Synthesis and characterization of new tungstosilicate aggregates assembled with a mixture of mono- and trivacant Keggin fragments

The reaction mixture of two lacunary Keggin-type polytungstosilicates K8[α-SiW11O39] and Na9[A- β-SiW9O34H] in aqueous solution with different pH values led to the isolation of two new aggregates K4Na11Li5[Si3W26O94] · ∼21H2O (1) and K5Na11[Si2W19O69(H2O)] · ∼22H2O (2). Single crystal X-ray diffraction analyses reveal that the polyoxoanion of 1 consists of two {B-α-SiW9O34} trivacant Keggin units and one B-type hexavacant {B-SiW6O26} fragment which are connected by two disordered {WO6} octahedra to form a C-shaped aggregate. Compound 2 is composed of two {A-α-SiW9O34} building blocks linked by a {WO(H2O)} segment. These two structural topologies are firstly observed in polytungstosilicate family and their possible assembly routes are speculated.