Polyoxoniobates(PONbs)have attracted increasing attention in the past decades,owing to their unique aqueous behavior and potential applications in virology,nuclear waste treatment and basecatalysis.Herein we present a new organic-inorganic hybrid,[Cu(en)2]3{[Cu(en)2] [H7GaNb18O54]}·25H2O(1,en = ethylenediamine),which contains the crescent-shaped polyoxoanion [H7GaNb18O54]8? and copper–organic cations.