Polyoxometalate-based heteronuclear complexes [Fe2M2 (H20)2 (FeW9034)21]n- (m = MnII, NiII) prepared by a pH-controllable degradation approach

Three new heteronuclear [FeW9O34 sandwich-type complexes [(Fe2Mn2II)-Mn-III(H(2)0)2(FeW9O34)(2)](12-) (1), [(Fe2Mn2III)-Mn-III(H(2)0)2(FeW9O34)(2)](10-) (2) and [(Fe2Ni2II)-Ni-III(H(2)0)2(FeW9O34)(2)](12-) (3) have been synthesized by an innovative method of pH-controllable degradation in aqueous solution, in which the [FeW12O40](5-) precursor could be predominantly degraded into the trivacant [FeW9O34](11-) anion. The active ligand of trivacant [FeW9O34](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. (C) 2016 Elsevier B.V. All rights reserved.