Cation-controlled assembly of Na~+-linked lacunary alpha-Keggin tungstosilicates

摘要

Two novel salts of lacunary tungstosilicates with guanidinium and alkali metal cations,(CH)_6N_3)7Na[SiW_(11)O_(39)]centre dot (CH_3)_2CO centre dot 8H_2O (1) and (CH_6N_3)K_6Na[SiW_(11)O_(39/)]centre dot 11.5H_2O (2),have been synthesized and their crystal structures have been determined by synchrotron X-ray diffraction.In both crystals,the Na~+ cations link the lacunary Keggin-type tungstosilicate anions into linear structures.The neighboring [SiW_(11)O_(39)]~(8-) anions are related by two-fold screw and translational operations in compounds 1 and 2,respectively.Second harmonic generation was observed for compound 1.