Flexible Structure of a Thermally Stable Hybrid Aluminosilicate Built with Only the Three-Ring Unit

Abstract

Organic–inorganic aluminosilicate hybrids are an attractive new class of materials that add organic functionalities to conventional properties of solid inorganic catalysts. ECS-17, a novel crystalline hybrid, was synthesized using 1,4-bis-(triethoxysilyl)-benzene as the sole silicon source. Its structure was solved by direct methods starting from high-resolution synchrotron X-ray diffraction data and is composed of inorganic layers, characterized by 10 rings, held together by phenylene rings. ECS-17 is the first aluminosilicate built from only the three-ring secondary building unit. This new material shows intriguing reversible collapsibility upon dehydration/rehydration. Mild thermal treatment under vacuum causes its crystalline structure to collapse due to facile elimination of the water molecules around the cations. Successive exposure to ambient atmospheric moisture gives back the hydrated crystalline form. ECS-17 shows remarkably high thermal stability for a hybrid, being stable up to 450 °C under vacuum and breaking down at 350 °C in air. Structural, thermal, and optical properties were examined by X-ray powder diffraction, thermogravimetric analysis, nuclear magnetic resonance, and ultraviolet–visible-near-infrared reflectance and fluorescence spectroscopies

One-pot synthesis of hierarchical porous layered hybrid materials based on aluminosilicate sheets and organic functional pillars

“…40,41 Even layered ECS-type materials with inorganic sheets built from only three-ring secondary building units have been recently described. 42 However, to the best of our knowledge, these interesting materials have only been successfully prepared with rigid and non-catalytically active arylic fragments intercalated in the interlayer space.…”

The role of boric acid in the synthesis of Eni Carbon Silicates

“…Finally, the influence of boron on the synthesis performed using BTEB as bridged silsesquioxane was examined (Table 3). It should be emphasized the fact that, among the disilane precursors used so far, BTEB is the most versatile having led to the crystallization of different ECS phases (ECS-1, 40 ECS-2, 40 ECS-3, 40,41 ECS-17 42 ) by varying only slightly the composition of the reagent mixture. Among the numerous exploratory syntheses carried out with BTEB, NaAlO 2 and NaOH, one (entry BTEB-1) attracted our attention because it led to the formation of an unidentified product of low crystallinity but with interesting features (Fig.…”

“…3b, facilitating the ab initio crystal structure determination and Rietveld refinement starting from synchrotron powder diffraction data. 42 Table 3 also reports the results of other synthesis runs performed for examining the influence of synthesis parameters on the characteristics of the crystalline product. The results indicated that pure and well crystallized ECS-14 can be obtained by keeping OH − /SiO 2 = 0.50 and H 2 O/SiO 2 = 20 or 40.…”

“…Crystal structures were determined for several hybrids. In particular, ECS-2, 40 ECS-3 41 and ECS-17 42 synthesized with BTEB possess 3D ordered structures with stacks of aluminosilicate layers covalently bonded to each other by phenylene rings. The aluminosilicate layers consist of [AlO 4 ] tetrahedra bound to four different [CSiO 3 ] tetrahedra, confirming that they act as spacers between the silsesquioxane units and give low density structures with different pore systems.…”

“…The aluminosilicate layers consist of [AlO 4 ] tetrahedra bound to four different [CSiO 3 ] tetrahedra, confirming that they act as spacers between the silsesquioxane units and give low density structures with different pore systems. [40][41][42] When the syntheses are performed in the presence of the bridged silsesquioxane and NaAlO 2 , ECS materials crystallize as aluminosilicates with low Si/Al atomic ratios (1.33 in ECS-3 41 and 2.00 in ECS-2 40 and ECS-17 42 ). Attempts to decrease the Al content in the structure by adding a conventional silica source (TEOS) is possible, provided that opportune measures are taken for compensating the mismatch between the rates of hydrolysis of the two silica sources.…”