A one-dimensional chain of manganese(ii) bridged peroxomolybdate isolated from an aqueous Mn–polymolybdate–H2O2 system

Abstract

A new manganese(II)–peroxomolybdate complex, Cs₄[Mn(OH₂)₂(Mo₇O₂₂(O₂)₂)]·4.25H₂O (Cs-1), was isolated from an aqueous solution containing manganese(II) sulfate, sodium heptamolybdate and hydrogen peroxide by the addition of Cs⁺ salt. Cs-1 was characterized by single crystal X-ray diffraction, thermogravimetry (TG), IR spectroscopy, powder X-ray diffraction (PXRD), cyclic voltammetry (CV) and ultraviolet-visible spectroscopy (UV-vis). The diperoxoheptamolybdate [Mo₇O₂₂(O₂)₂]⁶⁻ units were linked by Mn(II) ions to form a one-dimensional infinite chain of [Mn(OH₂)₂(Mo₇O₂₂(O₂)₂)]_n⁴ⁿ⁻, which represents a unique structure with the coexistence of the oxidant–reductant pair O₂²⁻/Mn²⁺. The interconversion between [Mn^II(OH₂)₂(Mo₇O₂₂(O₂)₂)]⁴⁻ and [MnMo₉O₃₂]⁶⁻ in the aqueous solution was monitored by UV-vis spectrophotometry. It indicates that 1 is a key intermediate during the redox cycle of Mn(II) and Mn(IV) in the Mn–polyoxometalate–H₂O₂ system. In the oxidation process of 3,3′,5,5′-tetramethylbenzidine and ortho-phenylenediamine by H₂O₂, Cs-1 shows notable activity as an enzyme mimetic catalyst.