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Covalently interconnected and separated vanadosilicate shells Xiqu Wang, Lumei Liu, Allan J. Jacobson Department of Chemistry, University of Houston, Houston, TX 77204-5003 ABSTRACT Four new compounds containing vanadosilicate clusters have been synthesized by hydrothermal reactions. The clusters are derived from the [V18O42] Keggin cluster by substitution of V=O caps by Si2O(O,OH)2 species. In Cs9[(V15Si6O46(OH)2Cl)(V2O4)](H2O)6.2, 1, the [V15Si6O46(OH)2] cluster shells are covalently interconnected by VO4 tetrahedra to form an infinite layer. In ((CH3)4N)4[V15Si6O42(OH)6(H2O)](H2O)20, 2, and ((CH3)4N)4(V(H2O)6)2/3 [V15Si6O42(OH)6 (H2O)](H2O), 3, separated [V15Si6O42(OH)6] cluster shells are interlinked by hydrogen bonds to form frameworks with wide channel systems. The separated cluster shell in ((CH3)4N)4((CH3)2NH2)((CH3)2NH) [V14Si8O42(OH)8(HCO2)] (H2O)4.7, 4, has four Si2O(OH)2 species in a tetrahedral configuration. The 2D structure of 1 and 0D structures of 2-4 complement the known 1D and 3D structures formed from such vanadosilicate shells. INTRODUCTION Polyoxometalate clusters have long been the subject of intensive studies due to their nanoscale size and tunable chemical and physical properties. [1-4] Using polyoxometalate clusters as building units to form extended structures, including microporous frameworks, is a promising strategy to explore new materials. [5-8] In this respect, modification to the conventional heteropolymetalate clusters such as the Keggin clusters are desired because they are usually surrounded by terminating metal oxygen double bonds. We have reported a number of vanadogermanate cluster anions that are derived from the V18O42 capped Keggin cluster shell by partial substitution of the [V=O]2+ “caps” by the [Ge2O(OH)2]2+ species. Each VO5 pyramid is thus substituted by a Ge2O5(OH)2 tetrahedral dimer. [9] Similar substitution by silicate tetrahedral dimers led to vanadosilicate shells that are readily interconnected to form extended structures through Si-O-V bonds. To our knowledge, only a 1D chain structure and a 3D framework composed of covalently linked vanadosilicate shells are known. In the 1D structure, [10] two dimers of silicate tetrahedra are on the opposite side of a [V16Si4O46] shell, while in the 3D structure, [11] four dimers of silicate tetrahedra are located on a [V14Si8O52] shell in a tetrahedral configuration. A recent computational study showed that the substitution by different tetrahedral dimers greatly modifies the electronic and redox properties of the clusters. [12] In this work we report the synthesis and structures of the compounds Cs9[(V15Si6O46(OH)2Cl)(V2O4)]( H2O)6.2, 1, ((CH3)4N)4[V15Si6O42(OH)6(H2O)](H2O)20, 2, ((CH3)4N)4(V(H2O)6)2/3 [V15Si6O42(OH)6 (H2O)](H2O), 3, and ((CH3)4N)4((CH3)2NH2)((CH3)2NH)[V14Si8O42(OH)8 (HCO2)](H2O)4.7, 4. Compound 1 has a 2D layered structure formed by covalently linking [V15Si6O46(OH)2] shells, while the similar [V15Si6O42(OH)6] shells are separated in compounds 2 and 3. Compound 4 contains the separated [V14Si8O42(OH)8] shel