Scheme 1. Schematic representation showing the double-templated synthesis of {M₃(HPO₃)Sb₃W₂₈} (M = Gd^III, Y^III, Yb^III) starting from a buffered solution containing KCl, the trilacunary {SbW₉} precursor and the first template added as Na₂WO₄. Addition of the corresponding metal center and phosphorous acid acting as the second template accompanied by room temperature stirring and heating lead to formation of the target compound featuring a labile acetate ligand bound to each of the three 8-fold coordinated Lewis-acid metal centers with square-antiprismatic symmetry. Blue and red spheres represent the M- and oxygen ions, respectively. Grey for Sb^III, purple for P^V and yellow polyhedra for {WO₆}.