[TMPA] 4 [Si 8 O 20 ] · 34 H 2 O and [DDBO] 4 [Si 8 O 20 ] · 32 H 2 O 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 [Si 8 O 20 ] · 34 H 2 O ( 1 ) and [DDBO] 4 [Si 8 O 20 ] · 32 H 2 O ( 2 ) have been prepared by crystallization from aqueous solutions of the respective quaternary alkylammonium hydroxide and SiO 2 . The crystal structures have been determined by single‐crystal X‐ray diffraction. 1 : Monoclinic, a = 16.056(2), b = 22.086(6), c = 22.701(2) Å, β = 90.57(1)° (T = 210 K), space group C2/c, Z = 4. 2 : Monoclinic, a = 14.828(9), b = 20.201(7), c = 15.519(5) Å, β = 124.13(4)° (T = 255 K), space group P2 1 /c, Z = 2. The polyhydrates are structurally related host‐guest compounds with three‐dimensional host frameworks composed of oligomeric [Si 8 O 20 ] 8− anions and H 2 O molecules which are linked via hydrogen bonds. The silicate anions possess a cube‐shaped double four‐ring structure and a characteristic local environment formed by 24 H 2 O molecules and six cations (TMPA, [C 8 H 20 N 2 ] 2+ , or DDBO, [C 8 H 18 N 2 ] 2+ ). The cations themselves reside as guest species in large, irregular, cage‐like voids. Studies employing 29 Si NMR spectroscopy and the trimethylsilylation method have revealed that the saturated aqueous solutions of 1 and 2 contain high proportions of double four‐ring silicate anions. Such anions are also abundant species in the saturated solution of the heteronetwork clathrate [DMPI] 6 [Si 8 O 18 (OH) 2 ] · 48.5 H 2 O ( 3 ) with 1,1‐dimethylpiperidinium (DMPI, [C 7 H 16 N] + ) guest cations.