Iron-Substituted Dawson-Type Tungstodiphosphates:  Synthesis, Characterization, and Single or Multiple Initial Electronation Due to the Substituent Nature or Position

Abstract

Isomerically pure α1- and α2-[Fe(OH2)P2W17O61]7- and α2[Fe(OH2)P2Mo2W15O61]7- were synthesized as aqueous-soluble potassium salts. The iron-substituted complexes as well as their immediate lacunary precursors have been characterized by IR, UV−visible, and 31P NMR spectroscopies. The acid−base equilibria were studied for the iron-substituted complexes. The hydroxo compound α2-[Fe(OH)P2W17O61]8- has also been synthesized, and its elemental analysis is correct. Its further characterization and study will be published elsewere. For a given pH value, the comparisons of the cyclic voltammograms reveal the influence of the location of the iron-filled site in the framework. This influence is strong in the α1 isomer and makes its electrochemistry clearly different from that of the α2 isomer. This observation is ascribed mainly to the large framework distortion induced by the vacancy in the α1 site, to subtle variations in the detailed protonation events which ensue, and to the nature of the iron substituent, which can be considered not to fill “completely” the vacancy. The distortion effect is found to favor the coalescence of waves, as also do lower and lower pH media. The combination of these parameters appears to be beneficial for the observation of multiple electronation processes on the first wave of heteropolyanions under very mild conditions.

Synthesis, Characterization and Electrochemistry of Complexes Derived from [(1),2,3-P2Mo2W15O61]10– and First Transition Metal Ions

“…In Figure 3A, two well-behaved redox systems are observed. In line with previous work, [1,2,10] the first wave is assigned to the reduction of the molybdenum centers. Whatever the substituted complex, only very modest peak potential and peak current intensity variations are observed compared to the same parameters for the lacunary species, provided comparable concentrations are used.…”

“…In the potential domains explored, no electrochemical activity has been detected for Ni II II as substituents in the present work, is the one likely to make the first wave of the corresponding HPAs involve n electrons (n ᮀ 2). The case of the Fe III complex has been described briefly, [1,2] 15 . This result is consistent with the merging of the molybdenum and iron waves at pH ϭ 2.…”

“…The apparent formation constant β app for the Fe III -substituted compound was determined potentiometrically in 1 HNO 3 , considering that in this medium, the lacunary polyoxometalates of this work do not complex Fe 2ϩ ions. [1] The formation constant for the V IV -substituted complex has been evaluated by comparison with the value obtained for the iron complex. For all the other compounds, a procedure derived from that described in detail for the stability constant measurements of Ce III and Ce IV complexes of both the α 1 and α 2 [P 2 W 17 O 61 ] 10-isomers [18] was used.…”

“…In recent articles, [1,2] we described the syntheses, characterization and the electrochemical properties of some monoferro-heptadecatungsto-diphosphates and pentadecatungsto-dimolybdo-diphosphates. This work constitutes a first step in our systematic examination of parameters and combination of parameters which could favor or counteract the merging of the first several waves in heteropolyanion (HPA) electrochemistry.…”

Synthesis and Electrochemistry of the Monolacunary Dawson‐Type Tungstoarsenate [H4AsW17O61]11− and Some First‐Row Transition‐Metal Ion Derivatives

“…With a systematic study of the relevant parameters, we have also established [11] the best experimental conditions for the synthesis of [H 4 7Ϫ . [12,13] Recently, we have extended the work on this new family of dissymmetric Dawson-type heteropolyanions to the first-row transition-metal ion substituted derivatives of [H 4 PW 18 O 62 ] 7Ϫ . [13] Herein, we report the synthesis, characterization and electrochemistry of the hitherto unknown monolacunary species of [H 4 AsW 18 O 62 ] 7Ϫ and its first-row transition-metal ion substituted derivatives.…”