Unraveling the condensation reactions of heterometallic {BiNb_(4)} moieties into hybrid Bi_(x)Nb_(y)-oxo clusters with mass spectrometry

The most effective methodologies for the construction of polynuclear complexes usually take advantage of preorganized building blocks.Herein,we successfully developed a new versatile heterometallic{BiNb_(4)}moiety,which can be applied for the assembly of less explored organic-inorganic hybrid polyoxoniobates.Through controlled condensation reactions,three{BiNb_(4)}moieties can be assembled into a pair of isomeric Bi_(3)Nb_(18)clusters at different temperatures;whilst four{BiNb_(4)}moieties can be combined into two unique Bi_(4)Nb_(16)and Bi_(4)Nb_(18)tetramers in different solvents.Interestingly,we have used mass spectrometry to probe the above condensation reactions,which clearly confirmed a stepwise bottom-up assembly process by capturing the presence of bismuth subsalicylate precursors,salicylate coordinated intermediates,Nb incorporated{BiNb_(4)}moieties and the final Bi_(x)Nb_(y)-oxo clusters,respectively.Moreover,the packing modes of the{BiNb_(4)}units induce different solution behaviors,and the{BiNb_(4)}units in Bi4Nb16can be recombined by post-synthetic recrystallization in acetonitrile to produce a new tetramer Bi_(4)Nb_(18)-R.Therefore,this work provides not only a useful{BiNb_(4)}building unit but also the mechanism for their condensation,both of which will promote the future development of metal-oxo clusters.