatalysts for Dioxygen Reduction

“…This demonstrates that the replacement of two As V heteroatoms in the symmetrical Dawson-type Mn 4 As 4 W 30 by two hydrogen atoms in the dissymmetrical Dawson-complex Mn 4 As 2 W 30 has no significant influence on the electron transfer within the molecule. This is understandable since in Dawson structure, the electron transfer starts from the W-centers located on the crown and passes to the W-centers located on the hat [36][37].…”

Transition‐Metal (MnII and CoII) Complexes with the Heteropolymolybdate Fragment [AsVMo9O33]7–: Crystal Structures, Electrochemical and Magnetic Properties

“…As shown in Figure 2, the linkage between the 1b unit and {MnO 2 (H 2 O) 4 } group depends entirely on a ligand oxygen atom coming from the end of a 1b unit. It is noteworthy that the ligand oxygen atom is one of two terminal oxygen atoms from a MoO 6 octahedron of 1b, and the other terminal oxygen atom from the MoO 6 [20][21][22] If this type of one-dimensional chain can be reduced reversibly, the additional electrons on the reduced heteropolymolybdate group will behave as electron delocalization, so that an indirect magnetic exchange interaction may happen between the magnetic groups and the reduced heteropolymolybdate groups. Thus, the development of such a magnetic chain is of considerable significance for exploring new molecular magnets.…”