Synthesis and Structure of the Pentacopper(II) Substituted Tungstosilicate [Cu₅(OH)₄(H₂O)₂(<i>A-α-</i>SiW₉O₃₃)₂]^10-

The dimeric, pentacopper(II) substituted tungstosilicate [Cu5(OH)4(H2O)2(A-α-SiW9O33)2]10- (1) has been synthesized in good yield using a one-pot procedure by reaction of Cu2+ ions with the trilacunary precursor salt K10[A-α-SiW9O34]. The title polyanion represents the first polyoxotungstate substituted by 5 copper centers and the central copper−hydroxo−aqua fragment is completely unprecedented. In the course of the reaction, two [A-α-SiW9O34]10- Keggin half-units have fused in an asymmetrical fashion resulting in the lacunary polyoxotungstate [Si2W18O66]16-. The vacancy in this species is stabilized by a magnetic cluster of five octahedrally coordinated Cu2+ ions resulting in polyanion 1 with C2v symmetry.