A new synthesis method for preparing spherosilicates with a double-four-ring (D4R) silicate core (Si8O12) and functional siloxy substituents such as (OSi(CH3)2Cl) on the vertices was discovered. Key to this achievement was the synthesis of [N(n-C4H9)4]H7[Si8O20]·5.33H2O D4R cyclosilicate hydrate precursor crystals having only 5.33 water molecules per D4R unit, which is much smaller than the number in the state-of-the-art tetramethylammonium- and choline-containing cyclosilicate hydrate crystals that have up to 65 water molecules per D4R. The low water content allows the use of bifunctional silylating agents such as dichlorodimethylsilane that lose their chloride functionality upon reaction with water molecules. Dissolution of [N(n-C4H9)4]H7[Si8O20]·5.33H2O crystals in acidified tetrahydrofuran liberates uncharged D4R [Si8O12][OH]8 cyclosilicate molecules, as shown by small angle X-ray scattering and 29Si nuclear magnetic resonance. A concentrated stable solution of [Si8O12][OSi(CH3)2Cl]8 spherosilicate co...