Electrochemical Synthesis and Structural and Physical Characterization of One- and Two-Electron-Reduced Forms of [SMo₁₂O₄₀]^2-

Abstract

Isolation of a soluble [NHex4]+ salt has allowed a detailed electrochemical study of the anion alpha-[SMo12O40]2- to be undertaken. Four reversible one-electron-reduction processes are observed in CH2Cl2 solution. Controlled potential electrolysis led to isolation of tetraalkylammonium salts of the one-electron-reduced anion alpha-[SMo12O40]3- and the two-electron-reduced anion alpha-[SMo12O40].4- [SMo12O40]3- is stable to disproportionation in dry solvents (Kdis = 10(-7.4). EPR and magnetic susceptibility data indicate that [SMo12O40]3- is a simple paramagnet (S = 1/2) while [SMo12O40]4- is paramagnetic with the mu eff values decreasing at low temperatures. Solutions of the two-electron-reduced species are EPR silent, but microcrystalline powders show very weak signals. The crystal structure of alpha-[NBu4]3[SMo12O40] has been determined (triclinic P1; a = 13.840(3) A; b = 15.587(4) A; c = 19.370(3) A; alpha = 94.82(2) degrees; beta = 93.10(1) degrees; gamma = 91.05(2) degrees; Z = 2). There is disorder around the C2 axis of the central SO4(2-) tetrahedron. In the presence of aqueous HClO4 (0.045 M) in thf/H2O or MeCN/H2O (98/2 v/v), [SMo12O40]2- exhibits five two-electron-reduction processes. Under these conditions, [SMo12O40]3- protonates and disproportionates into [SMo12O40]2- and the (2e-, 2H+)-reduced anion [H2SMo12O40]2-.

Two Supramolecular Inorganic–Organic Hybrid Crystals Based on Keggin Polyoxometalates and Crown Ethers

“…(3-F-4-MeAnis) and (3- 12 O 40 ] salts were prepared using procedures similar to those reported previously [19,31,32]. IR (400-7800 cm −1 ) spectra were measured using a Thermo Scientific Nicolet 6700 FT-IR spectrometer.…”

“…The exposed oxygen atoms (Ot and Ob) are potential hydrogen bonding interaction sites. Moreover, the charge of POMs can be modified by a chemical method to change the electrostatic interactions with an organic cation, resulting in the desired molecular assembled structures [19]. In addition, POMs with a large diameter can form an extended void space for embedding large organic cations [20].…”

Cyclic Voltammetric Studies on [SMo12O40]2- and [SMo12O40]3- at Macrodisk Electrodes in Acetonitrile With and Without Added Supporting Electrolyte

“…In conventional studies with ASE, an Ag=Ag þ (CH 3 CN, 10 mM AgNO 3 ) double junction reference electrode was sometimes used as an alternative to the Pt quasi-reference electrode. In this case, potentials could be referenced to the Fc=Fc þ (Fc ¼ ferrocene) potential scale, as previously described [2].…”

“…The electrochemical reduction of the polyoxometalate [SMo 12 O 40 ] 2À anion has been reported in H 2 SO 4 =CH 3 COCH 3 (50:50 v=v) [1], acetonitrile (CH 3 CN)=water (95:5 v=v) [1], tetrahydrofuran (THF) with and without water [2] and in dichloromethane (CH 2 Cl 2 ) [2]. In aprotic CH 2 Cl 2 and THF media, voltammograms showed the presence of four consecutive reversible one-electron processes [2] corresponding to the reaction sequence in Equation 1.…”

“…In aprotic CH 2 Cl 2 and THF media, voltammograms showed the presence of four consecutive reversible one-electron processes [2] corresponding to the reaction sequence in Equation 1. …”