Evolution of Polyoxoniobate Cluster Anions

A new geometry for polyoxoniobates is observed in {Nb24O72H9}15−, the largest isopolyoxoniobate cluster anion known to date. Its structural evolution from isolated Lindqvist anions [Nb6O19]8− and the cyclic pyrochlore unit [Nb6O30] through to the complex dimer [({Nb24O72H9} {Cu(en)2(H2O)}2{Cu(en)2})2]18− is discussed.