{Ti12} Cluster-Added Poly(polyoxometalate) Containing Mixed Trivacant Keggin and Dawson Fragments

A new high-nuclear Ti-oxo-cluster-added poly(polyoxometalate) Cs2Na19H12[(Cs@Ti12O18)@{(A-α-SiW9O34) (P2W15O56)3}]·29H2O (1) has been made by reacting two types of trivacant precursors with TiOSO4 under hydrothermal conditions. The polyoxoanion of 1 contains one Keggin-type [A-α-SiW9O34]10- and three Dawson-type [P2W15O56]12- fragments that synergistically induce the Ti4+ ions to aggregate at vacant sites, resulting in a large {Ti12}-oxo-cluster cavity sealing a Cs+ ion. It is worth noting that the {Ti12} cluster is built by three edge-shared Ti3O13 ({Ti3}1) cores and one corner-shared Ti3O15 ({Ti3}2) core bridged via 6 μ2-O, which has never been seen before in polyoxometalate chemistry. Significantly, 1 represents the first example of [A-α-SiW9O34]10- and [P2W15O56]12- simultaneously participating in making poly(polyoxometalate).