Niobium uptake by a [P8W48O184]40− macrocyclic polyanion†
Abstract
Reactions of inorganic macrocyclic polytungstate cavitands K28Li5H7[P8W48O184]·92H2O or Li17(NH4)21H2[P8W48O184]·85H2O with (NH4)[NbO(C2O4)2(H2O)2]·3H2O (Nb–Ox) in aqueous solution lead to incorporation of up to five {NbO(H2O)}3+ units into the {P8W48} cavity. The most stable species contain four {NbO(H2O)}3+ units. The uptake of {NbO(H2O)}3+ was determined by corroborative methods including single crystal XRD, inductively coupled plasma atomic emission spectroscopy (ICP-AES), 31P and 13C nuclear magnetic resonance (NMR), C–H–N elemental analysis (EA) and thermal gravimetric analysis (TGA). Solution speciation of the Nb-encapsulating macrocycles was studied by HPLC-ICP-AES and small angle X-ray scattering (SAXS).