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-SiW(9)O(34)](10-) has been studied. Starting from the potassium salt 1, K(10)A-alpha-SiW(9)O(34)].24H(2)O, the sandwich-type complex 2, K(10.75)Co(H(2)O)(6)](0.5)Co(H(2)O)(4)Cl](0.25)A-alpha-K(2)(Co(H(2)O)(2))(3)(SiW(9)O(34) )(2)].32H(2)O, has been obtained. The crystal structures of these two compounds consist of two A-alpha-SiW(9)O(34)](10-) anions 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-SiW(9)O(34)](10-) anions by tungsten atoms instead of cobalt failed whatever the alkali metal cation. Moreover, the nondisordered structure of Cs(15)K(SiW(11)O(39))(2)].39H(2)O is described. Two SiW(11)O(39)](8-) anions are linked through a potassium cation with a "trans-oid" conformation, and the potassium occupies a cubic coordination site.