Cation-Directed Synthesis of Tungstosilicates. 1. Syntheses and Structures of K10A-(alpha)-[SiW9O34]·24H2O, of the Sandwich-Type Complex K10.75 [Co(H2O)6]0.5[Co(H2O)4Cl]0.25A-(alpha)-[K2{Co(H2O)2}3(SiW9O34)2]·32H2O and of Cs15[K(SiW11O39)2]·39H2O

The influence of the nature of alkali metal cations on the structure of the species obtained from the trivacant precursor A-(alpha)-[SiW9O34]10- has been studied. Starting from the potassium salt 1, K10A-(alpha)-[SiW9O34]·24H2O, the sandwich-type complex 2, K10.75[Co(H2O)6]0.5[Co(H2O)4Cl]0.25A(alpha)-[K2{Co(H2O)2}3(SiW9O34 )2]·32H2O, has been obtained. The crystal structures of these two compounds consist of two A-(alpha)-[SiW9O34]10anions linked by a set of potassium (1) or cobalt plus potassium cations (2), and the relative orientation of the two half-anions is the same. Attempts to link two A-(alpha)-[SiW9O34]10- anions by tungsten atoms instead of cobalt failed whatever the alkali metal cation. Moreover, the nondisordered structure of Cs15[K(SiW11O39)2]·39H2O is described. Two [SiW11O39]8- anions are linked through a potassium cation with a "trans-oid" conformation, and the potassium occupies a cubic coordination site.