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Identification and isolation of secondary building units (SBUs) from synthesis media of zeolites still represent a challenging task for chemists. The cage structure anion Si₁₂O₃₀^12&#8722; known as the double six-ring (D6R) was synthesized from &#945;-cyclodextrin (&#945;-CD) mediated alkaline silicate solutions and conditions of its stability and reactivity in aqueous solution were studied by using nuclear magnetic resonance (NMR) spectroscopy. A single crystal X-ray diffraction (XRD) analysis revealed a novel polymorph of the hybrid complex K₁₂Si₁₂O₃₀&#183;2&#945;-CD&#183;<i>n</i>D₂O (<i>n</i> &#8776; 30&#8315;40), which crystallizes in the orthorhombic C222₁ space group symmetry with a = 14.841(4) &#197;, b = 25.855(6) &#197;, and c = 41.91(1) &#197;. The supramolecular adduct of the silicate anion sandwiched by two &#945;-CDs forms a perfect symmetry matching the H-bonding donor-acceptor system between the organic macrocycle and the D6R unit. The driving force of such a hybrid assembly has found to be strongly dependent on the nature of the cation present as large alkali counter ions (K⁺, Rb⁺ and Cs⁺), which stabilize the D6R structure acting as templates. Lastly, we provided the first ²⁹Si MAS NMR measurement of ³Q Si in an isolated D6R unit that allows the verification of the linear correlation between the chemical shift and &lt;SiOSi&gt; bond angle for ³Q Si species in D<i>n</i>R cages (<i>n</i> = 3, 4, 6).