An {As 4 Cu 4 [Cu(H 2 O)] 12 } Cluster Incorporated within Four [Nb 7 O 22 ] 9- Units.

A gigantic 16-copper-containing 28-niobate cluster, Na14 K7 H5 {As4 Cu4 [Cu(H2 O)]12 Nb28 O109 }⋅37.5 H2 O (1), has been prepared by a one-pot reaction, which is the first example of arsenic copper clusters containing polyoxoniobate, and the first tetrahedral arrangement of both the Cu cluster and the [Nb7 O22 ]9- subunits.