[TMPA]4[SI8O20]CENTER-DOT-34H2O AND [DDBO]4[SI8O20]CENTER-DOT-32H2O ARE HETERONETWORK CLATHRATES WITH 1,1,4,4-TETRAMETHYLPIPERAZINIUM (TMPA) AND 1,4-DIMETHYL-1,4-DIAZONIABICYCLO[2.2.2]OCTANE (DDBO) GUEST CATIONS

[TMPA]4[Si8O20] . 34H2O (1) and [DDBO]4[Si8O20] . 32H2O (2) have been prepared by crystallization from aqueous solutions of the respective q uaternary alkylammonium hydroxide and SiO2. The crystal structures hav e been determined by single-crystal X-ray diffraction. 1: Monoclinic, a = 16.056(2), b = 22.086(6), c = 22.701(2) angstrom, beta = 90.57(1)d egrees (T = 210 K), space group C2/c, Z = 4. 2: Monoclinic, a = 14.828 (9), b = 20.201(7), c = 15.519(5) angstrom, beta = 124.13(4)degrees (T = 255 K), space group P2(1)/c, Z = 2. The polyhydrates are structural ly related host-guest compounds with three-dimensional host frameworks composed of oligomeric [Si8O20]8- anions and H2O molecules which are linked via hydrogen bonds. The silicate anions possess a cube-shaped d ouble four-ring structure and a characteristic local environment forme d by 24 H2O molecules and six cations (TMPA, [C8H2ON2]2+, or DDBO, [C8 H18N2]2+). The cations themselves reside as guest species in large, ir regular, cage-like voids. Studies employing Si-29 NMR spectroscopy and the trimethylsilylation method have revealed that the saturated aqueo us solutions of 1 and 2 contain high proportions of double four-ring s ilicate anions. Such anions are also abundant species in the saturated solution of the heteronetwork clathrate [DMPI]6[Si8O18(OH)2] . 48.5 H 2O (3) with 1,1-dimethylpiperidinium (DMPI, [C7H16N]+) guest cations.