Polyoxometalate-based heteronuclear complexes [Fe 2 M 2 (H 2 O) 2 (FeW 9 O 34 ) 2 ] n− (M = Mn II , Mn III , Ni II ) prepared by a pH-controllable degradation approach

Abstract Three new heteronuclear [FeW 9 O 34 ]-based sandwich-type complexes [Fe III 2 Mn II 2 (H 2 O) 2 (FeW 9 O 34 ) 2 ] 12− ( 1 ), [Fe III 2 Mn III 2 (H 2 O) 2 (FeW 9 O 34 ) 2 ] 10− ( 2 ) and [Fe III 2 Ni II 2 (H 2 O) 2 (FeW 9 O 34 ) 2 ] 12− ( 3 ) have been synthesized by an innovative method of pH-controllable degradation in aqueous solution, in which the [FeW 12 O 40 ] 5− precursor could be predominantly degraded into the trivacant [FeW 9 O 34 ] 11− anion. The active ligand of trivacant [FeW 9 O 34 ] 11− anion can catch in situ the mixed transition metal ions to conduce a directed coordination assembly reaction. These three heteronuclear complexes have been characterized by elemental analysis, single-crystal and powder X-ray diffraction analyses, IR spectra, UV–vis spectra, and thermal gravimetric analysis, cyclic voltammetry, magnetic properties, and thermal gravimetric analysis. Complexes 1 and 3 exhibit obvious catalytic activities for electrocatalytic reduction of nitrate. Compared with 1 , the magnetic property of 2 shows a remarkable change by only a conversion of Mn(II) into Mn(III), so that a strong ferromagnetic interaction occurs in 2 .