The five manganese-containing, Keggin-based tungstosilicates [Mn-3(II)(OH)(3)(H2O)3(A-alpha-SiW9O34)](7-) (1), [Mn-3(III)(OH)(3)(H2O)(3)(A-alpha-SiW9O34)](4-) (2), [Mn-3(III)(OH)(3)(H2O)(3)(A-beta-SiW9O34)](4-) (3), [(Mn3MnO3)-Mn-III-O-IV(CH3COO)(3)(A-alpha-SiW9O34)](6-) (4), and [(Mn3MnO3)-Mn-III-O-IV (CH3COO)(3)(A-beta-SiW9O34)](6-) (5) were synthesized in aqueous medium by interaction of [A-alpha-SiW9O34](10-) or [A-beta-SiW9O34H](9-) with either MnCl2 (1) or [(Mn8Mn4O12)-Mn-III-O-IV(CH3COO)(16)(H2O)(4)] (2-5) under carefully adjusted reaction conditions. The obtained salts of these polyanions were analyzed in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric analysis. The salts of polyanions 1, 2, and 4 were further characterized in the solid state by magnetic studies, as well as in solution by electrochemistry.