Unusual redox activity of the central heteroatom manganese in Anderson anion: Modulating its oxidation state in a gas solid reaction

Abstract

The orange crystalline [N(C4H9)4]3[MnIIIMo6O18{(OCH2)3CNH2}2] (1) with central Mn(III), on exposure to vapors of conc. HCl is converted to green colour solid of tentative formula, [N(C4H9)4]2[MnIIMo6O18{(OCH2)3CNH3}2] ∙ [N(C4H9)4]Cl (1red). Compound 1, on exposure to conc. HNO3 vapours is converted to brown solid, which has tentatively been formulated as [MnIVMo6O18{(OCH2)3CNH3}2] ∙ 3[N(C4H9)4]NO3 (1ox). The color changes are associated with oxidation of central Mn(III) center of compound 1 into Mn(IV) in compound 1ox and reduction of central Mn(III) center of compound 1 into Mn(II) in compound 1red. Both solid state reduction and oxidation of Mn(III) center are accompanied by the protonation of amino group of tris(hydroxymethyl) aminomethane during the gas–solid interface reactions. The conversion of compound 1 into compounds 1red and 1ox in gas solid redox reactions has been characterized by various spectroscopic techniques, e.g., FT-IR, PXRD, EPR, DRS, 1H NMR, 13C NMR and XPS. Also, electrochemical analyses were carried out for all the compounds.