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Synthesis experiments in the simple system TMAOH/SiO 2 /H 2 O led at 160°C to the crystallization of two new tetramethylammonium (TMA) silicates, RUB-20 and RUB-22. The common feature of the two silicates is the presence of ordered defects within the silicate network, necessary to compensate the charge of the occluded TMA cation. RUB-20, [(CH 3 ) 4 N] 1.7 [Si 18 O 35 (OH) 4 ], is a layered material with a 0  = 10.493(2) Å, b 0  = 13.988(2) Å, c 0  = 7.411(1) Å, β = 97.80(2)° and space group  P 2 1 / m . It consists of ferrierite type ( fer ) silicate layers which possess a significant amount of defects. These defects apply only to one particular Si–O–Si bridge which is hydrolyzed to about 50% to form two additional Si–OH/Si–O -  groups which point to the interlayer region of the structure. These silanol groups together with the regular terminal silanol groups of neighbouring  fer  layers form a system of hydrogen bonds which binds the layers together. In addition, weak ionic bonds exist between the negatively charged silicate layers and the intercalated TMA cations. RUB-22 is a zeolite-like silicate possessing a microporous framework with double-cages, housing the TMA cations. The Rietveld structure analysis revealed a pseudo monoclinic unit cell with a 0  = 13.6626(2) Å, b 0  = 13.2400(2) Å, c 0  = 12.3009(2) Å, α = 90.003(3)°, β = 112.700(1)°, γ = 90.005(3) and space groupC   1  ¯   .    $C\bar 1.$    RUB-22, [(CH 3 ) 4 N] 4 [Si 32 O 60 (OH) 12 ], possesses an interrupted silica framework of the same topology as RUB-10, [(CH 3 ) 4 N] 4 [Si 32 B 4 O 72 ] (zeolite framework type  RUT ), however, with the difference that defects replace the [BO4]-tetrahedra. The defects can be regarded as “hydroxyl nests” surrounding a vacancy □(OH-Si) 3 ( - O-Si) instead of B(-O-Si) 4  groups. Heating the as made materials at 600°C led in the case of RUB-20 to a highly disordered zeolite of the  CDO  type and in the case of RUB-22 to a distorted and defective  RUT -type material.

zeitschrift für kristallographie - crystalline materials

Crystal structure analyses of two TMA silicates with ordered defects: RUB-20, a layered zeolite precursor, and RUB-22, a microporous framework silicate