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

Abstract

Detailed voltammetric studies are reported of the reduction of alpha-[S(2)Mo(18)O(62)](4)(-) at glassy carbon and platinum macro- and microdisk electrodes (stationary and rotated) in acetonitrile and in 95/5 acetonitrile/water mixtures containing 0.02 M perchloric acid. Experiments at -30 degrees C and at short time scales in acetonitrile detect eight one-electron processes in the potential range 0.1 to -2.7 V versus Fc(+)/Fc (Fc = ferrocene). The eight processes fall into four pairs. The differences in potential within each pair are remarkably constant (0.26 +/- 0.02 V), as are the separations between adjacent pairs (0.60 +/- 0.06 V). This periodicity is consistent with spin-paired [Mo(V)O](2)(&mgr;-O) fragments providing a significant contribution to the overall superexchange stabilization. The influence of the following chemical reactions (primarily protonation by trace water) increases with the number of electrons added, although the five-electron reduced species [S(2)Mo(18)O(62)](9)(-) has a significant lifetime on the voltammetric time scale. In the presence of aqueous acid and at short time scales, eight chemically reversible processes are observed in the range 0 to -1.5 V in which two, two, two, two, four, four, two, and eight electrons, respectively, are transferred. The four pairs of one-electron processes found in acetonitrile occur as the first four overall two-electron reduction steps, separated by about 0.1, 0.2, and 0.3 V, respectively. Addition of a further 10 electrons occurs in a range of 0.3 V only and results in an 18-electron reduced species, stable on the voltammetric time scale. This corresponds to formal reduction of all Mo(VI) centers in alpha-[S(2)Mo(18)O(62)](4)(-) to Mo(V). The species is able to accept a further eight electrons in a series of unresolved processes.

Experimental and Theoretical Investigations of the Sulfite‐Based Polyoxometalate Cluster Redox Series: α‐ and β‐[Mo18O54(SO3)2]4−/5−/6−

“…4À has been characterized [36] but there is a D 3d g* Wbased sulfate Wells-Dawson cluster. [35] Herein we describe the synthesis and structural characterization of the pure a and b forms of the clusters.…”

Electro‐Assisted Reduction of CO2 to CO and Formaldehyde by (TOA)6[α‐SiW11O39Co(_)] Polyoxometalate

“…(2) many POMs display reversible redox processes that are sensitive to the presence of protons [20][21][22][23][24] and have been used as electrocatalysts for the multiproton-multielectron reduction of nitrate to ammonia, or for hydrogen production; [25][26][27] (3) although they are weak bases, POMs could promote the formation of hydrogen-bond networks in the vicinity of the CO 2 coordination center to favor PCET.…”

Control of the modularity of {Mo2O2S2}-containing polyoxometalates. Synthesis, structure and characterization of tri- and tetra-modular assemblies based on the [β-B-AsW9O33]9− anion

“…Polyoxometalate compounds (POMs) constitute potentially attractive chemical systems able to generate large assemblies with targeted functionalities [1][2][3][4][5] and promising applications in diverse fields of science, such as catalysis [6][7][8][9], medicine [10][11][12][13][14], electrochemistry [15] and material sciences [16][17][18][19][20][21]. To this end, this class of compounds offers the possibility to use polyvacant anions as primary building blocks to step by step construct sophisticated well-designed multi-unit compounds.…”