Mixed-valence manganese cluster containing a sandwich-type polyoxometalate

Reaction of Na-12[alpha-P2W15O56] center dot 18H(2)O with Mn(CH3COO)(2) center dot 4H(2)O in the presence of K2S2O8 in acidic aqueous solution leads to isolation of a {(Mn2Mn2II)-Mn-III} cluster-containing sandwich-type compound: alpha beta beta alpha-K3Na11{(Mn2Mn2II)-Mn-III(H2O)(2)(P2W15O56)(2)} center dot 40H(2)O (1). Single-crystal X-ray diffraction analysis revealed that 1 shows the well-known Weakley-type sandwich-type structure consisting of two trivacant [alpha-P2W15O56](12-) Dawson moieties linked by a central symmetric rhomb-like mixed-valence manganese cluster via W-O-Mn and P-O-Mn connections. Mixed-valence Mn-cluster-substituted sandwich-type complexes based on trivacant Dawson units are rarely observed in polyoxometalate chemistry. Further, the sandwich-type polyoxoanions were connected by [K3Na2] clusters into a 4(4)-layer. Magnetic study indicates that antiferromagnetic interactions exist in this compound.