Mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (M(II) = Co, Mn): synthesis and stability. The molecular structure of [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14-

Two new mixed-metal sandwich complexes M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (abbreviated M2Fe2P4W30], M(II) = Co(II), Mn(II)) were obtained at pH 3 by addition of M2+ to Na2(H2O)2Fe(III)2(P2W15O56)2]16- (abbreviated Na2Fe2P4W30]) without substitution in the alpha-P2W15O56]12- (abbreviated P2W15]) units. Their X-ray structures are reported. At lower pH, back conversion to Na2Fe2P4W30] was followed by 31P NMR, electrochemistry and UV-visible spectroscopy. The preparation and the characterization in solution of the lacunary intermediate NaCo(II)(H2O)2Fe(III)2(P2W15O56)2]15- (abbreviated NaCoFe2P4W30]) is also described.