Strukturen und Schwingungsspektren des Tetramethylammonium -a -dodekawolframatosilikats und des Tetrabutylammonium-β-dodekawolframatosilikats / Structures and Vibrational Spectra of Tetramethylammonium a-Dodecatungstosilicate and Tetrabutylammonium β-Dodecatungstosilicate

Abstract

Abstract Dodecatungstosilicates free of crystal water were prepared for the first time by using tetraalkylammonium as cation. The crystal structure of the tetramethylammonium a-dodeeatungstosilicate [N(CH 3 ) 4 ] 4 SiW 12 O 40 (1) and tetrabutylammonium) β-dodecatungstosilicate, [N(C 4 H 9 ) 4 ] 4 SiWi 2040 (2) were solved by X-ray diffraction. (1) crystallizes tetragonal in the space group 14̅ with lattice parameters a = 14.642 Å; c= 12.706 Å; (2) orthorhombic, space group P2 1 2 1 2 1 with a = 29.277 Å, b = 22.181 Å and c = 15.381 Å. The differences between the two isomeric heteropolyanions are discussed, especially the distances and angles between the tungsten atoms. Comparison of characteristic differences in the vibrational spectra permits the identification of the isomeric anions.